Topic: main bearings

[stigy]

hi all, im having an issue with my mechanic he tells me thires only one size listed for main bearings he put the cases together and the crank locks, so tells me the cases must be miss mached, from what I have red on hear the crank sould have a code on it for crank bearing sizes black brown green yellow, is this correct?
all so would changing crank cases change the bearing needed or will different cranks fit different cases using the bearing sizes marked on the crank?

[stewonepot]

The cases should be matched pairs as they are machined together
regards Stew
merry christmas

[stigy]

thanks , but if the cases are a pair do you still go by the crank markings for bearing sizes?
and is it ok to use different crank

[Jerry Rxman Griffin aka MuthaF'er]

The top half and bottom case halves are matched when they are align bored so they should not be separated or mixed and matched. The top half has 5 letter codes stamped into it on the front. Those are the codes for the cases. The crank shaft has letter sizes scrawled onto it by the primary chain sprocket that represent the journal sizes. (It also has 4 numbers scrawled which are for the rod bearings so don't confuse those) The crank scrawlings take a trained eye to read usually as it's not easy to do. You use both these to size your bearings according to the charts in the manuals. That is a starting point. The final determination is based on the use of Plastigauge. And yes, there are 4 sizes of bearings that are referred to by the 4 corresponding color codes you mention. Hopefully this 'mechanic' will listen to reason. If not then direct him back here.

Yes, you can use a different crank but you still have to size your bearing according to the scrawled letters on the crank and the stamped letters on the case half according to the chart and they should be Plastigauged for final fitment.

[stigy]

thanks for the help much appriciated

[Whaleman]

I would maybe lose a little respect for your mechanics knowledge of this engine if he really believes there is only one size bearing listed. Dan

[MRieck]

What size engine?? CB500/550's have green mains available from Silvers and CMSNL....that should satisfy 99.99% of the bikes out there. 750's have all available I believe. 500/550 con rod bearings are another story but some are available.

[dave500]

if the crank locks he hasn't measured the assembly just torqued it all up,lose that guy.