Transmission shimming & undercutting

[argo1974]

TX750 transmission is pretty robust and does its job without excessive problems even in high mileage bikes. Well known issues are pitting on 4th gear pair and jumping out of gear under load though. The latter mostly happens in 1st or 5th gear due to rounded engagement dogs.

In service manual, Yamaha claims engine/transmission oil supply relation with pressurized oil being around 80:20. According to my measurements and calculations, 95:5 would be more real. In fact, transmission lubrication is mostly provided by oil fog present inside engine cases during engine running. To increase oil flow for better lubrication of the 4th gear pair, transmission oil orifice can be enlarged to 2mm by drilling.

Transmission shimming example:
Input shaft: I added two 25x35x0.2mm shims to have the side clearance of particular gears reduced to around 0.1-0.12mm.
Output shaft: I added one 20x28x0.3mm shim. Other gears were already well shimmed with toothed washers by factory. Note, output shaft diameter is 30mm in case you need additional shims. Install shim(s) between toothed washer and circlip then.

I found the circlip grooves little too wide for the actual (stock) circlips. When checking clearance while shimming, if there is another gear supported by this particular circlip from the other side (e.g. top right on the picture), be careful your clearance is still adequate if circlip is pushed inwards by another gear.

Undercutting: 4th driven and its neighbor gear were already undercut to 3 degrees by factory. The same applies to MikesXS replica gear I used on output shaft. MikesXS overdrive 5th gear on input shaft as well as all other stock round dogs/counterparts + 1st gear dogs/counterparts were not undercut, so I had them machined to the same 3 degrees on the load side.



1st gear undercut (output shaft)


3rd gear undercut (output shaft)


5th gear undercut (input shaft)

[bigskyforever]

Argo;

Can you tell me where the scavenge pump oil is diverted from the return to the tank to the transmission. Is this somewhere in the cases? or is it diverted in the pump housing, or is there a restrictor? Just trying to get a complete understanding of how the oil gets to the trans.
Your input would be appreciated.

Thanks

[argo1974]

On the photo, long red arrow is showing oil flow from scavenge pump to oil tank.
There is also a place oil flow is diverted. Oil flow to the transmission is restricted by an bronze orifice. From there, oil will enter transmission shaft and another passage (red arrow). From there, it will flow inside shift fork shaft with oil holes. Oil then drops continuously onto transmission gears.
Oil intake from oil pan is shown green.

[bigskyforever]

Argo;

Thanks for the great picture with the details.