Valve to piston contact?

Posted by Talyn, Jul 23, 2013
Cylinder Head & Short Block - 4G63 cams, valvetrain, pistons, rods, stroker kits, 6-bolt swaps, hybrids, etc. Read this Forum's Strict Guidelines.

  1. Talyn

    Talyn Proven Member

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    Long story short, I am rebuilding my engine(it was rebuilt before by a PO) reusing the .20 over ross pistons in a fresh block, but when cleaning them discovered that all 4 of them have valve contact marks. The indents are pretty minor and shallow, and I don't think the pistons will be unusable, but I am wondering what might have caused this? I haven't had a jumped timing belt or anything, and don't believe my valves are bent(will have to recheck after finding this, but the last time I had my head off they were good), also this is a 2g head with factory cams, springs, and afaik the valves too, on a 6 bolt block, I am wondering if there might be any kind of clearance issue using a 2g head on a 6 bolt block, or if that might explain why the contact marks are not inboard of where the reliefs are?
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  2. BogusSVO

    BogusSVO DSM Wiseman

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    The PO may have had the timing belt jump/break causing the contact marks on the pistons.

    The 2g head on a 6 bolt block is common enough.

    Factory stock valves will have 6T cast into the head.
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  3. hubz91talontsi

    hubz91talontsi Proven Member

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    If the damage is light on the pistons I wouldn't hesitate to run them at all. I had some valves that made contact, rebuilt the head and ran the pistons. Made 421hp.
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  4. UrbanSmoker

    UrbanSmoker Proven Member

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    It's common for valves to kiss pistons in a 6 bolt block 2g head combo? sh** i didn't know...
    Now i got another thing to have in the back of my mind.
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  5. Talyn

    Talyn Proven Member

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    I think you are misreading that, I am pretty sure he is saying that its common to run that combination.
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  6. slickers111

    slickers111 Proven Member

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    7 bolt head/6 bolt block is the common thing.

    Valves should not be making contact with the pistons at all.

    Its possible that the head was shaved, bringing them closer to the pistons. Too much shave, without a thicker head gasket will cause them to slap. But Im pretty sure if they make marks in the piston, it would bend the valve.

    Do you remember how much it was shaved? And the head gasket that was ran?

    Also, are you sure that they pistons arent indented, like the stock ones?
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  7. BogusSVO

    BogusSVO DSM Wiseman

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    You would have to be waaaay past min head thickness with stock cams for the valves to hit with the timing belt set proper.

    http://www.dsmtuners.com/forums/cylinder-head-short-block/464400-delta-hks272-regrind-info.html
    Post 1

    As most stock cams I have measured come in about .330 lift.

    So looking at the "Cams Zeroed" measurements then add another .060 clearance,for the smaller lift stock cams, the head will have to be milled .200 appox.
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  8. hubz91talontsi

    hubz91talontsi Proven Member

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    No machinist would shave that head far enough that the valves would make contact with the pistons.
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  9. UrbanSmoker

    UrbanSmoker Proven Member

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    Lol ok ok
    Glad i misread
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