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MG MGB Technical - B-series 'O' head

Can anyone enlighten me on the O head as used in the B series engine ?

I gather the O refers to oversize valve(s), and was used on the Austin 1800S.

That's all I have been able to find out. Was it used on other cars?
Is there much difference in power compared to a standard head?
Any other information?

Thanks.
g Harrison

Recent discussion on Magnette board and with
Peter Burgess, probably MGB tech board.

FRM
FR Millmore

If you get a chance read Peter Burgess' book "How to Power Tune MGB 4-Cylinder Engines". This explains difference of O series head - larger valves, small combustion chamber.
Note - This book is now available as an ebook on Amazon.
Mike
Mike Ellsmore

Thanks, I've previously searched this forum with no results (and still can't find anything!)

Sounds like the Peter Burgess book is the way to go.
g Harrison

Have you also tried searching the archive:
http://www.british-cars.net/mgb-technical-bbs.htm
Bernie
B Anderson

I'm sure the the 1800S had twin HS6s as standard.
c cummins

It did, C Cummins.

I bought the carbs and manifold from Dave's Car Spares in Bath for £10 (in about '86). Needed the float chambers swapping around and a new linkage made up, but then went straight on 'B. Never convinced it made any difference to performance, but did increase the number of petrol stops!

Peter



P A Allen

The MGAguru has all the details on the various cylinder head specifications for B series engines see
http://www.mgaguru.com/mgtech/engine/ch100.htm
Mike
Mike Ellsmore

What we in OZ call the "O" head came out on the series 2 austin 1800 and had the larger inlet valves and an "open" combustion chamber. Same head was used on the 71-72 MGB. The combustion chamber is much shallower than the earlier head and an exhaust valve clearance relief in the top face of the block is needed. The MK11 1800 was rated with an increase in BHP but I think it also had a defferent cam as well so who knows. The MGB was still rated with the same power. MGB went back to the old valve size in later models. The O head usually has a smsll 'O' cast into the rear behind the valve cover, at least the several I have seen have. Denis
Denis4

Rather than the Os and Es and Xs cast in we tend to look at the actual head casting number such as CAM1106, 12H1326, 12H906, and 12H4736 to indentify the type.

Peter
Peter Burgess Tuning

This thread was discussed between 10/07/2012 and 11/07/2012

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