Which O-Ring for piston ring?

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Jack3M

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There are so many out there, I have no clue which to use for a piston ring. The one I got at the hardware store lasted about 10 minutes of run time.
McMaster-Carr has a huge selection of types?
https://www.mcmaster.com/o-rings
 

Brian Rupnow

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Use a Viton o-ring. they are heat resistant and last forever. You want 1/16" cross section, with outside diameter to match the cylinder bore. Groove in piston should be .094" wide x 0.058" deep. Only use one ring.---Brian
 

BobsModels

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Jack

I agree with Brian on the Vitron (hard not soft), I have over 800 hours on my Gade with the same ring. I have found another ring that I am using on a steam cylinder that gets much hotter than our gas engines. It is an Ultra-Chemical-Resistant Aflas O-Ring, get it from Mc Master. I will be trying it on my next gas engine. Also you really want minimum wall pressure so the depth of the groove in the piston needs to be based on the cylinder diameter. I attached a PDF that shows how to calculate for whatever cylinder diameter you have relative to your piston. Also remember that a 1/16 O Ring is not 1/16 in diameter but .070 so you need to account for that also. Your goal should be to get a nice rock and bounce like this.

https://youtu.be/1QazAr4b3KY

Let us know how it comes out for you

Good Luck

Bob
 

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Ken I

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Backing up what Brian said - if you use two "O" rings - in any application, a pressure builds up between the two rings sufficient to cause extrusion / premature failure.
You can use two (to prevent "rocking" for instance) but then the gap between the "O" rings must be vented (just a small "drain" hole) to either the HP or LP side to prevent this pressure build up.
Two rings in a wide groove will fail - two grooves are obviously separated - but the void between them must be vented
Seems a bit counter intuitive but it does work.
Regards, Ken
 

Jasonb

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If the Viton are only lasting 10mins what is the surface of your cylineder like? At a minimum it wants to be honed but better if it is lapped.
 

lohring

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Has anyone considered these seals? The bronze filled ones are good to 575 degrees F.

Lohring Miller
 

BobsModels

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Here is where I get them, buy by the quantity and share them to other builders, what size do you need?

here are the Vitron - McMaster-Carr

Bob
 

awake

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Benno, I got a pack of 10 viton o-rings off of eBay. So far, the two in use - one on the piston, and one helping to seal the gas tank - have held up just fine.
 

popnrattle

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I get mine at the local hardware store for a little over a buck. Very pleased with longevity, especially with the temps involved. My engines power things with no forced cooling so, I have an excuse to tear them down clean the carbon from the valves, head and piston and replace O-ring after about a year. Chain reduction turns 2qt. ice cream maker for 30 minutes.
 

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Longboy

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I have used Nitrile O-rings from the hardware store when I didn't find the size needed in Viton. Viton performs just as well though and costs 3 times more from Ace.
 

TSutrina

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Parker handbook on o-ring has a temperature chart: Perfluorinated Elastomer (FFKM) 250C to 300C, TFE/Propropylene (FEPM) 235C to 250C, silicone rubber (VMQ) 210C to 250C, and Flourocarbon Rubber (FKM) 205C to 250C.
 
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