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MG MGB Technical - Cracked head

Can anyone tell me how common is a cracked head on an MGB as mine is spouting hot water out of the rad and I think that this is caused by the gases exiting into the water jacket. Thanks in advance, Seymoor.
Seymoor Cummings

Cracked heads on MGB - extremely common. Some castings are worse than others. Try looking in the archive for more info.
Mike Howlett

Seymoor,

Had a cracked head in my first B back in the 60s. Caused by rapid coolant loss at speed and resulting extreme heat build up. The crack was deeply across the exhaust valve seat in one of the middle cylinders. Soon solved it with replacement head.

What you describe could simply be head gasket failure. Check for that first. Good luck.
John McFeely

Seymoor-
What you're describing sounds like a partially blown head gasket. Be sure that the head has been skimmed flat before you put it back on. Also, replace your ancient (and almost certainly) head studs. After all these years they've almost certainly stretched and as such will not hold their torque settings. This is most often the root cause of a blown head gasket. Retorquing won't help and, if you keep retorquing a warped head due to stretched studs, the head will crack. In short, check everything and do it right.
Steve S.

Seymoor,

Very common, I just dropped a head off last week at my friend's shop for a customer's car. You need to pull the head no matter what, so do that. The radiator should come out at the same time to be checked. If it needs attention a recore is better than a new radiator. Have the head magnafluxed and pressure tested by a good cylinder head specialist. If it's bad, find another head. Odds on this about 50/50, in other words, half of the heads tested will be cracked.

Get a copy of "How to Powertune MGB 4 cylinder engines" by Peter Burgess, available through http://www.amazon.com. Smooth the ports and get a 3-angle valve job as described in the book, and get the head skimmed for trueness as Steve S. says. Make sure the top of the block is true, for that can crack a head also. Use a good quality head gasket (plenty in the archives on this) and I would get new head studs too as Steve suggested.

Follow the torque specs and sequence, and adjust the valves per the manual. After about 500 miles, retorque again by backing off and retightening to spec and reset the valves. Your car should run better than ever, barring any other items needing attention, although the jetting may need fiddling, due to the increased efficiency of the head.

Happy MotorinG!
Paul Konkle

Seymoor-
Brit Tek can supply you with OE quality head studs (Part #HSK001). If you're going to hop up the engine, you'd be wise to use their ARP Heavy Duty studs (Part # HSK002). Brit Tek has a website at http://www.brittek.com Also, use a Fel Pro headgasket from APT. They have a website at http://www.aptfast.com As Paul said, make sure that the block is flat, or it may indeed crack. If necessary have it skimmed and make sure that the stud holes are champhered and retapped or the edges will lift and the gasket will blow out again. If you need to recore your radiator, tell the shop to use an aluminum core and specify the highest number of fins per inch available. The core can be up to 1" thicker than stock and still fit.
Steve S.

Seymoor-
Sorry, but I should have mentioned this: when you install the head studs, don't torque them down or you may end up with a cracked block. Simply torquing the head stud nuts will be sufficient to hold them in place. Oh, yeah, in that statement that I made about "make sure the block is flat or it may indeed crack", the "it" I refer to is the head, not the block.
Steve S.

Well the head has been pressure tested and it was OK, so now I will refit it with new head gasket and see if that cures it, the head did have a 5 thou bow in it and 4 thou is the limit so it has been skimmed.
Will keep you posted. SM.
Semoor Cummings

Yep you guessed it, still the same. so what now? spoke to the engineer and he said that the studs do not stretch so that shouldn't be the problem.
Seymoor Cummings

Not much of an engineer that says the studs do not stretch.

It's possible that there is a crack in one of the cylinders (in the block).

Another idea is the thermostat is stuck shut. That would cause the coolant to boil up from the bottom of the radiator. Water pump bad can cause this, also.

But first, how much is "spouting hot water out of the rad"? When does it do it (i.e., rad cap off/on, at idle, under load, normal cruise, etc)?

Inquiring minds want to know.

Wayne
Wayne Pearson

Seymoor-
I have to agree with Wayne. Your "engineer" is dead wrong. Any engineer knows that head studs are made of steel, an elastic metal. Thats why a solid steel ball will bounce higher than the same size rubber ball. Don't believe me? Just drop a ball bearing on the floor and watch it bounce! Like any other elastic material, it will stretch over time, just like the elastic in your underwear. If your head studs are original, after 21+ years they're almost certainly stretched by now. Don't try to "cheapo" your way through this repair or you'll ultimately end up with a blown head gasket and possibly a cracked head. A set of OE quality head studs from Brit Tek will cost about $40, and that makes them cheap insurance. As for the overheating problem, do as Wayne said: check your thermostat. Using your wife's meat thermometer (she won't mind), just heat some water on the stove and use a wire to lower the thermostat into it. Don't let the thermostat touch the bottom as it's the temperature of the water that counts. The bottom is hotter. If it doesn't function smoothly and properly, replace it. Use a 165 degree thermostat for warm weather use and a 195 degree one for winter use. Also, the impeller in your water pump may be worn to the point that it no longer pumps enougn volume of coolant. While you've got the thermostat out, remove the hose from the water pump and use a flashlight to see if it's worn.
Steve S.

A number of things here:

Yes studs do stretch and "neck" if they have been tightened beyond their elastic limit. And yes over time the elasticity reduces.

But in my experience, studs - even 30 year old ones - are usually still serviceable unless they are corroded and weakened. Like all elastic things, as long as you don't overstretch them, they will return to size when loosened.

If the studs have a dimple or 22 stamped in the top, you can safely go up to 55 ft lbs.

The boiling up in the rad could be caused either by sludge in the block resulting in hot spots or an air lock preventing proper flow.

Only if the gas bubbles up when the engine is COLD, would I suspect a gas leak at the head gasket.

If the problem arises only when HOT then -

1. Check the thermostat for opening (don't leave it out, this will cause more problems)

2. Jack the front of the car up ( or park it on a steep driveway/hill ) and fill the rad whilst running the engine - open the heater valves as well.

3. Flush the engine out using a proprietary cleaner/descaler.
Chris at www.octarine-services.fsnet.co.uk

Ah, I have left out the thermostat because it didn't seem to work properly, it does only spout water when hot or least warmer because I turn it off when the water starts spurting out. I tried a rad flush but it kept spurting out and I didn't want to risk ruining my newly built engine. I will put in a new stat and see what happens and try jacking up the car to get any air out . Many thanks so far all .
Seymoor Cummings

Seymoor-
Now it sounds like you've got air trapped in the block. Here's a suggestion for the truly desparate: (This worked on an old Ford that I once had, and it might work for you) While you've got the car tilted back at an angle, try removing the thermostat cover and filling the block and radiator with coolant from that location. Be sure that the radiator cap is off and the heater valve is open when you try this.
Steve S.

This thread was discussed between 18/09/2001 and 23/09/2001

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