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Old 03-04-2021, 02:16 PM   #1
Cobra Jet
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Default Flat head pistons

I have the 4 ring FH v8 pistons. Can I leave off the bottom oil ring and run them with 3 rings?
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Old 03-04-2021, 02:47 PM   #2
flatjack9
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Default Re: Flat head pistons

Leave it off. I don't use the 4th ring on any of my builds.
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Old 03-04-2021, 02:48 PM   #3
leon bee
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Default Re: Flat head pistons

I saw the replies over on the other forum, there are some differing opinions over here. After a lot of reading, I've left that bottom ring out of two engines and am getting ready to on a third. Experts will be along soon.
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Old 03-04-2021, 02:54 PM   #4
KiWinUS
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Default Re: Flat head pistons

What FlatJack says you can’t go wrong.
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Old 03-04-2021, 03:22 PM   #5
tubman
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Default Re: Flat head pistons

I left 'em off my last build with no ill effects. I did have the assembly balanced that way to make sure.
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Old 03-04-2021, 03:24 PM   #6
jetmek
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Default Re: Flat head pistons

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Like they say on tobacco road. “Wont hurt the runnin of it nun”
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Old 03-04-2021, 03:31 PM   #7
moefuzz
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Default Re: Flat head pistons

It's been done for years, 4 ring pistons with only 3 rings,
You are not breaking new ground or forging new territory here.

moe
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Old 03-04-2021, 03:40 PM   #8
Ol' Ron
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Default Re: Flat head pistons

I also chop off the bottom of the piston as well. But, You have to be carful here. Most of these pistons are "Auto -thermic" and have a steel strut in them. I make a clamp for the ring area to clamp in the lathe as not to hurt the ring stack. This brings the weight down to to an Egge piston . Now you say "What about balancing" IF ( BIG IF) your using the original crank and rods, not to worry. If not, you have to have it balanced any way.
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Old 03-04-2021, 05:58 PM   #9
JWL
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Default Re: Flat head pistons

Again it is time for some real facts--it depends on the rings you are using. If you are using the dual scraper oil ring with expander, omitting the 4th ring is completely acceptable or even preferred. If you are using the original type, one piece oil rings it is better to install all 4 of the rings.
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Old 03-04-2021, 07:12 PM   #10
Desoto291Hemi
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Default Re: Flat head pistons

JWL,,,,,thank you for the info.
It always helps to have detailed reasoning with the answers .
Makes complete sense to me !

Tommy
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Old 03-06-2021, 04:41 PM   #11
Cobra Jet
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Default Re: Flat head pistons

Thanks everyone for your repies! I couldn't see any reason that they couldn't be run with 3 rings, just needed a little reasurance. Deen
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