cylinder head minimum 118.1mm how crucial

[220bhp]

What happens if the minimum of 118.1mm through the bolt holes is reduced,is the head
still usable in any way.

[220bhp]

I wonder how many people check this measurment after having the head skimmed.
Given the age of these cars and the fact that many of them have had several owners,
it is inevitable that there are some heads that have been skimmed more than once, thus increasing the chance that there are some heads being used below the minimum.
My car is a 3b which would have originaly had a paper gasket, I am useing an RS2 metel headgasket which I under stand is thicker, if so by how much,surely this has a bearing on the minimum measurement.

[Kieron20V]

I measured a scrap head I had before very roughly and it was very close. I think if you get any lower than the limit then the intake valve seats start to protrude.

[220bhp]

Thanks for that, it would be interesting to find out just how much is to much.

[JariP]

My coupe has been running last 5 years with a head skimmed atleast 0,9mm. It had couple of scratches that needed a 0,8mm skimm before it was ok to use, so it wasn't the regular rehaul skimm. It still can be skimmed maybe once before the intake seats get hit. I can't see any other limiting factor for skimming other than hitting the intake valve seats.

I think you should be more worried about valve stem length and hydraulic buckets adjusting range when refacing/recutting valve seats and valve faces.

[newsh]

There's the issue of CR too, not sure how much this is affected by skimming but if you're going for big power might be best to use a thicker HG.

[220bhp]

JariP did you measure the thickness of the head through the bolt holes. I have no idea of the original measurement from the factory,only the minnimum advised by audi.

[Rusty]

It's not ideal but a thicker HG could indeed compensate for an under-thickness head. Just use your common sense and see what can be affected by the over-skimming.

[JariP]

I tried but I didn't have proper tools to get a meaningful numbers. Or the numbers didn't agree with the factory manuals, or something like that. So I just checked the real world clearances and ran it.

If you are building a big boost engine, don't go by the internet facts or even factory numbers, check and measure everything yourself. Like the CR, factory says 9.3, Mahle/kolbensmidt say 8.75 (they designed and made the original pistons), my measuring and math say 8.8, who's numbers do you believe?

1.0mm skimmed off the head brings the CR up something like 0.8-0.9. Valve clearance with stock valves, cams and timing won't be a problem.

[Rocco]

It's not ideal but a thicker HG could indeed compensate for an under-thickness head. Just use your common sense and see what can be affected by the over-skimming.

my current cylinder head were skimmed at least 2 times and i was needing a custom thicker gasket fo drop compression a littlle (8.8:1 CR head gasket) and a adjustable Dhalback cam pulley...for keep the stock cam belt "0" position

and my car is very fine,no problem with it

[Rocco]

I tried but I didn't have proper tools to get a meaningful numbers. Or the numbers didn't agree with the factory manuals, or something like that. So I just checked the real world clearances and ran it.

If you are building a big boost engine, don't go by the internet facts or even factory numbers, check and measure everything yourself. Like the CR, factory says 9.3, Mahle/kolbensmidt say 8.75 (they designed and made the original pistons), my measuring and math say 8.8, who's numbers do you believe?

1.0mm skimmed off the head brings the CR up something like 0.8-0.9. Valve clearance with stock valves, cams and timing won't be a problem.

and skimming the piston by 0.1mm makes the same but in the opposite,so dropping comprression 0.8 o 0.9??

[220bhp]

Thanks for all the comments,much appreciated.
This is the situation I am in, I have two heads,the one in question, which is in realy good condition, but is below minimum, it is currenty 117.98.and it needs to be faced all be it buy the smallest amount.The other is off the doner car that I bought,
it has been ported and had no over heating issues, but it has some corrosion around the waterways, not alot but it is evident also that it as been skimmed, but still within the limets.
So which one,I would prefer to use the first one apart from the fact that it is below
the minimum.

[220bhp]

Can anyone please .tell me the original measurement through the bolt holes so I can calculate how much has been removed from my cylinder head.