head gasket thickness

[tdafforn]

I am sorting out how far to deck the 711m block I am converting to use with my twinc. Unfortunately to do the calculation I need the standard compressed copper head gasket thickness (and I have thrown my old head gasket). Anyone have a figure for this?
Tim

[types26/36]

Just measured two used and one new gasket, I don?t have my digital vernier with me but with a normal vernier I get:
New gasket = .9 mm
Used gaskets = .7 mm
Note: measured at the fire ring

[redskatejbf]

Tim, I found a used gasket and it measures:
.0285" _ .73 m/m. across the two fire rings in the middle.
.0275" _ .71 m/m. across a single cylinder fire ring.
.0240" _ .61 m/m. on a area other than on a fire ring.
Hope this helps.

John.

[dlbarnes1]

In Dave Bean's catalog/manual, he suggests a crushed thickness of
0.056 cm for computing compression ratio.

Dave 72 Sprint DHC

[rgh0]

I use 0.6 mm for a standard gasket. The used gaskets spring back a little when removed. The fire ring springs back more than the rest

Rohan

[tdafforn]

thank guys..
What compression ratio should I be going for on an engine (Big valve) for road use with UK road fuel? 10:1?
Tim

[CBUEB1771]

I also ran to the Bean catalog, recalling he has a section about calculating CR with typical values for the Twin Cam. Compressed thickness and "sprung back" dimensions will vary somewhat from one supplier and style of gasket to another. I take the anorak approach (let's see if I get Mopho going again) by performing a trial installation with the head fully torqued and check the separation between head and block with feeler gauges. That way I know for sure. I waste a head gasket but I didn't buy a Lotus to save money. Also keep in mind that most automotive machinists won't bother to make sure the deck is parallel to the crankshaft centerline and you end up with a monotonic change in piston-to-deck height going from front to back. Hence you get different compression ratios in each cylinder. You need to specify to the machinist that you want the block set up so the crank centerline, not the sump flange, is parallel to the cutting plane of his surfacer.