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MG Car Repair/MGB foamy rad head gasket


QUESTION: thanks Barrie - I will test my compression and try to determine if I have leaks from exhaust or intake or water jacket. hopefully not a cracked head! In the case of discovering a leak, is there any sense to try torqueing the head down to see if that helps? If removal is the way to go, should I be considering a full re and re of the head, valves at the same time?(I also want to take on the work myself as any MGB owner might understand!)

ANSWER: Hi Paul.  Do the tests first.  Then if necessary take the head off and inspect.  If it is a crack in the head, then you have no choice but to replace it.  

There is no point torquing down a leaky head.  It never fixes the problem.

If you have not already converted to unleaded then this is an opportunity to fix 2 problems at the same time.  No point in doing that yourself, just fit an exchange unleaded head with all the hard work done and guaranteed.    

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MGB plugs Jun 16 15
MGB plugs Jun 16 15  

MGB block Jun 16 15
MGB block Jun 16 15  
QUESTION: So - compression test done and a further clue to problem. Cylinders from  1 - 4 were respectively 145, 145, 140, 138 dry test. Attached is a couple of images that give perhaps more detail to the trained eye ( plugs 1-4 from right to left, and close up of the cylinder head ). I will try and get a compressor with a plug fitting to run the other test. By the way - How can one tell an unleaded head apart from leaded?
Thanks Barrie for your super quick responses.

Hi Paul.

Actually, your compressions are not far off.  However, cylinder #4 looks slightly low and plug #4 has some hard deposits on it.  I would suspect that you are in the very early stages of a leak.  This is possibly no more than a head gasket starting to blow and needing replacement. I doubt that any damage has been done.    

There is no way you can check for unleaded inserts without removing the head.  You would then have to remove one of the exhaust valves and carefully inspect the valve seating area for a circular insert pressed into the head.  The correct test is to run a sharp Swedish file over the insert.  If you can scratch the seat, then it isn't hard enough for unleaded.

When you have put everything back together, fit a new set of spark plugs at the same time and also do a mixture test on the carbs.  I suspect that the rear carb (#3 and #4 cylinders) is set too weak, causing slight overheating at the back of the engine and hence the head gasket problem.  

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Barrie Jones


MG Sports Cars from 1949 to 1980 - Including MGB, MGBGT V8, TF1500, TF, TD and modern Midgets. I also specialise in SU carburettors, Lucas wiring, suspension, steering & brakes.


I have owned my 1955 TF1500 since 1966. Technical specialist for the TD and TF with the MG Car Club T Register. Also owned 20 MGBs and currently own an MGBGT V8. Written 3 books on MGs and produced a DVD on how to strip and rebuild the TD/TF gearbox.

MG Car Club.

Barrie's Notes on the 1953-55 MG TF (author). /=====/ Barrie's Notes on the MGB (author). /=====/ Barrie's Notes on the MGB GT V8 (author). /=====/ The Essential Buyer's Guide to the MG TD, TF and TF1500. (author)

M Phil, C Eng, BSc (Eng).

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