manifold gasket

[win]

HI guys, i've had a mechanic change my manifold gasket twice now but within 3-4 weeks it starts blowing again. does anyone know why this is. The car is a 325 m20 engine.

Cheers

Win

[Martinaston]

Stripped thread in one or two of the stud holes. or
Does it loose water ? possible warpped head.

[E30Adam]

He's not doing a proper job then and I'd take the car back and tell them you want a decent job doing.

Sounds like he's not cleaned the surfaces of the exhaust downpipe or manifold properly. I've also seen people leaving the old gasket on before.

He needs to make sure the old gasket is removed properly. Both surfaces are flat and free of debris. Also make sure all studs are present in the manifold. The gasket should ideally have some exhaust sealant applied before assembly and the nuts should be done up nice and tight.

If you follow that procedure then you'll have no troubles. Your mechanic has obviously not done a proper job on it.

Ah just thought.... are you talking about the head --> manifold gasket or the manifold --> downpipe gasket?

[win]

Cheers Adam & Martin, its not losing water but i think what adam said is right i don't think he's doing the job properly i'm bringing it back to him tomorrow i'm just worried he'll do another bad job.

Win

[Martinaston]

Can you see all 12 nuts on it ?

[win]

I have'nt checked i'm going to have a quick look now.

[win]

i just had a look all th bolts sem to be there but they don't all look the same. is it worth buying new bolts to do it the next time

[Martinaston]

Probably not, the chances of getting them all out without snapping a couple are pretty slim. They should have copper nuts on them all.
As Adam said the guy may have bodged it the first time by not cleaning it or worse by snapping a bolt and not admitted to it because its such a pain to fix them.

[win]

So if a bolt has snapped how can that be repaired, and how can i tell if he bodges it again

[Martinaston]

Depends where it snaps, If it snaps just below the nut you can just unscrew the stud. But if it snaps below the surface it has to be drilled out and possibly the hole will need to be re-threaded (heli coil or a bigger bolt) this is even more of a problem if its the rear ports because the engine or just the head will have to be removed from the car.
What the guy may have done is fit a shorter bolt if he snapped one before and left the broken piece in the hole, it will then get ripped out as the manifold expands with the heat because its only held in by a couple of turns.

If i were you i'd get a socket on there and see if any come undone easily.

Did the gasket fail on the same port both times ?

[win]

i think it is from the same place. He assured no bolts had snapped but i'll try what you suggested. its not blowing as bad as it was before but i can still hear it plus i don't think he renewed the downpipe gasket either. I don't know if that makes much difference but it seems to be blowing more underneath the car.

[Martinaston]

If its the manifold gasket thats gone you can hear a distinct jet as that cylinder fires, it can sound like a tappet at some speeds (mines been doing it for 5 weeks now but i'm too lazy to fix it) best way is to start it from cold and just put your hand in there and feel for the warm (f**king hot) gas as it escapes. A small mirror is best, you can normally see the gasket where its forced out from behind the manifold.
If its the downpipe the book recomends fitting a new gasket each time but i've got away with the old one three times now.

[win]

ok martin cheers for your help. I'm getting fed up with this mechanic but i paid him good money to do the job and i'm gonna make sure he does it properly this time.