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MG MGB Technical - 1800 BMC Head

I have a spare BMC 1800 head; used on a 1967 MGB GB motor for 20 years with no issues. The head has a P/N 12H764 and the casting clock indicates 12/20/1961. I cannot trace this part number trough any of my source data. Anyone have any info regarding this type of head. I assume it was from an early 3 main block or another BMC B series engine application. The block has cut outs for valve clearance.
Rich Boris

My understanding is that it's not the vehicle manufacturers part number that is cast into these things, even though it is of the same format.
PaulH Solihull

Hi Rich

I think it is from an earlier than 1800 B series head, such as a 1500/1622. I think I have one at work. I will look and see what head it is and get back to you. I will also look in my MGA type heads list. Paul is right as the heads would normally be given one less as part number....eg 12H763

Peter
Peter Burgess Tuning

See photo

Rich Boris

Hi Rich most interesting with the 18 on, can you send a picture of the combustion chambers ?

Thanks

Peter
Peter Burgess Tuning

see image

Rich Boris

Thanks Rich

I will see if I can dig out any info.

Peter
Peter Burgess Tuning

Hi Rich

I do not have one and cannot find any info, you must have a rare one there.

Peter
Peter Burgess Tuning

Thanks Peter:

My plan is to tear in down soon & make some measurements of the valves; I guess new springs, guides & valves. My only real concern is that the 18GB block that it was installed on has cut-outs for valve clearance. I hope the head was not planed to meet MGB compression specifications. Other dimensions will be compared to another 12H906 head to be sure.
Rich Boris

Hi Rich

We can always check against 906/1326 if you need.

Peter
Peter Burgess Tuning

Hi Peter:

Stripped down the head today; and found that valves are early MGB(12H435/436). The valve guide height is aprox 0.6 inch above head. The combustion chamber has a max depth of around 0.42 inch. The chamber is 3.26 inch by 2.16 inch from spark plug wall. The deck seems to be 0.26 inch from deck to scaloped area on the push rod side. Are these rough order measurements consistent with a 12H906/1326 head?

Thanks: Rich
Rich Boris

Hi Rich

I checked over a couple of 906 and a couple of 1326, your measurements are about the same give or take 20 thou on the scalloped part. Oddly the best 1326 head I measured did not have the row of scallops to the block side of the inlet gasket face, it was cast 15th July 1970. The fitted height of the guides you measured is the same as ex guides but lower height than the in guides in standard fitment. I guess you have an earlier head than the 906/1326. Interesting how early your casting date is.

Peter

Peter
Peter Burgess Tuning

This thread was discussed between 19/01/2013 and 23/01/2013

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