Hello everyone, I am nearly done re-assembling my ‘94 Timberwolf 4x4 engine and have just run into a situation I am unfamiliar with and need help please. Long story short is I swapped most of my engine parts into a crankcase from a ‘96 Timberwolf. I have already transferred over my pinion drive gear and shim not knowing at the time that I need to potentially change the shim to ensure proper backlash with the driven gear. Looking at the Yamaha service manual, they are saying that since I am transferring my middle driven shaft, gears and transfer case to a new crankcase, I have to re-check all the shims in that area. My question is, how likely is it that I need to change all my shims and how critical is this step? My Clymer manual doesn’t say anything about this step? Is there really that much variation between engines?

 

Never had to do it on an engine but have done many ATV rear axle crown wheels and pinions, and all seem to take the same number of shims as they had originally. However changing cases is a fairly uncommon thing to do, so there may be more difference between engine cases. I used to build diffs at a truck and bus factory, and their cases, crown wheels and pinions varied wildly but, as usual in the UK, the machines they were made one were ancient and probably worn out.

 

Thanks. I tried to check my shim requirements using the Yamaha method but I’m running into an issue. I am supposed to use 3 numbers scribed into the crankcase for the shim selection math but I guess through years of mud and washing, they are too faint to see. Would there be a database with this information anywhere? Would there be any other method to figure this out?

 

As I wrote, I haven't done an engine bevel box but, there should be some way of checking when it is right, usually by backlash using a dial test indicator and painting yellow oil paint on a crown wheel tooth, then rolling round to squeeze the paint into the correct footprint. I would shim up same as it came apart and check backlash etc, then re shim if needed.

 

Thanks again for your help. Final question. I have determined the backlash on my reverse gear is too great. Unfortunately, Yamaha has discontinued the shims for that area so I am stuck with this condition. My question is, reverse not being used as often as forward and the engine only having 16 horsepower, should I be concerned about chipping teeth or just live with it?

 

Although Partzilla's list doesn't make much sense to me, nearly all the shims are still available from them. https://www.partzilla.com/catalog/ya...dle-drive-gear A couple of thosanths of extra backlash won't affect things much but, with it being spiral bevel, if it is well out, all the loading goes onto the wrong part of the tooth so may lead to chipped teeth.