2003 WR450F Gearbox Rebuild Question(s)

Just doing a complete rebuild on my 2003 WR450F and have a question.

I received and installed my new output shaft and transmission shaft bearings to the sprocket side

crankcase half, but noticed that the new yamaha oem bearings have come with covers installed on

one side of the bearing.

I have currently installed both bearings with the covers left in, and facing into the crankcase as per

the attached photos but the old bearings had no such covers.

Will the covers stop any lubrication reaching the transmission and output shafts gear set. ie: splash fed ??

Will removing the covers create a drop in oil pressure behind the output shaft seal preventing the oil

feed behind the collar and into the output shafts internal oil gallery ??

Will it cause a drop in oil pressure to the transmission / clutch shafts oil delivery pipe ??

I'm inclined to remove the covers but these were genuine yamaha bearings i received so i'm a bit

confused as to why they would ship with a cover if it wasn't required and needed removing before

installation. The bearing part numbers that were ordered and received were 100% correct.

Leaving the covers in also makes sense as it would allow the bearings to sit in an oil bath

and also maintain oil pressure allowing more oil through the output shafts oil gallery and better

pressure to the transmission shafts oil feed pipe. The only problem i can see is that leaving the

covers in will prevent splash feeding to the gear set through the bearings race. Im not even

sure the gearset gets splash fed from these bearings.

Any advice or comments would be appreciated.



If I were installing them in my bike I would remove them.

You would be wrong to remove them, since that would cause a pressure drop in the transmission branch of the oil system. Oil is fed to the clutch release arm bore, where it splits off to these two bearing pockets. The difference between these two and the originals in that you have them installed backward. The sealed side goes in to the pocket, and the bearings are lubed by incidental splash, as are the rest of them.

When working with Yamaha stuff, the bearings and/or seals are installed with the lettering facing the installer. You see none on either of these two bearings.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now