Cylinder head valve to piston clearance

[Janner]

I am about to install the rebuilt cylinder heads and I just would like confirmation that my assumptions are correct and I do not have a clearance issue between the pistons and cylinder head valves. Have I forgotten something!
I have taken measurements of the following:

• All pistons are +0.010” proud above the block face.
• Piston are County LC dished type, STD size , depth dish measures -0.040”
• #8 inlet valve is the most proud of all the valves above cylinder head face at+0.025” *
*Measurements of valve height above cylinder head face taken with camshaft removed

I am planning to use a Payen extra thick head gasket with new ARP head stud/bolt set.

Thank you,

Janner

[flying farmer]

Best to measure it with the camshaft installed and the valves on the overlap on no 8 cylinder, that is with the exhaust closing and inlet opening, both valves open the same amount.

Easy to do with no 2 cylinder as you can use the timing marks, and measure how far the valve is off its seat.

If the head will sit flat on the piston at TDC, without the head gasket fitted, and not rock on the valves, then you will have about 50 thou clearance with the thick gasket fitted.
Thick gasket is approx. 60 thou compressed less 10 thou piston height above the block.

If the head does rock on the piston because a valve is touching then you will have to apply some feeler gauges and estimate by how much, and how much clearance you have left with the gasket thickness.

Also be very careful with the cam timing when fitting the chains and sprockets.

Neil

[Janner]

cylinder head valve to piston clearance

Hello Neil,
I did as you described and installed the cylinder head on the block with the valves on overlap and #8 piston at TDC. The cylinder head rocked slightly, I got a reading of 0.0014" and with the pistons 0.010" proud of the block there is 0.004" interference. I put engineers blue on the piston to confirm where it was contacting. I measured the valve height above the cylinder head face and the edge of the inlet valve was 0.047"

Question is, What is the minimum clearance I can get away without further modifications or will using extra thick head gaskets and LC dished pistons suffice? I will take note of your suggestion and modify the cam sprocket and timing chain guides to maintain settings.

Thanks for your help,

Malcolm

Best to measure it with the camshaft installed and the valves on the overlap on no 8 cylinder, that is with the exhaust closing and inlet opening, both valves open the same amount.

Easy to do with no 2 cylinder as you can use the timing marks, and measure how far the valve is off its seat.

If the head will sit flat on the piston at TDC, without the head gasket fitted, and not rock on the valves, then you will have about 50 thou clearance with the thick gasket fitted.
Thick gasket is approx. 60 thou compressed less 10 thou piston height above the block.

If the head does rock on the piston because a valve is touching then you will have to apply some feeler gauges and estimate by how much, and how much clearance you have left with the gasket thickness.

Also be very careful with the cam timing when fitting the chains and sprockets.

Neil

[flying farmer]

If you are getting a clearance of 14 thou with the valves resting on the piston then you should have 46 thou piston to valve clearance with the thick gasket fitted, and this should be sufficient to prevent problems.

IIRC I had a clearance of 30 thou on the second to last engine I built and that gave no problems, though I increased it to 50 thou on the last engine I built as I am using a higher lift cam and am revving to 7000 rpm.

It is possible to make cut outs in the piston crown using an old inlet valve with teeth cut into the rim, then bolting the head down without a gasket and spinning the valve with a drill.

If you spend hours going through the Flying farmers new project thread you will find some pictures somewhere, but as I say I don't think it will be necessary in your case.

Neil

[trunt]

Best to measure it with the camshaft installed and the valves on the overlap on no 8 cylinder, that is with the exhaust closing and inlet opening, both valves open the same amount.

Easy to do with no 2 cylinder as you can use the timing marks, and measure how far the valve is off its seat.

If the head will sit flat on the piston at TDC, without the head gasket fitted, and not rock on the valves, then you will have about 50 thou clearance with the thick gasket fitted.
.

Neil

Just what I was looking for but a bit Confused!


EDIT Ohhhh I got it Original post was referring to #8... but #2 is easiest!

So take any piston on the overlap and check it at tdc..

amazing what you can do when you read it properly

Terry