Head Gasket thickness

[xyz500]

Head Gaskets are listed as Standard and thick. With the BGA thickness being 0.020" over the original and the Cometic being about .015" thicker than standard.

But does anyone know on average for the standard BGA head gasket, what is the compressed thickness?

I'm working out the compression ratio and valve clearance (I've done all my volume measurements etc) so I can then decide on which gasket to get.

Thanks

[flying farmer]

You can also get standard thickness BGA gaskets from places like LD parts.
Standard gaskets are about 40 thou thick.
I have recently fitted a set and re-torqued them once and they went down nearly a flat of the nuts/studs. I need to do them again and measure the gap, I have not bothered so far as I knew they would settle from previous postings on here.
Neil

[xyz500]

Thanks Neil.

My exhust valves are slightly below the head face (haven't got the measurement on me). Each combustion chamber volume is 37ml and I have 20thou over size high compression (domed) pistons, so protrude above the deck by 0.012". Based on all my other measurements, if the standard BGA gasket is 40 thou after torquing down, that would give me a compresssion ratio of 9.6. So on high octane that appears still managable.

Phil.

[xyz500]

Neil,
You seem to have pushed the limits a few times, what's the lowest valve to piston clearance you've ever got down to?
Phil.

[flying farmer]

Piston to valve clearance isn't too much of a problem with the standard cams as the valves go into the recess between the outer rim and the central dome of the piston. Longer duration cams are more of a problem as the inlets open and close earlier.

As a simple test, rest the cylinder head on the top of a piston at TDC with no head gasket. Make sure the cam is on the timing marks so both valves are open the same amount.

The head should fit flat if the valves are not touching the piston which will give a minimum clearance of 40 thou once the standard gasket is fitted.

This clearance has never given me any problems

[xyz500]

I did your simple test and put the heads on with no gasket. Valves are clear, with valves in a exhaust/inlet overlap position, ie both open slightly and same amount. I also put a very thin layer of plastecine type material on, and there was no mark from the valves. So that accords with my measurements, that the valves are clear of the piston top (but will not be by much). I'm also using standard cams.

Only thing being that the domed pistons sit max 0.010"above the deck, so that would mean the squish area clearance would be only 0.030" assuming the gasket was 0.40". But even so on my measurements and calcs only be at a compression ratio of 9.6.