Piston to Valve Clearance

[peerless]

Ok guys building a engine for a customer. Nothing too radical and its a BMW straight six engine. I am getting conflicting information regarding the P to V clearance.

Right now I have about .065 (1.65mm) I am being told that I need .080-.100" clearance. The camshaft is a new billet with about .452" lift and 272 duration. 7K rev limit

I had another guy tell me:

I run around 0.6-0.7mm clearance on my race engines that go to 9k.

Which is only about .025"

The pistons are stock cast pieces with a single notch for the intake valve. Clearance is checked using a used stock headgasket at factory torque specs. I am using playdo and then check the depth.

Will .065 be enough or should I go deeper?

I ask you guys because I know the engine building experience here is above and beyond what I might get from a BMW board filled with mostly teenagers whose idea of rebuilding an engine is changing rings and bearings and calling it a day.

Thanks,

[af2]

Ok guys building a engine for a customer. Nothing too radical and its a BMW straight six engine. I am getting conflicting information regarding the P to V clearance.

Right now I have about .065 (1.65mm) I am being told that I need .080-.100" clearance. The camshaft is a new billet with about .452" lift and 272 duration. 7K rev limit

I had another guy tell me:

I run around 0.6-0.7mm clearance on my race engines that go to 9k.

Which is only about .025"

The pistons are stock cast pieces with a single notch for the intake valve. Clearance is checked using a used stock headgasket at factory torque specs. I am using playdo and then check the depth.

Will .065 be enough or should I go deeper?

I ask you guys because I know the engine building experience here is above and beyond what I might get from a BMW board filled with mostly teenagers whose idea of rebuilding an engine is changing rings and bearings and calling it a day.

Thanks,

Intake or exhaust? Exhaust will be .080 min and .060 intake. Most people disagree so it is what it is!

[bobqzzi]

Ok guys building a engine for a customer. Nothing too radical and its a BMW straight six engine. I am getting conflicting information regarding the P to V clearance.

Right now I have about .065 (1.65mm) I am being told that I need .080-.100" clearance. The camshaft is a new billet with about .452" lift and 272 duration. 7K rev limit

I had another guy tell me:

I run around 0.6-0.7mm clearance on my race engines that go to 9k.

Which is only about .025"

The pistons are stock cast pieces with a single notch for the intake valve. Clearance is checked using a used stock headgasket at factory torque specs. I am using playdo and then check the depth.

Will .065 be enough or should I go deeper?

I ask you guys because I know the engine building experience here is above and beyond what I might get from a BMW board filled with mostly teenagers whose idea of rebuilding an engine is changing rings and bearings and calling it a day.

Thanks,

.065" is plenty on the intake side and I would be comfortable with that on the exhaust side as well.

[Ron C.]

The intake side is safer because the valve is chasing the piston, the spring is not as big a factor, so .60-.070 is usually safe. The exhaust is a different story since the piston chases the valve. Spring maintance is important if you run close clearances. So if that's not a factor then you can tighten it up to intake clearances. But I would keep your customer happy and be safe on the exhaust side.
If it's your own motor then tighter is up to you.

That's my story.........blessings.............Ron Clevenger.

[peerless]

Thank you very much

And yes this was on the intake side, exhaust has plenty of clearance. New cam rockers and springs so everything is right and tight.

You have put my mind at ease, now I can button this thing up and get paid.

When ever I need good solid engine building advice I know it can be found here every time. Thanks again.

[Hendrens Racing Engines]

We have found that you can run the same minimum int valve to piston clearance as you do deck clearance. if you run .040 piston to deck you can run the same clearance on the int valve,if it doesn't hit the deck it wont hit the valve.Bill

[Tony B]

Plus another .010.TB