Transmission Axle Shims

[3Phase]

The transmission axle shaft bolt under the clutch basket keeps working loose. Even Locktite won't hold it and the transmission begins to make a light knock at speed after twenty or thirty miles. After fifty to one-hundred miles it's loud and it starts to rattle on deceleration, too.

After removing the clutch cover, kicker and clutch basket to tighten that bolt three times in the last two weeks I'm going to pull exhaust pipes and drop the oil pan so I can check the gears and their clearances on the axle shaft. Something is out of kilter and it needs to be fixed before I tear up the transmission or it locks up in a corner at speed.

On the bright side, the engine has lots of power! I took a ride out to the beach and back this weekend, returning to civilization via Decker Canyon (narrow and twisty and it goes steeply up and on for miles) from PCH. The bike accelerates and handles better than it ever has for me and now it's time to go tear it apart again.


Regards,

Scott

[bikerphil]

Thay's an unusual problem you're having. As far as I know, that bolt with the built-in washer just tightens down against the bearing. Thread lock RED might do the trick. Of course, clean the threads of the shaft and the bolt first with contact cleaner. Is the bearing in good shape? JAT

[3Phase]

Thay's an unusual problem you're having. As far as I know, that bolt with the built-in washer just tightens down against the bearing. Thread lock RED might do the trick. Of course, clean the threads of the shaft and the bolt first with contact cleaner. Is the bearing in good shape? JAT

Phil, I re-shimmed the transmission and I think I may have added one too many shims between the 1st and 5th gear wheels. Torquing the special bolt brings the axle shaft assembly up against the inner race of the end bearing that's pressed into the case.

When the special bolt on the transmission axle shaft end is loose, turning the clutch shaft (without the clutch basket on it) makes a gentle, "thunk, thunk, thunk," and the clutch shaft moves in and out of the transmission. It's hitting something and it's possible that the 4th gear dogs are hitting the edges of the 1st gear slots.

I'll know more after the oil pan is off and I can see the gears, shims, dogs and slots.


Regards,

Scott

[trbig]

Not sure what's going on with that bolt. I had one loosen up on me once also. It backed out and the gear on the back side of the clutch basket ATE it. It was a hell of a racket.

On the clutch... that bearing that is around the clutch shaft is pressed on and shouldn't move. It lets the clutch basket clunk back and forth if it works loose.

I did a write up about this a while back, but the washer that goes on the back of the clutch basket next to the bearing, and the washer that is in the bottom of the clutch basket under the friction plates is easy to confuse. The first pic is the washer I had against that bearing and is the incorrect one. Notice the heat marks where the bearing was getting hot due to no oil being able to get through..





And here's the correct washer that leaves a gap for oil that you can see the bearings behind...





I have some video of pulling that shaft back and forth and clunking, but I can't seem to get to it here at work.

I think that if you shimmed something wrong on the actual gears, it would be grinding them. I got some washers that were exactly half the thickness of the stock washers on the transmission. I moved 1st gear 1/2 the distance closer to the 4th gear cog, and you could hear the gears hitting slightly in 4th gear.. and prematurely wore out 1st/4th. If you put a whole extra washer in there, I think you would be having some serious problems. You say you have one too many between 1st and 5th, but they are on opposite ends of the gear shaft. I don't know how tight you're putting on this bolt... but I hit mine pretty hard with an impact. That bolt has lots of threads to hold.. so it can take a pretty good snug.

I can't tell you for sure that the clutch shaft needs to be replaced... but in my motor and one I helped redo for another member.. we bought another one off Ebay to replace it that still had that bearing tight and pressed on the shaft. It just doesn't seem to me like it should be clunking in and out like that. When you pull in your clutch, the pressure plate isn't pushing against the basket and it lets it clunk back and forth.

Tod

P.S. See if this video will work.. Clunk

[3Phase]

Omf

Not sure what's going on with that bolt. I had one loosen up on me once also. It backed out and the gear on the back side of the clutch basket ATE it. It was a hell of a racket.

That's what almost happened the first time. Fortunately, I caught it before the loose bolt destroyed itself and the clutch. This time I was wrong. The axle shaft is what's thunking, not the clutch shaft. The clutch and clutch shaft are fine.

I think that if you shimmed something wrong on the actual gears, it would be grinding them. I got some washers that were exactly half the thickness of the stock washers on the transmission. I moved 1st gear 1/2 the distance closer to the 4th gear cog, and you could hear the gears hitting slightly in 4th gear.. and prematurely wore out 1st/4th. If you put a whole extra washer in there, I think you would be having some serious problems. You say you have one too many between 1st and 5th, but they are on opposite ends of the gear shaft. I don't know how tight you're putting on this bolt... but I hit mine pretty hard with an impact. That bolt has lots of threads to hold.. so it can take a pretty good snug.

When I was rebuilding the engine I had 2nd gear machined to accept a washer on both sides. I measured and re-shimmed everything between 1st and 5th gears with the transmission in the case sitting in my lap. I put one, final, shim between 1st gear and the Middle Drive gear. After running for a while it appears that, as you wrote above, 4th gear is a little too close to 1st gear and the dogs and slots have been hitting one another. Fortunately, I have a couple of spare gears and some thinner shims to move 1st gear away from 4th gear.

The part that merits the OMF is that by shimming the transmission in my lap with the cases separated, I removed the slop in the transmission but, unfortunately, I failed to notice that the transmission axle shaft is now precisely the thickness of one shim too far into the bearing in the case.

I can't just remove the oil pan, clutch and gear shift covers then sneak the axle shaft out through the bottom of the engine to change the shims, I have to pull the engine and split the case again!

I need a beer....


Regards,

Scott

[3Phase]

I have the case split and of course everything lines up perfectly. Now, 1st and 4th gear are not even close to hitting one another.

The gears all look good, so do the bearings and shims. It's time to give it up for the night; look again tomorrow after some sleep, then button it up and go for a ride.


Regards,

Scott

[3Phase]

The Shim Problem and Solution

Found the problem: the aftermarket shim I put in is too thick and too wide. It's 1mm (~0.40") thick and it needs half of that because it makes the 5th and 2nd gear dogs and slots sit too close and hit one another.

The shim is also to wide for where I put it between 1st gear and the Middle Drive gear. A stock Yamaha shim is narrower and would ride only againt the Middle Drive gear and 1st gear collar. The aftermarket shim rode against both gears and the 1st gear collar. As the shim wore thinner between the gears, the transmission axle shaft bolt would loosen up and the whole gear stack would lose tension.

Clockwise from left:
Middle Drive gear
1st gear and collar on the transmission axle shaft
Aftermarket 1mm shim
Yamaha 1mm shim




Yamaha 1mm shim matches 1st gear collar




Aftermarket 1mm shim is too wide. Notice the wear mark it left on 1st gear




Aftermarket 1mm shim is too wide for the 1st gear collar




Aftermarket 1mm shim in place between Middle Drive gear and 1st gear. It looks good, but it's doomed!




Yamaha 1mm shim. It looks wrong but it won't wear out rubbing against the gears



I don't have any pictures of the 2nd and 5th gear dogs and slots hitting each other but a 1mm shim is too thick. It makes the 1st and Middle Drive gears line up nicely but it moves the entire gear stack over to the left.

For my bike the shim needs to be half of that: 0.5mm (~0.020") thick between 1st gear and the Middle Drive gear and it must be a Yamaha shim or something very close to it. The Yamaha shim in the photos above is a spare I'll try to grind down but they're mind-bogglingly tough. I'll probably wind up with no finger tips and a nicely polished 1mm shim.


Regards,

Scott