lamb chops

My head has just been removed and it seems ive had some piston contact the head measures 138.5 how much can be safley skimmed from these? its 2wd if that makes any odds..

cheers

rapidcossie

depends on comp ratio of pistons

Karl

Do you mean you have had piston to head contact, or valve to piston contact?

lamb chops

yeah its being rebuit with new pistons etc Euan so can go lower comp but was just interested as to what people would say is a head which has been to skimmed as it were. what are they standard?

lamb chops

valve and piston contact karl, one of the main bearings has collapsed and the rods had lots of movement

Karl

The best solution is to machine the pistons with valve cut outs. With this done it is fine to use a YB head down to 138.0mm thickness. (They are 139.0mm new)

Jasesapphy

iTrader: (1)

you always get some markings on a piston, i have run 138.4 no probs and people have said they have run 138.3 / 138.2 but only hearsay,

I have run a 138.4 on standard comp and pistons, but cant you just valve cut the pistons

Jasesapphy

iTrader: (1)

Karl beat me to it

rapidcossie

Take as little of the head as poss but it will still be ok even under Ford's min thickness if its on lower comp pistons.( might even be on standard comps)

lamb chops

yeah i can get round it with piston cutout and a low comp piston i guess. thanks chaps. ive not seen the damage yet so hope its not to deep

glancy2081

a thought the problem with the skimmed head was that the more its skimmed the less the pressed in part has holding it in ?

PGT

my head is 137.4mm and works fine - the valve seat inserts are on the face though

lamb chops

just been told there are some other marks on the head so its going to be pressure tested before any work commences.. can see this getting expensive!!

good to know i have another mm if needed PGT, every mm counts

Micky The Finn

ive ran loads of group A escorts at 137.4mm with no troubles at all.

Karl

Just to add to what has allready been posted, the issue with heads below 138mm is NOT to do with valve seat inserts coming out, but simply that it is impossible to mill an alloy head with a diamond cutter once the seat inserts or valve heads are flush with the head face. (Not to mention the obvious issue that C.R goes up considerably with over 1mm from the head face.)

markk

iTrader: (2)

im willing to pay for cylinder heads at or below 138.00mm if anyone is not wanting to use them.

RWD_cossie_wil

iTrader: (9)

Cool, my mates car dropped a valve, will need to go to about 100mm to loose the damage .. How much for that?

markk

iTrader: (2)

send me a pic, my ally welding is not bad now !

Turbosystems

iTrader: (5)

I have a brand new 2wd cosworth head yes brand new

bigchez

How much? I'm guesssing I'll need a mortgage!!

NEIL A

iTrader: (6)

Just found these pics in my photobucket of head to piston contact, deep enough pockets so no valve contact but piston top had mushroomed.

lamb chops

yeah thats what my number 3 is like Neil, other are ok though. I went round and saw the engine last night and No3 has a full MM movment up and down on the rod. Think i was very lucky this didnt let go while it was running..

rsnissan

iTrader: (9)

still have my old head if you need one, needs an ex valve though

NEIL A

iTrader: (6)

What comp ratio were you running.
Those pics are of my old engine that i had problems with, was a brand new 200 block with 7.2:1 cosworth pistons

lamb chops

not sure Neil as it wasnt built by me last time and i have no reciepts, standard pistons though and stardard bore so presuming standard comp. Also motorsport 200 block

Lambchop

iTrader: (1)

i have one that may be of use to you as i probably wont use it. melted a piston so the head is marked. already was low so didnt skim it again, just got another head. might do it and see if its worth anything.

rsnissan

iTrader: (9)

do you have to run a remote oil filter etc for this?

lamb chops

Not for that one Andy, thats the WRC one your thinking of with all the machining done. This is like a normal 200 without the rear core plug for some extra strengh

NEIL A

iTrader: (6)

Yip Mountune WRC block you have to run a remote filter and cooler as there is no place left to fit a filter, also has some extra machining for oil jets and twin oil return

frog

Same here but it's attached to the block in our 2wd

Cost us Ł990 + VAT direct from Cosworth a couple of years ago

Daxcossie

Chops,

Who is doing your rebuild ?

costina

iTrader: (1)

Stu needs to read this and then he will explain about the squish area!!

Alloy welding a head? I would not do that due heat related problems as the head and the welded area will heat up at different rates..

If the weld dropped out due to expansion of the head it would kill a expensive bottom end..

I've seen 139mm heads which have been tig welded and skimmed and passed off as a unskimmed headu could clearly see around the water jackets that it had been welded!!!!

Paul

lamb chops

It’s being done by a good friend who runs TS Performance, he’s a professional engine builder worked for Pro-Drive and was on the Mcclaren race team for awhile. He knows his stuff, the old girl is in safe hands.

Hes on here sometimes Legend247 i think he is..

frog

You mean this !

https://passionford.com/forum/technical-essay-archives/42723-minimum-cossie-head-thickness.html

I believe Karl Norris does this welding work too, when we found out that ours was too thin we considered it as an option as decent heads are few and far between these days. This is until we found a brand new one from cosworth, but not cheap