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Help checking piston to valve clearance?? UPDATE
#851571
11/11/10 11:09 PM
11/11/10 11:09 PM
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Junky
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383 engine with the heads on, engine in the car. Heads are the 346 kind.
Do I have to have the cam in to check? I have a dial indicator and a valve spring remover, and a weak spring for checking. Never done this before, and really don't know how to.
The cam that I'll be installing has a .518/.518 lift. My concern is that the heads have been milled 0.030", flat top pistons are 0.020" in the hole, no valve reliefs. Running steel shim head gaskets. Stamped steel rockers are virtually never 1.5:1 ration, more like 1.45:1 ratio at best. With 1.45:1 real ratio the lift would be like 0.490" in reality.
I know I need to check piston to valve clearance. My question is, does it look good that I can run the "518" lift cam okay? I'm concerned about clearance.
Last edited by Junky; 11/15/10 12:26 AM.
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Re: Help checking piston to valve clearance??
[Re: Junky]
#851572
11/12/10 12:48 AM
11/12/10 12:48 AM
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s.w.fl
bonefish
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yes you have to have the cam in to check it.then you can just stack feeler guages at your min.clearance.there may be a way to do it without the cam but i dont know of it.
Last edited by bonefish; 11/12/10 12:49 AM.
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Re: Help checking piston to valve clearance??
[Re: AndyF]
#851574
11/12/10 01:31 AM
11/12/10 01:31 AM
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Junky
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Quote:
You can measure the valve clearance at TDC without the cam. Once you know how much room you have, you should be able to calculate the VP clearance. Most cam companies publish the lift at TDC so once you know that you can figure out what the valve lift will be.
I understand. I'll be checking VP tomorrow and post what I discover.
For discussion's sake: If there's .650 max VP clearance at TDC, and max cam lift is .490, that would leave .160 clearance. Correct?
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Re: Help checking piston to valve clearance??
[Re: goldmember]
#851576
11/12/10 01:39 AM
11/12/10 01:39 AM
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Junky
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Quote:
NO. Check your pm's
pm's as in Private Messages?
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Re: Help checking piston to valve clearance??
[Re: AndyF]
#851578
11/12/10 08:00 AM
11/12/10 08:00 AM
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Frederick
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Quote:
You can measure the valve clearance at TDC without the cam. Once you know how much room you have, you should be able to calculate the VP clearance. Most cam companies publish the lift at TDC so once you know that you can figure out what the valve lift will be.
This would give you an indication, but I recommend you check the P/V clearance again when the camshaft is installed.
Reason being that the minimum piston to valve clearance doesn't occur at TDC.
383B, 9.8:1, Lunati 60302(220/226@0.050 262/268Dur, 0.475"/0.494", Stealth heads, Performer manifold, QF SS-750-AN carb, 3.31Diff, A833 4-speed manual.
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Re: Help checking piston to valve clearance??
[Re: Frederick]
#851579
11/12/10 09:49 AM
11/12/10 09:49 AM
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U.S.S.A.
JohnRR
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Quote:
Quote:
You can measure the valve clearance at TDC without the cam. Once you know how much room you have, you should be able to calculate the VP clearance. Most cam companies publish the lift at TDC so once you know that you can figure out what the valve lift will be.
This would give you an indication, but I recommend you check the P/V clearance again when the camshaft is installed.
Reason being that the minimum piston to valve clearance doesn't occur at TDC.
 Yep better place to check for a ballpark is 10 before and 10 after but to know your actual it's best to have the cam in .
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Re: Help checking piston to valve clearance??
[Re: Junky]
#851581
11/12/10 01:21 PM
11/12/10 01:21 PM
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Oregon
AndyF
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Quote:
Quote:
You can measure the valve clearance at TDC without the cam. Once you know how much room you have, you should be able to calculate the VP clearance. Most cam companies publish the lift at TDC so once you know that you can figure out what the valve lift will be.
I understand. I'll be checking VP tomorrow and post what I discover.
For discussion's sake: If there's .650 max VP clearance at TDC, and max cam lift is .490, that would leave .160 clearance. Correct?
That is the basic idea. You'll typically have something like .350 inches of clearance at TDC. The cam lift will be about 0.100 at TDC which works out to .150 lift at the valve with 1.50 ratio rocker arms. So .350 - .150 gives you .200 of clearance.
If you have a lot of clearance at TDC and the cam is fairly slow then you won't have any VP problems. If the clearance is tight at TDC then you'll probably have a problem.
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Re: Help checking piston to valve clearance??
[Re: Junky]
#851584
11/12/10 01:50 PM
11/12/10 01:50 PM
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Aurora, Colorado
451Mopar
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It is difficult to estimate the Piston/valve clearance on paper unless you know the true cam lobe profile (duration at multiple lobe lift points), lobe seperation angle, and installed center-line.
The cams maximum lift does not mean much because the piston will have moved down in the cylinder quite a bit by then. Other information needed for an estimate would be the closed valve position to piston clearance at TDC, and the stroke/rod length to figure the piston movement around TDC.
Like I said, using math to estimate (model) the PV clearance is not easy.
The easy solution is checking with the actual cam installed. Both intake and exhaust will need to be checked. First you need to install your checking springs, a solid tappet (or tappet that won't compress under the checking spring load), and set the lash. Setting zero lash is best, you can add in lash to the PV numbers later.
With the dial indicator setup on the valve retainer, you just push the valve down till it contacts the piston and take the PV reading directly, but you have to do this at several crank positions because the least clearance point is unknown.
Usually the PV is tightest around 10-20 degrees Before (exhaust) and after (intake) TDC depending on the above mentioned cam parameters, including the cams installed position.
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Re: Help checking piston to valve clearance??
[Re: 451Mopar]
#851585
11/12/10 04:14 PM
11/12/10 04:14 PM
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michigan woods
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Quote:
It is difficult to estimate the Piston/valve clearance on paper unless you know the true cam lobe profile (duration at multiple lobe lift points), lobe seperation angle, and installed center-line.
The cams maximum lift does not mean much because the piston will have moved down in the cylinder quite a bit by then. Other information needed for an estimate would be the closed valve position to piston clearance at TDC, and the stroke/rod length to figure the piston movement around TDC.
Like I said, using math to estimate (model) the PV clearance is not easy.
The easy solution is checking with the actual cam installed. Both intake and exhaust will need to be checked. First you need to install your checking springs, a solid tappet (or tappet that won't compress under the checking spring load), and set the lash. Setting zero lash is best, you can add in lash to the PV numbers later.
With the dial indicator setup on the valve retainer, you just push the valve down till it contacts the piston and take the PV reading directly, but you have to do this at several crank positions because the least clearance point is unknown.
Usually the PV is tightest around 10-20 degrees Before (exhaust) and after (intake) TDC depending on the above mentioned cam parameters, including the cams installed position.
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Re: Help checking piston to valve clearance?? *DELETED*
[Re: Yancy Derringer]
#851587
11/12/10 08:53 PM
11/12/10 08:53 PM
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Lincoln Nebraska
RapidRobert
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Post deleted by RapidRobert
live every 24 hour block of time like it's your last day on earth
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Re: Help checking piston to valve clearance??
[Re: RapidRobert]
#851588
11/12/10 09:26 PM
11/12/10 09:26 PM
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Junky
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I checked the P to V clearance at TDC. It's .285, for what it's worth. However, a friend of mine who owns a performance shop said he'd stop by tonight to degree the cam and check P/V clearance. He's been doing this stuff for 40 years.  Me happy. I'll post the verdict tomorrow.
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Re: Help checking piston to valve clearance??
[Re: AndyF]
#851590
11/12/10 10:36 PM
11/12/10 10:36 PM
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Junky
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Quote:
You're probably fine then. That cam probably is about .100 lift at TDC so that gives you 0.135 of clearance. The valves will try to catch up with the piston after TDC but with 1.50 ratio you'll most likely be fine. It is close enough to do a double check though.
Thanks Andy, your comments make me feel better about it working out. 
I'll post tomorrow.
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