Re: Cylinder and piston wear

Posted by Owen_Dyneto On 2014/9/30 22:18:30

I'm not surprised you found no specification for allowable taper, you might find that recommendation in a Motors Manual but car manufacturers would frown on fitting new pistons and/or rings in worn bores. Years back when money for engine work was quite limited, we often did what we called "semi" rebuilds on engines with a good crankshaft and taper of perhaps 0.007" or less and we expected to get maybe 10,000 or 15,000 miles of reasonable service life from our efforts. We cut the ridge of course, honed the cylinder walls, and either knurled the piston skirts to expand them a bit or fitted piston expanders. Ring grooves were usually well-worn so they were often recut for new standard rings with spacers. We usually fit oversize wrist pins, new rod bearings, new timing chain and sometimes new gears, and often did a valve grind.

This surely isn't the best way to go, but if it's all the budget allows you can get some further mileage from your engine, though certainly not to true rebuilt standards and it begs the question was the money well spent as opposed to saving enough to do the job properly. If you need to replace one or more pistons, replacement pistons should be the same weight as the OEM but best to check on a scale to be sure they are within +/- perhaps 7 grams or less of the old pistons. Kanter, Max and Egge all have replacement pistons though I don't see from your pictures just what damage yours have.

I don't know what engine you're speaking of, perhaps a 115C? For that engine I don't think compression of 85-95 psi is all that low so I'm not sure that's the cause of your smoking condition. If the engine has only been driven 10 or 20 miles since it's been back in service, perhaps tearing it down was premature? In particular, were the oil control rings unbroken, free in the grooves, and the oil drain holes in the piston groove open and clean?