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Welcome to my Pistons, Rings and Cylinders Tips page. Below are a few tips for engine piston and cylinder repair and restoration.
Probably the most mis-understood areas of an engine are the pistons, rings and cylinders.
Here, I'll try to explain the science behind these apparently simple parts - which are also among the most complex.
The cylinder - pretty straightforward to check - and fix. Important factors to consider regarding the cylinder are:

Bore taper - The maximum taper is a matter of judgement - there is no hard fast rule that applies to ALL engines. Some can get by with as much as .020" taper and be rerung, while others may not be able to operate satisfactorily on as little as .005". Manufacturers limits are the best ones followed here, where you can find them.

Out of round - When cylinder out of roundness exceeds .005", it should be rebored or resleeved since it will be difficult to get round rings to effectively seal such a cylinder.

Taper and out of round are best repaired by reboring or resleeving. Honing alone cannot properly repair cylinder which exceed the above limits. If boring a cylinder, it is recommended that the cylinder be bored to within .002" to .003" of desired size, then finished with a good quality hone.

Cylinders that do not have a wavy or scuffed finish do not necessarily need to be honed provided the proper break-in procedures are followed. A good glazed finish is also an anti-scuff finish. These break-in procedures call for applying a load to the engine for short pereiods and in rapid succession after warmup. This forces the rings outward against the cylinder walls, and allows for the wear needed to seat the rings. Vary the RPM during initial use. Rapid acceleration from low speed to full rated speed with load will aid breakin.

A common misconception is that honing actually causes wear, or failure. This simply is not the case. Proper honing and cleaning result in quick breakin and proper ring seating. Where the failure occurs is in the cleaning stage AFTER honing. Gasoline, kerosene and commercial cleaners do NOT properly remove the grit left after honing, leading to premature engine failure. Thus it is lack of proper and thorough cleaning that lead to failure, not the honing. S.A.E. 10 oil, or ATF, and clean cloths used to swab out the cylinders do a better job. Usually 3 such applications are needed. Clean until a clean white rag shows NO sign of discoloration when wiped through a cylinder bore.

If not reboring, be sure to remove ALL ring ridge from the cylinder with a good quality ridge reamer. Dana Corp. recommended removing the ridge if the difference between the diameter of the worn part of the cylinder was .004" or more larger than the diameter of the ridge area. If less than .004" difference in diameters, no need to remove the ridge. If too large a ridge is left, the sharp top corner of a new ring will catch the ridge, and cause the ring to break.

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Last Updated on January 17, 1998 by
Bill Dickerson