piston scuffing advice

Discussion in 'PSI Superchargers Tech Questions' started by caseyspradlin, Jun 6, 2018.

  1. caseyspradlin

    caseyspradlin Member

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    #1
    caseyspradlin, Jun 6, 2018
  2. jay70cuda

    jay70cuda Well-Known Member

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    What is the tolerances. How many runs is that? Was it all new when you started ?
     
    #2
    jay70cuda, Jun 6, 2018
  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.
     
    #3
    caseyspradlin, Jun 7, 2018
  4. Bob Meyer

    Bob Meyer Comp Eliminator

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    Might be too much timing, check if you or the mark moved !
     
    #4
    Bob Meyer, Jun 7, 2018
  5. kosky racing

    kosky racing Comp Eliminator

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    #5
    kosky racing, Jun 7, 2018
  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?
     
    #6
    caseyspradlin, Jun 8, 2018
  7. jay70cuda

    jay70cuda Well-Known 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.
     
    #7
    jay70cuda, Jun 8, 2018
  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!
     
    #8
    kosky racing, Jun 8, 2018
  9. sean70ss

    sean70ss Member

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    I run mine at .30 top .35 2nd never had that and at 64lbs of boost
     
    #9
    sean70ss, Jun 8, 2018
  10. kosky racing

    kosky racing Comp Eliminator

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    With 64# boost how fast did that thing GO?
     
    #10
    kosky racing, Jun 8, 2018
  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
     
    #11
    caseyspradlin, Jun 8, 2018
  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 !
     
    #12
    JNR, Jun 9, 2018
  13. TADHemiracer

    TADHemiracer Member

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    May be too much cylinder clearance to wall and/or out of round bores.
     
    #13
    TADHemiracer, Jun 9, 2018
    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.
     
    #14
    Will Hanna, Jun 12, 2018
    bandit496 likes this.
  15. secondwindracing

    secondwindracing top alcohol

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    .040 on both never a problem
     
    #15
    secondwindracing, Jul 1, 2018
  16. Mike Canter

    Mike Canter Top Dragster
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    Can’t tell in the pictures but are they gas ported?
     
    #16
    Mike Canter, Jul 2, 2018
  17. Nitro Madness

    Nitro Madness Super Comp

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    Here is a photo of #1 and #3 pistons from a few years ago before I figured out what was tearing them up...this was after just a few runs...
    [​IMG]
    Ended up being too rich on the burnout and washing the oil off of the cylinders.....and the solution was simple....Our driver just leaned the fuel for the burnout until the idle speed increased by 200 RPM and the burnout was crisp and clean...no more pouring raw fuel in the cylinders and scuffing skirts...turned the fuel back on 100% for the run...
    We could have come up with a high/low system but trimming the fuel worked just fine....hope this helps...
     
    #17
    Last edited: Jul 3, 2018
    Nitro Madness, Jul 3, 2018
  18. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    I think that may work for a nitro motor but I have ran some alcohol combos that were pretty rich at idle and never had a piston scuffing problem. There is more than one way to "backside" pistons like that in the burnout with nitro I've been told.
     
    #18
    Will Hanna, Jul 5, 2018
  19. Nitro Madness

    Nitro Madness Super Comp

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    This was in 2006 when we were on alcohol...trimming the fuel on the burnout worked great...was not too rich at idle but blubbered (technical term) fuel on the burnout with the fuel lever on all the way...EGT's were fine on the run...
     
    #19
    Nitro Madness, Jul 5, 2018
  20. Dale H.

    Dale H. Member

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    When I warm my motors up I usually lean the motor some with the fuel shutoff . I figure no sense to have such a rich mixture going for the time to warm the thing up. Just make sure that it is richened back up before whacking on the throttle.
    -Dale
     
    #20
    Dale H., Jul 10, 2018

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