Topic: Typical mileage for transmission bearings before replacement

[zabzob]

So I'm doing a rebuild on my CB750 and thought I would do every possible thing I could while in there. Primary chains and tensioner are definitely being replaced, but I am unsure about transmission bearings. Things are getting expensive and I'd like to avoid replacing them if I can. I suspect the answer will be to rotate the shafts and listen for bearing noise, which I will do. I am wondering how long the bearings on these transmissions typically last though. At 36,000 miles is it likely they'll need replacement? Anybody experienced a failure of these bearings before?

[Don R]

 I'd assume I the engine was well maintained and no junk went through them they would be good to go for a long time. On the other hand if they are standard sizes it might be cheap to buy the peace of mind and get the new ones.

[bryanj]

As long as there is no metal crap in there they are just run in

[Kevin D]

80000 miles and counting.....

I have heard stories of running the chain too tight, abusing the output bearing.

[ofreen]

The ones in mine have just a hair under 162,000 miles on them and are still fine but I know how the engine has been treated for the last 40 1/2 years.

[slikwilli420]

A full set from Yamiya is under $100. Just go for it if you're worried.

[PeWe]

80000 miles and counting.....

I have heard stories of running the chain too tight, abusing the output bearing.

I have heard about towing the bike and let it roll without engine running. The final shaft bearing will not get any oil.

Early CB750 had single row final shaft bearing. Replace to double if it is the early type. The axle need to be replaced too in that case. My K2 cases had traces of an early output shaft with its 2 bearings. Replaced with the later. Not too late (k7---)

Yamiya pic is the early design. Later has double row inside the front sprocket and no grooves in those bearings
http://www.yamiya750.com/index.php?main_page=index&cPath=246_21_250_53

I replaced all bearings when rebuild at 65.000km. Just for sure I had no signs of bad bearings but bike had have 50.000 tough km's by me  with bad oils
The bearing in lower case is a standard bearing. Others mounted on the trans axles are trickier to replace and 3 of them have a groove.
The needle bearings inside the primary drive hub are cheap std bearings. Tricky to replace without special tool
Clean all bearings, roll them around and feel for a sandy feeling,like particles in it. If it feel like that replace it.
Yamiya750 has almost all trans bearings

Check this guide:
https://wrenchandspanner.wordpress.com/2014/12/16/cb750f-transmission-bearings/

I think it can be an idea to replace the cush rubbers inside the primary drive hub. They can be hard after 40 years.

Check the clutch pressure plate (alu) The bearing is OK and will not fall out by itself? I had one that did like that replaced by a used in good shape. I think the clutch lever might have had not enough play so the bearing has rolled constantly and not only when using the clutch.

The other side where a std bearing sit inside a cover attached by 4 countersunk M6 bolts. Is this also sitting way too lose? falling out by itself?