Head gasket thickness?

bhodgkiss

Veteran Member
Joined
Sep 11, 2006
Location
Banbury, UK
TDI
AFN Passat Wagon
hi all,

I have a different head to go on my AFN passat at the end of the month :) so i'll be needing a new gasket.

My current head gasket is the 2 hole version (thickness) but i want to order a replacement in advance ideally, as i only have the weekend to change it and it'll be too late to measure it when the head is off as i won't have access to a VW garage (unless this is how it has to be done.....)

so..... as the block and pistons aren't changing, the piston protrusion from the block at TDC is staying the same.

The only thing that may change is the valve recess in the head. The new head is being skimmed and a 3 angle valve seat on the valves.

My quesiton really is..... what is the head gasket thickness actually determining?

If its the gap from the piston at TDC to the head (to stop it hitting) then I can simply fit the same thickness gasket again, as the head face is controlled by the gasket and as I mentioned before, pistons and block are the same. So I will still have the same airgap from piston to head as before.

But if its valve clearance to piston, this will have changed (even if only slightly). But is this important, by 0,1-0,2mm? How close do the valves run to the pistons? And can they hit? If the valves open into the piston bowl then they will miss? Please explain!

Should I stick the same thickness in again and order from VW in advance?

Many thanks
 
Last edited:

bhodgkiss

Veteran Member
Joined
Sep 11, 2006
Location
Banbury, UK
TDI
AFN Passat Wagon
thanks for the info.

so the gasket just determines piston to head gap. And valves should be positioned with seating, without taking so much off that the valve sits high up int he head and overworks the cam/lifters.

thats great, thanks
 
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