American MGB Association Message Board

Technical Area => Engine Related Items => Topic started by: december2006 on November 02, 2006, 10:11:00 PM

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Title: MGB Cylinder Head Identification
Post by: december2006 on November 02, 2006, 10:11:00 PM
Is there a way to tell a low compression Head from a High while on the car. I expect the head on my 68 is cracked as I lose coolant when driving at interstate speeds, especially on warmer days. I am quite certain it is exiting through the overflow. I have a 1977 parts car from which I would like to use the head. I know that a 1977 head should have connection for a water choke, but cannot find any so expect the head is a replacement. The car has a weber Carb and the tap for the choke comes from a tee in the top radiator hose and goes into the heater. Both heads on both cars appear identical with a cast in number 18 and the letter "L" on the rear horizontal surface.
My 1968 engine is lettered with an H indicating the higher compression ratio, and I want to be sure I replace it with another High Compression Head.
If necessary, and I choose to plane the replacement head, to what thickness would I go to get a compression ratio of around 8.8 to 9.0.
Any help would be appreciated. Thanks

Title: Re: MGB Cylinder Head Identification
Post by: amgba on November 02, 2006, 10:12:17 PM
Posted by Art Isaacs ( on June 12, 2006 at 19:55:45:

In Reply to: MGB Cylinder Head Identification posted by John Motycka on June 09, 2006 at 12:26:34:

Hi John,

MGB cylinder heads are pretty much interchangeable and fall into (2) types - early and late. The early 62-67 head is a plain casting with no outlets for pollution controls. The external differences on the later engines is broken down to 68-74, which has tapped holes for the AIR rail above the spark plugs, and 75-80, having the AIR holes, a water choke adapter and use a unique rear rocker pedistal, which you would have to take the valve cover off to see. Beyond this, the head would have to be removed to really determine the exact year.

Engine compression is more determined more by the piston/rod combinations. The later engines have the lowest compression ratio (about 8.0:1) to cope with the fuel and pollution control requirements.

Moss and others offer only (2) OEM style versions of very early (62-67 18G & GA engines)and very late (75 up 18V engines), as well as a stock and cross-flow design aluminum head. The minor differences in valve types and and other internals would be near impossible to tell with the head on the engine.

I hope that helps you.


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