Piston to wall clearance ?
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Piston to wall clearance ?

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    Senior Member 2savage4you's Avatar
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    Default Piston to wall clearance ?

    If they are in the block, how do you check clearance... I used a feeler guage is that right or was it hillbilly

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    Senior Member ol guy's Avatar
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    Hey Bahner, Not kicking sand or insulting, the only way to check piston to wall is o.d.the piston and i.d. the bore. Anything else is precision geuss work. IMLAO M

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    steelcomp was here
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    Nothing wrong with a feeler gauge if you do it right. The trick is doing it right.
    If God is your co-pilot, change seats!
    Acts 2:38, the perfect answer to the perfect question.

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    Senior Member 2savage4you's Avatar
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    well No body wants to let the secret go on how to do it, so i guess i have to take it to someone that knows how.

    Thanks anyway

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    Senior Member 2savage4you's Avatar
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    Quote Originally Posted by ol guy View Post
    Hey Bahner, Not kicking sand or insulting, the only way to check piston to wall is o.d.the piston and i.d. the bore. Anything else is precision geuss work. IMLAO M

    Really just want to know before i buy parts for it , is if it needs to be bored. It had cast pistons and im going to run forged in it...

    Not boring it saves me about $100 and thats more parts money

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    Fresno Calif Dhondagod's Avatar
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    IMO it cannot be done accurately (sp?) with the pistons still in the block. Most pistons you measure the skirts with a micrometer 90deg from the pin, just below the oil rings.

    Measure the cylinder bore and subtract to get the clearance.

    The piston is larger at the bottom of the skirt and smaller at the compression rings to allow for expansion of the piston dome. Pistons are also "cam-ground" (egg shaped, not perfectly round) as well so measureing somewhere other than the piston mfgr reccomends will give you an inaccurate number.

    If the pistons are in the bore then the rings are in place yes? How will you get a good "feel" of the feeler guage with the rings pushing against them? For that matter, how will you get a feeler guage past the rings without screwing them up?

    If you concerned about clearance just drop the pan and knock the pistons out. Is the motor still in the boat?

    Chris

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    It's what we do BDMarine's Avatar
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    Quote Originally Posted by 468Bahner View Post
    well No body wants to let the secret go on how to do it, so i guess i have to take it to someone that knows how.

    Thanks anyway
    It has to be measured .500 up from the bottom of the skirt perpendicular to the pin so obviously the pan would have to be off. I ALWAYS mic the piston and dial bore gauge the bore. I really don't see how you could put a feeler gauge between the skirt and cylinder and get an accurate reading. Maybe one feeler gauge on each side of the skirt then add the two together?? You will only get an approximate, not exact size that way.
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    Senior Member 2savage4you's Avatar
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    Quote Originally Posted by Dhondagod View Post
    IMO it cannot be done accurately (sp?) with the pistons still in the block. Most pistons you measure the skirts with a micrometer 90deg from the pin, just below the oil rings.

    Measure the cylinder bore and subtract to get the clearance.

    The piston is larger at the bottom of the skirt and smaller at the compression rings to allow for expansion of the piston dome. Pistons are also "cam-ground" (egg shaped, not perfectly round) as well so measureing somewhere other than the piston mfgr reccomends will give you an inaccurate number.

    If the pistons are in the bore then the rings are in place yes? How will you get a good "feel" of the feeler guage with the rings pushing against them? For that matter, how will you get a feeler guage past the rings without screwing them up?

    If you concerned about clearance just drop the pan and knock the pistons out. Is the motor still in the boat?

    Chris
    Yeah i understand now........ The block is bare. I installed the crank and one old cast piston minus rings to get some kind of measurement. I can see now that it would only be a guess and im waisting my time.. Looks like i need to see a machine shop

    Thanks for clearing that up...........

  11. #9
    steelcomp was here
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    Quote Originally Posted by 468Bahner View Post
    Yeah i understand now........ The block is bare. I installed the crank and one old cast piston minus rings to get some kind of measurement. I can see now that it would only be a guess and im waisting my time.. Looks like i need to see a machine shop

    Thanks for clearing that up...........
    Chances are you're going to need a few more thou anyway, weather it needs boring or not.
    You can slide a piston in a cylinder upside down and hold the skirt against the cyl wall with one hand (a couple of fingers) and use a feeler gauge on the other side of the skirt. Hold the piston in the hole far ehough that where you're measuring is at the right point on the skirt. If you do it right, and things are clwean, you can be very accurate this way. Problem is, this only tells you what the clearance is. It dosen't tell you anything about the bore size or piston dia. Those are the numbers you need.
    Most pistons are set up for a nominal bore size.
    If God is your co-pilot, change seats!
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    Senior Member 2savage4you's Avatar
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    Quote Originally Posted by steelcomp View Post
    Chances are you're going to need a few more thou anyway, weather it needs boring or not.
    You can slide a piston in a cylinder upside down and hold the skirt against the cyl wall with one hand (a couple of fingers) and use a feeler gauge on the other side of the skirt. Hold the piston in the hole far ehough that where you're measuring is at the right point on the skirt. If you do it right, and things are clwean, you can be very accurate this way. Problem is, this only tells you what the clearance is. It dosen't tell you anything about the bore size or piston dia. Those are the numbers you need.
    Most pistons are set up for a nominal bore size.


    Thats how i did it the first time and i got .006 all eight pistons

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