piston scuffing advice

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by caseyspradlin, Jun 6, 2018.

  1. caseyspradlin

    caseyspradlin Member

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    #1
  2. jay70cuda

    jay70cuda Member

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    What is the tolerances. How many runs is that? Was it all new when you started ?
     
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  3. caseyspradlin

    caseyspradlin Member

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    Bought motor. Had 6 runs when I got it. Pistons Now have about 300. Pistons looked same after 100 runs at first set of rods cycle through. This time I figured I might ask someone about it. I don’t have a cylinder mic but I could probably barrow one if you think I don’t have enough clearance. When I file rings they are 5 over and most have zero gap initially if that helps.

    Thanks.
     
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  4. Bob Meyer

    Bob Meyer Comp Eliminator

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    Might be too much timing, check if you or the mark moved !
     
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  5. kosky racing

    kosky racing Comp Eliminator

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  6. caseyspradlin

    caseyspradlin Member

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    Using .008xbore top and .0075xbore second according to total seal directions. Max 32 # boost. Should I have more?
     
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  7. jay70cuda

    jay70cuda Member

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    Wow that’s tight. My total seal rings for my blown app is in the .020s for gap. I have a problem scuffing my #2 piston. Had to open the bore to .011 to get it to stop.
     
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  8. kosky racing

    kosky racing Comp Eliminator

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    End gap depends on how lean you run the motor -A big gap saves a lot of problems -harms nothing-unless your ego is into O-leakage STUDY up!
     
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  9. sean70ss

    sean70ss Member

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    I run mine at .30 top .35 2nd never had that and at 64lbs of boost
     
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  10. kosky racing

    kosky racing Comp Eliminator

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    With 64# boost how fast did that thing GO?
     
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  11. caseyspradlin

    caseyspradlin Member

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    .008xOD top comes out to be .036
    .0075xOD 2nd comes out to be .032

    Y’all saying that’s to tight causing those black marks?

    Thanks
     
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  12. JNR

    JNR TA/FC

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    as the scuffing is on one side of the piston only , my best guess is lack of lubrication, or diluted lubricant (from fuel).
    If it is the exhaust side (outboard side of block, it could be from fuel wash-down (from being too rich) as that is where the extra fuel will go.Get the correct oil lean it out !
     
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  13. TADHemiracer

    TADHemiracer Member

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    May be too much cylinder clearance to wall and/or out of round bores.
     
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    Will Hanna likes this.
  14. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    First thought is detonation, but hard to believe it would make it 300 runs with detonation.

    Most people gap their rings too tight. If gases get caught between the rings and have nowhere to go, flutter happens and causes way more blow by than opening the gap a few more thou.

    If the rings are tight enough to butt, will cause problems similar to what is pictured.

    If you have made 200 runs with pistons that look like that (after the first 100), I'm going to guess the cylinders are not round, and that the skirts may be collapsed.

    I think you got your money's worth out of those pistons. Let them move on to the great scrap pile in the sky.
     
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