MG Car Repair: No Start/Water In Oil, plug gap, head gasket

Question
QUESTION: Howard,
I appreciate all your help in the past. I have; 71MGB, bought a yr. & half ago, ran so-so. While car was in garage past year, completely replaced entire braking system. Could not get Carburetors to adjust. Rebuilt carbs(set to all specs), started engine & ran great! after it reached temp., it quite, and would not restart, after checking spark, fuel, fuel pressure, timing,; would intermittently start for about a minute, then quite, as if it was not getting fuel or spark. Replaced distributor,(w/rebuilt), points, condensor, rotor,cap,wires,plugs,Confirmed great spark form coil and through plug gap(checked w/plug laying on block),timing is right on the money, valves are operating, fuel pressure is just over 2#(use inline regulator), after trying to start, checked plugs, and they appeared dry! even tried fuel in carbs and plug holes, and no start. Pulled dip stick to get to plugs, found oil REALLY thin, and clear liquid all the way up the stick! Radiator did not appear low. Compression test showed;
#1-116lbs. #2,#3  all 115lbs. After a squirt of oil in ea. cylinder, #1-121lbs, #2-120lbs. #3 & #4 both 125lbs. It doesn't seem like a head gasket to me since the cylinders seem so close in compression, but I am unsure, perhaps it's more severe than the gasket. Originally, there was nothing in the oil but oil! I am completely lost at this point. Any advice would be greatly appreciated. Thank you in advance. Bryan

ANSWER: Hi Bryan,

If the oil was very thin you need to note the color. If it looked just like very thin oil it was most likely gas in the oil not coolant. Any time coolant gets into the oil it turns at first brown and then as more gets in it turns light brown and finally light tan and is even milky looking with foam.

Your compression readings are all low but you didn't say if you opened the throttle when testing and that can give you a low reading. An MGB should show from 125 to 170 (throttle open)

You need to correct the oil before proceeding.

If the oil is tan in color you need to get a fitting to adapt an air hose to a spark plug hole and pressurize each combustion chamber one at a time while at TDC and in 4th gear and hand brake on hard. Then open the coolant cap and note if you get any raise in coolant level with at least 125 to 150 PSI air pressure in the combustion chamber. This test will show even the very slightest leakage in a head gasket. You can also listen in the carburetor (throttle open) for any hiss. even the slightest leak in a valve will hiss. Listen at the exhaust too. It is no use removing the oil filler cap and listen for ring leakage as even a new engine will hiss into the crankcase.

This it a 100% good test for a head gasket.

Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks Howard, I appreciate your help! Oil is not brown , or milky, just very thin, dark(like dirty oil), I will get an adapter to try the head gasket test as you described. Would there be any other way that gas could be getting into the oil, other than past the rings? Sorry not to have mentioned, but yes, I did have the throttle open when testing the compression. Thank you again very much!

Answer
As you use an engine you get ring blow-by and some of that is unburned gas and it condenses in the crank case and thins the oil out. If however your oil got thin in a short time you may have gas entering through a vacuum hose from the vapor system which may be bad and getting saturated with gas so first check your charcoal canister for fuel.

Howard