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MG MGB Technical - Pinhole leak

All,

My 71 MGB has a pinhole leak on the top of the head underneath the valve cover gasket. This weeps antifreeze when the car gets hot. There's no evidence of antifreeze in the oil, no evidence of any cracks. I've seen threads about cracks in the outer water jacket, but I'm hoping there might be an easier fix for a lil ol' pinhole. I haven't checked compression, but the head was pressure tested two years ago when it was off for a rebuild, and was fine.

Thanks in advance. Any and all comments appreciated.
Greg
Greg Peek

Is it a leak between the gasket and head or an actual hole in the head?
kids1

It's an actual pinhole in the top (flat) edge of the head. The valve cover gasket covers it and prevented it from leaking for some time.
Greg Peek

This is a new one ...but then, these cars can be full of surprises.

It's hard to imagine a leak coming from underneath the valve cover gasket because the casting is
thickened all around the gasket mating surface - except where it nears the thermostat housing.

Is this where the leak is at?

If so, aside from pulling the head and having it welded - you might try draining the antifreeze,
remove the thermostat, rinse and clean and let dry that area inside the head. Then take some soapy
water and compressed air and blow it through the top of the pinhole. This way, you might be able to
spot exactly where the leak originates. It would help to have a small inspection mirror and flashlight
for this.

You can then try plugging it from inside using a fingertip smear of JB Weld (a 2-part, super epoxy).
Let the JB Weld set for at least 24 hours, preferrably more. Home Depot sells this stuff.

I would have this area welded - later - during it's next valve job, however.

Hopefully this is all that is wrong, and that the head is not cracked in some way.
Daniel Wong

Daniel, thanks for the input. The leak is directly above the no. 2 spark plug.
Greg Peek

Greg. Cast iron expands when it gets hot and a hole or crack will not get smaller in use. JB Weld, as mentioned by Daniel, is one of the stronger, generally available epoxies. But, the use of any epoxy is more of a "get you home" thing than any form of cure. The marine supply stores may have available Marine-Tex which is a much better form of epoxy for this use. But, again, it is a short term, rather than a long term, solution. Welding on cylinder heads is covered in the archives, generally under the "cracked cylinder head" threads. A few people have had this work for them. Most have not. The welder I checked with, a very experienced, aero-space qualifed individual, stated that his experience was that welding on cast iron cylinder heads was sucessful no more than 10% of the time.

If you go to my website, www.custompistols.com/ you will find a tech article on checking for cracks in the cylinder head and demonstrating the use of the dye-penetrant testing system which is suitable for hobbyist use. Click on the MG section, then articles. Also has a very good article on how to bench bleed the master cylinder written by one Daniel Wong. Les
Les Bengtson

Les, thanks. I'll check out your site.
Greg
Greg Peek

Greg: without seeing the leak I can only mention a method that I have used with some success on small block chevy heads in my misguided youth. Drill a hole at the leak, thread the hole install a threaded plug machine it flat Better then glue or welding.Ric
R E L Lloyd

Greg - Ric's fix works quite well on a small hole like you are talking about. It even works on cracks in the water jacket and is termed "stitching". A hole is drilled and tapped at one end of the crack and a plug threaded into it and ground flush. A second hole is drilled, overlapping the newley installed plug, tapped and the second plug iinstalled and ground flush. This procedure is continued to the other end of the crack. I just had this done to the imfamous head crack between cylinders 2 & 3 and have had no problems at all with it (theis is the second head I have had stitched). Good luck - Dave
David DuBois

I agree with Ric. Have a machine shop drill and tap a hole and then insert a plug. BTDT
Mike MaGee

Mike. I have seen this method used in both the automotive and aircraft fields. The drilling of a "stop hole" to prevent cracking is a common practice. I have, however, never seen it work well for any length of time. I have also seen the use of either a pin or a threaded plug inserted into the stop hole. This has not worked well either and some friends cooked their engine after the machine shop assured them such a repair would correct the problem. Thus, while I would never tell anyone not to try such a thing, I would not use it myself, nor would I recommend it. Based on my experience, it does not work for any length of time. Les
Les Bengtson

The real issue is how fast you're losing coolant and what kind of driving you do. If you're losing a lot of coolant, or racing or something, you're probably in for a new head. If the 'weep' is sustainable over some period you're comfortable with, and you're not driving to the ragged edge, it could go quite a while just staying topped up.
In regard to most of the repair comments, a rebuilt head can be had for $500 or less, and the real risk (and potential cost) is in removing and then trying to reinstall the head and other paraphrenalia. I'm thinking of seized studs, warped deck, etc. And frequently after a rebuild you get a weep at the head gasket anyway. The other risk in drilling and plugging is that you're actually making the whole bigger and (potentially) worse.
Unless you could get someone to do a patch for less than $100 and on the car, you're probably better off either letting it ride or doing a whole new head.

Steve
Steve Aichele

Thanks everyone - found some local shops to look at it.
If it has to be replaced, I'm going for aluminum. Has anyone had one for more than 6 months to a year? I think they must be fairly new.

Greg
Greg Peek

I used JBWeld on a cracked block (about an inch long) on a Honda Accord nearly a year ago. Still no sign of renewed leaks. Saved a TON of dough.
J. L. Randolph

I just had to kick in on this thread. During the Christmas holiday back in 1989 we had one hell of a freeze here in Jacksonville. One of the local refuse management companies had a fleet of Mack trucks that had somehow ended up with straight water in the cooling systems even though there were several pallets of 55 gallon drums full of antifreeze in the maintenance garage. A freak snowstorm accompanied by lows in the low teens closed down I-95 and pretty much kicked central to north Florida in the teeth. Well, every one of those Mack diesel engines ended up with frozen and cracked blocks and were sent to the local Mack dealership where a friend was the service manager. He told me that they repaired the blocks with Marine Tex and when he left the dealership two years later, those trucks were still collecting garbage with no additional repairs.

Am I impressed? You bet. Would I risk my own engine with a welded or epoxied head or block? Not on your life.
David
David

I had a similar problem back in the mid 1970's and my mechanic suggested, before I replaced anything to try a simple radiator leak stop product which the theory goes suggested that the product would seep through the crack and once the car was cooled would make a cement like seal. I tried it and to my amazement actually worked. The product was called 'Barsleak'. simply put in rad and run for 15minutes and turn off car for a few hours or more. Any auto parts store sells it or a similar product.
S. Hepburn

Greg, I've had an aluminum head for almost 2 years now. Make sure to spend an extra $3-400 at the time of purchase to have the head ported, or you will be sorely dissapointed with its performance. The biggest problem seems to be that the pressed in valve seats need to be blended into the runners. With that done and some gasket meatching, you will be pleasantly surprised!
Jeff.

Jeff Schlemmer

That leak over number 2 plug is certainly a crack that will extend ( soon, if not already ) from the plug hole to the centre of the head.

It may only be leaking in one place now, but it will inevitably start leaking elsewhere - possibly into the cylinder where your first sign will be an empty rad and mayonnaise for oil!

Start looking now for a replacement head - and use the "Bars Leaks" or "Rad Weld" product in the coolant to limit the effect of the damage till tou can replace the head.
Chris Betson

This thread was discussed between 21/08/2003 and 24/08/2003

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