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Ring end-gap

I am replacing rings and the book calls for .010/.020 ring end gap for

my engine. Is this a range of acceptable gaps, a tolerance? Seems they

would have listed a range as .010-.020 if that is what is intended.

Also, what results if the gap is too small?

I know what happens if it is too big because burning oil is why I am replacing them.

Thanks for any guidance

The gap is provided to give the ring room to expand as it heats up from combustion of the fuel. If the gap is too small the ring will expand anyway, and break.

Your gap should be set between .010 and .020 inches. If you have any doubts consult the manufacturer of the new rings.

The old rule from when I last overhauled an engine was .003" gap per inch in piston diameter.

Which ring gap are we talking about? The top or bottom compression ring or the oil wiper rings. Don’t know if they are all the same. Would help to know make, model, year and engine size of car.

I would go with what rebuild manuel says and if in doubt call dealership shop and they should be able to tell you.

do not forget to stager the gaps o not line them up

So if the gap is at the higher end of allowed, there is still possible a small gap
when up to operating temp? And at lower end of tolerance, perhaps a gap of zero at
operating temp? This is what I’m thinking is the objective.

Thanks for this rule of thumb, I will check it in this situation.

The manual gives only what I have stated. I assume this applies to all rings and
will proceed as such… Thanks for your help.

See below response oops.

the gap is dictated by being large enough to compress to install, but large enough to leave enough for thermal expansion to seal, but not bind on the liner. again, this is specified in the manual.

this gap is lastly checked on the piston, before you put itside in the cylinder. you put the rings on, and push them to the side, so the gap is partially out, and you feeler gauge it then.

Rings that have too small an end gap may seize up in the cylinder bore after running for a few minutes.
Also make sure the rings are not installed upside down. Often there are subtle differences and sometimes the rings may not be marked too clearly; if at all.
Some rings may have a bevel on the inside edge that may face up or down as an example.
Read the instructions supplied with the ring set very carefully.

Also check the ring side clearance (between the flat surface of the ring and the edge of the ring land (groove). Too tight a fit here will be just as bad as worn out rings and make sure all of the crud is cleaned out of the ring lands.
The up and down is just as important as the end gap.

Sorry. But that’s not how to properly check the ring gap.

Position the new ring into the cylinder. With one of the pistons, push the ring half-way down the cylinder. This ensures the ring is set squarely in the bore. Now take a feeler gauge and measure the ring gap.


Tester wins the prize.

In my time as a mech I’ve reringed and did Vjs on about 600 engines from old Chevys to industrial and marine engines. All rings made in standard, .010 thru .040 are gapped at the factory to the right clearance. I’ts a good idea to try one ring in the cylinder to be sure you got the right set but it’s never been a problem to anyone I know.

Just speaking for myself, I have seen a few rings in which the end gaps were not correct from the factory and had to file them accordingly. That’s why they make this tool:

I would never install a piston ring into an engine without checking each and every ring to make sure that’s it’s correct.
Fail to do this, one ring in the bunch is too tight, and you have a pretty expensive re-do when that piston seizes in the bore. Especially if the ring gouges the cylinder bore when it does seize.

One should also never place all of one’s faith into machine work done on the engine block or crankshaft either. I’ve seen cylinders bored .013 over, crank journals turned .007, etc. It’ll work if you can get .013 over pistons/rings and .007 over bearings I guess. :slight_smile: