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Thread: Fitting oversized bush to little end to adapt piston with smaller gudgeon pin - OK ?

  1. #1
    Registered User dave1600's Avatar
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    Fitting oversized bush to little end to adapt piston with smaller gudgeon pin - OK ?

    So, bought some fancy new H-beam rods for an engine build, correct length but little end is 22mm. I need to fit a piston with around a 19-20mm gudgeon pin. Any dramas with fitting a little end bush that has a smaller id to make it all work ? If no problems doing so, suggested material for said bush ?

    I can't really alter the piston, not enough room for a 22mm pin without it interfering with the oil ring. Other option is to see if I can get a custom piston made with 22mm pin, just sussing out options at the moment.

    Use is in a high-revving race engine, using forged H-beam rods and slipper pistons.

  2. #2
    Registered User lukevl's Avatar
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    Is 22mm the ID of the rod or the ID of the current bush in the little end?

  3. #3
    Registered User jimmyg's Avatar
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    It's fine. Evo/Vr4 guys do it with 7 bolt pistons in a 6 bolt motor.
    Mmmmmmmmm beer.

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  4. #4
    Registered User dave1600's Avatar
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    22mm is the ID of the current bush.
    Last edited by dave1600; 07-12-17 at 04:37 PM.

  5. #5
    Registered User lukevl's Avatar
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    Well I donít see an issue replacing the current bronze(?) bush with a new one. Standard process for an engine machinist.

  6. #6
    That's Sir Cunt to you... krisr's Avatar
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    Put a pic up of the piston? I pulled these out of a 468 cube motor i'm building for a mate, the pins are well into the oil rings and doesn't look like it had any oiling issues. I was more concerned with the 7" rods putting the pin so high and letting the piston rock around so much with short skirts than the pins inside the oil rings.

    Click image for larger version. 

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  7. #7
    Registered User dave1600's Avatar
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    Going by your pic, may not be an issue to run a 22mm pin. The smaller pin isn't even in the oil ring groove yet.

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  8. #8
    Non Compos Mentos Gammaboy's Avatar
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    No problems at all, you can even have the bush offset if you need to tune the compression height...
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  9. #9
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    No big deal at all.

    Look into getting Ampco 18 material for the bushings, there is nothing better. It is *NOT* normally an inexpensive material though, due to minimum quantity purchases.

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