Here's the basics of how to do it. The bike is a '73 R75/5, I'm sure that a lot of this will apply to later bikes, but it looks like in '79 there were some pretty major changes made to the timing chain and its tensioner(s).
I already had the points, the ignition cam, and their backing plate off. I was changing the cam seal when part of the old one fell into the engine. That's what started the cam chain change. Why pull the timing cover off w/o changing the chain, I thought. Especially since engine clatter had been getting worse lately.
First take off all of the rest of the parts mounted on the timing cover. It's pretty obvious, with only a few points worth mentioning.
You should really disconnect the battery before removing the diode board. Trust me, you will regret it if you skip this step.
The alternator rotor is on a tapered shaft. To pull it, remove the screw. It will act weird, after disengaging the threads in the crank, it will engage a second set of threads in the rotor. Those threads are used to pull it. When the screw is out, slip a three inch long metal rod into the hole. Run the screw back in until it hits the metal rod and then tighten it a bit. That should pop the rotor off. Use a stout metal rod. I've heard stories of rods getting bent and making a real mess of this job.
While I've never had any trouble with my 1/4 inch mild steel rod, I got several reports from people who mushroomed the ends of mild steel rods in this service. They suggested either a hardened rod or a special tool made by grinding the ends off of a hard bolt. If I was concerned, I'd probably go with the harder rod. I'd probably cut the head off of a hard bolt with a cutoff wheel. If you do this, make sure that you don't get it too hot. Depending on the material, you could soften the end of the new rod this way.
Now you'll notice that there is one wire that goes through a hole in the upper portion of the timing cover and connects to the starter motor. To remove it easily, the starter motor cover must come off. Take out the air filter and loosen the right hand air filter cover. Remember that these directions are for older boxers with the round air cleaner. Then remove the two cover screws and lift/rotate the cover off. At first it will seem like you need to remove the coils for clearance, but you don't.
Some people reported getting this connector off through the hole in the timing cover with a pair of needle-nose pliers. Your choice.
Remove the bolt that holds in the tach cable (for those with mechanical tachs). Pull the tach cable out. Mine was stubborn, I never did figure out what was holding it, it finally just popped out.
Now remove the fasteners that hold the timing cover on. There are 9 allen head capscrews and 3 funky looking allen head nuts.
Remove the timing cover. I had to gently whack the upper portion with a rubber mallet to break the gasket sealer loose. Mine popped right off, the manual suggested heating the area around the front crank bearing if there are problems. They also mentioned that a puller existed. I suspect that if needed, a puller could be cobbled together out of hardware store materials.
Now make some marks so that you can align the gears again. I could find the factory mark on the cam gear, but not on the crank.
Now remove the cam tensioner. At least on a /5 this is a good idea. The pictures in my manual seem to indicate that '79 and later tensioners are different. The /5 had one, the 79 and later seem to have two. Use your judgment. On mine, one circlip and one bolt removed it and its spring.
Now remove the cam chain. If it is the original chain, you'll have to cut it. You can use a pair of bolt cutters or a cutoff wheel in a die grinder. A Dremel Moto Tool qualifies. Be careful not to get debris into your engine. I was planning to use a dampened cloth to protect the engine.
If your cam chain has already been replaced once, you might already have a chain with a master link. Count your blessings and pop the clip off and slide out the link. Expect two plates to fall out as well.
I was surprised to discover that my timing chain was a master link equipped unit. It appeared identical to the new Luftmeister part, except that it had noticeably more slack than the new part would later exhibit.
Now install the new chain. Make sure that the sprockets are still lined up correctly. The master link will have to be installed from the outside, as there is not enough room to slip it in from behind. In fact, it's so tight that the clip is hard to get on. It took me several tries and a lot of bad language to get it on. Don't forget the two plates that must be slipped in.
The clip on the master link should be installed so that the open end is trailing as the engine rotates. This makes it less likely to come undone. An uncomfortable thought....
While you are doing this, be careful. there are several openings that could allow parts to drop into the sump. Covering them with a rag would be a good idea.
Now remove the old cam and crank seals from the timing cover. Don't put the new ones back in yet. It's tempting, but they might get damaged while heating and tapping the cover back on.
Now put the timing cover back on. I used a very light coat of Permatex #2 (the non hardening kind) on the gasket.
The instructions in my manual talked about gasket shims above the area that forms the timing chain cavity, but below the starter cover. The gasket doesn't go up that high, there's nothing to seal. But I suppose that tightening the top two bolts w/o something in the gap would flex the cover. My new gasket didn't come with shims, there were none present when I took the cover off and my Haynes manual did not have any pictures of them. So I winged it and cut some strips of gasket material and stuck them to the front of the engine with some of the Permatex.
It turns out that the shims are actually supposed to be doughnuts of the same material as the main timing cover gasket, one for each of the two upper bolt holes.
To get the cover back on, you might have to heat it to expand it. That way it will slip over the front crank bearing more easily. Try it cold, but might have to heat it. I had to heat mine. I used a propane torch. I got it just hot enough that touching the area around the crank bearing bore for a prolonged period of time was uncomfortable.
You can use a rubber mallet to *gently* tap the cover back on. Just be make sure it goes on straight. And be gentle.
Once the cover is on, loosely install the fasteners. Don't tighten them down until you center the cam bore on the camshaft. If you don't have it centered, you'll have a tough time keeping a working cam seal. In fact, you can get it so far off-center that I suspect you might have trouble setting the points.
Now install the cam and crankshaft seals. You can use an appropriately sized socket to tap them in. Rub motor oil on them first to lubricate them. Be careful to get them straight. I had a tough time getting the crank seal in straight. The cam seal was easy.
Once the timing cover is on, the rest of the job is pretty straightforward, just put the parts back on in the reverse order of removal. Don't forget to put the wire back on the starter motor before putting the starter cover back on. This would be a good time to clean the connections going to the starter motor.
When I got my engine back together and the bike was running again I was quite pleased with the reduced clatter. Well worth the effort.