Cracked head?

[brennon]

M20 engine.
Head gasket has clearly gone, head is off and gasket was split between chamber and water gallery.
Mayo literally everywhere, even the afm is caked!
No coolent in system at all, unsure if it was run hot as only just got the car.
Gave the head basic observation to see if it was clearly warped and with straight edge it looks surprisingly good!

So the question is - how do I examine for cracks? Where should I be looking?

If it's a case of sending it to be pressure tested how much should I be looking to pay?

[maggspower]

The classic place is under the cam for an m20 to crack. You should be looking at around £50 to have the thing hot pressure tested.

[brennon]

would cam removal be necessary to inspect? should cracks be visable from the underneath?

what is a hot pressure test? is there a cold pressure test?

[maggspower]

Yes the cam will need to come out. But even then any cracks can be hard to spot.

A hot pressure test, means the head is brought up to near working temp then tested for cracks. This is the only way of doing it as sometime cracks do not show up when the head is cold.

Where abouts are you?

[kam-325i]

this is where my head cracked after getting a little too hot !

[brennon]

Cheers guys!

I'm assuming a pressure test would just be mating the head to a gasketed surface and then air pressure applied via spark plug hole?
If my assumption is correct where would the instrument for measurement be located?

Guildford area

[Brianmoooore]

would cam removal be necessary to inspect?

Will be if the head has been removed, but if you'd run the engine at working temp. and pressure with the cam cover off, you would have been able to see small beads of water emerge from the cam journal and scoot off to one of the oil return holes. Usually cracks at the rearmost two.

[maggspower]

Cheers guys!

I'm assuming a pressure test would just be mating the head to a gasketed surface and then air pressure applied via spark plug hole?
If my assumption is correct where would the instrument for measurement be located?

Guildford area

No, the test is to check the integrity of the water jacket, so all the holes on the face of the head are sealed using rubber pads and clamps, then the head is pressurised usually using the hole at the back of the head (the stub that connects to the heater).

The head heated in a hot bath, then removed and sprayed with soapy solution. Any bubbles is a bad sign.

A visual check is very important too, as cracks may not necassarily breach the water jacket. I learned this the hard way, as I once rebuilt a head only to find that one of the rocker shaft holes was cracked

[reggid]

cracks near the chamber have better chance of being repaired, if the cam tunnel is cracked its basically scrap (if you want a long life) and weld fix is temporary only. ive heard many head guys say they can weld it no worries but most of them come to their senses. ive seen a few run after being welded and it works for a while but ticking time bomb really

[B7]

Is this a 2.5 or a 2.0 litre.

As above, the heads are prone to cracking below the camshaft. With the cam out (which you are going to have to do to have it pressure tested) it will be visible under close inspection along the casting between the inlet and exhaust valves. The crack will run (normally) from cylinder to cylinder and will be easier to spot in the machined cam bearing faces. It's more common up at Number 6 through to 4 as that's where they run hottest I'm led to believe.

I do have some photos somewhere which I'll post later if I can find them.

I would have it pressure tested as you say the gasket has definitely blown and that could just be your problem. But they do crack when the get hot and it sounds like yours has got very hot.

If it does prove faulty I have one good 885 (2.5 litre) and a good 731 (2.0 litre) heads at the moment. All with stud threads (which is another issue) and from known good engines. And I'm only just the other side of Dorking to you.

[brennon]

Thank you guys, info on pressure testing was really good, it's always nice to be able to add to my knowledge pot!!


B7 that could be a much easier solution for me! Can you pm me with a price on the 2.0 head? I think mine is a 200 but all are interchangeable?!

[B7]

You have PM

[Andyboy]

As far as I'm concerned, a cracked head is scrap. Weigh it in and find a good uncracked one - they're not rare.