Bearing Clearacnce

[Tom Neimeyer]

I have put together 6-7 CBX motors in the last few years. Usually I record the numbers from the crank and the end of the case, buy the bearings the book references for the corosponding number/letter and all is fine. Usually between 0.0015" and 0.0025" clearance. However, this time, all are very close to .003" which is the service limit.



Now for the questions. If it calls for a "A" (black) bearing, can I replace it with a "AA" (blue") bearing? Re-check and if clearance is now O.K. run it? Likewise, if it calls for a "C" (green) bearing can I use a "B" (brown) bearing to take up some of the clearance?



I have other cranks, should I just put in another crank? This is the crank that was in the motor when it last ran. Since it did not belong to me, I do not know if it had low oil pressure, the crank does look good. I am not very good at "miking" the journals but I will try.



Any and all opinions are welcome and needed.



Cheers, Tom

[6bx]

Hi Tom



First you have to determine what the use of the motor it will be,then try to keep the clearances as close as possible (lets say 25) all the main bearings so you keep the OIL Pressure STABLE.Have you try plastigauge?.On my engine i use half A and B to bring it where i whant.

I hope i have help you.



George

[Tom Neimeyer]

George,

Yes, I did use plastigage, that is how I was able to determine the .003" clearance.



If I understand your message correctly, you are saying I can use different bearing halves on the same journal? This is the first time I have ever heard of mixing bearings on a journal.



Thanks for the info.

[6bx]

Hi Tom

On my opinion yes they do,because with a micrometer you will see that the edges are the same,so by using different shell "colours"we can achive as close as possible the same clearances,because is the area in the middle wich it lift,oil flow,and hold the crank.If you have spare shells plastigauge them and let me know the results.



6bx

[CBXDaveSwanson]

I say try the next size bearings, plastigauge them, and go for it. But be sure to check the crank OD's at a number of spots to make sure it's not egg shaped.