A10/7 head bolts, will they fit anM20?

[Greybeard]

Could I be losing compression past the rings?, If so would there be any signs to evidence this?

If you have access to a compression tester put oil down the plug hole before testing; if the rings are loosing compression the oil will make a temporary seal and the chamber pressure will increase.

[muskrat]

Test before you put any oil in. Then put 1/2oz down there and test again. Compare readings, big difference = rings, small difference could be valves or head gasket. Use full throttle when testing.
Cheers

[Big Seven]

Lovely job, will try that when I get the chance. I happen to have inherited a tester, let's hope it works ok😐

[chaterlea25]

Hi,
Maybe a piston shaped  like one on the left in the pic will help the M20 performance

John

[Big Seven]

Looks like it might just knock my head orrf 😨.What the heck is it?

[chaterlea25]

Hi Big 7
The pistons are BSA B31 standard comp on the right and the HC one left,
I think it maybe for alcohol fuel ??
I will measure th compression ratio if I get time

John

[Brian]

M20's have BSF head bolts.

[duTch]

M20's have BSF head bolts.

 But aren't also A7/10