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Author Topic: Piston ring gap
vitesse
Beginner
Posts: 36
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Post Piston ring gap
on: December 2, 2015, 18:21

I'm in the process of rebuilding an early Spitfire engine. I had the block bored, honed to match the new pistons etc. I checked the piston ring gap. The factory spec is 0.008-0.013", the piston ring manufacturer recommends .008-.011". I'm measuring 0.017" on the top ring, 0.015-0.016" on the 2nd rings. All rings are pretty consistent. I'm half tempted to just go ahead and install them, but I really don't want to have to do this job again.

Previously, the new 0.040 pistons came with 0.020 rings, so I'm already on the 2nd round of rings.

Should I send them back and try again or just go with these?

Thanks

Cecil

jd
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Posts: 30
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Post Re: Piston ring gap
on: December 6, 2015, 21:28

Cecil, I think I would go ahead and put it together. The ring gap is not that far out of spec and with the quality of rings we are getting today it might be the best you can do. If you want to try different rings you might order some high quality rings like deve's or maybe Hastings or you order some file to fit rings from some of the racing companies. Is this a street engine or a track engine? Personally i like a little extra end gap in case you might have some detention with the junk gas we have nowadays. There is nothing worse than a end butted ring on a cylinder. Call me at work if you have any questions or just want to chat.....JD

vitesse
Beginner
Posts: 36
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Post Re: Piston ring gap
on: December 8, 2015, 17:35

Thanks Jon.

I found an interesting article that discusses ring gaps. They claim some research was done back in the late 70s that showed that engines were not all that sensitive to ring gaps. After reading that article, I decided to go ahead and build the engine. The engine is together, I'm hoping to start it next weekend.

Article is here: http://www.diagnosticengineers.org/journal_%20articles/Ring%20Gaps%20vs%20Knowledge%20Gaps.php

jd
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Post Re: Piston ring gap
on: December 8, 2015, 21:21

Interesting article, a good read for all. The thing i always worry about is having the minimum end gap or hopefully just a little more. I have been known to file for more end gap. End butting rings are sure death of a engine, especially with power adders like a turbo or supercharger. I always go with a little more than less, as the old saying goes "a engine on the loose side lives longer than one that is too tight".

vitesse
Beginner
Posts: 36
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Post Re: Piston ring gap
on: December 20, 2015, 18:14

I went ahead and assembled the engine with the wide gap. When I started the engine, there was no perceptible blowby and the engine seems to run well.

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