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MG MGB Technical - Cracked Cylinder Head

76'MGB ,Had a cracked cyl. head,so we took the head to get welded and resurfaced.They did find two cracks,so we put everything back together still shooting white smoke water mixed with oil.So we took head back to shop ,they did pressure test everything O.K.I ,I see no cracks in the block, I put a straightedge on the block seems flat and smooth. How hard is it to see a crack in the block,someone suggested new studs, am I missing something can anything be done short of tearing down the motor?
Thanks Casey
Casey

Casey;
Sorry to hear of your troubles. Have been working on Bs since the late 60s and have never seen a cracked block. Other then rod through side. My bet would B that the head has a crack that only shows when warm? Also my experience is except for the most minor problems welding B heads is a waste. Good luck and keep us posted Bob Thompson/International Auto.
Bob Thompson

Casey-
It may well be a crack that only opens up when the metal of the head expands under heat, as Bob says. It may also be possible that your head studs have stretched through sheer old age (metal fatigue). If this is the case they won't hold a torque setting and the gasket could blow, perhaps not completely, but just enough to let coolant into the combustion chamber. However, as Bob rightly pointed out, welding a cracked cast iron head is usually a waste of time. At best it's only a temporary fix. To do it right the head has to be heated in a furnace and the weld immediately applied while the metal is still red hot, then the head has to immediately go back into the furnace and be cooled down in stages. When cool, the head will be warped, so it'll have to be remachined to get a flat mating surface. In the end, for what all this costs, you may as well just go get another head.
Steve S.

Casey. I have spoken to several experienced welders over the years about welding up cylinder heads. None of them recommended it and gave full reasons why. (Hard to get perfectly clean for a good weld, not knowing the exact alloy of the cast iron to know the exact welding rod to use and a number of other complex issues, often beyond my level of comprehension.) Like Bob T, I have never seen a cracked block other than when a rod does the damage. John Twist mentioned in his manual that he does not waste the money on having a block checked because he had never seen a bad one. Hence, we are looking at how straight the top of the block is, how straight the bottom of the head is, the quality of the head gasket and the torquing procedure. If you have water mixed with oil, you could have an internal failure of the head, but how is it getting into the combustion chamber. If it is a head problem, I would expect that you would have to have a crack in the combustion chamber, which also entered a water passage and allowed oil, mainly from the upper valve area, to mix in. If my memory of the oil circulation system is correct, the only place oil comes through the interior of the block is up to the rear of the rocker arm assembly. I would inspect that area first for cracks. I would also find out what they mean by a pressure check at the machine shop you are working with. Did they pressure test the oil passage? Water is at 7-15 psi, while oil is at 45-70 psi. This provides a clue as to which way the fluids normally flow. Les
Les Bengtson

FWIW, back in the 1960s, my 3-bearing B suffered a cracked cylinder head. The small crack was directly accross one of the middle cylinder exhaust valve seats. There was also a small half moon cut out on that exhaust valve maybe eroded by relatively cool coolant in contact with a hot, very hot exhaust valve when there was a near total loss of coolant during a high speed run (in those days there were no overall speed limits .... :o)). There must have been fluid/gas movements both ways through that crack. I guess coolant into cylinder on induction stroke, gases in the opposite direction into the coolant galleries on ignition stroke. The cooling system was hugely over pressurised. A replacement head rectified it perfectly and I used all the 7 valves which were still in good condition.
John McFeely

fwiw, I have been running my 1500 for 2 summers with a cracked block - and I must say i'm proud of the little beast. The crack is directly above the oil filter boss and runs horizontilly about 1.5 inch. Coolent seeped out so I cleaned it up, ground it a little and applied(wince)JBWeld. That was about 4,000 miles ago.

I must admit that I cringe when the rpms get a little high but it adds to the excitement;).

signed, anonymous
Fred Horstmeyer

Les,
A question on oil pressure. While the oil pressure is 40-75 psi in the oil gallery. What is the pressure at the rocker arm shaft? Having run several MG engines with the valve cover off, the flow/pressure at the top end doesn't seem that high.

Regards,
Lee Bradley
Leland Bradley

Here's one for your files.

There are welders...ie: exhaust system welders, marine welders, certified structural welders,
cast iron welders, etc...then there are Cylinder Head & Engine Block Welders.

One of the best in the business is: Kelley Block Welding
12910 W. Washington Blvd.
L.A., CA 90066
phone: 310-827-6795

They've been doing this for as long as I can remember. The guy who runs the place, Dennis, is
a straight-talker; has decades of BMC experience including MGB, midget, Sunbeam, etc. (as well as
Chevy, Ford, Mopar). He'll thoroughly examine and test your part in a day or two - then sit you down
and go over all the caveats with you. He'd rather turn down basket cases rather than let the sparks fly
unnecessarily. He tests all of his work before letting them go out the door.

Besides welding, he has a full machine shop and he has valve jobs down to an art. He can also install
hardened, no-lead valve seats on "B" heads.

Granted, welding an engine part is to be considered as a last resort, but if you are exploring going this
route, choose your welder very carefully.

This is an unpaid, unsolicited endorsement.
Daniel Wong

Fred,

You mentioned applying "JBWeld" to your cracked cylinder head. What is this JBWeld and where can I get some for my cracked head. Also please advise under what conditions did you apply this JBWeld.

Thanx in advance

Gary
gary n. hansen

Gary. J-B Weld is a two part epoxy available at most hardware or auto parts stores. It is not one of the high temperature epoxies, like Marine Tex, which can be used on a cylinder head. Note that Fred used it on the outside of the block, not the head. J-B Weld breaks down at about 450 deg F, as do most of the more common epoxy mixtures. It is designed to bind, not fill. If used in an area of significant expansion, it would tend to break down and allow a leak to re-develop.

Lee. I do not know of any way to test the oil pressure at the rocker arm. It would require that you drill and tap the rear pedestal for a pressure take off fitting or to drill and tap the hole in the head and attach a fitting. You are perfectly correct that pressure within the system will be lowest at the end of the system (the rocker arm assembly) and could be significantly lower than general system pressure. It is also possible to lower pressure (and this is what I believe is happening) by restricting the amount of oil flowing through the rear pedestal (by using a small flow), then having the oil go into a larger opening this would drop the effective pressure at the valves/rocker arms while maintaining a high system pressure at the rear pedistal and through the head. Les
Les Bengtson

Les:
I called the machine shop about the pressure test they told me they put the head on a machine that does an air pressure test on the water jackets at that point they use a water and soap solution to check for leaks,they also did a sonic test also the work is warranted so if the welds do fail back it goes.the mechanic also mentioned the head didn't look like it was sealed at the gasket making me think of torque. I think I'm going to try a new set of studs,maybe the old ones are stressed.
Thanks for all the input Casey
Casey Stephenson

Casey,

If they did not surface the head after the welding, then it could easily be warped. If they DID surface the head after the welding, it again could be warped. Once you subject a cylinder head to that kind of localized heating, it will have a lot of internal stresses. So if you ran it and got it hot enough in use, it could lose some of those stresses and again warp. So I wouldn't doubt that you are getting a gasket problem.

Cast iron can be welded very successfully if you do it correctly, Steve mentioned the basics and any other way is haphazard at best. Usually the cost outweighs the benefits.

Sean
Sean Brown

This thread was discussed between 30/10/2001 and 01/11/2001

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