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MG MGB Technical - total compression failure--theories?

Driving down the road as normal, I begin to hear a rythmic kind of squeaking, it begins to run as though missing a cylinder. I now have zero compression on number 1 and number 2 both, 3 and 4 are normal approching 170. It still runs (badly, apparently on two cylinders)but I haven't heard the noise again. I have the valve cover off and everything seems normal, the valves are all coming up all the way and everything is turning. There is no water in the oil and there was no abnormal smoke on the two mile drive home after this occured. I thought valve train at first, but I don't see anything abnormal, or some failure between the cylinders, but what was the squeaking and why is there no missing water or extra smoke. Speculation? I will try to pull the head tomorrow.

Greg '73 B
G Holmes

Greg - Sounds like the intake valve for #1 or #2 valve is stuck open or you have a blown head gasket between the two cylinders. cheers - Dave
David DuBois

Greg,

I'll vote for the head gasket problem as Dave describes. The squeaking may have occurred as it was blowing, but didn’t continue after full failure.

Blowing a head gasket between the cylinders is not a location that would cause oil in water / water in oil.

You could do some more diagnosis by pumping compressed air in one of the spark plug holes while the valves on 1 & 2 are closed.

However, since you have already seen that the valves are operating normally, I can't think of a failure that isn't going to require removing the head. So, if it were mine, I would pull the head.

While the head is off, you may want to have it magnafluxed and/or pressure tested to search for cracks.

Charley
C R Huff

I would vote for the head gasket failure between cylinders theory. I had this exact problem once and curing it permaently involved lapping the block face. So act quickly and fit a new gasket at least with the venerable B series the job is well with the scope of a keen amatuer.
Stan Best

Head gasket it is. I didn't realize a failed gasket would give absolutely 0 compression like it did, and I think Charley is right that it squeaked as it was blowing, it sounded mechanical at the time but if I could hear it again I bet it could be understood to sound like compression pumping through a small opening. I also note the sound changed its nature as the car ran worse and worse. The entire little bridge of gasket between 1 and 2 is missing. I have a gasket on hand and should be on the road shortly. If it blows again I guess I will have to start looking at the route Stan had to take. Another note, I've been using the cheap head gaskets, but also had to use the wire/silicone trick (which worked well)to stop the water leak. May have to upgrade gaskets. Thanks for your responses.
Greg
G Holmes

Greg,

If it was me, I'd use a good gasket and skip the silicone. I think it's too much work to use a second rate gasket.

Charley
C R Huff

This thread was discussed between 29/06/2008 and 30/06/2008

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