Broken Piston Skirt
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Broken Piston Skirt

  1. #1
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    Default Broken Piston Skirt

    Is there a typical reason for what causes the piston skirt to fracture off at the bottom oil ring grove?

    Just want to make sure it gets addressed during any rebuild. 468 BBC with forged pistons, many years old.

    Thanks
    Chuck
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    Village Idiot fc-Pilot's Avatar
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    Had an sbc years ago that had multiple skirts break in my hands as we pulled the running motor down. The skirts on the trw forged pistons literally fell apart in our hands. The engine had been overheated a number of times but did not have skirt scuffs. I can’t say for sure. It may have been do to excessive piston clearance.

    Paul

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    Senior Member ol guy's Avatar
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    Quote Originally Posted by flspectra View Post
    Is there a typical reason for what causes the piston skirt to fracture off at the bottom oil ring grove?

    Just want to make sure it gets addressed during any rebuild. 468 BBC with forged pistons, many years old.

    Thanks
    Chuck
    I have seen this before. Normally it is caused by lack of oil to the wrist pin "especially" with a pressed pin application. I would bet that the piston did not swing easily on the rod. Main reason I say this is the skirt broke right at the oil ring land. So with all that being said, it is was probably caused by lack of lube. Although you state it is many years old could it have ran dry or got galled by lack of lubrication? M

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    Anything is possible, but at disassembly the rod motion was smooth to both extremes. Also the piston to cylinder clearance was right on. Going to hone the cylinders and put a new set of pistons in and see what happens. Thanks for the input

    Chuck

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    severe detonation can cause that.espically with a cast piston.

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    Unless somebody already ran a hone through the wrist pin holes I'm thinking they are tight. Pressed or floaters, they all get a few passes. If you don't have proper tools the amount of clearance you have is only a guess but rule of thumb ways says a clean and dry wrist pin will just barely slide through (vertically)a clean and dry piston propelled by the weight of the pin. Depending on what new pistons you buy without specifying that the pins are fitted they come street motor (to )tight (for boat) If you buy press fits again and you don't have a way to hang the rods your totaly competent and completly trustworthy local marine engine shop might be able to take care if it for you...and yes, it is caused by lack if oil...in an area that fits tight enough the room for oil is limited.
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