3aj gearbox bearings

[Peen]

Hi All,

Im currently rebuilding my 1988 3aj engine as 5th gear did its thing and spat bits of metal around the engine.

The output shaft bearings felt a bit rumbly so I am replacing them but I cant determine whether the left side output shaft bearing needs to be something special or regular clearance bearing will do. I have read conflicting reports on various forums about it. People on here have said normal clearance good quality bearings are fine, others elsewhere suggest C3 and one person apparently spoke to one Dave Lambeth who told him it its a special bearing and may need to be Yamaha OEM.

The numbers on the side of the bearing arent entirely clear, TMB305 is common enough but does the TMBX3 mean its C3 clearance? Have bearing codes changed slightly since 1988?

The bearing from Yamaha is around £70 in the UK, the same size from bearing suppliers is around £10-£15.

Does anyone one have some experience on this?

Thanks

Peen

[motorang]

Oh yes. Hell yes.

As that bearing seal is critical to keep the oil return and gearbox lubrication working, the seal needs to be able to cope with the oil temperature. Oil is guided between bearing seal and outbut shaft seal.
Normal NBR material can cope with up to 120°C short term, while long term working temperature is maxed out at 100 °C.

Yamaha uses FKM material (Viton) for higher wear and temperature resistance.

If you can get other bearings with an RS2 code (which stands for the single seal in better quality than the usual RS) you can use them. Usually half the price as the OEM part.
C3 is optional here as far as I know (only needed for the crankshaft bearings).

Andy