head gasket

[rhedges]

i have just re fitted the cylinder head on my 2007 megane 1.5 dci 86. the problem now is that the engine runs but is knocking. on removal of the cly. head again, i found that the pistons have being touching tha valves. the timing was spot on, the valve clearances fine. on further inspection all four exh. valves have touched slightly and it would suggest that the head gasket is not thick enough, as this provides the only clearance between piston and valves, save for the ever so slight indentations on the pistons. old gasket gone so nothing to compare. new gasket measures 0.8 ml thick. any suggestions please.
ps. head not been skimmed before re fit.

[davelowe]

You torqued it up to the recommended Nm I hope?

[tomalamix]

Hy there,

Why did you change the head gasket? Overheat? Oil or water leaks?

Cheers

[moggiemegane]

if it is a F8Q engine there are 3 different thicknes of gasket depending on how much the the piston crown is above the cylinder
DETERMINING THE THICKNESS OF THE GASKET
Checking piston protrusion
Clean the piston crowns to eliminate any deposits.
Turn the crankshaft in the normal operating direction
by one turn to bring piston No. 1 close to
TDC.

Measure the piston protrusion.
ONLY TAKE INTO ACCOUNT THE DIMENSION FOR
THE PISTON WITH THE MAXIMUM PROTRUSION
For a maximum piston protrusion :
- less than 0.868, use a gasket marked by a tab
with 2 holes,
- between 0.868 and 1.000, use a gasket marked by
a tab with 1 hole,
- greater than 1.000, use a gasket marked by a tab
with 3 holes.