K Engine Output Shaft Noise Diagnosis & Repair Procedure
By John A. Brown
Indications: A buzzing created at higher engine RPM (2000+ RPM) originating from the alternator area of the engine. Initial thoughts might lead to checking the alternator bearing, which is a likely culprit. If this is NOT your problem, you most likely face loose or broken rivets in the lash gear assembly.
Special tools: gear puller, Uni-Moly C220 spray lubricant, Torx T30 bit for bell housing removal, calipers, torque wrench capable of 102 ft lbs torque for clutch nut.
I am going to start at the point at which the transmission is pulled off the bike since there is a FAQ already on performing a clutch spline lube which describes the procedure to get into the clutch area.
I won’t duplicate information you can find in Clymer’s and Hayne’s manuals either, they do a good job describing how to remove key parts in this process.
You will need to remove:
- Lower faring parts and front cowling
- Gas tank
- Side bags and mounts, topcase
- Rear tire
Also, Drain oil from crankcase and remove oil filter, leave filter cover off.
- Remove the alternator and the alternator drive dog. The drive dog is a spline gear and will need a gear puller or similar pry tool to remove it.
- Remove the clutch following the Clymer’s instructions.
- Remove the water/oil pump assembly following Clymer’s instructions, BUT note that where Clymer indicates there are 6 bolts holding the assembly to the engine housing there are really 7!
- Remove oil sump pan.
- Remove the clutch bell housing, or “intermediate housing” as Clymer refers to it. To do so, you will need to take the weight of the engine off the frame by placing a transmission jack under the rear of the engine. Since the sump pan is removed, place a 2×4 on the jack and raise it to come in contact with the rear of the lower engine housing. Remove all the Torx bolts on the inside of the bell housing then remove the frame bolt holding the bell housing to the frame. Remove the bell housing.
- Insert a bar or screw driver shaft into the water pump end of the output shaft. It should slide far enough into the shaft to ensure it will not slip out when engine weight is applied to it. Using crate straps, or similar strap (I used a cargo strap) loop one end around the output shaft, and secure it to the frame. Loop another cable around the protruding bar (or screwdriver) end on the front of the output shaft and secure it to the frame. The absorber gear and idle gear are under tension and we do NOT want the tension to force the output shaft out on us when the lower engine case is removed! The rear crate strap is going to support the weight of the engine, when you remove the transmission jack… make SURE it is tight and secure!BMW requires that the output shaft position be marked, with cylinders 1 & 4 at TDC, so that it can be replaced in it’s original position. I do not see that this is necessary and, indeed, my output shaft popped out of position before I had a chance to mark it. I’ve noticed no adverse effects of just replacing it in any position. So, follow steps #7, 8, 11, 12, 15 if you wish to follow BMW’s guidelines for realigning the output shaft and crankshaft upon reinstallation, it certainly cannot hurt! Also note: these gears have different names depending who you are talking to! The gear attached to the aluminum carrier is called: absorber gear, the “free” gear is called: lash gear, tensioning gear, or idle gear. I will use Clymer’s terms: absorber and idle gear.
- Remove the hall timing cover at the front of the engine to access the crankshaft.
- Thru the hall timing area, turn the crankshaft COUNTER CLOCKWISE (as viewed facing the front of the engine) so cylinders 1 & 4 are at Top Dead Center. Mark the timing plate to indicate the TDC position.
- Remove the transmission jack. You can now remove the lower engine case.
- Clean the gear teeth (idle gear AND absorber gear) with contact cleaner, or a little brake cleaner on a cloth like I did.
- Double check that cylinders 1 & 4 are at TDC.
- Paint a reference mark on the teeth of both the idle and absorber gears that line up with the edge of the housing. You will need to realign these marks upon reinstallation.
- Replace the transmission jack under the rear of the engine case and lift the engine just enough to take the tension off the crate strap.
- Carefully support the output shaft and loosen the crate straps holding it in place. The output shaft bearing is held in place with Loctite, you may need to heat it up in order to remove the output shaft. Mine just dropped right off. Remove the shaft.
- Scribe a reference mark on the aluminum carrier lining up with the painted mark in case the paint is removed while working/cleaning the assembly. Scribe the idle gear too.
- Be VERY careful with the two gears, you do NOT want to score or otherwise damage the teeth!
- Remove the circlip securing the bearing.
- Use puller tool BMW #008400 and center support BMW #331-307 to remove the bearing. OR, use a gear puller like I did. A Sears combination 2 & 3 clamp gear puller worked just fine!
- Check annular spring location pin on absorber gear for wear, it is known to wear a groove in it. If it’s worn, there is a procedure to replace the pin (see below: Location Pin Replacement). Check the pin on the idle gear also. If worn, idle gear will have to be replaced.
- Check the annular spring for wear and replace if necessary.
- I would highly recommend replacing the needle bearing and main bearing, you don’t want to have to come back in here if you can help it! They are not very expensive either.
- Check the rivet heads. At first glance, mine seemed OK. I was expecting them to be visibly loose, mine were not. I took a pair of pliers and tried to turn each head, two were definitely loose. Placing one end of the rivet on a anvil, I tamped the other end flat to snug up the rivet, then reversed the gear placing the rivet head on the anvil, and inserted a phillips screwdriver in the other end, and tamped it to spread the rivet more. This fixed my buzzing problem.
- Early model K bikes will have a tension spring between the main bearing and the idle gear. This spring was superseded with a shim. Discard spring and follow step #24 to select replacement shim. If yours has a shim, check that the shim is the correct size! Mine was NOT!
- Checking the shim: Place the idle gear on the absorber gear WITHOUT the annual spring in place. Use a caliper to measure the height above the surface of the idle gear to the shoulder the main bearing rests on when pressed into place. Select a shim between 0.07 to 0.09 mm of this measured value. If you cannot find one within this range, which was my case, buy the closest oversized shim and use emery paper to work it into tolerance.
- Spray all surfaces of the absorber and idle gears, and annular spring with Uni-Moly C220 lubricant. If you cannot find this lubricant, any spray Moly lubricant will work. Allow to dry. Check (dare I say it?) your Honda dealer and while you are there, buy some Honda Moly Spline lube! You’ll need it for the clutch spline lube job!
- Use circlip pliers and install annual spring followed by idle gear.
- Install shim.
- Warm main bearing in oven. I set it to 400 degrees and allowed the bearing to sit in the oven for about 20-30 minutes. Press bearing into place on output shaft. I used the old bearing lying on top of the new one for tamping it into place.
- Install new bearing retaining circlip with dished side TOWARD the bearing. Use a drift to seat circlip into the retaining groove.
- Clean the spline and socket engagement and spray with Uni-Moly. Allow 30 minutes drying time. Apply a coat of oil to the needle bearing and main bearing.
- Preload idle gear. This is tricky! Do NOT pry on the teeth of the gears!!! You may damage them! Instead, use a blade screwdriver to pry against a rivet head and one of the holes in the idle gear. Have a pair of vice grips with several wraps of duct tape around each jaw to clamp the gears together when they are tensioned. You want to tension the idle gear so the teeth of the two gears are aligned.
- Apply loctite 1110B to rear output shaft bearing and location ring.
- Double check that engine is still at TDC.
- Align the timing mark scored on the aluminum absorber gear carrier with the engine case and reinstall the output shaft. Check that location rings at either end are properly lined up in the engine casing.
- Use crate straps to again hold output shaft in place. Make sure the rear crate strap holding the output shaft is tight enough to hold the shaft in place when under tension!
- Remove vice grips from gear assembly. Check that the output shaft is properly meshed with crank shaft and has not slipped.
- Prepare lower engine housing surfaces with 3Bond 1207B sealant (or equivalent). Allow 10 minutes to cure so solvents can evaporate.
- Replace oil and coolant passageway o-rings in upper engine housing.
- Align lower case with bearing location rings on output shaft. Place into position against upper engine housing and again ensure engagement of location rings.
- Insert 2 hex bolts into rear 2 allen bolts in front of output shaft to secure lower case engine housing.
- Torque the hex bolts to 40 Nm and the allen bolts to 18 Nm
- Replace lower housing cover outer bolts and torque to 7 Nm
Reassemble remaining components.
The noise you will hear should now be different than before and will diminish as the new parts wear in.
Location Pin Replacement:
Note: I did not have to perform this procedure and merely include the procedure BMW specifies.
- Mark location of pin on the inside of the aluminum absorber gear carrier.
- Punch mark at the base where the new hole will be drilled to punch out the pin.
- Use a 3mm drill bit and drill a hole in the aluminum housing ONLY! You will need a LONG bit to do so.
- Press out the pin from the inside of the aluminum carrier using a 1/8″ drift.
- Coat new pin with loctite and press in to a height of 5 to 5.5 mm above absorber gear surface. To make this process easier, place a 5mm nut around the pin to act as a stop and drive the new pin in place.
Engine Output Shaft Diagnosis
By Spike Cornelius
Driving to work one day the engine suddenly stopped making my FY K100 roll. Output shaft rivet failure was my first thought.
I followed the same preliminary steps in the repair of my output shaft as John Brown, but following the advice of Haynes I removed the engine from the frame. This allowed me to turn the engine on the valve cover, making access to the lower innards much easier.
When the bottom came off, the heads of the rivets that secured the shock absorber to the drive gear fell out, confirming my diagnosis.
The first picture shows the difference in the new versus old driven gears. The second picture shows where to look to see if your rivets are loosening. The crankshaft cover can be moved out of the way without draining the cooling system by flexing the drain hose and swinging the cover on it. You will need to be careful when reassembling to get the crankshaft cover seal into its groove properly to prevent leakage, but I did not find it difficult.
Rotating the back wheel with the transmission in gear, while peeking under the back of the crankshaft should let you see if there is any play between the driven hub and the gear.