Posted by Steve@Advance on August 31, 2018 at 10:51:06 from (66.169.147.211):
In Reply to: engine rebuilding? posted by jl ray on August 31, 2018 at 10:27:35:
Yes, you have to match the piston and rings to the bore size.
Typically, when an engine is rebored during an overhaul, the pistons are purchased before it is bored. They are measured then the cylinders are bored to the proper clearance for that particular piston set. If a piston needs to be replaced afterward, you can purchase a single over size piston, check the clearance with a micrometer and telescoping gauge, and it should be within tolerance provided the bore isn't worn. If too tight the cylinder can be honed. If too loose, you will have to go to the next oversize and and rebore the block.
The rings will also be sized to the bore spec. They will need to be checked though, the compression rings need .004" end gap per inch of cylinder bore. Oil rings are not as critical, generally .010" gap minimum.
The crank bearings are more critical. The crank will need to be miked for diameter and out of round conditions. If it has been ground undersize, that amount is deducted from the original size, and replacement bearings are ordered accordingly. Still, everything has to be check for final fit. Also the connecting rods need to be checked for proper bore. If any doubt, if the bearing spun, the caps have been switched, they will need to be reconditioned back to factory spec.
Most home shop mechanics don't have the proper equipment to take the measurements, and certainly don't have the necessary machinery to make corrections. Best to leave that up to a reputable machine shop.
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