Cylinder Head & Valves
(see also the Cylinder Head & Valves mk2 page)



Special Devices Dept.

Sooner or later the cylinder head will need attention. It's a good idea to do some inspection work even if all seems well, especially if you do not now the history of the engine. The A10 rocker box looks like one of those everlasting inventions, as long as the oil supply is right. I've change the tappet adjusting bolts & nuts to some  very light allen-type from SRM, as the originals square-headed bolts were quite destroyed & difficult to adjust..

Loosen all 4 tappet adjusting bolts, then loosen the rocker box, 5 screws & 4 nuts. Loosen the 9 head bolts in sequence, a little at a time. Decarb the combustion chamber with a rounded knife, the deposits gets quite soft if left to soak for a while in some degreaser or petrol (keep the plugs in). While the combustion chamber is filled up you can check for leaky valves. If the liquid flows out quickly trough one or several valves remedial work is definitely needed.

Regrinding the valves is the first thing to try. Remove the valve with a suitable valve compressor tool (I use an inexpensive slightly modified car valve tool) then grind it for a short period with a fine grinding paste. Any serious pitting will quickly show. If deep pits are apparent it's better to go for new valves than trying to grind the damage away, as too much grinding will recess the valve into the head. In my case I will have to get a set of new  valves, new springs & new guides. May just as well go for a total overhaul with lead-free inserts. For the moment I grind them a little and continue driving while I evaluate what to do & when to do it...

Clean the valve stem and valve guide, scraping away all carbon deposits. Then insert the valve in the guide & check for play. If excessive (everything over barely noticeable) new guides and\or new valves are needed. Worn guides will among other things draw oil from the top into the cylinder. Check the springs' length. Weakened springs will give trouble at higher rpm. Make 100% sure the valve locking collets are properly in place, you may not want to find out what happens if a valve falls into the cylinder while you're doing 80 mph. Check the pushrods for straightness.

If possible soften the copper gasket by heating it with a blowtorch then plunge it in cold water. Tighten the bolts according to the book, in sequence & evenly to avoid bending the head, then finally make them "real tight", as it says in the BSA service sheets. Someone on the Yahoo BSA group recommended 32 lb\ft, tightening the bolts in sequence with 5 lb\ft, others mentioned up to 50 lb\ft. Will try 32 lb\ft and see if it's oil tight.

When refitting the rocker box you will desperately need the pushrod aligning tool. Right tappet clearance seems to be .010 in and out for the early 50's model, although I've seen .010 in and .016 out listed some places. Needless to say, adjust clearance on a cold engine. Recheck the clearance after some time, after retightening the rocker box screws as the new gaskets compress slightly.

Tightening Sequence. Reverse when removing head.