Ok, I took the head off a mates Escos today, due to a suspect head gasket ( losing a small amount of water, & a misfire after cold start for a few seconds).

On removing the head, #2 & #3 combustion chambers have 1 small crack each, running from the spark plug hole to underneath the exhaust valve seats. #1 has a similar thing, but it is hairline, so needs further investigation.

All the exhaust valves are heavily coked, however the inlets are immaculate, which to me points to valve guides or stem seals on the exhaust side?

Has this caused the head to crack, due to the valves not being able to shed heat properly, or has the cracked head caused the valve coking from leaking oil?

The engine has 85k on it, with no reports of high oil or water consumption, and the head is 139mm, almost new ....

Can this be repaired in a safe manner?

 

Pic of the crack:

 

Not much help but saw this before on a 4x4 head!

 

Get it welded up mate and pressure tested I have been told that can be repaired

 

Don't weld it put it back on how it is.

if the weld falls out which can happen due to expansion of head it will take your mates bottom end out aswell. Not good and expensive.

Paul

 

Well, the engine shop I have taken it to recon it might not be a problem if it passes a pressure test?

 

Mine had cracked across the valves and I was advised not to reuse the head even if I had it repaired.

 

Who gave you that info mate? Just interested in opinions at the moment as personally I am not mega comfortable reusing it as it stands, but be interesting to hear some views

 

Im affraid the head is essentially scrap. You cannot successfully repair that type of crack in the chamber.

Even if the crack does not currently pass through to the water jacket (i.e. it passes a pressure test) it will only be a matter of time until it does.

I deal with these issues on a weekly basis as we repair heads that for example have dropped a valve, but when you have a cracked chamber it is a futile effort. Strip it for its parts (i.e. valves etc) and replace the head casting with an uncracked item.

 

Any idea why it has happened like the Karl?

Exhaust valves not being able to shed heat properly due to lots of coking?

 

It's hard to give a definative reason why, except to say its caused by excessive heat.

The reason for excessive heat can of course be down to many factors, the obvious one being excessive cylinder temperatures, a prime culprit being excessive boost on small turbine housings which creates very high exhaust back pressure.

Of course poor fueling, engine coolant problems, poor valve sealing, even head gasket proplems can and all do contribute, hence why theres no definate answer, except to say its knackered!

 

It's a standard big turbo Escort Cos (std .63 housing?) , with a stage one chip... If we replace the head it would be nice to eliminate the problem to stop it doing it again.

Interestingly, the turbo has a number if cracks around the wastegate, would that be related?

 

Ironically thats one of the most dangerous setups for an escort cosworth. The standard injectors cannot support a stage 1 setup using a 0.63 T34 as they run very lean at high rpm if running anything over 12psi boost.

In this case I would suspect lean running on boost to be the culprit rather than exhaust back pressure. (As it is again excessive heat that causes the wastegate area to crack)

Solution is to run bigger injectors and have it mapped properly.

 

Silly Question, but standard T34 Escort Cosworths come with a .63 don't they?

 

Yes they do. Dont forget std fuel pump is also terrible, so bare minimum is bosch 023 in tank pump, but preferably a swirl pot setup and 044.

 

Yes they do , but running a lot less boost as standard

 

I have some ideas / thoughts but it is theory only! the coking is only on the exhaust side as it engine might be mapped a little rich this means that the fuel does not quite burn 100% so you get carbon deposits. Also as engine goes through the 4 stroke cycle (suck, squeeze, bang & blow) it will be pulling in a cool (ish) mix of fuel air and may be N2O this especially as liquid fuel is vaporising and the N2O will be if used too is very good as keeping the inlet valve(s) cold and minimising the heat stress on that part of the engine head, unfortunately on the exhaust side of the head the valve(s) have a super hot mix gasses rushing past them as they exit the cylinder this will maximise heat stress in this area. This is why bronze valve guides and sodium filled valves are used in some highly tuned engines as they aid in the transfer of heat away from this part of the head. Ford actually at one point had a water cooled valve guide system for F1 to aid in the transfer of heat out of the head to stop them failing!

I had this done on my CVH engine and it makes a huge difference! unfortunately the first head was cracked by then! Though it was used as we cut it to bits to work out how to do the mods we wanted!

 

Will I got that info off Dave Brown R.I.P, my head was also a good one with loads of life left in it. Mine very leaked oil or water and I only spotted it when I was rebuilding my engine.

 

pm me of you want more info on any of it!