Leaking gearbox oil GT750

[GTandcbr]

This copied on behalf of Scorch a new member who posted in the wrong place.
Hello group, I have a good running 73 GT750 that is burning gear oil and smoking (like a train) from the right cylinder. No drips or leaking from the weep hole at pump cover. Would this be the transmission oil seal that needs to be replaced? If so does anyone know a part # or dimensions so I can order? Thanks for your help

[tz375]

From that description, it sounds like the crank oil seal - second from the right. The primary drive gear is between center and right cylinders and on older bikes like your mate's that oil seal was retained by a steel plate that didn't do a great job of retaining the seal in place. The design was changed at engine #49895 at the same time as the change to crank design.

To test it, do a leakdown test on all 3 cylinders and listen for the air leak. When the crank is rebuilt, later style seal can be fitted but the motor will need old design pistons. Another fix would be to get a later crank and rebuild that and when it's time to fit it, get the barrels bored at the same time for new design pistons.

For the moment, it will still run but will smoke a lot and eventually the leak will create other problems.

[jabcb]

...
For the moment, it will still run but will smoke a lot and eventually the leak will create other problems.

My 75 GT750 ran reasonably fine but was increasingly hungry for burning tranny oil. Put the rebuild off longer than I should have and ended up having to buy a few new tranny gears.

[tz375]

For me that's not a problem because fortunately, I inherited way too many sets of transmissions.

The new oil seal will fit the old style crank, as will all the other seals, but the cranks has to come out and be split to do it. It's not a hard job, but those motors are a touch on the heavy side to lift.