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Head gasket failure


GT6boy

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Possibly the 2nd casualty of Cadwell Park.
Turns out, looking at the trail of evidence, my car was suffering a minor HGF prior to Cadwell. The car lost a fair degree of water on the way to Cadwell, which I mistakenly took to be from the minor crack in the radiator filler neck.
Some quite rightly spirited driving at Cadwell with the Flea-bay Tacho hitting 7000rpm ;D, saw the car lose quite a lrage amount of liquid and the rad carck get bigger.
Then mid-afternoon, the HG gave out at No.6 cylinder fire ring and it was game over :B.
I'm happy to accept that the underlying cause is that I skimmed the head too much, in-spite of the warnings about likely failure here. You may recall from my recent thread, that as the head had bizarrely been gas-flowed to give an actual CR of 8.3/1, I sanctioned the further skimming down to give a best possible of 9.1/1. Wheezy as this may be, it did end up giving the car a boost to a healthy 135bhp.

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So the head wasn't able to compress the fire-ring sufficiently, as the head probably gave slightly instead.
The studs did feel a little tired but only No.7 felt like it actually 'stretched' somewhat when it was being tightened to 65lbs torque.
I had been careful to ensure the head was tightened in the correct seqence and incrumentally to that figure and then tightened down twice subsequently.
  

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The head has loads of meat on it through the water channels for cylinders 1-5, but No.6 suffered from core shift issues and consequently is really thin above the squish area adjacent to the stud.
It should be remembered that this head would only get to 9.1/1 CR, due to the issue mentioned.
So then, it was planned to get a head made up that would let me set the CR to 10.1/1.
That then is where I am now :). Perhaps a bit sooner than I would have wished, but hey-ho.

I have a mk2 GT6 head from Stafford that will be given a go-faster gas-flowing and fettling in readiness to set co-ordinates for light-speed at Oulton Park in November.

In the meantime, any clues as to what to do with the old head? I understand that some people can 'let-in' new metal in the head?

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I wouldn't bother getting the old one fixed when good used ones are pretty cheap. You've already got a replacement so if I were you I'd just concentrate on that.

Think of your last head as R&D! After all, the only way to know the full potential of an engine for sure is to modify it to the point of destruction and then get a new one and modify it slightly less!

It's a bugger to have to get and pay for the seats and porting done again but ultimately a better option, I think. Maybe follow Neils instructions and DIY port it - if you're feeling brave!

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I would  say the failure is just lack of applied torque,, if the head is skimmed to the extent are the stud threads clean and long enough ?? to clamp and did you use the correct high tensile nuts if the heads been off a few times then new studs should be invested we know they are not torque to yield studs but the  re-use life is limited     Pete

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peterhlewis wrote:
I would  say the failure is just lack of applied torque,, if the head is skimmed to the extent are the stud threads clean and long enough ?? to clamp and did you use the correct high tensile nuts if the heads been off a few times then new studs should be invested we know they are not torque to yield studs but the  re-use life is limited     Pete


Was think along those lines as I am running about 9.5/1 with no problems yet on a 2.500. Is been running for 2 years no probs

Nuts can be a problem I was torque a Midget 1500 head last week end and threaded 4 nuts,

I think what happens is the gasket starts leak oil and then some one comes along and pulls the head down to try and stop it.

Only a thought so dont take me to task on it!

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I understand the feelings about applied torque, but the head is dramatically thin at that area- far more so than the rest of the head. I mean REALLY thin.
The studs and nuts have been correctly torqued initially when the engine was built up, then re-used just the once when this head was removed and re-instated. I use a calibrated torque wrench and am zealous about gently increasing the applied torque incrementally across the head as per the correct sequence. There is more than enough thread to tighten down on.
The bottom line is this head cannot be made to go any higher CR, so the cost of new head gaskets and the fag factor of changing the head makes me dis-inclined to fit a new gasket and stretch a new set of studs and nuts.

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Well I was very lucking with my engine it was from a one owner car and had never been apart

Other than to fit a set of bottom end bearing at 30000 miles and fit a modded oil filter.

Until I bougt the rusted out car with 42000 miles on the clock.

So yes your probabley best to follow the replacement head route,

Studs and nuts ant cheap as found out, shop around as well I used Jigsaw

good luck

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Must admit, if it was me I'd invest in new studs, nuts AND washers and really wind the mutha back on with a good quality gasket. The money won't be wasted as they'll easily be re-usable (not gasket obviously).
At least you may be able to use the car and you won't feel pressured into finishing the new head so quickly.
I won't insult you Bruce by asking if you've checked block deck is flat (Granny, eggs, sucking etc.)
Be good to dice at Oulton eh??

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I have a quality old Payen gasket on the way. Any clues as to where to get tip-top quality studs/nuts/washers? Looking to save that for the new head- but I can see me going garage-stir crazy and wangin' it back on before the new head becomes available!
I'm really looking forward to Oulton Keith 8). I fancy going around with you for some tips. As an aside, i was astounded at the speed you flew past me, even more so when you said you were in 4th gear(as was I )- then I remembered yours is a 5 speed! :B

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Bruce, correct me if im wrong,

but the way i see this head,   Is that it   ..is.. flat,   But  that the  head is  thin in one area alone, so has blown the gasket,

if   it is  flat,  then i cant see why the gasket has gone, the way you think it has gone

unless it has some minute porosity in the head metal, letting water in, as what i see is that it is a stud hole, and not a water passage,

so for water to be getting in to cyl head, or  gas into water, then it has to be  some form of a hole there!!!

stud  hole to water jacket!!

you also say that you think that cos the head is thin, then it has dented the head down wards when you tightend the head down

is the   head flat now, or is it dented in, as i cant see the head returning to a flat position, cast iron does not act this way.

you may be  aware of this, but a dry thread will not clamp  as much as an oiled thread, and an oiled thread will not clamp as much as a thread that has been coated with some slippery stuff

the difference is quite a lot, so you may not have had the camping force you thought you had

good luck any how

regards Marcus


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At the end of the day 9.1/1 is not that high their are focks out the like myself running higher, some a lot higher.

I know said "So yes your probabley best to follow the replacement head route"

But I still think that your head gasket failure was to stud or nut problems or even a duff torque wrench? they are about!

Easy stuff it back together with new studs whats a gasket cost £15

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I think its conclusive- the head is fubar.
Nipped to the shed tonight and this is what I found with a straight edge.
The picture is of the thin area in the immediate area of the fire ring failure. Once the 'soot' deposits were very gently cleaned off, it transpires the straight edge shows a concave deformation to the head in the 'thin' area of at least .004"! :D  
Not surprisingly, all the other firering areas were tip-top-tiddly-poo flatter-than-a-witches-tit flat.
"Cheer up Brain: worse things happen at sea..." :)

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Ah- that picture was seconds before 3 Mile Island ;D!
Not sure if it will be back together before July :B. I'm looking to do a number of things- none particularly radical, but I can see the list getting longer and June/July is a holiday extravaganza. If it's back together, I'd like to try to get to the Autosolo, but its getting the time(and money) to achieve it all.
Oulton Park is the absolute MUST be ready to rock'n'roll in time for 8).
  
A number of irons in the fire at present regarding the headwork. I'd like to use Dave Powell again:  the detail and execution of his work is of the highest quality, and I have tentative plans to use someone else either as well, or instead of for part of the headwork. It's all a question of 'plan of work to be achieved' at present, allied to timescales.

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