Login or register (free and only takes a few minutes) to participate in this question.
You will also have access to many other tools and opportunities designed for those who have language-related jobs (or are passionate about them). Participation is free and the site has a strict confidentiality policy.
Having seen the pictures and read the explanations in the answer sections - not to mention a blow by blow account from my other half about the function of piston rings (!) I'd have thought you could use any of the alternatives - but I'm no mechanic!
Sorry, have just noticed that the proz glossaries also have a few entries for this: either "top ring" or "top piston ring". Would be interested to hear what anyone thinks of these, as they're straightforward glossary entries not backed by any other reference.
For gaps to be the villain of the peace, the gas would have to find the gap in the top compression ring and pass through. It would then have to circulate to find the gap in the second ring and pass through that and so on. Now this may be possible if the power stroke lasts for 10 minutes but it doesn't, does it?