piston to valve clearance... is this method ok???
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piston to valve clearance... is this method ok???

  1. #1
    Senior Member matt1840's Avatar
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    Default piston to valve clearance... is this method ok???

    Ok im wanting to check piston to valve clearance.. Like ive said before ive build plenty of engines just never measured anything, just a quick slap together nothing really to highperformance.

    But now that ive got alot of money sunk into this motor, id like to know all my clearances, not to mention know how to do everything for when i build my bbc this winter.

    So i was thinkin, ive got my heads installed and dont really wanna remove them. To check valve to piston clearance could i set valve lash to 0 and bring the valves to "overlap" and then depress the valve considering its only on a "test spring" and check the clearance between rocker and valve tip with feeler gauges as my valve to piston clearance???

    Any suggestions would be great.
    Last edited by matt1840; 10-09-2008 at 09:56 AM.
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    Set zero lash. Set a dial indicator on the retainer parallel with the valve. Get on the stroke that is opening the intake valve and start about 20 degrees before TDC and check every 1 degree or so through TDC to 20 after TDC. Zero the indicator of course each time. For the exhaust you want to check about the same area except when the exhaust valve is closing. Valve to piston clearance is closest when the intake is opening and the exhaust is closing!!!
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    Quote Originally Posted by matt1840 View Post
    To check valve to piston clearance could i set valve lash to 0 and bring the valves to "overlap" and then depress the valve considering its only on a "test spring" and check the clearance between rocker and valve tip with feeler gauges as my valve to piston clearance???
    Without getting too technical, this will work just fine. Make sure the engine is in overlap, and check the exhaust 10 degree's before TDC and check the intake 10 degree's after TDC (always turning the engine over in the direction of rotation). As long as you have plenty with this method, there is really no reason to get into a more more involved procedure.
    Depending on combo and application, anything over .100 is good on the exhaust and anything over .075 is good on the intake. If they are less than that we can get more presice with the method.
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    steelcomp was here
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    Have you degreed your cam?
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    Senior Member matt1840's Avatar
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    Quote Originally Posted by steelcomp View Post
    Have you degreed your cam?
    I have no degreed my cam that is in the works for today, i fugred after i did that i may wanna check the v2p clearance. It shouldnt be close only 9.5:1 compression, and a cam with only .520 lift. Its a dished piston there arent even any cups for the valves on the face. I just more than anything wanted to learn the process.
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    it will be a learning experience because they won't come anywhere close. You stated the lift, but lift play a minor role in vp clearance compared to duration and timing.



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    Quote Originally Posted by matt1840 View Post
    I have no degreed my cam that is in the works for today, i fugred after i did that i may wanna check the v2p clearance. It shouldnt be close only 9.5:1 compression, and a cam with only .520 lift. Its a dished piston there arent even any cups for the valves on the face. I just more than anything wanted to learn the process.
    Cool. Sounds like you're moving in the right direction. Knowledge is power...in more ways than one!
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    Quote Originally Posted by gn7 View Post
    it will be a learning experience because they won't come anywhere close. You stated the lift, but lift play a minor role in vp clearance compared to duration and timing.
    very true i didnt think about that... all i had in my head was how far the valve opened, not how long it stayed open.. Good call.
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    "The" masheenist wsuwrhr's Avatar
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    I am just curious, .52 lift with only 9.5 comp?

    Seems like alot of lift for such low compression.
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    Quote Originally Posted by wsuwrhr View Post
    I am just curious, .52 lift with only 9.5 comp?

    Seems like alot of lift for such low compression.
    well i bought the cam before i got the pistons.. I was gonna go with more compression, but with iron heads i was told it wasnt smart to do. I wasnted 10.5:1 but like i said i was talked out of it. But from what i understand now with the cooler temps of a boat motor i woulda be ok with it.
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    Quote Originally Posted by matt1840 View Post
    well i bought the cam before i got the pistons.. I was gonna go with more compression, but with iron heads i was told it wasnt smart to do. I wasnted 10.5:1 but like i said i was talked out of it. But from what i understand now with the cooler temps of a boat motor i woulda be ok with it.
    10.5 would have been fine IMHO. If you pull skiers with this (jet) boat, I think it will be a little lazy off the bottom.
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    Default Not sure it's right, but I usually...

    .... degree the cam in, then put a piece of clay in each valve pocket. Grease the valves a bit so the clay won't stick. Drop the head on, necessary valve train (0 Lash), then rotate the engine a couple times.
    Pop the head off, cut the clay in half with a razor and you can check minimum v2p with a depth mic or calipers. This way you can see exactly where the valve is relative to the valve pocket.
    Not sure it's right, but the way I was taught.
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    Distinguished Member David 519's Avatar
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    Quote Originally Posted by gn7 View Post
    he doesn't have any valve pockets
    Well.... if you put a blob of clay on the top of the piston, you'd at least see what it would look like if it had valve pockets
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