Cylinder base O-Rings

[frogwash]

I have completely pulled this 1982 CB900F engine apart. Replacing and freshening up everything including, of course the o-rings. The cylinder base itself has o-ring grooves around the outside of steel cylinder sleeves.. These grooves are much deeper than the o-ring diameter so there will be no interference compression when assembling the barrels to the top half of the crankcase assembly. Of course, I have a base gasket but still trying to figure out the purpose of these o-rings! The groove is about 2.85 mm deep X 1.8mm wide. The o-ring is 2mm diameter (66.8mm x 2mm). It fits a little snug in the groove.

Thanks!