77 SE Extra Transmission Shim?

[nshaffer]

So I’m rebuilding a mystery motor from an 81 special that I got with the motor out of the frame. The motor is from a 77-78 special from the serial. I’m into the bottom end now and took apart the gear clusters for a cleaning. When I was putting it back together I noticed there was an extra shim near first gear not shown in any of the assembly drawings or service bulletins I could find. Anyone know if it’s supposed to be there?

Also, thanks for all the knowledge you guys have added to this forum. This is the first time I’ve had to ask a question!

 

[jetmechmarty]

If you remember where it came from, my inclination would be to reinstall it in the same position, especially if you have been riding the bike without transmission issues.

 

[nshaffer]

Haven’t had the bike running, so I’m unsure of how the transmission was running. Of course, that’s the part that stuck to my hand when I was repositioning things on the bench and I’m not sure of the order (although there’s only a few places it could go due to the ID). First gear seems to have a bit more play than the first gear I have on another gear cluster I compared it too, but that could be my imagination. Measured axial movement without the shim to compare the two and they were the same.

 

[nshaffer]

Not really sure what the purpose of an extra shim in this area would be except to try and correct for a worn out 1st gear?

 

[member28833]

You need to be aware of early 80's Yamahas having a history of transmission issues regarding the 1st and 2nd gear cogs / dogs.
Primarily the 3 and 4 cylinder models which made enough power to force the gears to move apart rounding the corners of the dogs.
Transmission then jumping into neutral. Resulting in bent shift forks too. This was real. Whether to blame slop or spacing or inferior hardness of the gears themselves is irrelevant. Both perhaps. There were service bulletins regarding gear lash shimming. I personally experienced this with an XJ650RJ, FJ1200, and a friends XS750.
You need to figure out where the shim was. Where to measure sloppy clearances and decide about shimming further.
XS650'S are not that powerful and this may not be as common in the XS650 reputation, but do be aware

 

[jetmechmarty]

You need to be aware of early 80's Yamahas having a history of transmission issues regarding the 1st and 2nd gear cogs / dogs.
Primarily the 3 and 4 cylinder models which made enough power to force the gears to move apart rounding the corners of the dogs.
Transmission then jumping into neutral. Resulting in bent shift forks too. This was real. Whether to blame slop or spacing or inferior hardness of the gears themselves is irrelevant. Both perhaps. There were service bulletins regarding gear lash shimming. I personally experienced this with an XJ650RJ, FJ1200, and a friends XS750.
You need to figure out where the shim was. Where to measure sloppy clearances and decide about shimming further.
XS650'S are not that powerful and this may not be as common in the XS650 reputation, but do be aware

I modified my XS1100 transmission when I had to replace the gears for this issue. I moved a shim like pictured from one side of the gear wheel to the other for tighter engagement of 2nd.

 

[nshaffer]

So the other gear set I’m comparing it to is a “low mileage” set from an ebay 76 motor. It is the older pre 77 spline design and does not have the shim. I measured axial movement of first gear with a dial indicator with the shaft fixtured in a vice. Without the extra shim, first gear was free to move .018” for both gear sets. With the shim, first gear on the 78 transmission moves around .010”

Any insights on which clearance is closer to optimal?

Thanks for your help!
Nick

 

[nshaffer]

This is with the shim between pt #25 and #26 on the above diagram…

 

[jetmechmarty]

Any insights on which clearance is closer to optimal?

I don't feel very qualified to provide and answer, but my inclination is to opt for less slop. Also, I like to use all of the parts in the diagram. Typically, because of my professional history, I don't often make changes to and original design, my XS1100 transmission being a notable exception.

 

[nshaffer]

Going to assemble it by the diagram without the extra shim and see how it shifts on the bench…will report back

 

[nshaffer]

Found this service bulletin TooManyXS1Bs posted up in reference to another issue. Looks like the 0.018” is too large of a clearance. It references 0.003” - 0.005” for spinning gears on the older transmissions. Not sure if 1st gear has a bit more clearance…think I saw a few people talking about that. Sounds like the shim was in there for a reason…