Run out on valves

[Jrh5220]

What is the acceptable run out on new valves?

[Larry Hill]

You would prefer the needle on the indicator not move. Less than .0005”

[Alan Roehrich]

Larry is correct. You have to be careful, it may take a couple of tries to get the valve true in the grinder chuck, especially on older grinders. The new ball style chucks are more accurate.

[Larry Hill]

I check the run out in a R8 collet after I checked the runout on the ID of the spindle. Most things are not as good as advertised. I trust but verify. I have a lot of stuff that are “good parts” but just not good enough to race.

[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.

[Bob F]

And how much clearance should be run guide to stem??

[Larry Hill]

You have used up all of the tolerance. If the valve is out of concentricity the valve will hit the high side of the seat on the side with the greater run out. The spring will cause the valve to conform, bend, to the seat. How many cycles will it take for metal fatigue to appear?

[SBillinson]

Originally Posted by Larry Hill

You have used up all of the tolerance. If the valve is out of concentricity the valve will hit the high side of the seat on the side with the greater run out. The spring will cause the valve to conform, bend, to the seat. How many cycles will it take for metal fatigue to appear?

Guide wear too.

That's not to say that if the valve pounds into the seat you won't have the same issue.

For me, it's a simple question: Why start with poor run-out when you don't have to?

Is it the valve or the valve-grinder? Quality valves with good margins tend to eliminate a lot of guesswork. Same goes for quality grinders that are well maintained and have the right stone and good, clean oil.

[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.