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  1. #1
    tiderider's Avatar
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    Wiseco piston to wall clearances for 40038M10050 100.50mm Pistons , 4 tec

    Hi, can anyone confirm piston to wall clearances for the wiseco 40038M10050 pistons for a maximum of 13-15 psi at wot? Wiseco USA says .0020 - .0025 and Wiseco Canada says, on the box states .0019

  2. #2
    ptscon's Avatar
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    You won't run for long if you run those clearances, 0.0035 - 0.004" is where you want to be. I run 0.004" just to be on the safer side, no extra blow by that I notice.

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    tiderider's Avatar
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    Quote Originally Posted by ptscon View Post
    You won't run for long if you run those clearances, 0.0035 - 0.004" is where you want to be. I run 0.004" just to be on the safer side, no extra blow by that I notice.

    Hey Thank you!
    How much psi are you doing at WOT with your setup?
    Last edited by tiderider; 12-13-2019 at 08:54 PM.

  4. #4
    ptscon's Avatar
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    Quote Originally Posted by tiderider View Post
    Hey Thank you!
    How much psi are you doing at WOT with your setup?

    17.5-ish

    If I were you I would not run less than 0.0035 and just round it up to 0.004 Running slightly looser will not cause any issues or performance loss. It will give the motor a bit more margin in case things get hot for whatever reason.

  5. #5
    tiderider's Avatar
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    Quote Originally Posted by ptscon View Post
    17.5-ish

    If I were you I would not run less than 0.0035 and just round it up to 0.004 Running slightly looser will not cause any issues or performance loss. It will give the motor a bit more margin in case things get hot for whatever reason.

    My other engine with et137+4mm got the .0033 treatment using 100.5 CP 8.4:1 and coated skirts.. Only 1.5 hours on it though... Did a couple 8200 rpm WOTs with no issues..
    CP Piston rings were set at.. TOP Ring .0400 Second Ring at .0480 and Oil Ring at .1110

    What ring gaps should I use for the 100.5 skirt coated Wiseco Pistons in the Up to 13-15Psi, 8500 rpms?
    Thank you!

  6. #6
    ptscon's Avatar
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    Quote Originally Posted by tiderider View Post
    My other engine with et137+4mm got the .0033 treatment using 100.5 CP 8.4:1 and coated skirts.. Only 1.5 hours on it though... Did a couple 8200 rpm WOTs with no issues..
    CP Piston rings were set at.. TOP Ring .0400 Second Ring at .0480 and Oil Ring at .1110

    What ring gaps should I use for the 100.5 skirt coated Wiseco Pistons in the Up to 13-15Psi, 8500 rpms?
    Thank you!

    Not sure what CP calls for ring end gaps but those numbers look large, my current motor with Wiseco is 0.023 / 0.028.

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    tiderider's Avatar
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    Quote Originally Posted by ptscon View Post
    Not sure what CP calls for ring end gaps but those numbers look large, my current motor with Wiseco is 0.023 / 0.028.

    Hi, yes your right about the large gaps. I listed the wrong information from the spec sheet... I listed the Groove width for each ring, not the gap. I guess my machinist did his magic for the ring gaps and would be the one who knows. Sorry for the confusion!

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  8. #8
    tiderider's Avatar
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    How many trouble free hours do you now have on the Wiseco pistons and .0040 clearance set up?

  9. #9
    tiderider's Avatar
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    Quote Originally Posted by ptscon View Post
    Not sure what CP calls for ring end gaps but those numbers look large, my current motor with Wiseco is 0.023 / 0.028.
    So far, machinist is saying .0040 is common for piston to wall clearance where as Wiseco is saying that .0025 (States .0019 on the box) is plenty for 15 PSI which would be measured off the coated skirt. Pistons are 2618 Alloy.
    Using the Wiseco piston rings that came with the pistons and the provided specs..
    Machinist is disagreeing with the .023 and .028 ring gaps. Machinist will get back to me on their recommendations..
    Wiseco is recommending .018 for top ring and .021-.022 for second ring.. For 15 psi..
    Wondering if this is all guess work??

  10. #10
    ptscon's Avatar
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    I wonder if Wiseco suggestion is a generic one for all their forged pistons or application specific. Jetski motors run at very high RPMs under boost for extended periods of time. It's not like a street car that might hit WOT for a 1/8 mile or light to light.

    I don't think any engine builder on greenhulk would suggest running 0.0025 clearance. Ring end gap you could play with, I'm running slightly larger gap because it has no affect on performance/blowby and it gives me more margin for "error". Nothing worse than having to do a rebuild caused by silly ring contact.


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