SOHC.co.uk Forums > CB350/400

Main Bearing Shells proud of Crankcases

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hairygit:
I wouldn't advise it, as the plastigauge gave the right sizes, little point increasing clearances, just reduces the oil pressure at the mains and big ends, as the oil can squeeze past them more easily.  :o

simco1964:
Hi,
   Please tell me if my assumption is wrong!! but why cant you put the next coloured shell up? ie go from yellow to green? would that not reduce the clearance?

hairygit:
You could, but you would need to run it in VERY gently and carefully, really only recommended if the correct shells are not available. Motorcycle engines are built to much tighter tolerances than car engines, and when running in new shells, using the revs is not the issue, it's making sure you use the gearbox sensibly, not allowing the engine to "labour" during the running in period, as that would start scraping the surface of the shell, which you really don't want! After all, the film of oil under pressure is all that separates the crank from the shells, and imagine an engine rotating at 9-10,000 rpm, a split second of low oil pressure can cause catastrophic wear and damage. Mr Honda's engineers done a lot of research and development to decide the optimum clearances for parts, and why risk going against their advice? There are many high mileage 40+ yr old Hondas out there, many still on the original bottom ends, which says it all really. Get the clearances right, change oil and filter regularly, and they just keep on going!

simco1964:
Cheers, as you have mentioned in previous messages, bigger the clearance lower the oil pressure, thats why I'm concerned regarding Main Bearing clearances, 4 off 0,063 and 1 off 0,076 which basically is max limit on clearances.
     So was hoping by using the next size shell up, it would hopefully bring clearances more in to tolerance, am I right in thinking this way? :)

hairygit:
Yes indeed, but make sure whatever you do not to go below Honda's recommended clearances! ;D

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