Fitting Piston Rings

Originally Posted by ben98gs

It was in response to the person saying that you could not be "sure" that it was square by just pushing it down with a piston.

I get you man, don't know what I was thinking. Thanks for being nice about it.

Originally Posted by Poorboy5

I have also found that a couple of passes with a fine wire brush across the file teeth after file each ring helps keep the file clean and the cutting uniform. A squirt of WD-40 once in a while does not hurt either.

they even sell a tool to clean files... AKA file card. lol

Originally Posted by ben98gs

I agree with Mike. The tolerances for the piston/bore will basically ONLY let you slide the piston in if it is square. If you are pushing the ring down with the squared piston it SHOULD basically line up the ring. If you were REALLY worried about it, you could put a piston in the "correct" way and then use another piston from the top to "sandwich" the ring squared, but IMO this is overkill. Just using the piston from the top should be fine for a street/strip motor. If you are going for an all out race car, then you probably either have the correct tools or are paying somebody with the correct tools to assemble your motor that requires more exactly tolerances.

Using a piston will NOT get the ring in square, it will be close. If you want close enough just buy pre gapped rings not file fit.
A simple and cheaper method to the squaring tool is to take an old non domed piston and install an old ring in the 2nd gap. The 2 piston method will not work with dome pistons and sure sounds like a good way to scratch up your pistons and cylinder walls.

Im not trying to take away from this article or bash in anyway. Im just trying to help out.

Had not thought about the domed pistons. And again, I was really not advising that method just saying I have seen others do it (with flat/dished pistons) and thought it was dumb/overkill, but "can" be done. You should no more scratch the cylinder walls than if you were installing the pistons. If you have everything oiled down and are careful there should be no scratches.

OK you bunch of nitpicking wankers.


Scenario: You slide the ring down into the cylinder and eyeball it for square, then you measure it (yayyyy). (when all of the sudden)
OH MY GOODNESS! I just filed my ring to a gap if .018 but I remembered that one side of the ring was 1/4 inch higher than the other! OH NO!

The GAP is now .017923 when the ring is squared by using a piston or a tape measure (anyone ever think of using one of those?) (presumably a flat top you silly geese's) Now you shave off that last .00077 to get your .018, and where are you now? Well smart guy, you're now gapped to .01834 because it is REALLY REALLY hard to take of .00077 with just a thin hand file.

So you are ALL going a little overboard with your ring positioning arguments.

You would have to be more than 1/4 inch out of square for your ring cut to be enough out of specs to make a difference in the margin of safety that most ring gap specs allow (.018- .022).

1/4 inch out is a LOT and easy as hell to see, so if you are out that much and don't notice, then you need glasses.

lol... I thought about getting into all of the math and running some numbers, but I was not bored enough to do it.

Now that's funny Gary. I knew going into this article that there would be a bunch of different opinions and comments. Really, that's the point... to generate the discussion.

I will add to your point that 50% of the effort in fitting the rings at the "suburban garage hobbyist level" is to just make sure the right damn ones are in the box.

Originally Posted by Mikelonis

I will add to your point that 50% of the effort in fitting the rings at the "suburban garage hobbyist level" is to just make sure the right damn ones are in the box.

LOL, I've experienced the wrong set before and filed .020 off about 4 different rings before looking at the box and getting pissed and embarrassed....

Originally Posted by FEandGoingBroke

OK you bunch of nitpicking wankers.

assuming you measured the bored at the exact spot your measure your rings. Make sure to measure the exact spot at the top of the ring, the mid point of the ring and the bottom of the ring. Then do this at various parts of the bore. I mean if there is any taper or it is not exact, then you are just screwed and the motor will grenade at start up. Cheers.

Hahahahahaah, you got me Coo! that's a good one