big end shims

[Darrell Taylor]

the biggest problem with too tight clearances is space for lubrication and allowing for expansion a small clearance can diminish to nothing.
during assembly if the cranks conrod big end has 0.5mm clearance and the piston has 0.5mm clearance it gives space for potential or unavoidable off centre assembly , what can happen is if the crank sits off centre in the case by say 0.25mm the rod will centre up that 0.25mm leaving clearance but if you only have 0.25 on the big end the clearance is lost and the rod will contact onto the web or shim also clearance is lost for oil
this is also assuming that the conrod is straight which often arent,this can be checked with piston fitted into bore with no rings and a feeler gauge slid down along the gudgeon pin line to check for uneven clearance top and bottom and left to right