Over the long production period of the B-series engine a number of different cylinder heads were produced. Because this component is often replaced, and often by owners with tight budgets, it is possible that an engine is wearing a head that was not intended for it originally. This is especially true of the MGB engine because it had a long production run in the various 1800cc variants and cylinder head design progressed along the way. If you are intending to fit an MGB engine or one of the similar 1800cc units, it is a good idea to know what you've got before deciding whether you want to spend money on it, for instance before getting it converted to unleaded petrol.

All B-series heads will fit all B-series engines but there is no point fitting one older than your engine. A later one, especially with bigger valves, may enhance performance but be careful fitting 1800cc heads to smaller capacity engines. IOf you choose a later version of the MGB head, you will need to relieve the top of the cylinder block next to the cylinder bores so that the valve edges do not hit it. Also, be aware that if you fit a head with a larger capacity combustion chamber, you will reduce the compression ratio unless you change the pistons to a flat-top or less dished part. Conversely if you fit a smaller combustion chamber you may create a compression ratio that is far too high for the engine to function properly.

Engine specialists Flowspeed have produced a very good article about identifying MGB cylinder heads. Click here to read it. Their main website is also worth a visit if you are interested in seeing what a specialist engine shop has to offer.