Valve to piston clearance?

Hans Olsson · 08-20-2007, 04:27 AM

What is the least amount of clearance i can have.Motor is 351C 4V with steel valves, hydraulic cam and schubeck lifters.

Fishlips · 08-21-2007, 01:08 AM

Hans,

There are so many variables I'm not sure anyone can give you a definite answer. It depends on your, rpm, spring rate, valve weight, rocker geometry and flex, 4 speed or automatic and last but not least, Driving style. I know a few guys that need to run more clearence since they are hard on the car in the water box and others run a little extra just in case they miss a shift or break a drive line part.

I guess what I am saying is you may have to find out by the old trial and error method. Most folks use the rule of thumb that .060" on the intake and .100" on the exhaust is safe. I have run less and got away with it but had to be careful. I have also had engines that I could not rev hard in neutral because they would bend valves. As long as it had a load on it it was fine, would rev to 7200 RPM on the track, but one good rev in neutral with no load and it would bend the intakes.

I would start big and work my way down over the next couple of tear downs. Check each cylinder! They are not all the same! Good Luck!

Hans Olsson · 08-21-2007, 03:01 AM

I will start with as big a clearance as i can get and work my way down.I guess that 0.100 on the intake and 0.125 on the exhaust is a safe starting point.

Thank you!

08-20-2007, 04:27 AM	#1
Hans Olsson Member Join Date: Nov 2001 Location: Sweden Posts: 103 Likes: 0 Liked 0 Times in 0 Posts	Valve to piston clearance? What is the least amount of clearance i can have.Motor is 351C 4V with steel valves, hydraulic cam and schubeck lifters.

08-21-2007, 01:08 AM	#2
Fishlips Junior Member Join Date: Jun 2007 Posts: 9 Likes: 0 Liked 0 Times in 0 Posts	Re: Valve to piston clearance? Hans, There are so many variables I'm not sure anyone can give you a definite answer. It depends on your, rpm, spring rate, valve weight, rocker geometry and flex, 4 speed or automatic and last but not least, Driving style. I know a few guys that need to run more clearence since they are hard on the car in the water box and others run a little extra just in case they miss a shift or break a drive line part. I guess what I am saying is you may have to find out by the old trial and error method. Most folks use the rule of thumb that .060" on the intake and .100" on the exhaust is safe. I have run less and got away with it but had to be careful. I have also had engines that I could not rev hard in neutral because they would bend valves. As long as it had a load on it it was fine, would rev to 7200 RPM on the track, but one good rev in neutral with no load and it would bend the intakes. I would start big and work my way down over the next couple of tear downs. Check each cylinder! They are not all the same! Good Luck!

08-21-2007, 03:01 AM	#3
Hans Olsson Member Join Date: Nov 2001 Location: Sweden Posts: 103 Likes: 0 Liked 0 Times in 0 Posts	Re: Valve to piston clearance? I will start with as big a clearance as i can get and work my way down.I guess that 0.100 on the intake and 0.125 on the exhaust is a safe starting point. Thank you!