Fitting Piston Rings

okay...
So, usually, press-fit damages when disassembled?
when i put a pipe under the piston to brace it when pressing the pin out, what are the chances of damaging the piston then?

this attention to detail is the difference between someone who just puts the parts together and wonders why the compression is low, the KB top ring just busted and it make only 250hp and the guy that has it cranking out 400hp for 500 passes. When assembling a motor, take your time...

Great article. I do have a question. When you put the ring in the cylinder and push it down with a piston whats keeping the ring square in the bore? If the ring is crooked then the gap measurement will be different then when it is installed on the piston.

Originally Posted by mmico28

Great article. I do have a question. When you put the ring in the cylinder and push it down with a piston whats keeping the ring square in the bore? If the ring is crooked then the gap measurement will be different then when it is installed on the piston.

They do make specialized ring squaring tools to ensure the ring is perfectly square. Using a piston is not as precise but is accepted at the hobby level. Honestly, I just picked the technique out of Tom Monroe's "Ford Engines V8". I'm sure many race engine builders are using the specialized squaring tool along with a dedicated filer among other things.

Originally Posted by mmico28

Great article. I do have a question. When you put the ring in the cylinder and push it down with a piston whats keeping the ring square in the bore? If the ring is crooked then the gap measurement will be different then when it is installed on the piston.

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.

Jon, I'm glad that you are finally stepping up and earning your keep for once

Ben, using the piston to square the ring is done and is more than correct for any application.

When I was working my machine shop position, the builder did it exactly the same way for every motor regardless of HP.
Using a piston sitting in the hole then 'sammiching' the ring then measuring is not only over kill, but it's simply no advantage whatsoever.

Nice write-up... some additional comments...

The file used should be a single cut mill file... that is one that only has the teeth running in a single diagonal direction. Don't use a file that has a crosshatch tooth pattern.

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.

Originally Posted by Poorboy5

The file used should be a single cut mill file... that is one that only has the teeth running in a single diagonal direction. Don't use a file that has a crosshatch tooth pattern.

Oooh, yes. That is a great suggestion. I need to add that to my tool drawer. Even though the file I use is pretty fine, I don't like how much it "bites". I'm sure the "single cut mill file" would solve that and provide a little more touch. I'll edit the article to include that. Appreciate the suggestion and proper name for the file type.

Originally Posted by FEandGoingBroke

Jon, I'm glad that you are finally stepping up and earning your keep for once

Gary, you caught my jab. Hah!

Originally Posted by FEandGoingBroke

Ben, using the piston to square the ring is done and is more than correct for any application.

When I was working my machine shop position, the builder did it exactly the same way for every motor regardless of HP.
Using a piston sitting in the hole then 'sammiching' the ring then measuring is not only over kill, but it's simply no advantage whatsoever.

I completely agree that using on piston to push the ring square should work for any application, but some people like the peace of mind from using the "correct" tools in a high HP build.

And as I said in my original post, it is overkill to sandwich the ring between two pistons, BUT if it would make you feel better that it was "square", you could do it to "be sure".

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. If you want to be "sure" (but again overkill) then the double/sandwiching piston method will work and might give that extra peace of mind that the person was looking for. Again, I do think it is PERSONALLY a waste of time to do it this way and that just pushing it down with a piston is plenty accurate.