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MG Midget and Sprite Technical - blown head gasket
|I seem to be blowing head gaskets at an alarming rate -see attached photo - both copper and "black"|
The engine is a 1275cc block bored to 1301cc (+ 30thou).
There doesn't appear to be a lack of metal between cylinders 2 and 3
The engine doesn't run excessively hot
I do thrash it at least once a week - do i just need to calm down a bit or is there a more technical reason?
(When the HG blows between 2 and 3 there is no mixing of oil and water to give the tell tale signs in the rocker cover. It does however sound like the exhaust is leaking as it blows back through the carbs. Ive also learnt that it can cause the float chambers to overflow on SU's but Im not exactly sure of the theory behind this.)
|S G Macfarlane|
|Have you checked your head and deck for flatness? I wonder if that bit between 2 & 3 isn't being "clamped" firmly enough.|
|Try a 0.8 mm strip of mig wire across the gasket where it blows and , as Gryf says....is the head flat and is the block flat? What head torque are you using?|
|torqued to 50|
looking at it i think the head has been damaged slightly with the surface between 2 and 3 becoming pitted, although i wouldn't know if its enough to cause failure of the HG
ill try one more gasket and see how it goes
Anybody know where i can get the head skimmed and rebuilt in cheshire / merseyside. Its a 12G 1805 head so i would like to have it rebuilt rather than exchanged
Can you explain how / what you do with the mig wire?
|S G Macfarlane|
|You may well have low spots or pitting in places and that needs to be checked. |
Otherwise, read the nearby thread "Oil in coolant...". The dark places on both the copper faced and on the metal rings of the Payen are indications that the head was not torqued correctly; this may be the entire problem.
|You cut a short length of wire and put it across the block on the block side of the gasket. Not guaranteed to work but I have seen it used in quite a few race engines and it did not cause any problems. It is a sort of poor mans Wills ring :)|
There is no substitute for a flat block and head though!!!!
|Yes, if it has blown twice in quick succession there is a problem that needs to be addressed rather than put it back together in hope.|
This isn't a problem caused by overheating, it happened on my 1380 when the engine builder got the compression ratio wrong.
So, what's happened?
Have you recently rebuilt the engine? Have you checked the CR? Did you check the head for flatness? And the block?
I would try and obtain another head to start with, purely as a control, and get it checked before fitting it, then run the engine. I know you want to keep the old head but that's not always possible. Try a standard one, I had that on my 1301 and it went tolerably well. Really these small bore engines should be bullet proof.
Perhaps use a bit higher torque but not too much!
Should be 68Nm done in the correct order.
|Keep the 12G1805 head, it's the best! ;P|
|Alex G Matla|
|50lb ft - but you knew that already, didn't you?|
I'll try it one more time, using as much of the good advice as I can handle in a single sitting - if it doesn't hold then I'll get it skimmed (I've already said the head looks a bit pitted between 2 and 3).
I'm quite adept at changing HG's now so I'll take the risk on another, if i get to use the car for the last couple of weekends this summer then it will be worth it!
|S G Macfarlane|
|get it skimmed first!|
there should be no pitting.
And no I did not have a clue about what type of torque rating you ment.
Here in europe we have the metric system so it is hard enough to remember all the bolt/nut sizes ;P
|just rushing out but don't some go to 42 lbs|
|depends on the lube used|
|Two blown head gaskets is quick succession and you are adept at changing head gaskets suggests to me that the two surfaces are not flat. Check the block between 2 and 3 and get the head skimmed to remove the pits. Or wait for three blown head gaskets in quick succession.|
Assuming the block between two and three is ok a skim should sort it out.
Fix the problem once or continually fix the symptoms.
|I like Peters idea of the mig wire,,,,id heard that before, but had forgotten it|
On a somewhat related note,,,,,ive got a small hg leak in my truck agian at the oil side....oil in the coolent
Im wondering, can I just but some brass tubing in the oil and water passages where the head meets the block, just make sure its good and tight
That way the oil / coolent cant escape into the gasket...it just a thought ive had for a while
Third HG fitted (black Payen), torqued cold then hot, after condensing everyone's good advice - right up to 52 "monkeys" with no lube, all seems good ticking over in the garage, ready for an 0500hrs blast this weekend.
BTW - I cant be that adept.................
|S G Macfarlane|
|Did you bother to read all the stuff I wrote in the other thread?|
"with no lube" = error
"52" = a bit high, do you always make up your own numbers? More of a problem with "no lube", especially on retorque.
But I suppose that you didn't read that part either.
After doing thousands of gaskets, and often measuring the results after some and/or many retorques, I can assure you that most especially when there may be some question about the sealing surface conditions, the retorques can make the difference between success and failure. I've saved quite a few "iffy" heads/blocks (and a few reused gaskets) by careful retorque - some of which are still in service after 20 or more years, and none of which have ever blown a gasket.
Do yourself a favour and retorque again tonight or before you set out - it could make the difference. Before you do that, mark the studs and nuts so you can see how much if any the final nuts position is from where you are.
If it works the first day, retorque again after a week, and again after a month; time at torque and heat/cool cycles are the most important factors.
|Get a grip man - i used to run a midget every day to college with (what i now know to be) a blown gasket, first I'd bump start it down the hill to blow out the water then stop midway - about 5 miles ( and about 5 years before i knew what a HG was)to recharge with river water whilst me and my mate listened to zz top and rolled another fat one, the last mile to college was down hill, we would shut off the engine and coast all the way.|
We would tighten the nuts as far as we could, no matter what lube, temp, bolt etc etc and it would probably be OK, we are talking 1960's not F1, it worked for me then and I'm hoping nothings changed - in fact back then i didn't even know what a torque wrench was.
I'd rather drive it and learn by experience than spend all day and night discussing what if!
I'll take it well into the red tomorrow and let you know the result - you'll probably say "I told you so"
thousands - really?
|S G Macfarlane|
|On a pre war mg itis rather hard to get a socket and torque wrench on th head studs!|
And even with an manual spanner "that is about right" by the feel torque these cars work fine with out blowing HG every month.
So indeed the torque story can be taken with a grain of salt.
Visible pitting in a mating surface however ....
Careful what you admit to around here.:)
A "fat one"?.
Smoking whilst driving? Shame shame. :) The 'elf and safety brigade will get you LOL.
Not sure that listening to zz top is likely to have improved your head tightening skills either :)
|I used to torque my racer down to 55 whatever they ares on the torque wench thingy. Well, 55ish, my torquey wotnot wasnt that accurate. It was somewhere between 50 and 60, depending on how I looked at it. |
The only HGF I had was when the engine was built by a "pro". For some reason it didn't like 15:1 CR.
Lube? What do you lube? I've never used lube.
|Thanks guys, its seems to be holding so far, which is more than can be said for the weather.|
|S G Macfarlane|
|You could try E Hidderley in Bootle,Liverpool, Google it,you will find their website|
|"I've never used lube."|
"Careful what you admit to around here.:)"
Max you are making this to easy.....
|I agree with Peter|
Placing a short piece of wire between cylinders 2 and 3 can often work wonders.
Peter, we generally used copper wire in race engines but I have never tried mig wire but I suspect it would work just as well.
The vast majority of A series engines will have some contamination in the area between 2 and 3 although not completely blown like the one noted above.
I am surprised that the block has not burnt in the same area?
|Robert (Bob) Midget Turbo|
This thread was discussed between 17/08/2011 and 27/08/2011
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.