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Piston slap in a 400 SB

Discussion in 'The Garage' started by blazin topless 75, Mar 2, 2004.

  1. blazin topless 75

    blazin topless 75 Registered Member

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    Can anyone tell me if a broken Piston Skirt only makes noise when the engine is warm? That is what the PO told me about my "new" engine...I ran it around a little bit and am getting some kind of noise at temperature, but I can't tell if it is exhaust or trans or something else...I would think that it would make noises cold or warm. There is no fluctuation in oil pressure or anything else to tell me that there is a problem What do Y'all think?
     
  2. SUBFAN

    SUBFAN 1/2 ton status

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    Traditional piston slap occurs mainly when cold, going away when things warm up.

    I would not like to run a half broken piston in my motor....

    I would check elsewhere for the noise. Use a stethescope, piece of hose, or a screwdriver to help isolate it.

    Check the valve lash if it only happens when warm. If it were me, I would pull the pan, as I would want to see the 'broken skirt'. I might run it if there was just a little nick and no scoring of the cylinder wall.

    A bad valve/seat????
     
  3. blazin topless 75

    blazin topless 75 Registered Member

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    I ran the truck some more tonight-it definitely doesn't have a sound when it is cold. It is a tapping sound that slows down when I come off of the throttle and virtually disappears at idle (although it may be masked by the exhaust). The engine seems to be running very rich as well. Please help!!
     
  4. POWERMAD

    POWERMAD 1/2 ton status

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    A broken skirt will make all kinds of racket regardless of engine temp.
    I would reset the valves and see if it is still there.
    If it is it could be a bad lifter.
    This is what my "new engine" is doing.
    After resetting the lash it will run quiet for a bit then tappity tap tap. Now it is so bad that it does it cold, hot any rpm and at 3grand will not open the valve and it sounds kinda like a Jake brake.
    You need to isolate the sound and go from there.
    If it seems to be coming from the basement then drop the pan and start lookin for loose rods ect.
    What's the oil pressure when at operating temp?
     
  5. nicotine

    nicotine 1/2 ton status

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    what does it mean when there is a piston slap when it is cold?

    what could cause this?
    mine is doing it only when cold is it someting i should worry about? should i pull the pan and see whats going on?
     
  6. SUBFAN

    SUBFAN 1/2 ton status

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    This is usually associated with forged pistons. They tend to grow a bit more than the other types when warm, and require a bit more clearance in the bore than a cast or hyper type.

    If your motor was built with these, (forged) and the clearances are correct, there is nothing to worry about.

    If you are running one of the different types, and the machinist/rebuilder was lazy, then there is just a little more to worry about. The motor will be fine, but it will not last as long....

    Piston slap is the very slight movement of the piston rocking in the bore from the pin. When the skirt taps the cylinder wall, that is the noise you hear, until it warms up and expands to fit in the bore better. Just use a good warm up before getting on the gas to prevent damage.

    Hope this helps....
     
  7. SUBFAN

    SUBFAN 1/2 ton status

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    Look/think elsewhere and isolate the sound. A slight crack in an exhaust manifold can act like that, making someone think the motor is terminal. A friend of mine got a sweet deal on a BBC because of this. Installed headers, problem was gone....

    Nothing like getting a BBC for trade on a generic 350 block that needed rebuilt....Some guys have all the luck....
     
  8. 88Silverado

    88Silverado 1/2 ton status

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    Just go buy yourself a new LS-1 engine.
    You get factory piston slap with cast pistons for free!
    Mine does it sometimes when its cold and others when its warm.
    GM says its normal in the LS-1 /forums/images/graemlins/rolleyes.gif

    You can take an oil sample and send it to Blackstone Labs for analysis. They can tell you if theres metal and what type.
     

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