here is nothing wrong with a chain drive primary if it is properly set up and tensioning the chain by the adjuster on the mounting plate as most manuals suggest is wrong. This is what will break the rollers on the chain and deposit them in the bottom of the case. Sound familiar?
You will need a good straight edge that will bridge the clutch basket and the engine sprocket and a depth gauge micrometer or the tank on a caliper. Remove the primary cover, alternator rotor and stator and the chain and loosen all adjusters on the transmission, rear wheel and axle.
The secret is in getting everything lined up right and here is how to do it.
Bridge the clutch basket with the straight edge forward to the engine sprocket. Use the depth gauge to measure the distance from the straight edge to teeth of the engine sprocket on the front and the rear of the sprocket. If it is not the same – snug up the trans mounting bolts a bit and using the rear chain and the transmission adjuster twist the transmission until the measurements on the front and rear of the engine sprocket are exactly the same. See where I’m going with this?
Now – noting the measurement from the engine sprocket – measure the distance from straight edge to the teeth of the clutch sprocket. If there is a difference, then shims must be added or subtracted behind the clutch basket until the measurements are all the same. There may be some wobble in the clutch basket from the bearing clearance so you might have to do some averaging. If the bearing is junk, any industrial bearing supply has them.
Install the chain and put some tension on it using the rear chain. Put the straight edge back on and using the measurements (You wrote them down, right?!). Set the alignment of the clutch using the adjuster on the mounting plate. You can only get a measurement on the rear of the engine sprocket with the chain on but it will be the same as the distance to the teeth on the clutch basket with it properly shimmed and the transmission aligned.
This may not be the best form of a written procedure for this job, but I think you’ll get the idea of it and can fill in the ambiguous areas when you get one of these in front of you. Let me know how you make out email and pass this along to others. I can also tell you how to set up the clutch so that it works properly – none of the fixes I’ve seen come anywhere near and it’s not that hard to do but I’m going to need some serious stroking – as in I’m looking for cheap 74-850 or disc brake equipped 750 basket case – because I’ve gotta take mine apart again to see how I did 15 years ago.
You are welcome.