How to check P to V clearance?
How to check P to V clearance? Lets see if I have all of the necessary steps right...
1. Place piece of Play Doh or similar clay on piston surface.
2. Bolt head and gasket on snug, not necessary to torque.
3. Setup valvetrain (install rocker arm and pushrod) on one cylinder.
4. Turn over engine at least one full revolution.
5. Remove head and take clay off of piston, measure clay thickness with caliper.
Now, .080 intake/.100 exhaust is the minimum acceptable clearance, right? How much to compensate for gasket not being fully compressed? .005? .010? Anything else I've overlooked?
Thanks, Shawn
1. Place piece of Play Doh or similar clay on piston surface.
2. Bolt head and gasket on snug, not necessary to torque.
3. Setup valvetrain (install rocker arm and pushrod) on one cylinder.
4. Turn over engine at least one full revolution.
5. Remove head and take clay off of piston, measure clay thickness with caliper.
Now, .080 intake/.100 exhaust is the minimum acceptable clearance, right? How much to compensate for gasket not being fully compressed? .005? .010? Anything else I've overlooked?
Thanks, Shawn
Not sure, but sounds good. I would torque the old gasket for safety sake. Also, you can use a low tension spring and dial indicator setup, as was explained by a local builder.
As for measuring the clay, wouldnt you want to measure while its on the piston? If not seems like you would be stretching it.
As for measuring the clay, wouldnt you want to measure while its on the piston? If not seems like you would be stretching it.
I've done this a couple of times and the only things I'd change from what you have above is.
1. DO NOT use your valve springs that are on the heads, they are too stiff and will push the pushrod down into the lifter and give you a wrong reading. Get a soft "tester" spring. I got two suitable springs from work.
2. Use a used head gasket if you have one (I have loads of them
) that way you don't have to worry about compressed thickness and stuff.
3. I've ran closer than .080/.100 and been ok. IMO .65/.80 is safe with good springs.
4. Lube the combustion chamber and piston with cooking spray.. LOADS easier to get the clay off.
Have fun
1. DO NOT use your valve springs that are on the heads, they are too stiff and will push the pushrod down into the lifter and give you a wrong reading. Get a soft "tester" spring. I got two suitable springs from work.
2. Use a used head gasket if you have one (I have loads of them
) that way you don't have to worry about compressed thickness and stuff.3. I've ran closer than .080/.100 and been ok. IMO .65/.80 is safe with good springs.
4. Lube the combustion chamber and piston with cooking spray.. LOADS easier to get the clay off.
Have fun
Joined: Nov 2001
Posts: 3,043
Likes: 0
From: Texas and Qatar
Originally Posted by 99 Black Bird T/A
Clay isn't as accurate as using a dial gauge. I think the dial gauge w/a solid lifter would give you the most accurate reading.
I did both once to see what the difference was. I used clay first with lightweight testing springs, then I went back and checked again with a dial indicator. With clay the readings were .020" more on both valves than my readings with the dial indicator, I trust the dial indicator reading more. Now if you used solid lifters clay would probably be more accurate vs. measuring with a stock lifter.
Originally Posted by -Joseph-
I did both once to see what the difference was. I used clay first with lightweight testing springs, then I went back and checked again with a dial indicator. With clay the readings were .020" more on both valves than my readings with the dial indicator, I trust the dial indicator reading more. Now if you used solid lifters clay would probably be more accurate vs. measuring with a stock lifter.
Clay isn't a good way to test as you note above because give or take .020 that could end being end up being important. My friend that did my H & C install did the P to V checks. He used solid when checking everything on his mock up LS1 before doing the install. On the car he checked with the hydrolic lifter. I should have been more specific. Thanks.
Trending Topics
How do you measure this with a dial gauge? I would assume that you turn the motor over, then when the valve is all the way down, you set the dial gauge at zero on the valve tip, then compress it until it hits the piston, giving you P to V clearance? Is that correct? What do you measure from and how, using the dial gauge method?
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo Joined: Nov 2001
Posts: 3,043
Likes: 0
From: Texas and Qatar
Your not checking the PtoV clearance at max lift, you need to check it during the camshaft overlap period. For instance if your checking cylinder #1 your overlap would be really close to where the timing chain dots line up. You set the valvetrain to zero lash with both valves closed, your cam gear timing mark will be at 12 o clock, overlap occurs 360 crank degrees from that, or 180 cam degrees, so overlap would be when the upper timing gear is at 6 o clock. Check intake and exhaust 10 degrees before TDC and 10 degrees after TDC during overlap and everywhere in between.
I usually put the dial indicator against a retainer and have it clamped to a long metric bolt using rocker arm threads, usually from the next cylinder over (#3). You zero the guage when you make piston contact with the valve by pushing the valve open, then when you let it go, that reading is your clearance. You can also use feeler guages to measure the clearance between piston contact and the rocker arm, but I always use one of my dial indicators.
I usually put the dial indicator against a retainer and have it clamped to a long metric bolt using rocker arm threads, usually from the next cylinder over (#3). You zero the guage when you make piston contact with the valve by pushing the valve open, then when you let it go, that reading is your clearance. You can also use feeler guages to measure the clearance between piston contact and the rocker arm, but I always use one of my dial indicators.
