i know its been asked loads and loads of times but want an accurate useable thickness

i know they are 139.1mm as standard

how much is taken off in each skim normally,or does it all depend on damage(how much is needed)

ive heard people saying they know people on 138mm flat but im not confident with this

as others say 138.6mm min

been offered 1 at 138.7mm

but dont want to spend a few quid on 1 that might be on its last skim

cheers

 

up

 

up again

 

i'd also like to know this. think mine has ha 1mm skimed off it so far

 

well mine was 137.4 when i took it off and was running ok but had started to get valve to piston contact nms told me about 138 i think as a min but others say 137.5

 

and some say 138.4

 

Use a group a gasket as it is thicker and it will be fine.
tabetha

 

oh i forgot to say mine has a cometic 1.42mm thick gasket, although i think the thickest they now make is 1.3mm

 

Are you sure a Group A gasket is thicker All the group A gaskets i have ever seen arnt thicker than a std item

 

I just put mine back on, didn't measure it, had never been skimmed before I needed it doing, head had never been off since the car was new!

 

my block aint wire rung so id rather not use a group a at my power level

the cometic multilayer ive been useing has been fine,think il get another of these

but what i really need to know is the measurment indicated on its last legs?

 

You dont have to have a wire rung block for a group A gasket

 

A group a will laugh at 420bhp!!
No problem at all at this power level.
I meant a group a was thicker than steel, sorry for the confusion!!
tabetha

 

i know that paul

but at 400+bhp ive heard the group a isnt much cope without it getting a good bite on a wire rung block

 

If surfaces prepped well it will be fine, they tend to break through the water jacket if anywhere.
I know of a 540bhp cos running group a, well was years ago but did at least 40 odd thousand miles on it as well as track days and it WAS hammered.
tabetha

 

Well i would say thats bollocks ,,My 450bhp had a group a on std block and covered 23,000 hard miles and was perfect

And as for head thickness FORD cover there arse by saying 138.6 is min ,, you can use at less but there are many things that determin how low you can go

Block depth
Lengh of rods and pistons etc etc

All items are within a min / max tolerance and if you have the longer items within the tolerance your fooked ,,if you have items at the min tolerance your ok

 

cheers paul

my pistons are really low comp when you turn crank,they sit slightly down the bore when at full height,with no valve cut outs,on bd14s

and everyone says that cant be done on bd14`s

but if im going to get this head it will be 4x4 head so might up my cam spec too and sell the 14s

 

The minimum recomended head thickness is 138.68mm and this is because after that you are leaving too little material around the valve seat area, which are, as many of you will know, a totally seperate part pressed into the head. Ask anyone who has a had a valve seat come loose in their engine why you dont really want it to happen to you. LOL

I have used YB heads a LOT thinner than that, but you do so at your own risk of course.

 

a great explaination that most of us (me included) didn't know!
I thought it was about comp ratio and valve/piston contact!

steve

 

as said ive used really low and not had a probelm its just how lucky you are

 

so a modded head at 138.7

at a few quid would yous buy it?