Right hand crank bearings

[2-strokefanUK]

Reading the latest Classic Motorcycle Mechanics today ( Oct.2016 issue ) has left me concerned as to what state my crank bearings are in.
The article on pages 82 / 83, by Stan Stephens, says that usually between 21,000 and 23,000 miles the right hand main bearings crack around the circlip groove.
My engine, as far as I know, has never been apart, and has covered 74.000 Kms, which is a lot more than 23,000 miles. There are no nasty noises, I give it a good thrash every so often, should I be worried ?

[steveho]

Whilst these failures are documented, I would suggest that not a common occurrence. You can't plan or do anything to really avoid the bearing failure, so just enjoy the bike as it is. 74k kms is going some.! Well done!

[silverstrom]

I wouldn't worry about it. While Stan is recognized as one of the best in the business, not even he can predict the life of a bearing. There are many variables, including oil quality, temperature, etc. Yamaha bearings are not known for failing. Stan has also said that the TZR250 (2MA) crank is good for 70,000 km. That would include the bearings.

If you are still concerned about it and want to change the bearings you might as well do a full rebuild.

[2-strokefanUK]

Whilst these failures are documented, I would suggest that not a common occurrence. You can't plan or do anything to really avoid the bearing failure, so just enjoy the bike as it is. 74k kms is going some.! Well done!

I can't take the credit for the bike's mileage - I bought it early this year from an 84 year old German gentleman, who had bought the bike new. He had / has a holiday home in Portugal, and I think a lot of the mileage was amassed going to and fro it.
I have to say though, the bike does go well.

[silverstrom]

Your speedometer may have been replaced once or multiple times. Disregard what it says now because unless you have the full history it means nothing.

You say the bike has 73,000 KM. It's not a UK market bike? It would be miles if it was.

[WVWRZ500N]

Having built over 40 500s in the past 15 years I can partially agree with Stan's conclusion. I say partly as I don't inquiry as to the mileage of the engines I'm working on. However, in particular the upper crank especially has a bad habit of going out of true on the primary side. I speculate it has to do with the torque pulse within the 50* V but can't be for sure. Regardless, the outer fly weight will run out of true and then beat the bearing/case. If not caught soon it will typically beat out the case aluminum and then cracks will occur in the bearing outer race. I have had several that fell off the crank when I removed them from the cases. For this reason I ALWAYS have them welded when trued. Simply a safety net to keep them from walking later.

If you have a bearing cracked or crank far out of true it will make noise and you should notice it. Don't run it anymore if you do notice a sound as it will only cause more damage.