MGB: Head gasket?

Went to take the GT to get a PA state safety inspection last night and it started running really poorly about a mile from home. I limped it home and started checking out the obvious stuff and finally did a compression test #1-150, #2-145, #3- 45, #4-45. On the plus side, it is cool to know that a MGB will get you home on two cylinders. On the bad side, I am guessing that the gasket is blown between 3-4. There was no overheating, no white smoke and no oil in the anti-freeze, so I am hoping it is just the gasket. I will pull the head tonight and see if anything else is wrong. It has been leaking a little,on the side of the head since I bought the car. I guess it just took another 750 miles to let go. I will report back on what else I find.

Blown gasket is very likely all that happened.

Before you fire it up for any more tests, check the oil. If it is milky shut it down immediately. Oil and water don't mix and water is a pretty poor lubricant for the bottom end.

Also check the coolant for signs of oil getting into it.

Also, after you get the thing all back together, with a full oil and filter change of course and a careful cooling system flush you might want to repeat both efforts several times to make sure all of the liquids are where they are supposed to be.

Jack

Before you go pulling it all apart, remove the valve cover and verify that the valves are moving up and down. Are they moving all about the same amount? Are the pushrods all where they belong? Are the valves adjusted correctly? More than once, I have saved pulling a head because of a no answer to any of the above questions.

Mine blew like that a few years back:



Ignore the mangled part at the top. That happened getting the head off.

Thanks for the input guys! Chris, I did your checks last night and everything seemed ok, so I pulled the head before I went to work this morning. I found the gasket burned between 3-4. The weird thing I found was three pistons with the usual carbon build up and one completely clean piston, with no carbon at all. Is this from a bad valve job,or no spark? It looks like it has been like this for a long time. Any input on this would be greatly appreciated.

Boy, that looks really familiar Andrew!