I am installing new piston rings and had to go with oversize filed down to spec because the standard had gaps too big. The ends of the oversize oil expander seem like they are overlapping when placed in the groove. I know they are supposed to compress like an accordion but that doesn't happen readily, instead, the excess length seems to obstruct slider rings that go under and above it. I had multiple incidents where the sliders didn't sit in right precisely because of that and they would even pop out when I was putting the piston compressor around, which is scary because they could go in the cylinder not lodged properly.

Should I clip the expander just a little (e.g. 1/16" or roughly 1-2 mm), with something like small electrical angle cutters to avoid this overlapping?

1 Answer 1


Oversized rings are only used when boring the cylinders and installing oversized pistons. You cannot expect to use oversized rings on regular sized pistons in regular sized bores. The reason they are overlapping is because they are hugely too big and will not work. You cannot clip the expander ring as it will ruin it. If you look at the ends of the expander, you'll see as the ends meet together, there is a specific shape they form together. If the standard sized rings provided too big of a gap, you need to bore the cylinders.

  • I don't think it was inappropriate for me to use oversized rings because I filed them down to within the range specified by the manufacturer. The standard had a gap slightly outside the range because of the cylinder wear
    – amphibient
    Aug 24, 2022 at 2:04
  • It is absolutely inappropriate, because that's not how it works. You've filed them down to get the right ring gap, but the rings themselves do not have the correct geometry. They will not fit either the piston (as you pointed out with the ring expander), nor the bores correctly. These rings will most likely never seat in the bores, which means you'll continue to have issues with blow-by and leakdown tests. As I stated, this is not how you use over sized piston rings. Aug 24, 2022 at 9:48
  • I will know that very soon, when I do the leakdown test, I will put the cylinder head back on without torquing to yield, which is sufficient to see if I am leaking
    – amphibient
    Aug 24, 2022 at 13:22
  • You can't get any type of assurance in your leakdown tests until the rings are fully seated, which can only be done by running the engine. Aug 24, 2022 at 13:40
  • 1
    Here: Quora - Grassroots Motorsports - Hot Rodders - While these are forum posts, they absolutely back up what I've been trying to tell you: Oversized rings are for oversized pistons. This is more or less common knowledge to any engine builder. Aug 24, 2022 at 15:09

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