JTECH James

iTrader: (13)

i would imagen if a larger seat was to be used taking the seat closer to the edge of the combustion chamber, the seats would be set adequetly deep into the head giving a larger surface area to hold the seat in place,

the fact remains,seat failure can also be caused from boring the center out when porting, and now given the measurements its an easy check to make.....thin seats that have been ported are obviously going to have a reduced strength, being pounded by double valve springs, the seat can crack, then break up,

a combination of these two factors, can, and does end in a massive failure

Turbo Zetec

iTrader: (1)

i'm afraid that i can't see the thickness of the head causing this problem at all, not unless it's actually been skimmed down into the seat area, which would only really cause problems if the seat itself was mega-thin. it's more than likely caused by the head having been hot, being machined out too far or poor original fitment. This is speaking from experience by the way, not quoting off the internet or guessing like some do. i've seen/worked on hundreds, if not thousands of heads since becoming a machinist and haven't had a problem with a single seat unless it's had problems like i've described above.

we had a jag v12 head in today that had an inlet seat fall out... this was a fitment problem, as it's a common on them. we've also got a 1.8d ford head with a seat out, it's been majorly hot! i've also got an st170 head here with the centre 8 seats all loose, it's also about 20 thou bent on the face now thats hot!

also, about the comments 'i'd only trust this person or that'... what a load of bollocks i bet that most of the tuners named don't even have the facilities to replace valve seats themselves. it's not like its a complicated process either, i could probably replace and re-cut 16 seats in a morning . if your local machine shop can't do it properly, they shouldn't be in the business

evo200

iTrader: (1)

No takers?.......or have I asked a dumbass question??? lol

Miller 3

iTrader: (4)

Good read that Stu' nice one mate

Rab

Once you've welded it you've changed the properites of the alloy itself. While a small weld to cover a crack won't cause too many issues, a load of weld all over the face of the head will. While you could re-face it so it was perfectly flat, no garuntees could be given on the strength or ability to dissapate heat correctly.

Basically, cosworth need to re-cast as many heads as possible, because all cossie owners expect a bit of head now and then.

PGT

IIRC karl norris once posted up here saying that he could offer this service.

it would seem likely that the old seats would be removed first then the face welding process, then machining, then refitting the (oversize) seat inserts

GARETH T

very very time consuming to weld the face of a head! maybe in a few years it will be our only option!

The DIVA

iTrader: (3)

http://www.cosworth.com/shop_item.php?productid=158

Showing back on Stock, will have to ring them later

GARETH T

well theres that sorted,,, well unless they was cast in your know where PMSL

The DIVA

iTrader: (3)

I`ll have to double check mate, but i know that a new batch was on the cards and they weren`t on the website a while back so here`s hoping

Jay,

iTrader: (4)

spoke to Jeremy as far as he knows there not in stock wont be for a while and when available only in small numbers

The DIVA

iTrader: (3)

He`s been giving that corporate spiel for the last two years

dojj

iTrader: (3)

why not just use 2 head gaskets

or a sandwich plate

dreamer

I wonder why Stu, Tony, Mdcos and Gareth T didn't suggest that pmsl

dojj

iTrader: (3)

they obviously mised that guy who was making 900 wheel horse power in his civic, who head he'd modified with a nail file

dreamer

i remember that car

If only these guys would open their eyes to new advances in technology

Stu etc should just watch the internet for new ideas

Internet mongs are leading the way forward ha ha

gingeRS

you can tell that by the way you measured it stu

only messing.....very interesting and informative thread

foreigneRS

very timely post after what i discovered today

this is the damage that i found on my 'ring taxi engine after picking it up from belgium on thursday.

both an inlet and an exhaust valve have lost heads and the piston is smashed open and the head severely damaged. i don't know the cause, but doubt that it's the thickness (unknown, but nowhere near the brass insert) as it survived a weekend thrashing around the 'ring with that thickness of head a year and a half ago and this damage occurred whilst cruising along a motorway

i would like to know what might have caused the failure, and can the head be repaired? if so, what would be the estimated cost?

dojj

iTrader: (3)

is it just me or does that head look thinner at the fornt than the rear?

jaimesdna

iTrader: (3)

fuck me you dont do things by halfs. kinda looks like the valve seats might have fallen out & caused the valves to break. good luck getting it repaired

Jim Green

Arghhh.......I actually cringed when I saw that first pic.

Mechanical Torture.

Ginge

Oh you recommend that do you ..

http://www.aa1car.com/library/ar993.htm recommends the same thing.

Ginge

Micky The Finn

so why do all group A cars with mountune engines run heads at 137.4-8mm with zero valve seat trouble?remember these were fords multi million pound budget cars run on the world rally championship as their showcase to the world,and a rally car that sold millions of standard road cars in so many different guises.i dont remember ever seeing one mountune engine with a valve seat fall out (harvey may have seen some?),now ive seen and owned more than most folk in the world and drove over 50 stage events in such cars with zero valve seat faliure,so hows that possible if its 1.2mm under your sugested limit?


that statement of 138.68mm is just not correct at all,its your own personal thoughts,

mapping a car to run lean would be a more common way,if not the only way,of making the head temperatures so extreme that the valve seat falls out wouldnt it?

Micky The Finn

Actual size of the over skimmed head measured face to face at the front.




but it wont actually be the exact size measured with a set of digital sliding rulers though!!

dojj

iTrader: (3)

but why do these failures occur on heads that have been skimmed and not heads that haven't?

is it perhaps a combination of things going wrong perhaps?

and, to be fair, how many miles did you do before pulilng the engine part to do stuf to it and how may people have spent 10's of thousands of miles and 20 years with their engines running fine and do the same sort of rally stages?

in these cases, surely it's more age related than engine build up?

Micky The Finn

how often then have you seen a valve seat fall out of a yb head?

not run lean etc,detonate etc,then fall out,i mean just fall out on its own with a perfectly running engine?


and no head on this planet will get the abuse a rally car would get,how many intense heat cycles can one head get in a day!!!

dojj

iTrader: (3)

but that's what i'm saying

in a rally car everything is going to be tippity top with a gauge bolted on to measure virtualyl everything that's going on

your normal saph driver will be spanking it round corners with braely the slightest inclination that whoever set their engine up to run with 50 lb's or boost just tweaked some mechanicals to fool the electronics to give them 500 horsepower for 10 minutes before it goes bang

when these guys then get the engine rebuilt they'll have had it done hopefully by someone who's got the skill to build it proeprly, but if the damage has alrady been done to the valve area, unless you reseat them all and take the utmost care to do it, these things will happen more often than not

i do think it's soemthing to do with having the head skimmed, but ultimatly there must be another contributing factor to bring on this failure

Stu @ M Developments

iTrader: (12)

This was intended as an educational post for Jo Bloggs, not a lesson in engineering Tim.

Stu @ M Developments

iTrader: (12)

Not that many over past 15 years really Maybe 30? Te rest have been in shonky sheds. LOL

Anyway, why all this talk of valve seats falling out? This topic is about head thickness. Start your own!

Stu @ M Developments

iTrader: (12)

Are you absolutely sure Tim?
Want to publically put money on that statement?

dojj

iTrader: (3)

stu, is this an average of one every 6 months or have there been peaks and troughs in the timings of these?

as in, in your experience, have there been engines that have had specific things done to them to make them more prone to the seats falling out due to everyone jumping on the "this is a great mod, let's do it" bandwagon?

and if you have seen this problem 30 times, how many others have seen it over the years? which would suggest it's a more widespread problem than we might be lead to believe, although i still think it's based on the life of the engine over the years above all else

if tim's started anotehr therad on this matter i'd be happy to read your reply there

Turbosystems

iTrader: (5)

These are the reasons for failure

Stu @ M Developments

iTrader: (12)

Why do we bother when nobody reads what we write?

Turbosystems

iTrader: (5)

so true

GARETH T

did someone say something? LOL

dojj

iTrader: (3)

but tim's engine hasn't dropped any seats despite being run much harder than a "normal" cossie engine so do they still count?

silky16v

iTrader: (1)

its clearly printed in the Cosworth Technical Manual

glancy2081

so is there any precautions or checks that can be done to ensure this does not happen

Andreas

Good thread, ive been conned myself once but it involved my own engine head.

Engine rattle turned out to be worn out cam cap threads.

Discussed about getting a new head instead of repairs but was told that repairs would be much cheaper.

Let the garage do the repairs and then they presented me with an invoice that was more than a new head would cost me.

I hope bad kharma comes their way....

This happend many years ago when I was newbie, had it happend today when im wiser, fatter and with less hair I would have taken them to court.

Stu @ M Developments

iTrader: (12)

Damn, you spoilt my chance of a quick earner!