Run out on valves

[Dave Noll]

Question: it's not a big deal but it's nagging at me. I understand why an egg shaped valve head ( 2 high spots showing on the indicator in 1 rotation) would be bad. But why would a valve head not concentric to the valve stem by .0015 be a problem if the valve stem has .003 clearance to the guide?

[Adger Smith]

Go ahead and split hairs.
Then TQ the head down and distort everything.
I bet very few use a TQ plate doing the seats.

[Dwight Southerland]

Originally Posted by Dave Noll

Question: it's not a big deal but it's nagging at me. I understand why an egg shaped valve head ( 2 high spots showing on the indicator in 1 rotation) would be bad. But why would a valve head not concentric to the valve stem by .0015 be a problem if the valve stem has .003 clearance to the guide?

.003 clearance on the guide does not equate to .003 movement at the head. Stick your valve in the guide with oil on it and see if you can measure how much movement it has at the seat level. The length of the guide, the diameter of the stem and the distance from the guide to the seat all play into the stability of the valve. I would be surprised if it is a measurable amount with a dial indicator.

[SpeierRacing]

I don't know anything I would run .003 guide clearance on! Most 11/32 intakes should be .0010-.0012 and exhaust .0013ish. 5/16 and under well under .0010..

People ask me all the time what is acceptable seat run out. Whatever your guide clearance is! .0000 is cool but doesn't matter in the grand scheme of things!