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Cylinder head question

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Michael Oritt

Michael Oritt

Yoda
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The casting numbers on the top surface of the cylinder head on my Elva's MGA engine's are "12H2709" and "AF1H". I have another head available to me with casting numbers "12H1326" and "AI1". They are both 1800 heads.

Are these two heads interchangeable and if not what are the points of difference?
 
All B heads are interchangeable, though very late model head have a differant heater valve.
The 12h2709 is a European spec smog head with a 38cc chamber,single valve springs, 1.625 intake, 1.343 exhaust.
The 12h1326 is from a 65-76 MGB, 43cc chamber, dual valve springs, 1.5625 intake, 1.343 exhaust
 
Michael,
The main difference of concern to you with a MGA 1500 block is the combustion chamber volume. Stock is 38.2cc to 39.2 cc. Putting the larger 43cc chamber head on a 1500 block will give you poor performance due to the lower compression ratio due to the increased volume. The problem with the later mgb head with the larger valves and 38cc chamber volume is that the valves will hit the side of the cylinders. You could machine ears in the top of the block to solve this but I would say the easiest solution is to pick up a MGA "15" head used on both the MGA 1500 and 1600 engines to up your compression ratio and you will get LOTS of power.
Check the mgaguru site for info on mga and mgb heads and check British Automotive https://www.mgbmba.com for info on combustion chamber volumes and valve sizes. Larger mgb valves seem like a good thing but with the larger chamber volumes sort of defeet the purpose.
Also while you are on the mgaguru site check out what he says about bumping up you timing from 7 BTDC to 14 BTDC. My 1500 has never been happier.

Liam
57 MGA
 
Something you also need to look out for, is the oil supply to the rockers, i.e. the feed from the head itself to the rocker shaft via the stand. Note the feed on the rear stand, earlier ones are straight, later (post 1974, I think) are offset. If, for example, you put an offset oil feed head with a straight feed rocker stand (It's the rear most one), you will not have oil flow to the rockers & eventually they will fail. If you have the rocker assembly off the head, it's pretty obvious which one it is.


Ask me how I know this.

Colin
 
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