Spec sheet for Johnson indicates 0.0049" as max piston to cylinder clearance. I assume this means all around so overall piston diameter should be max 0.0098" less than the cylinder bore. I recently had my cylinders bored 0.020" over and I installed new 0.020" over pistons. I should have measured before assembly but assumed the machine shop work and the pistons ordered by the marina were OK. Current bored cylinders measure 3.205" and standard is supposed to be 3.188" so they're about 0.017"oversize.
The engine has probably only been run 20 minutes total and all at idle or slightly higher rpm...couldn't get it to run higher. Tore it back down and checked cylinders among other things. The hone marks are gone in large areas on the upstroke side of each cylinder and I can insert the corner of a 0.022" feeler gauge between the piston and cylinder wall, measured at the side and top non-concurrently. That much clearance seems excessive per the spec sheet, about double what it should be.
Should I indeed be working toward the specs or does it work OK to have almost double the spec clearance?
The bore seems right on but I suspect the pistons are undersized for 0.020" over.
The engine has probably only been run 20 minutes total and all at idle or slightly higher rpm...couldn't get it to run higher. Tore it back down and checked cylinders among other things. The hone marks are gone in large areas on the upstroke side of each cylinder and I can insert the corner of a 0.022" feeler gauge between the piston and cylinder wall, measured at the side and top non-concurrently. That much clearance seems excessive per the spec sheet, about double what it should be.
Should I indeed be working toward the specs or does it work OK to have almost double the spec clearance?
The bore seems right on but I suspect the pistons are undersized for 0.020" over.