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Thread: Propane Model aluminum piston with oring dims needed

  1. #1
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    Default Propane Model aluminum piston with oring dims needed

    Hello,
    I'm going to make a new aluminum piston with an oring to replace the cast iron one with steel rings on a kerzel hit and miss engine.
    What shape is the ring groove? Round or square?
    The oring that's going to be used is an 1/8 inch cross section. The cylinder bore is 3/4 inch.

  2. #2
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    Use a 1/16" cross section o-ring. (they actually measure at 0.070") The piston groove should be .093" wide (a standard parting off blade) and .058" deep. Use a Viton ring--they are much more heat resistant than the normal Buna N series rings. Only one ring is required per cylinder.
    Brian Rupnow

  3. #3
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    Thanks Brian

  4. #4
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    If I understand, you propose using an elastomer oring for piston combustion seal/oil control on an internal combustion engine?

    I doubt this will work. I would expect combustion temperatures to exceed oring capability, wear to be excessive, and heat transfer out of the piston to be reduced. Happy to be shown otherwise if I am wrong.

  5. #5
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    Strokersix--check out some of my engine builds. I have 20 engines running with Viton rings and they work fine.
    Brian Rupnow

  6. #6
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    These engines are only run for a few minutes, that's why the rings work. Try them in a car or motorcycle and they would only last a few seconds.

  7. #7
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    OldMart--My engines run for hours at a time with no damage to the O-rings.
    Brian Rupnow

  8. #8
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    That would probably be related to the very low power factors, they are not exactly running in the 100 hp per litre are they.

  9. #9
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    Your go to for O-ring information is the Parker O-Ring manual. It will tell you how make virtually every kind of O-ring gland imagineable.

  10. #10
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    Quote Originally Posted by old mart View Post
    That would probably be related to the very low power factors, they are not exactly running in the 100 hp per litre are they.
    Viton is rated at 400 deg F for extended use, it can take more for short durations. Combustion temperatures are not that low of course. Although they "work", the numbers don't lie.... Its also a pretty safe bet that the manufacturers know their temperature limits.

    I won't quote any combustion chamber temperatures, those number ranges are easily found. I didn't see anything remotely as low as 400F though.
    Last edited by Sparky_NY; 08-15-2019 at 05:49 PM.

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