1962 Valve lash settings

[Richard L.]

The Competition Cams spec card for the solid lifter camshaft (Comp Cams part# 12-223-4) installed in my '62 FI engine calls for a setting of .022 for both the Intake and the Exhaust valves. These settings are for a warm/operating temperature engine but, in trying to avoid an oily mess, I would prefer to set the valves with the engine cold. What should the settings be for both INTAKE and EXHAUST with a cold engine?
This 327 was rebuilt some time ago, so it's properly broken-in but has relatively few miles. Since the car is a recent acquisition I'm going through all of its systems to make sure everything is in good working order.
Thank you for your help and advice.
Ric

[Timothy B.]

Richard,
I may get corrected about this but IMO, I would set them at .022 cold and not worry about it, I think it will be fine.

[Ray K.]

Richard

I would allow .002/ .003 for cold adjustment of the valve ( .024 /.025 ) which should allow for hot expansion.

Ray

[Duke W.]

The thermal expansion coefficient of cast iron and mild steel is slightly different, but over short distances like the length of the pushrod the difference in thermal expansion is noise level.

I've measured "hot" (engine idling) and "cold" (room temperature) clearance on mechanical lifter small blocks several times over the years and have never found a difference. Anyone who claims otherwise has likely never done the above measurements, but are merely quoting misinformation that's been around since long before the internet.

At idle the exhaust valve stem doesn't get much hotter than the surrounding cast iron. Under high continuous load the valve stem heats up more and likely expands a few thou, which is why most mechanical lifter cams provide taller constant velocity clearance ramps on the exhaust lobe that allow more room for exhaust valve stem expansion. For example, the Duntov cam inlet and exhaust lobes are identical with the exception that the exhaust clearance ramp is .004" taller than the inlet clearance ramp.

Aluminum heads or aluminum block and heads do require some "adjustment" to specified clearances, depending on whether they are specified hot or cold. The difference is computed on overhead cam engines by multiplying the length of the valve stem by the difference in thermal expansion coefficients. It computes to .002" on my Cosworth Vega, and I've confirmed by measuring. To obtain the .016" hot clearance, both sides, I set them cold at .014". The surrounding aluminum expands more than the steel valve stem.

On an all aluminum pushrod engine like a ZL-1 big block the difference would be greater since you're dealing with the length of the pushrod rather than just the length of the valve stem.

The Chevrolet recommended clearances on the engineering drawings are based on multiplying the height of the clearance ramps by the "rocker ratio", which they claim is 1.5:1, but the fact is that the rocker ratio is not constant , but varies. How do I know this? Because I measured the rocker ratio on several lobes when I rebuilt my SWC's 340 HP engine back in the seventies using two dial indicators, one on the valve retainer and the other on the rocker arm pushrod socket taking readings about every ten degrees crank rotation. The data from the multiple data sets consistently showed that the low lift rocker ratio started out at 1.37:1 and peaks at 1.44:1 with about a 0.3" high lobe.

So applying this to the specified 0.22" valve clearance, which is likely determined the same way Chevrolet did, set the cold clearance at .022(1.37/1.50) = .020. It's up to you whether you want to use 22 or 20. That cam is pretty big and has more effective overlap than I would recommend for a road engine, so it is probably torque shy with a pretty lumpy idle. The tighter clearances will have the following effects you may or may not notice.

1. Lumpier idle

2. Slight loss of low end torque

3. Quieter valve train.

The last is because with the tighter clearance the clearance distance will be taken up at clearance ramp velocity. Looser clearance means the clearance ramps aren't taken up until the lobe is slightly onto the opening flank, which meas higher velocity and valve train shock loading. This shock loading is the valve train noise you hear. Some mechanical lifter cams with the "factored" clearance may even sound like a hydraulic lifter cam the reduction in valve train noise is so significant.

Back in the day Chevrolet recommended valve clearance checks every 12,000 miles. With the tighter clearance and no more than a thousand miles per year you may never have to adjust the valves again.

Download and read the following two-page paper. Regardless of what clearance you decide to use, use the recommended indexing scheme to ensure the lifter is on the cam's base circle for each valve you adjust.

https://www.metroli.org/pdf/WHITE%20PAPER_Solid%20Lifter%20Cam%20Valve%20Adjus tment.pdf

Duke

[Richard L.]

Thank you all, got it done yesterday in the cool part of the morning. All were a bit loose, so I expect it'll run a little quieter and maybe idle smoother.