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  1. #1
    tiderider's Avatar
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    CP 100.5mm skirt coated Pistons at .0040 Piston wall clearances fails big time

    Just helped a buddy pull his engine out of a seadoo speedster 150 with CP Pistons set at .0040 PTW clearances measured off the skirt coating. 100.5mm oversized pistons. He had the ET137+4MM SET UP, 60 injectors, external fizzle f1000.

    1 Piston skirt touched down and pistons appear to be to loose at .0040 piston to wall Clearance.

    So CP pistons with with coated skirts at .0040 Piston to wall clearance measured off the coating does not work well for the boats. CP spec sheet states .0033 PTW clearances..

    Yes, it was professionally machined. Everything new, like oil jets, injectors with flow test, fuel filter, new fuel pump. It is tuned and was running with a logger. It ran well for a couple hours with a total of 10 hours, made the last wot run at 8300 Rpms for a few seconds. Docked it for an hour. Got the trailer out in the water, started the boat and plenty of oil smelly smoke was pouring out the tail pipe.

    I am going to recommend Wiseco Pistons.
    Last edited by tiderider; 06-08-2020 at 01:12 AM.

  2. #2

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    Same thing happened to me with weisco pistons....

  3. #3

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    I think some pistons need at least 3 heat cycles before wide open throttle.. ???

  4. #4
    ptscon's Avatar
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    Pretty weird, 0.004 is a safe bet for a supercharged setup, especially with only ET137. Could a boat be putting more load, heat, on the motor requiring even more clearance?

    What kind of AFR?

  5. #5
    Quote Originally Posted by ptscon View Post
    Pretty weird, 0.004 is a safe bet for a supercharged setup, especially with only ET137. Could a boat be putting more load, heat, on the motor requiring even more clearance?

    What kind of AFR?
    Fair question. A boat is a lot heavier.

  6. #6
    tiderider's Avatar
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    Quote Originally Posted by ptscon View Post
    Pretty weird, 0.004 is a safe bet for a supercharged setup, especially with only ET137. Could a boat be putting more load, heat, on the motor requiring even more clearance?

    What kind of AFR?

    Maximum engine temperatures on logs shows 188-191F.
    Only a few short, WOT runs where done after 7 hours or so.
    Approx 5 heat cycles within the 10 hours
    12-12.3 AFR on Idle
    13-13.8 up to 5000 Rpms
    13.9-14.2 5000-5800 RPms
    12.5 6000- 7900 Rpms
    11.9-12.2 8000-8400 Rpms.

    CP recommended PTW Clearances .0033-.0035 but was machined to .0040, it was verified by another machine shop after it failed.
    Wiseco recommended specs .0025 Piston to Wall clearances for the et137+4mm set up. 8500 rpms and 14 psi.
    Just wondering if Wiesco are using a different alloy for them to recommend .0025 unlike CP with .0033-.0035?
    Last edited by tiderider; 06-08-2020 at 01:16 AM.

  7. #7
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    How were the rings gaped?

  8. #8
    tiderider's Avatar
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    Quote Originally Posted by ptscon View Post
    How were the rings gaped?

    Machinist measured .019 top .030 second ring.
    No damage or signs of the gap closing in on itself. It was not a piston ring gap issue.

  9. #9
    ptscon's Avatar
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    Quote Originally Posted by tiderider View Post
    Machinist measured .019 top .030 second ring.

    If it was my build I would not run the top ring that tight and bottom ring is way too loose compared to the top.

    Did you personally see the piston to wall clearance being measured? Just looking at the ring end gap your shop used I would question/verify their other measurements.

  10. #10
    isa alnoaimi's Avatar
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    based on jerry’s recommendation for CP pistons

    piston to wall clearance : 0.0045

    first ring : 0.0025

    second ring : 0.0030

    i just order CP’s pistons from jerry , because i discovered that my new wiseco pistons are 4032 alloy !!!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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