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Rebuilding an R90/6

Ron Chambers, Melbourne, Victoria, Australia –
(original publish date unknown)


“A few years ago I rebuilt my R90/6. Being the obsessive/compulsive that I am, I wrote a complete “how to” piece which may be of interest to anyone contemplating a similar project”


I bought the bike – a 1974 R90/6 – in April ’91 with about 157,000 km on the clock. I had bought the bike with the idea of doing it up some day but I rode it a fair bit and did the routine repairs and maintenance, new cables etc myself. My local BMW specialist had overhauled the clutch and the front forks and steering head bearings.

In October ’92 I rode from Sydney to Philip Island for the Superbike World Championships. On the way back, the electrics progressively shut down. Fault finding was made difficult because the wiring loom was very tired. When the clutch was replaced, my BMW specialist had to have the tank repainted for me after another bike in the workshop fell on the R90.

Because half the work had already been done, and because I would have to strip the bike back to the bare frame to repair the electrics, I decided then to do a full refurbishment.

Note that I have used the word “refurbishment”. This is not a description of a total strip and rebuild. In my case this wasn’t necessary but such a project would not only require special tools but would also exceed my skills!

This as a record of that project, written for my own benefit mainly, but it may also help anyone planning a similar project. Whilst the following relates specifically to BMW’s R90/6, much of it would apply to any R-series BMW produced between 1969 and 1985.

I can recommend such a project as excellent occupational therapy with a lot of satisfaction coming along the way and at the end.

Any BMW club wishing to reprint this article may do so as long no filthy lucre changes hands.


2. Caveat:

3. Preliminaries & Preparation:

3.1 Manuals:

3.2 Containers etc:

3.3 Method:

3.4 Funds:

3.5 Know your own limitations…and the limitations of others:

3.6 Clean the bike:

3.7 Time & Space:

4. Tools:

4.1 Generic Tools:

4.2 Special Tools:

5. Lubricants, Cleaners and Solvents:

5.1 Lubricants:

6. Parts:

6.1 Factory Parts:

6.2 After Market Parts:

6.3 Secondhand Parts:

6.4 Fasteners:

7. Frame and Fittings:

7.1 Main Frame, Subframe, Swingarm & Pannier Frame:

7.2 Tank:

7.3 Seat:

7.4 Other Bits:

7.5 Suspension & Brakes:

7.6 Wheels and Tyres:

8. Clutch, Gearbox and Final Drive:

8.1 Clutch:

8.2 Gearbox:

8.3 Final Drive:

9. Engine:

9.1 Bottom End:

9.2 Top End:

9.3 Carburetors:

10. Electrics:

10.1 Alternator:

10.2 Starter Motor:

10.3 Diode Board (Rectifier):

10.4 Voltage Regulator:

10.5 Wiring:

11. On The Road Again:

12. Appendix

A. Components and Costs:

B. Resources:

13. Bibliography

2. Caveat:

I am not a qualified mechanic nor a BMW expert. The following does not constitute advice. Anyone who follows or adopts any of the methods or procedures contained in this article does so at their own risk.

I would appreciate any corrections, feedback, advice etc.

3. Preliminaries & Preparation:

3.1 Manuals:

Before I bought the R90, I had already bought and read the Haynes owners workshop manual. This might be a bit dry for some but, I would recommend reading a manual as the necessary first step to a project like this. Not only is it an essential resource for a major overhaul, but it will generally help you to know your bike and its brethren and help you prepare for the project.

There are three main sources of manual for BMW’s – Haynes, Clymer and BMW. Each is valuable in its own way but, of the three, the English Haynes publication is probably the best if your budget is limited to buying one manual; the latest 1997 edition is a significant improvement on the older 1985 edition. It has lots of tips and techniques and, whilst the illustrations and photos are not as profuse as the Clymer publication, the clarity is better and often more relevant; it contains many tips and techniques for avoiding special tools or making your own.

The American Clymer manual has copious text, photos and illustrations but is arguably less lucid and clear, although is does cover more and in more detail.

The BMW manual (if you can get it) is aimed at the qualified BMW mechanic and is more terse; the major benefit of this manual is the use of BMW special tools. Don’t forget the rider’s handbook if you still have it. If you can afford it, buy both the Haynes and Clymer manuals.

Also well worth the investment is the BMW parts catalogue. The exploded diagrams will help disassembly / assembly and make parts ordering much more precise. I got the printed version from MOTO-BINS in the UK. They can also supply these on microfiche (OK if you have access to a reader/printer). It is probably good advice to get hold of these whilst they are still available because BMW are now only supplying their parts catalogue on CD-ROM which may not be publicly available.

A good general publication is Motorcycle Workshop Practice from Haynes. This is very good if you are a mechanical novice.

Another helpful book is BMW Twins Restoration by Mick Walker. It does not go into deep technical detail but it does cover a lot of the cosmetics, features and options very well with many useful photos; this can be handy if your bike has been modified and you want to take it back to original specs.

The Illustrated BMW Motorcycle Buyers Guide by Stefan Knittel and Roland Slabon is worthwhile if you need to determine the value of your bike. They have a best-out-of-five star rating which – whilst it might not apply to your home market – will give you an idea as to the relative rarity and desirability of your particular bike. This publication is probably essential if you are specifically buying a machine to restore.

See the bibliography for details of these publications.

3.2 Containers etc:

Get hold of various sizes of sturdy cardboard boxes and several packets of zip closure plastic bags (the one’s I used are Union Carbide’s Glad brand which have a white band on them for noting the contents).

Store frame components, engine components, electrical components and bodywork together with their related fasteners and bits and pieces in dedicated boxes and bags – like with like.

It’s amazing how such a compact thing as a motorcycle can grow in size as you remove and store bits. Help yourself through using adequate storage containers and being tidy and free of clutter. There is nothing worse than having to turn the workshop upside down looking for a particular widget – the lack of which can make a critical assembly step impossible or make a ten minute job take hours.

Buy an A4 or similar exercise book or spiral bound pad for taking notes and making drawings. The ones with a faint ruled 5mm grid are good. Pens, pencils and rulers of course.

3.3 Method:

The problem with any do-it-yourselfer (almost as bad as confessing to being a yuppie), is that he or she only has generic mechanical experience to draw on – and that may be non-existent. The expert – particularly one who specialises in a particular make – has done the same task many times over, but it’s all more-or-less new to the first timer who has to learn all the tricks of the trade from scratch with no mentor other than books.

It’s not as difficult as it sounds providing that one is methodical and – like a good student – lots of notes and drawings are made along the way. Take your time, it should be a pleasure and this won’t be realised if you are over hasty. Bag or box all assemblies with a notation on each as to what they belonged to; make sure that assemblies are stored as they came off the bike or make notes on the order and sequence of bolts, nuts washers etc. Make lots of notes and drawings – particularly of electrical connections. It’s surprising how much one forgets over a protracted period and how much is not self evident in the reassembly.

3.4 Funds:

Don’t even start a project if you don’t have the funds. As you will see in costs in Appendix A – my rebuild exceeded the buy price of the bike by a considerable margin – and I wouldn’t recoup that extra cost by selling the bike – at least not this century.

Apart from having adequate cash reserves in the first place, some of the funding decisions will be determined by the intrinsic value of the bike. In Australia for example, the R90S is getting rarer and more valuable; it may not be worth spending a lot of money on a less desirable model. Your choice.

Decide if it is to be a cost-no-object project and how faithful you want to be to original. Make sure you include a provision for the unexpected. A rebore with new pistons and rings will cost a lot more than a bore hone and reuse of the old rings. For example, I needed to replace the rocker arms which was $600+ of unexpected expense that I didn’t know about before removing the heads. It may even be worth doing a partial strip down before estimating your budget.

3.5 Know your own limitations…and the limitations of others:

If the manual says “this is a difficult operation and is best left to an expert” take heed. Do not undertake any major element of the project unless you have the tools and expertise. Your local BMW dealer or independent BMW specialist will be only too happy do the work for you.

Beware of mechanics and engineers who do not know motorcycles in general and BMW boxers in particular. The tools and expertise used in the car and truck side of the automotive industry are different and can really screw things up if applied to a motorcycle. This applies to paint, electric’s and everything. The best thing is to ask around and find out who the local BMW community have found to be good with motors, gearboxes, final drives, painting, plating etc. and who should be avoided – like everything else, there are a lot of cowboys out there!

One of the beauties of the BMW boxer is that a minimum of special tools are needed, but there are some jobs which can’t be done properly without the right tools and parts; these include much of the bottom end, the gearbox, the final drive, valve guides and seats, reboring, balancing etc.

As Lou Reed says… “believe none of what you hear and half of what you see”. Seek out experts and other people who have had the same or similar experience and listen to what they have to offer but double check what they say. For example, the BMW specialist whom I got to do my barrels and heads out told me that I needed a secondhand head because one valve guide in one head off my bike was loose. I asked if another head was necessary because I was sure that oversize valve guides were available. He replied that there was no such thing as oversize valve guides and fitting valve guides was a very difficult job to do properly. It turned out that BMW do make two oversize guides and a correct oversize was fitted at no great expense. The “expert” was not incompetent – availability of oversize guides was just a piece of minutiae he didn’t know – but it meant a several hundred dollar saving to me.

Finally, manuals have been known to be wrong – particularly in the data sections – so make sure you check Haynes against Clymer if at all possible for all major settings and tolerances.

3.6 Clean the bike:

As much as you can, degrease and clean the bike before starting work – cleanliness is next to godliness when doing any mechanical work.

This maybe one and only occasion when a high pressure water cleaner could be used – if you were careful. These gismos do a great job but they are normally far to vicious to use under normal circumstances; not only will they remove paint but they also blast critical lubrication from bearings and other key components quite indiscriminately. Since the bike is going to stripped and rebuilt, any wash damage would be automatically rectified.

3.7 Time & Space:

You will need time – time to do the actual work, time to chase after bits and pieces and time to arrange for parts to be dropped off and collected for major work (paint etc) to be done. Don’t start unless you have the time to do it or can take your time to finish. It took me about 14 months from go to whoa.

A good workspace is essential. You don’t have to have a professional workshop – just somewhere that is roomy, dry, and where you have some control over heating and cooling.

4. Tools:

4.1 Generic Tools:

If you haven’t got a reasonable set of hand tools you will need to buy some for a project like this but the necessary tools can be acquired without going overboard. The standard BMW toolkit is enough to do most things but better tools are more satisfying to work with and will do the job better and faster.

Basically, it would appear that there are three quality grades of engineering hand and measuring tools. The best (usually from Europe, USA or Japan), the middle of the road (inevitably made in Asia – Japan and Taiwan) and the cheap (also made in Asia – Taiwan, Korea, China and India). The best are very expensive, and work very well. The middle of the road are priced accordingly and also work very well. At the cheap and cheerful end of the spectrum the quality can vary from good to awful, but the prices tend to be so low that they can be used – domestically at least -until they break at which time you buy more; an entire set of these cheap tools can be bought for less than the cost of a single top quality spanner.

Being a lover of quality tools, I have built a collection of the best I could afford at the time. Stahl-Wille (German) open box spanners (open at one end, ring at the other), a set of Facom (French) CDX super 3/8th sockets (these use an X profile drive – as opposed to the normal square drive – and have the torque ability of 1/2in. with the handiness of 3/8th.), and a set of Rothenberger 1/4in. sockets (Japanese – despite the Germanic name). The open box spanners and the 1/4in. sockets get the most use.

Since most nut sizes are very common it is possible to build a kit by buying the best of the most commonly used sizes and buying el-cheapos for the less common sizes. Against this is the fact that an entire mid-priced or cheap set can be bought for the cost of a few top quality tools. Table 1 shows the most common bolt and nut sizes used on BMW motorcycles (the spanner sizes in the standard tool kit are no accident!):

Most of the nuts and bolts on BMW are Metric Course (Note: DIN Metric, not ISO Metric) whilst a few – cable adjusters, tappet adjusters – are Metric Fine.

Bolt size (Metric Course): Nut size (Width Across Flats):

  • 5mm 8mm
  • 6mm 10mm
  • 8mm 13mm
  • 10mm 17mm
  • 12mm 19mm
  • 14mm 22mm
  • Brake unions 11mm

Table 1. Common bolt and nut sizes on BMW motorcycles

There are some deviations from the above table; the one’s I can recall are head/rocker block nuts (14mm) and tappet adjusters (12mm).

The following table indicates a typical tool kit with a subjective qualification as to grade and usefulness.

Tool: Usefulness: Quality Grade: Comment:
Spanners – open box. Mandatory Mid to best If you can afford it, buy the best. They are a delight to use, fit perfectly and will last forever.
Flare wrench – 11mm Desirable Best Used for hydraulic brake unions. A ring spanner with a gap to allow the spanner to slip over the brake line. The only way to undo and do brake unions without rounding the flats.
Sockets – 1/2in. drive with a ratchet or fixed handle Mandatory Mid to low Either buy a few good quality sockets or a mid to low price set.
Sockets – 3/8in. drive Compromise Mid Could be a compromise between a mix of 1/2in. and 1/4. drive. Not as strong as 1/2in. for high torque – not as small and handy as 1/4in drive.Sockets – 1/4in. drive with ratchet handle Desirable Mid to best Small size is very handy for nuts up to 13mm. A good quality set can handle torque up to about 30nm.
Hexagonal bits. Mandatory Mid These bits can fit a 10mm socket and can hence be used with a ratchet handle or torque wrench. BMW’s use a lot of socket head cap screws which should be torqued to the right tension.
T-handle Allen wrenches Desirable Mid Quicker than hex head bits or Allen keys. Worth it because of extensive use of socket head cap screws on BMW’s.
Vernier callipers Mandatory Mid If you can’t afford a quality unit, the Chinese make cheap ones which are quite good.
Taps and Dies Mandatory Mid Used to clean up threads. Alternative to a complete set is to buy the few major tap sizes and a T-handle tap wrench (can get in tighter places than a tap handle) and some die nuts.
Tension or torque wrench – 1/2in. drive Mandatory Mid to best The ones with a positive signal (usually a click) are probably better than the basic units with a pointer and scale. I also use a small 1/4in drive tension wrench for fastenings up to 25N m.
Micrometers & gauges Depends Quality micrometers are expensive but essential for fine measurement. Only needed if you’re not getting the work done by an expert. The Chinese made examples are quite OK at reasonable cost.
Piston ring clamp Desirable Mid Make sure you get one which comes apart so that it can be removed after the barrel is past the rings. This type is also used in VW beetles. I use a Lisle from the USA which has a split band.
Shifting spanners Handy Mid to best
Hacksaw Mandatory Mid to best
Files Mandatory Best
Hammers and mallets Mandatory Best Apart from an engineers ball pein hammer, a soft faced mallet is very handy.
Drifts and punches Mandatory Best
Valve spring depressor Depends Best If you are going to get the heads seen to by an expert, don’t buy one. If you intend to do the job yourself make sure you buy one which will fit a motorcycle head.
Electric heat gun Handy What’s on sale Very good for heating components. The only way to safely shrink heat shrink tubing.
Multimeter Desirable Mid Very handy for checking out the electrics – both to measure a component to see if it’s serviceable or to check that you have the right connections on reassembly.
Table 2. Suggested Hand Tools.

4.2 Special Tools:

The only special tool I bought was a crows foot extension for torqueing the drive shaft flange bolts. According to Haynes, these bolts require an absolutely precise torque because once they are done up to the specified torque – only attained by using the special tool – they deform by a pre-determined amount. These bolts cannot be reused. The tool is an extension to fit a 3/8in. square drive torque wrench. Problem is that it is all but impossible to achieve the desired result unless the torque wrench used, fitted with the special tool, has sufficient clearance to fit between the frame and the bolt head. This knowledge may help if you plan to buy a torque wrench. My BMW “expert” confessed that he just used a ring spanner and “feel” and never had any problems. Be warned!

I made a push rod grommet sealing tool from a piece of 25mm ID pipe according to the diagram in the Haynes manual – worked a treat – and I fashioned a piston support for refitting the barrels from 12mm plywood and it too did the job.

Time commitments and distance from home made it difficult for me to use my BMW Club loan tool service; loan of special tools is a valuable resource which many BMW clubs offer and can be a great boon.

5. Lubricants, Cleaners and Solvents:

5.1 Lubricants:

It seems axiomatic that workshop manuals always refer to special lubricants which are either unobtainable or difficult to get readily.

Table 3 lists some applicable lubricants; if you can’t get them at your local bike/auto shop or engineering supplier, ring the manufacturer. In Australia, the recommended Starburags and Optimol products are not readily available (although any of the overseas BMW specialists can supply the real McCoy).

Lubricant: Manufacturer: Application:
Molykote 1000

Dow Corning

Exhaust flange threads, spark plug threads.
Molykote BR 2 Plus Dow Corning Brake actuating rod on master cylinder, brake calliper pivot, swingarm bearings, pre-assembly lubricant for most bearings.
White Lithium Grease Various Low stress applications like twistgrip, side and centre stand pivots etc.
General Purpose Grease Various Use name brands from Shell, Mobil, BP etc. Bel-Ray make a good waterproof general purpose grease.
Dewatering and anti-corrosion spray Various Use name brands such as WD40 for cables and general light lubrication.
Engine and transmission oils. Various Use brand names, grades and viscosities as per the manual. I buy brand name oil when it is on special at the supermarket and change oil and filter frequently since I think this is better and cheaper than using expensive synthetics at extended change intervals.
Table 3. Suggested Special Lubricants.

5.2 Cleaners, Paints and Solvents:

General Degreaser:

Shell makes an industrial detergent branded in Australia as Teepol; I’m sure other companies make a similar product. Spray it on with a household spraypack, work it in with a nylon brush and hose it off. Cheap, effective and much less environmentally challenging than a solvent based degreaser; much less destructive than high pressure water or steam.

Alloy Cleaner:

Whilst the various alloy castings on the R90 were clean, they did have 20 years of accumulated grud on them which I wanted to clean up whilst retaining as much as possible of the protective oxidisation. After checking around, I decided not to have the crankcase, fork sliders etc bead blasted. For starters, the component to be blasted must be completely disassembled; once its done, all the blasting material must be thoroughly removed from oilways etc. If the grade of grit or bead is wrong, or the blasting is not done by an expert, it can ruin the casting (making them porous etc). In my opinion, blasting also tends to leave the castings unnaturally bright.

As an alternative to bead blasting, I ended up using a proprietary alloy cleaner. This is sprayed on and worked in with a stiff brush then hosed off. Since it tends to open up the pores of the casting, I finished off with WD40 rubbed in with a Scotchbrite pad and wiped down with a rag. Whilst not as “good” as bead blasting, it is very effective at cleaning up dirty alloy. The best was Mothers mag. wheel cleaner – a product from the USA (be sure to use the one for bare alloy).

Brushes etc:

Household dishwashing brushes are great. 3M’s Scotchbrite scouring pads do a great job on alloy and baked on oil and road grime. Bronze wire brushes are very useful for non-destructive cleaning of nuts, bolt heads, threads etc.

Bright Metal Cleaner:

Products such as Autosol and Goddards Glow work well on bright chrome and stainless.

Brasso or a similar brass cleaner does a great job on carburettor bodies. Clean with a proprietary carb. cleaner first then use Brasso with an old tooth brush. The die cast bodies will shine.

Parts Washing:

Kerosene is the best and safest. Proprietary carby cleaner is good for doing just that, but be careful – it’s pretty nasty stuff.

Electrical Cleaner:

Buy an aerosol can from an engineering supply shop or electronics supply shop. Good for degreasing shafts and threads that require a dry (ie not lubricated) fit.


Most of the major painting was done by professionals but I needed to paint odd bits and pieces so I ended up using small aerosol tins of matt black, gloss black and aluminium finish paint for metal. No particular brand seemed to work any better than another. Provided the part is clean and back to bare metal it is not necessary to use undercoats and primers. All the bits looked quite good and the paint has adhered quite well.

6. Parts:

6.1 Factory Parts:

One of the benefits of BMW ownership – probably part of the high initial buy price – is that the spare parts are both readily available and reasonably priced (I know some will disagree but check out the price of Japanese spare parts – when you can get them!). The factory supply of pre 1969 parts are beginning to dry up but for the /5 and later R-series, the supply is still pretty good. That’s the case in Australia and I have no reason to think that the situation would be any different in most major BMW R-series markets.

In most circumstances it makes sense to use factory parts. I used factory parts for all the major items for which there were no suitable aftermarket equivalents or which I thought were better – switches, cables, wiring looms, etc.

Be aware that as these older BMW’s age, some parts not known to wear are beginning to fail and there may well be no replacement in the catalogue. Examples which I know about are certain bearings and bushes in the gearbox. This fact may well force you into after market or secondhand parts.

6.2 After Market Parts:

Unless you want to be absolutely faithful to the original, there are plenty of examples where aftermarket parts will be better and/or cheaper than BMW parts. I’ve never had any experience with club judges in veteran, vintage and classic shows nor am I familiar with the rules of such “contests”. I do know that they can be very pedantic about originality.

Chosen well, many of these aftermarket parts would probably pass muster as being of the era or acceptable deviations. Exterior parts such as Krauser panniers and racks were so supported by BMW as to be original BMW. Other after market parts such as those made by Luftmeister were/are so ubiquitous as to be almost genuine.

Some examples of commonly used and available aftermarket bits for the /5 and later BMW’s:


  • Triple Clamp Luftmeister. Much better than the original flimsy excuse.
  • Rear Dampers Koni 7610’s are probably the most popular.
  • Disk(s) Luftmeister and others

Brake Lines The original spaghetti tube is pretty useless. Replace with braided stainless lines. If the look of the silver colour and slimness bothers you, 10mm split plastic cable tidy can make an effective shroud to cover the braided line – readily available from spare parts outlets.


  • Fork Springs Progressive Suspension. Much better than the original
  • Bearings Quality equivalents from reputable makers are just as good as BMW original (probably the same product at half the price).
  • Gaskets & seals etc. You pays yer money, and yer takes yer chances. I used factory parts but aftermarket equivalents are probably OK.
  • Voltage Regulator An electronic replacement for the original mechanical unit will be better and cheaper. Available from Bosch and others.
  • Ignition If your BM still has points ignition throw it away and fit an electronic equivalent from a reputable maker such as Boyer Brandsen or Luminition.
  • Brake Pads Quality, branded aftermarket units are fine.

6.3 Secondhand Parts:

These are parts from wreckers, reconditioned parts and parts removed from the bike.

As parts are removed from the machine and measured and tested, it is necessary to make a judgement as to what needs to be replaced or reconditioned. In my case, the previous owners had looked after the machine and repaired or replaced various bits along the way, so, even though it has done a lot of kilometres, most of the key components had plenty of life left in them.

If your machine has not been well treated, you may have to use more new, aftermarket or secondhand bits. If in doubt, err on the side of caution and repair or replace. There is little point in tearing a machine to pieces only to have the clutch go south a few thousand km’s later.

6.4 Fasteners:

Fortunately, BMW use a lot of good quality fasteners such as socket head capscrews; their metallurgy also seems to be good, with high quality materials well chosen for the intended application. This tends to all but eliminate the need for tools like impact drivers.

One of the problems I faced was that most of the nuts and bolts used are plated or phosphate treated which tends to look a bit tired with age; the same goes for hose clamps.

I could not find anyone who was willing to clean and re plate these fasteners (if anyone could advise me on this I would be grateful), so I decided to replace them with stainless fasteners wherever possible. This would probably offend the purist but the overall look certainly adds to the appearance of the finished bike.

Since I am not a metallurgist and couldn’t test each fastener – old and new – for tensile strength, torque etc, I did not use stainless for any application I thought was critical (say axles or brake caliper bolts on models with Brembo’s) but this was not a major issue on the R90. In any case, I think it would be pretty safe if the fasteners were good quality bought from a reputable specialist because stainless fasteners – although of lower tensile strength than the normal fasteners used by BMW – resist corrosion which eventually weakens plated steel fasteners anyway.

One stainless fastener which I couldn’t track down was hose clips; these are used extensively on R-series boxers for fork gaiters, inlet manifolds etc. BMW use a lot of clips with a band of 9mm width which is not a size readily available in Australia – certainly not at the common diameters used. I have found since that some hydraulic hose specialists do stock 9mm stainless hose clamps.

7. Frame and Fittings:

7.1 Main Frame, Subframe, Swingarm & Pannier Frame:

Main frame and subframe:

After the bike was completely stripped and the swingarm and subframe separated, I degreased the whole lot (took a bit of time, kero, Teepol, and elbow grease). The frame has to be sandblasted and the blasters won’t touch if it’s greasy and dirty. When it was clean, I inspected each piece. I probably should’ve done this after the frame was sandblasted but this was not practical in my case – guess I just have to trust the sandblaster and spraypainter.

The main frame appeared to be in good condition as did the swing arm, but the rear subframe looked pretty tired. These are a weak part of all twin shock R-series, being too light and flimsy for solo riding let alone loaded up with panniers, gear and probably a pillion. Touring is a BMW forte; the previous owner had done a lot of two-up miles and it showed. The subframe had had gussets welded to strengthen the damper mounts but these were showing signs of cracking. I located a secondhand subframe from a wrecker which was in much better condition; one of the seat hinge trunnions was missing but I just had the old one removed and welded to the “new” subframe.

I talked to a lot of experts about 2-pack paint versus stove enamelling versus powder coating. I could not find any stove enamellers in the Yellow Pages (the paint companies don’t even make it) so the choice was 2-pack versus powder coating. The consensus seemed to be that powder coating, expertly done was great but that it was safer to have traditional 2-pack paint applied which I did. In hindsight, I think powder coating may be better. Whilst the paint job was well prepared and applied, it does chip easily. From what I have seen of powder coating applied to miscellaneous metal products and a few motorcycle frames, it would seem that powder coating is tougher and more resilient than paint. Anyone have any experience – good or bad – of either paint or powder coat?

Before beginning reassembly, I padded the newly painted frame with corrugated cardboard and masking tape. This is very necessary because it is very easy to scratch and chip the paint during the reassembly.


I intended to replace the tapered roller bearings in the swingarm, but when I removed them there was no brinelling or roughness in the cups so I decided to leave well enough alone. The tapered cup which remains in the swingarm is a bugger to get out unless you have a special puller or you weld on a piece of scrap and destroy them (I’ve never done it, but apparently the heat of the welding causes the bearing to deform). Anyhow, I just taped them up with masking tape.

The drive shaft is retained by a nut on the female splined part which engages with the splined shaft on the final drive. This nut is held on with over 250N m of torque and, since there was no need to remove the drive shaft, I decided to leave it in situ and strip the paint back to bare metal with paint stripper and hand rubbing rather than sandblast.

On refitting the swingarm/driveshaft to the frame, I used the old bearings and replaced the dust seals (which have to be destroyed on removal). The dust seals are a tight fit but can be gently tapped in with a hammer using a large socket as a drift; make sure they are fitted the right way round. After the bearings were lubricated, I installed the swingarm in the frame then set the preload and adjustment as per the manual.

Pannier Frame:

The pannier side frames were stuffed. One mounting point had completely separated and rust had started to badly effect the chrome, so I decided to replace the side frames with new ones and use the original central frame. This was very straight forward but it begs a small digression.

Krauser and BMW specify load limits for their panniers – the R90 Rider’s Handbook specifies the limit as 7kg gross weight per pannier – which is not much for a long journey, especially with two people. So, there is a natural tendency to pack a bit more in and hence overload. I know that such overloading drastically changes the handling, but it also put enormous stresses on the already weak rear subframe and on the pannier frames. Seeing the result of overloading on my bike – cracked subframe, broken pannier frames and 6mm capscrews bent from the stress – I will try to make sure that I stick to the recommended weight limits in future.

7.2 Tank:

This was pretty straight forward since one of the reasons for deciding to refurbish the R90 in the first place was that the tank had been damaged and repainted – you know, nice new tank, tired old bike!

The only real decisions were whether to keep the old fuel taps (which leaked badly) and whether to treat the tank with anti-rust whilst it was empty.

Since the tank interior was not rusty at all, I decided just to replace the fuel taps which leaked badly so I got new Karcoma taps. There are two common types – one with the spigot exiting the tap at 90 degrees and one with the spigot exiting straight down. I fitted the 90 degree type which makes setting the tank down when off the machine easier because the spigots can’t get bent. Anyhow, the only issue was the cost – new fuel taps are not cheap!

7.3 Seat:

The seat covering was in pretty good condition so I decided to do nothing except remove the chrome grab rail for thorough cleaning of it and the seat material. This was straight forward except that the 5mm screws that retain the grab rail broke off because they were rusted in place which necessitated drilling them out with a 4.2mm drill, retapping them and using stainless screws to refix the rail.

Having said all that, the seat base is getting pretty rusty and the alloy trim is creased in a few places. I would like to get this done but I don’t want to loose the original Denfeld upholstery, which still looks as good as new. One of these days I’ll take the seat to an upholsterer who knows motorcycle seats and see what can be done.

7.4 Other Bits:

The seat locking mechanism was removed, painted, lubricated and replaced. I fitted a new lock keyed the same as the new ignition switch by a local locksmith (who also managed to rekey the old steering lock).

One piece of refinishing which defied me was the engine badges and the seat badge. Most are still available as a replacement part they are very expensive which prompted me to try and clean up the old examples. These badges are black paint on chromed alloy; the engine badges are stuck to the starter motor cover and the seat badge is screwed to the seat tail. I touched them up with a black paint pen but the result was only average. Perhaps I should’ve tried a fine brush and enamel paint – any bright ideas on how to repaint these would be appreciated.

7.5 Suspension & Brakes:


About six months prior to starting the refurbishment, I had replaced the front springs with Progressive Suspension units and replaced the seals and steering head bearings so there was no need to do anything apart from change the fork oil. The only trick here is to bounce the front end a few times with axle and pinch bolts loose. This allows the sliders to align themselves before everything is tightened to the correct torque.


I had replaced the rear spring/damper units with Koni 7610’s when I did the front end so there was nothing to do here.

Front Brake:

There was no evidence of any leaks in either the master cylinder or the slave cylinder so I decided to leave these as they were. The Clymer manual contains an excellent section on ATE brake overhaul which is not covered by Haynes.

The hydraulic line from the master cylinder to the slave was the original rubber one that came on the bike so I decided to replace this with a braided line; I also replaced the brake pads, the brake cable, and lubricated the pivot bolt. After the system was refilled, bled and adjusted, all worked well. The braided line certainly helps the front disk to stop better but a single ATE caliper – even with an aftermarket Luftmeister cast iron disk – is not the worlds best brake (BMW’s first attempt at ABS!). The only way of dramatically improving the brakes on the R90 would be to replace the forks, disks, master cylinder and callipers with units off a later model BMW or by cobbling something together using Brembo, Nissin, Lockheed, Tokico etc components off another make of motorcycle. If you were to do this, it would also be necessary to take expert advice about the ability of the standard spoked wheels to take the increased load arising from better brakes.

Rear Brake:

I wanted to replace the zinc plated actuating rod with stainless but to do this I needed to remove the fork which connects the brake rod to the brake pedal lever. This appeared to be screwed and sweated in place so I heated the fitting to a cherry red and was then able to unscrew the fitting. Once the fork fitting was removed, cleaned up and painted, I screwed it on to the 5mm stainless rod (which I had threaded) and secured it with red Loktite.

7.6 Wheels and Tyres:

The bike came with a good set of tyres so I didn’t think too much about this aspect at the time.

However, when it came time to get the bike back on the road after the work was completed, I realised that the rear tyre was well worn and – on closer examination – one size too big for the rim. I replaced the worn tyre with a Metzeler ME77 of the correct size.

On examination, the front tyre – a Metzeler ME33 – was also well worn. My BMW specialist suggested that I replace this with a Metzeler ME11 which is a semi ribbed type tyre. According to him the ME11 is not quite as grippy as the ME33 – only an issue when riding at 10/10th’s – whereas the ME11 gave a more stable front end than the ME33 for every day riding.

I took his advice and I have to say that the combination of the correct size ME77 on the back with an ME11 on the front is certainly a good combination for this model.

Other than tyres, the rims, hubs and bearings all went straight back on the bike after cleaning, polishing and checking for any loose spokes.

8. Clutch, Gearbox and Final Drive:

8.1 Clutch:

Another easy one. About 8 months before the rebuild I had fitted a new pressure plate and had the clutch plate machined so the clutch was in good shape as was the cable, actuating bearing and pivot pin.

8.2 Gearbox:

The gearbox was working quite well before the project so since it wasn’t broken – I didn’t fix it. Apparently, shimming these ‘boxes on reassembly is quite critical so I didn’t want to turn a gearbox into a Pandora’s box.

When mating the gearbox back to the engine, I lubricated the splines on the input shaft with Molykote D321R. This is not an approved BMW lubricant but, since the dealers I contacted did not stock the lubricant recommended by BMW, it would appear to be a good alternative. There appears to be no ill effect to clutch operation from using this product although it will take a few years to see if this really is a better way to lubricate this point. I doubt that use of D321R would do any harm.

On examination, the 8mm stud on the bell housing (top right) had been broken at some early stage in the bike’s life and the stud itself and female part of the thread was stuffed. I used a thread insert and fitted a new stud, screwing this in until it bottomed thinking that this was the correct depth (I found out later that the rule of thumb for setting stud depth is 3 times the diameter – 24mm in this case – screwed in finger tight). Not only is the gearbox retained by this stud but so too is the right hand aircleaner cover which has a slot that slips over the stud. When it came time to fit the aircleaner cover there was not enough free thread left on the stud to attach the cover and the nut. Rather than just unscrewing the stud or fitting a longer one, I removed the stud and used an M8x65mm high tensile bolt instead; it was a bit tight to fit but worked quite well. I probably should’ve used a stud rather than a bolt – studs do not stress the female thread in the casing so much – but I doubt that it would make a major difference in this case. If I hadn’t been able to remove the stud in situ, I would’ve had to remove the gearbox so this small detail could’ve cost me a lot of unnecessary work.

8.3 Final Drive:

Once again, everything in the final drive was working fine with no noise or excessive free play so it was just a case of putting it back together. The only thing to watch is to fit the final drive with the four nuts which join the final drive unit to the swingarm done up finger tight, and then replace the wheel to align the whole show before tightening the four nuts to the necessary tension (Haynes does not specify this torque, Clymer says it’s 46 N m, and the BMW manual is ambiguous; I used the Clymer figure).

9. Engine:

9.1 Bottom End:

I could not detect any free play in the big ends nor was there any apparent wear on the cams or the followers. The duplex timing chain had been replaced at 100,000km. There were no oil leaks. Experts tell me that boxer bottom ends are pretty bullet proof so – based on evidence and anecdote – I decided to leave well enough alone and not do the bottom end.

9.2 Top End:

I got a BMW specialist to measure and examine pistons, barrels and heads. This turned out to be some good news and some bad news.


The barrels showed slight glazing but were within tolerance for roundness and in generally good condition. Measurement showed some wear but not enough to justify a rebore so I made a decision to have the bores lightly honed and to fit new (standard) rings.

Pushrod tubes showed the ususal rusting caused by abrasion from road grit. It is possible to get new or aftermarket stainless pushrod tubes but I had heard that it is not easy to remove the old tubes or to fit the new ones. They are also difficult to paint in situ. After cleaning and treating the rust, I covered the tubes with large diameter heatshrink tubing; early days, but it seems to be working OK.

Pistons & Con Rods:

The gudgeon pins on both sides were tight so I made up a draw bolt to remove them – they were in good condition as were the little ends. Each piston looked and measured fine after cleaning. One ring was broken on one side.

When measuring the end gap of the new rings in the honed bores, the gap was approximately 0.10mm over the specified limit. The next oversize rings would’ve been too big so I decided to go with what I had. The engine will almost certainly need a rebore with new pistons and rings next time round but for now everything was acceptable. A subsequent compression check when the motor was going indicated that compression was “good” (about 130 psi on the left and 140psi on the right side).


On checking the heads, one of the valve guides was loose. An oversize valve guide was fitted by a specialist workshop. Valve springs were okay so the valves and valve seats were machined the valves were lapped and the whole lot reassembled. New inlet manifold stubs were fitted.


The rocker spindles felt good but the bad news was that the hard facing on the valve actuating arms on all of the rockers was badly worn.

My BMW specialist advised that the best solution was a rocker upgrade kit which adapts the rockers for the later models to fit the earlier twins. This was expensive but cheaper than having the rocker arms hardfaced.

The kit comprises the four rockers, the spindle support blocks (which can’t be used on this model), rubber sound dampers to fit between the fins and sufficient shims to obtain the correct end float. These rockers have a plastic insert which sits at the top of each rocker and are shorter than the original rockers by about 4mm. A side benefit of fitting this kit is quieter valve operation.

On assembling these rockers, the first task is to measure all the shims – they come in .50mm, .40mm, .35mm, .30mm, and .25mm. I measured each shim with a vernier and ended up with 5 piles arranged by thickness; I then divided each pile of shims by four to end up with a set for each rocker. On the later models, only one shim is used at the top of each rocker, so I placed most of the shims at the bottom of each rocker – to make up the gap on the shorter rocker – with one at the top.

Getting the correct end float is a fiddly job because you can’t really get an accurate end float setting until the head bolts are tensioned to the correct torque. I tried to set the end float to the specified 0.04-0.07mm but what I was really looking for was no detectable end float with free movement of the rockers. This involved removing several shims and mixing and matching to achieve the desired end float. Not difficult but fiddly and time consuming. As an alternative to repeatedly tensioning / relaxing the head bolts, I used a large G cramp to squeeze both rockers enough to achieve the desired end float whilst torquing the head bolts up in the recommended three stages. Non of the manuals gave any advice but this method seemed to work OK.

The end result seems to be effective. The new rockers are marginally quieter (as quite as these older boxers can get, I suppose).

PS: After about 500km I decided to fit Luftmeister chrome moly pushrods and needle roller bearings on the bottom of the rockers to replace the shim stack. These pushrods fit with zero valve clearance and work because they expand at a different rate to the heads and barrels, thus maintaining clearance. I set clearance by adjusting the tappets so that I could just rotate the pushrod. Works well except that they are no quieter than standard – noisier if anything.

9.3 Carburetors:

BMW/Bing make two overhaul kits for the Bing CV carburetors – one with new diaphragms and one without. The kit without diaphragms replaces all the “O” rings and gaskets and this was the one I used.

The only tricky part here is identifying which “O” rings go where, because they are of differing sizes. I methodically stripped and cleaned each carby individually. The old “O” rings fell to peices on removal but it was fairly obvious which size fitted which component.

One problem was the throttle butterflys. These have an “O” ring on the shaft but to free the shaft, it is necessary to undo the two brass screws which retain the butterfly valve on the shaft. One of these screws is on a normal thread but the other is locked in place by deformation of the free threads after insertion; as I found out, this screw tends to strip the last few threads on removal (the reason why Bing only lock one screw in this way and not both is not obvious). On reassembly I cleaned up the thread with a small tap and used red Loctite on both screws.

After getting the throttle butterflys off and removing the shaft, the “O” ring was in good condition on both carby’s. If the throttle butterflys move freely without any apparent slop or looseness, I would omit replacing this “O” ring. Also, if you do choose to do the butterflys, use a felt pen and mark each butterfly for “up” and “out” to make reassembly in the correct position easier.

10. Electrics:

On a ride from Sydney to Philip Island in 1992 the R90’s electric system had started to shut itself down, losing the starter motor all together and indicators and various other functions working erratically. On finally making it home, I checked out all the wiring connections but could not achieve reliable electrics so I decided to replace the main loom. This was one of the main reasons for refurbishing the R90.

The electrics on this model are not bad but not really up to modern standards. I guess the alternator is the main culprit – compare the 280 Watts produced by this unit to the 700w units fitted to the current K’s and R259’s! To work effectively, R-series need all electrical components and wiring to be in good condition and the battery needs to be kept trickle charged if not used regularly.

Motorcycles give their wiring a hard time – lots of heat, flex, rain, dust etc so the wiring on this R90 was pretty tatty after 160,000km and 21 years on the open road.

Apart from a soldering iron, a multimeter and cable ties, the use of various sizes of heat shrink tubing is useful to achieve a neat and rugged job on the wiring harness.

I was methodical on reconnecting everything, referring to the notes and drawings made during disconnection and using a multimeter and wiring diagrams to check for correct connections.

10.1 Alternator:

Since the electrics were suspect before starting refurbishment, I did not check the alternator, saving this for later (subsequently checked out OK). All I did was to check that all wiring and connectors were in good condition and that the brushes were servicable.

10.2 Starter Motor:

This was working well before the rebuild so all I did was check the brushes, and clean out the grooves on the commutator. On reassembly, the end-float was out of spec. so I shimmed this as necessary.

I had replaced the starter relay about eighteen months previously, so I knew this unit to be OK.

I did replace the positive cable from the battery to the starter motor because the old one looked tired. I used the genuine BMW part but on reflection it probably would’ve been cheaper to get one made to the right length by an auto electrician.

10.3 Diode Board (Rectifier):

Apart from some basic checks with a multimeter, there was not much I could do but trust that everything was OK. Rebuilt units can be had from some BMW aftermarket specialists.

10.4 Voltage Regulator:

The old voltage regulator was of the mechanical type which I decided to junk and replace with an electronic one. After checking around, the Bosch electronic equivalent – designated RE57 – was what I was looking for but I ended up with an Australian-made equivalent Ingram unit for $38 from a local auto electrician.

Replacing the voltage regulator is about the only improvement that can be made to the electrics. It won’t create watts where none exist but it will ensure that the charging circuit is running as efficiently as possible.

10.5 Wiring:

Main Loom:

There are two parts to this. The primary loom runs from the tail light – through the top left subframe tube – to the headlight whilst the secondary loom makes the connections from the alternator/diode board to the main loom and starter motor.

This was replaced entirely with nothing remarkable except that the notes and drawings made during disconnection made reconnection easy. Most of the notes involve noting wire connections and colours to the interconnect board in the headlight and main components like the starter relay.

Switch Assemblies:

The left hand switch assembly – horn and lights – had been replaced not so long ago so this went straight back on with no worries.

The right hand switch assembly – starter and indicators – was well past its “use-by” date so I decided to get a replacement. BMW could not supply the correct one and substituted a USA market (high handlebar) unit. The switch is identical but the wiring colours are different so a few minutes with a multimeter and the wiring diagram was needed to figure out the differences. Because the extra length of cable (needed for high bars) would create clutter in the headlight, I shortened the wires by about 20cm. I guess this type of substitution will become more common as the early R-series get older and inventory of spares get used up.

Other Wiring:

All the other wiring – such as for the headlight, gearbox neutral indicator etc – was all reused.

Remember to connect the two wires to the neutral indicator switch on the gearbox before the gearbox is rejoined to the engine. I forgot and it was difficult to reconnect these wires with the gearbox in situ.

The wires leading to the front indicators were originally soldered to the spade connectors inside the headlight but since the indicators have to come off to do any major work on the front end, I used screw connectors to reattach these wires to the spade connectors. Not elegant but easy.

The old horn was well and truly past it so I fitted and aftermarket Fiamm unit which is much better than the standard unit; Fiamm’s became standard fitment on later models in any case.

11. On The Road Again:

After all the bits were screwed back together and adjusted, and after all the wiring had been connected, the great moment had arrived.

First thing was to connect a new battery. Then a test of the electrics. Lights? Parking light? Low beam? High beam? Indicate left? Indicate right? Stoplight? Tail light? All systems “go” so far (apart from a dud indicator bulb and parking light).

Four litres of fuel in the tank. Fuel taps down. Choke full on. Ignition on. Deep breath and press the starter. Silence. Check for spark – all OK there. Think. No relay click. Tank off, connections to the relay showed two wires switched. Fix that, tank back on, repeat the drill.

One or two revolutions of the starter motor and the flat twin fired, a faint cloud of white smoke as the oil used in assembly burns and the motor settles into a fast idle. Ease the choke and the old girl is doing well.

What a great feeling! A great reward for a year of interesting – if somewhat obsessive – therapy.

After the first feeling of elation it was helmet on and off for a few tentative backstreet circuits. Brakes OK (as good as they’ll ever be, probably). Gear box OK. No loud bangs, whines or unusual noises. The R90 felt different – but it felt good.

The weeks that followed this initial startup were spent getting the bike registered again, riding it gently and letting everything bed in.

After 500km, I reset the tappets, checked the timing, and re synchronised the carburetors. I also tested the compression and check alternator output. Everything going well with the bike going better with each kilometer.

12. Appendix

A. Components and Costs:

The following costs are 1996 Australian dollars; they serve to illustrate relativity – ie you will need more parts than you first thought, parts costs will be high in any such project and will likely cost much more than the cost of the bike!

Item Cost Cumulative Cost Total
Replacement Parts:
Voltage Regulator (Ingram)


Inlet manifold


Hose clamps for manifolds


Battery carrier rubber mounts


Drive shaft coupling bolts


Swing arm dust cap


Swing arm dust seals


Ignition switch assembly


Seat lock


Main wiring harness


Engine wiring harness


Crankcase/gearbox stud


Gasket – swingarm to drive housing


Pannier frames


Gaskets – rocker cover


Gaskets – barrel base


Gaskets – cylinder head


Pushrod tube rubber grommets


Switch assembly – RH


Fuel taps


Side cover transfers


Swing arm boot


Swing arm boot hose clamps


Battery hold down strap


Battery hold down strap nuts




Speedo cable


Tacho cable




Centre stand spring




Dust cap




Feeler gauge


Head nut


Brake cable


Piston circlips


Rubber boot – front brake switch




Battery acid


Carburetor gasket kit



Stainless fasteners



BMW Workshop:
Rear tyre




Rocker kit


Valve Guide




Inlet manifold rubbers


Front tyre





Braided brake line (Earls Performance)







Sandblast and paint frame



B. Resources:

The following list is not exhaustive but are the resources I have found most useful in Australia:

Resource: Contact Details: Comments:
Internet BMW Riders web site Probably the most useful resource available. Has links to just about everything to do with BMW motorcycles plus lots of other interesting motorcycle links. If you don’t have access to the Internet – then do something about it!
MOTO-BINS Ltd 16 Surfleet Road, Surfleet, Spalding, Lincolnshire, PE11 4AG Tel. +44 1775 680580
Fax. +44 1775 680860

MOTO-BINS are well stocked, well organised and efficient. The airmail service between the UK and Australia means that most orders arrive in few days (providing they are under the dutiable limit of A$400).
Munich Motorcycles Unit 6, 9 Hayden Court Myaree 6154 Western Australia Tel. (08) 9317 3317
Fax. (08) 9317 3359

I suspect that Paul and Bruce are ex MOTO-BINS employees who have come to live in W.A.. They source new and secondhand parts from Germany and the UK and provide a good service – especially if you need something one-off or unusual.
The BM Shop 28 Wolverhampton St Stafford, Brisbane Qld, 4053 Tel. (07) 3356 6128
Fax. (07) 3356 5293

A good source of new and secondhand parts in Australia.

13. Bibliography

BMW Twins 1970 to 1988 Owners Workshop Manual by Jeremy Churchill. 1986, 1989Haynes Publishing Group, Sparkford Nr Yeovil, Somerset BA22 7JJ, England. ISBN 1-85010-492-1

BMW 2-Valve Twins ’70 to ’96 Service and Repair Manual by Jeremy Churchill. 1997 Haynes Publishing Group, Sparkford Nr Yeovil, Somerset BA22 7JJ, England. ISBN 1-85960-283-5

Clymer Motorcycle Repair Series. BMW 500-1000cc Twins 1970-1989 by Ed Scott. Randy Stephens Editor. 1990. 1991 Clymer Publications. Intertec Publishing Corporation. PO Box 12901, Overland Park, Kansas 66212 USA ISBN 0-89287-480-5

BMW Twins Restoration. All BMW Flat Twins, 1955-1985 by Mick Walker. 1992 Osprey Publishing, 59 Grosvenor Street, London, WIX 9DA ISBN 1-85532-191-2

Illustrated BMW Motorcycle Buyer’s Guide. by Stephan Knittel and Roland Slabon Motorbooks International Publishers & Wholesalers, PO Box 2, 729 Prospect Avenue, Osceola, WI 54020 USA ISBN 0-87938-404-2

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