Why did the head gasket blow again?

[kwerrett]

Right this is the story. 1993 Disco 200TDi. Head gasket blew out the back of No. 4, not water oir oil loss just compression leak as it split the gasket. No overheating, no other problems. Pulled the head, cleaned up everything and fitted new gasket. Tightened down in sequence as per factory manula and to torque and angle specs as per manual. 40nm/60 degrees/60 degrees.
Ran it for 3 weeks no probs did a lot of driving in fairly hot conditions (I am in Brittany France). Went for a long jaunt one day and it started to overheat on the return up a very long gradient. Not far from home and got home ok. Let it cool down but the sytem was pressurised. Topped up and ran for another week. Then one morning on the school run, big white smoke syndrome.
Got back and checked, yep pressurised again and definately head gasket.
Pulled the head, only this time I could undo the bolts using just a 1/2 drive ratchet. On onspection the wtaer was going into the combustion chambers of 2+3 due to head being too loose.
Had the head checked and its straight and no cracks, block is OK.
So, I am going to do the same job again but need to ask:
1) Should I torque down harder?
2) Should I retighten after a couple of short trips when its bedded in?
3) If so, what torque to use or what angles on the retightening?

Would appreciate any views and advice from you guys who know your stuff. I'm a qualified mechanic and usually have no probs with this sort of thing.

I know the bolts and stretch bolts and can be used up to 5 times so should be OK.

Thanks in advance.

Karl

[Geobloke]

Ok you have had some trouble haven't ya!

The trick with heads is that once you have torqued up the bolts in order (which you did) you run the motor for a hundred or so miles and then re-torque the bolts. then run it for a bit longer still and then check the torque on the bolts.

The thing that peeps forget (or don't know) about is that a gasget changes in dimensions over time due to heat, pressure and age. The problem you found is that the gasget wasn't bedded in properly!

For example, I have recently had am axle problem, the breather was blocked, and it started to spew loads of EP90 from the gasget between the diff and axle casing. Now a beam axle is not that far removed from the engine in that it gets very hot and pressurised if the breathe ris blocked. What I found was that the blocked breather highlighted another future problem, the nuts holding the diff on were loose, I could get about 3/4s of a turn on them all! A case of the gasget shrinking with age slightly! Did the nuts up and the leak stopped. No worries!

Ok being that you ahve now found water in your cylinders you may want to check for warping in the head and block, advised! But follow this and you should be ok! And since you ahve had water in the cylinders you are going to have to change the oil, oil filter and coolant too!

Hope this helps!

[kwerrett]

Geobloke, many thanks for the helpgul advise. Willinform how I get on.
Thanks again to this forum for their good members help.

[KKK2]

What Geobloke says is true, I would also get the head checked to make sure there is no warp in it. Did you fit the updated TDI 200 headgasket ?

[kwerrett]

Hi, I didn't know that there was an updated gasket. I bought mine from Paddocks in UK as they mail it to France OK. Please advise if I should be using something different.
Thanks

[imspanners]

There should be no need to re-torque the head down after running-in. The gaskets are designed to be compressed once.
I'm not sure if the 200 is the same, but the 300 has 10- 12mm x 140mm long bolts that require a further 20degree tighten over all the other bolts.

I would get the head skimmed to make sure it was perfectly flat, as a matter of course.

Finally, why did the gasket fail initially? Is there an underlying problem that caused the engine to overheat and blow the gasket, not the gasket blew and caused it to overheat? Things like a low-flow radiator (partially blocked), viscous fan not working correctly (not locking up when hot), thermostat sticking etc.

[kwerrett]

No maybe there should be no need, but I spoke to a LR specialist yesterday before I came on here and he told me exactly the same thing as explained by Geobloke. That was before I posted here and I never mentioned it, wanted to see what the views were first. Si the general concensous of opinion by those in the know is that you should retighten a couple of times. My question is: As they have been angle tightened how much further should you do them. Should you slacken right off and then start again or just give a further tweak. Allright to say another 20 nm or so. What is that actually on top of 40nm +60 degrees + 60 degerees?

The head has been checked and is true.
The original gasket blew compression from the back of No. 4, no overheating that time and no water ingress into cylinders.

Only overheated second time, due to as I believe now, not retightening.

[BrendanB]

I'm not an expert by any measure, but the local independent LR place advised along same lines as imspanners when my head was replaced a few months back (on a 300Tdi). The head was torqued just the once at the LR workshop as per specifications and I have had no problems since - say 10,000+ km - touch wood. It is also my understanding that the bolt tightening procedure leads to the bolts being tightened to 'yield'. This means that the bolts are tightened to the point where their elastic limit is reached and they actually just start to yield (permanent strech). This is why there is a finite number of times that the bolts can be re-used - preferably you should go with new ones when fitting a head just to be sure. Anyway, in terms of your question about how much to re-torque I don't know, but you should be aware that the bolts are already well and truly stressed, so take care!

I also understand that with the 300Tdi there are at least 3 different thickness gaskets that can be fitted, and the choice depends on how many times the head has been skimmed to ensure sufficient clearance above the pistons. Good luck.

Cheers,

BB

[kwerrett]

BrendanB. Thanx for your input, I cant agree or disagree with either and take all suggestions on board I am aware of the gasket thicknesses and have done my homework there but yes, it's a valid point you make. I think I will go with the initial 40nm plus the 2 angle tightening stages, but maybe do an extra 30 degrees or so in sequence at the end. Its either that or do the initial stage 60nm instead of 40.

Will let you know what happens.
Thanx again