Author Topic: Choosing headgasket after head milling (Read 5830 times)

rallydiesel · « **on:** May 02, 2007, 07:57:03 pm »

I am going to be pulling my head soon and chances are the head will need to be milled. I am wondering, if the head is milled, do I need to use a thicker HG? If so, how would I go about measuring the thickness of the head to find what size HG I would need?

In other words, will I run into valve/piston contact if I run the original thickness HG? I am planning on using a metal HG with ARP studs for re-assembly.

Thanks for any advice.

Vincent Waldon · « **Reply #1 on:** May 02, 2007, 10:17:07 pm »

Greetings fellow canuck.

The head was (mostly!) flat before you mill it and will be flat after you mill it, so as it happens the standard method of determining the head gasket thickness (measuring piston protrusion height) is independent of milling the head (unlike gassers where the combustion chamber is mostly formed in the head).

Here's the relevant passage from The Gospel According to Robert Bentley:

http://www.oneilcastro.com/A2Bentley/GE01/ch6.2.3.html

You're switching over to the 1.9 gasket which I believe has slightly different ranges between versions of the gasket so you may need to track down the relevant thicknesses and match them up... something we need to add to a FAQ someday.

Vince

MacGyver · « **Reply #2 on:** May 03, 2007, 07:48:40 am »

I'd bet a common consensus around here would be to use the thickest gasket you can, then use that as an excuse to crank the fuel & boost up a little, you know, not for performance, but because you had to :twisted:

jimfoo · « **Reply #3 on:** May 03, 2007, 08:31:06 am »

Quote from: "Vincent Waldon"

Greetings fellow canuck.
You're switching over to the 1.9 gasket which I believe has slightly different ranges between versions of the gasket so you may need to track down the relevant thicknesses and match them up... something we need to add to a FAQ someday.

Vince

My manual for the 1.9 states:
1 hole - .0260 - .0339
2 hole - .0343 - .0354
3 hole - .0358 - .0402
I have no idea why there are gaps in the ranges.

rallydiesel · « **Reply #4 on:** May 03, 2007, 08:33:43 am »

Thank you very much! So the milling amount will be so small that it doesn't affect the valve to piston clearance?

jtanguay · « **Reply #5 on:** May 03, 2007, 02:04:22 pm »

Quote from: "MacGyver"

I'd bet a common consensus around here would be to use the thickest gasket you can, then use that as an excuse to crank the fuel & boost up a little, you know, not for performance, but because you had to :twisted:

hehe :twisted: cold starts would be a bit shaky, but o well!

rallydiesel · « **Reply #6 on:** May 03, 2007, 02:54:14 pm »

I guess I could have the machine shop machine the valve seats the same amount they took off the head.

Vincent Waldon · « **Reply #7 on:** May 04, 2007, 08:12:28 am »

Quote from: rallydiesel

Thank you very much! So the milling amount will be so small that it doesn't affect the valve to piston clearance?

It's my understanding that yes, the small amount milled off the head doesn't lower the valves enough to cause them to hit the pistons, assuming your timing is good of course.

Mind you, VW says not to mill the heads in the first place, so what do we know ??!!!!

BTW, the other thing to keep in mind is that if the head is quite warped the cam bearing alignment may well be off... this is something for your machine shop to check and if there's a problem they will need to align-bore the cam bearings. When you hand off the head give them the cam and the top cam plates and nuts as well so that they can do it all at once for ya.