Lambchop

iTrader: (1)

Righto i have a wee problem.

Cossie head needs skimmed after a melt down.

Current head depth is 137.53 mm.

According to cossie workshop manual minimum depth is 138.68 mm and thats with a max of 0.13 mm machined off.

Now 0.13 mm is 5 thou. My head measures almost 40 thou UNDER the MIUIMUM limit!

So wtf is going on? could my head really have been machined soooo far over the limit?

Can anyone confirm that 138.68mm is minimum head depth?


Heeeeeeeellllllllllllllllp


chop

GARETH T

time to start shopping for a new head

Fudgey

iTrader: (4)

stick a zetec in, can get another head for Ł30

PGT

my head is only 137.5mm and runs greys low comp t34 and mapped at msd.

afaik ford have min thickness to avoid valve/ piston contact but this would not apply if valves pocketed. some tuners say that the seat inserts come too close to head face and others say this is not important. some say that the face of the head is hardened and that you lose the hardness by excess skimming (this is the case with k series heads) but this can only be true if the material is exotic stuff like LM25 which is capable of hardenning but i dont know if YB heads are made of this. spoke to karl about this and he says skimming the head has no effect at all.

Lambchop

iTrader: (1)

Gareth
I guess

Dan
Hahahahahaha, i'd rather get my cheque book out

PGT
Interesting info mate. I take it you mean pistons pocketed? Well mine aren't


On my head you can see that the piston has touched near to cylinder 3. Theres a small dent where it looks like the plug tip was hit by piston and made a wee mark.


I really dont want any fucking about so i guess its a new head

Fudgey

iTrader: (4)

cant you just use a thicker head gasket?

my mate cooked the head on his skybus, and had 26thou skimmed off, nealry 0.5mm lol

std liner head gasket is 1.2mm, hes just got a 1.8mm gasket to compensate... its an idea at least

Lambchop

iTrader: (1)

Its an idea yes...BUT...i dont want a shoddy car! Its cause enough problems up until now so im going to pay what it takes to get it back to how it deserves to be

foreigneRS

fuck me - a scot that isn't tight

is somebody else using your log-in?

rocky_robin

Yeh, good answer.

Now, can a 2wd head mate with a 4x4 block (i.e. the piston's/stroke ain't different????)

Lambchop

iTrader: (1)

fuck off

Try getting a drink from me

Rob
Mine already is a 2wd head and 4x4 200 block...

rocky_robin

I know that, but wasn't sure about the pistons you have currently.

I thought that they have a slightly less stroke.......i.e. lower compression?

PGT

yes pistons - and as regards karl i meant he said in terms of the effect it had on the life of the head but would of course reduce cr.

Lambchop

iTrader: (1)

yes the 4x4 pistons with a 2wd head lower the comp slightly.

Shings

Chop


other problem is the cambelt... obviously its closer...

My mate who has my old white car has the same prob now as he's skimmed over.

I explained.

"If the valves hit the pistons its only gonna happen once"

I think he spoke to Karl/Ollie who suggested some verniers would dial out the problem?????

I dont know for sure though.

Jake

Billabong

Cossie heads can go 'soft' if they've been subject to major overheating, you can get a hardness check done on the head to establish this.

IAIN ABZ

mmmm all good info.....

Chop - get the cheque book out..... or pay cash and Gemma will never know hehehehehe

you may have to invest in a set of verniers to dial the cams in right if too much has been taken off your head, as long as there is no contact with the pis-tonskis you should be braw min!!


Hope you didnt eat too much cake the other night

PGT

not being funny billy here but could you explain this concept of 'going soft' in terms of the type of aluminium they are made of because as far as i'm aware the aluminium they are made of will not work harden or anneal. how exactly does it go soft?

Billabong

We may be at cross purposes here, possibly my fault for quoting you. I wasn't suggesting that skimming the head face will soften it, simply that seriously overheating the cylinder head will soften it - how else would the head warp/bow?

I was also under the impression that if the head is overheated too much, then the head could be basically scrap, as the material properties could change (regardless of bowing/running out of true). I can't recall where I got this info' from (which may render my comments useless , but it is something I remembered - if not the specific details), and so yes I could be wrong. If you or someone else knows different, then I'm happy to be better advised

I don't know the makeup of the cylinder head material, the Cosworth web site used to have a lot of info' on the casting processes etc. but it's all pretty much gone after successive buyouts and redesigns of the website and the company's change in focus. Again, my memory of this is that it was Cosworth's superior casting techniques that made them such a good head for a production engine, not necessarily the materials used.

JjCoDeX75

Interesting comments about the overheating - it makes sense.

What I recall from the last time that the matter of the head thickness was raised I can comment as follows;

The minimum thickness does not relate to the valve piston clearance (assuming stf cams etc). This I can absolutely assure you as I have in the past run below the proposed minimum thickness with no such issue in this regard.

The wisdom is that it actually relates to the amount of material around the valve seats. Specifically on the inlet side (i believe) it gets dangerously thin, which theoretically can allow the valve seat to become dislodged.

In addition, I believe that it alters the squish area of the cylinder head, which can adversely affect the combustion.


JJ