Need some help, measuring PTVC!
Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
Need some help, measuring PTVC!
Ok guys I am in the middle of installing my TEA stg 2 LS6 heads, they have a 2.04I and 1.57E valve and have been milled .020, I am using a stock MLS gasket and as of right now I have about .050 clearance on the exhaust valve (I have not measured the Intake valve yet) BUT I am using the 7.425 pushrods I was using when I was cam only, my question is should I be using STOCK length pushrods to check this instead? Also I am measuring all this using my Yella Terra UL roller rockers.
Tech Contributor
Joined: Apr 2007
Posts: 10,924
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From: Forney Texas
I think it was vettenuts that had the great post on rocker arm geometry, but you need to make sure your rocker geometry is correct to determine the proper pushrod length as well as verifying your P2V clearances. 
Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
I am using checking springs and a stock lifter (dont need to shim due to checking springs) I am using a feeler gauge between the rocker roller tip and the top of the valve stem to measure. Should I just go the clay route? Am I on using the 7.425 pushrods?
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
You are likely not at zero lash and may be holding the valve open due to the pushrod. You should use an adjustable for the method you are using and just lengthen it to zero lash, then take your measurement.
Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
Ok, I am going to run up to my tuner he is going to let me use a adj pushrod...
Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
Well I flycut the intake side and now I have .085 clearance so I am good there but now the exhaust (which I have not flycut) is at .090, can I get away with that? I know it should be at .100.
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Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
Sry about that the intake is a .080 (where it should be) and the exhaust is also right a .080 
, I really dont want to flycut the exhaust but it looks like I may have to. I know I have seen ppl running their H/C cars with ~.060I and .070E without any problems
, I really dont want to flycut the exhaust but it looks like I may have to. I know I have seen ppl running their H/C cars with ~.060I and .070E without any problems
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Double check your measurements, exactly how are you measuring? Before you make a decision, just make sure of the measurements.
"If" you were going to be short on one measurement, my opinion would be intake. The piston is chasing the exhaust valve (closing) while on intake the valve (opening) is chasing the piston. So a mishap will likely show itself on exhaust side first.
"If" you were going to be short on one measurement, my opinion would be intake. The piston is chasing the exhaust valve (closing) while on intake the valve (opening) is chasing the piston. So a mishap will likely show itself on exhaust side first.
Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
Double check your measurements, exactly how are you measuring? Before you make a decision, just make sure of the measurements.
"If" you were going to be short on one measurement, my opinion would be intake. The piston is chasing the exhaust valve (closing) while on intake the valve (opening) is chasing the piston. So a mishap will likely show itself on exhaust side first.
"If" you were going to be short on one measurement, my opinion would be intake. The piston is chasing the exhaust valve (closing) while on intake the valve (opening) is chasing the piston. So a mishap will likely show itself on exhaust side first.
Last edited by Corvette Don; Sep 8, 2008 at 09:17 PM.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
I did double check everything 2 times each on 2 different pistons before and after I flycut the intake side. The exhaust is right at .080 (no flycut) and the intake is now at .080 after flycutting. I am measuring using a feeler gauge set to .080 and putting it between the roller on the rocker and the top of the stem and rotating the engine by hand and there is VERY minimal (.001-.002) play at about 10 deg btdc (smallest part), thats how I got the .080 measurement
Just an idea on my part.
Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,979
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From: Wichita KS
One other thought on your situation. I would suggest you run this by Brian Tooley at TEA for a sanity check. I believe part of the minimum clearance requirements is due to lifter pump-up. If you run a lifter that requires less pre-load (Morel would be my recommendation) then the amount the lifter can pump-up is limited. I run my Morels at 0.040". The preload requirement for them is 0.030" - 0.050", so running them closer to the lower end of the preload range would in effect limit the amount they can pump-up. Downside is they are not cheap lifters. Other thing is loss of valve train control with any clearance will likely still result in problems.
Just an idea on my part.
Just an idea on my part.
Team Owner
Joined: Mar 1999
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From: At the beach in little Rhody
The minimum quoted clearances are 0.080" and 0.100". I believe what partially drives those numbers is the ability for a hydraulic lifter to pump up and basically hold the valve open. My thought is that a lifter tha would pump up less may buy you more insurance for running under the minimum clearance, but you should discuss this further with someone like Brian Tooley at TEA where you got your heads.
This is more or less an idea on my part, and as such you should discuss with someone with more expertise.
This is more or less an idea on my part, and as such you should discuss with someone with more expertise.
Thread Starter
Le Mans Master
Joined: Jun 2006
Posts: 6,979
Likes: 31
From: Wichita KS
The minimum quoted clearances are 0.080" and 0.100". I believe what partially drives those numbers is the ability for a hydraulic lifter to pump up and basically hold the valve open. My thought is that a lifter tha would pump up less may buy you more insurance for running under the minimum clearance, but you should discuss this further with someone like Brian Tooley at TEA where you got your heads.
This is more or less an idea on my part, and as such you should discuss with someone with more expertise.
This is more or less an idea on my part, and as such you should discuss with someone with more expertise.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
That is the idea, but the stock/LS7/Caddy lifters won't like that. The Morels are designed for it. But before you do anything, speak with a real knowledgeable engine guy. It doesn't fix the problem, but it might lower risk depending on how much of the minimums is based on hydraulic lifter pump-up.
