It all started when I noticed that my BSA M21 had ceased charging. “Bugger,” says I , time to check the electrical system. Having established that the wiring was OK I decided to check the dynamo output. This requires the engine to be running - so I prepared to kick-start the bike. As I lunged downwards on the kick start a loud crack came from the gear box and the kick start arm failed to return. The return spring had snapped! Damn and blast! This required the faceplate to be removed from the gear box to replace the broken spring. BUT to reach some of the face-plate bolts required the exhaust system, the footrest and the gear lever to be removed and as expected the very final face-plate bolt would not budge. Even Graham couldn’t shift it - so it had to be drilled out. THREE days later a new spring and new bolts and rubber shock pad had been fitted and the engine was started in readiness to check the dynamo. OH MISERY!- vast volumes of black smoke emerged from the exhaust and filled Nan’s sacred kitchen with evil-smelling fumes - the bloody bike was wet sumping , something it had never done in all the years we had owned it! After enduring a lengthy bollocking from Nan, a quick consultation of the handbook showed this could be the result of the sprung pressure-release ball valve in the timing cover getting fouled up - so off had to come the timing cover in order to clean the valve -but the cover wouldn’t shift! The previous owner had glued it on with some black tarry stuff and it took over an hour of tapping and levering to get it off. Having drained the sump and cleaned the valve, the timing cover was replaced and Graham came round to help start it. OH DOUBLE MISERY! When the fuel tap was switched on, highly flammable fuel spewed out of the tap in an unstoppable stream all over the dynamo commutator. (good Brit design there!!) Furthermore, the carburettor float had also stuck and was hosing the engine with fuel. It was impossible to proceed further because of the fire risk! We have now cleaned out the float chamber and are currently waiting for a new petrol tap and new carb gaskets before we start right back where we were two weeks ago - to test the dynamo!! What’s worse is that my wallet is fifty quid lighter and we haven’t even started on the charging problem! Who would think that such a small task would escalate so monstrously! But I bet you’ve all seen it many times before.
What a lovely story of a bike you luv so dearly. Now I remember and miss my old M21 which I rode for 2 decades. Funny eh... it had both generator and alternator as it was an ex AA radio Patrol bike so I used a 12 A65 alternator for light... So I did not encounter problems such yours
Well after burning a exhaust valve real oval and piston on a hot long trip with the whole family on it while restoring the engine I found two allen keys and a long withworth screw in the oil sump. Forgotten there by the prevoius owner probably after a few pints...
Grandad, might I suggest the reason your dynamo isn't throwing out leccy, is that very leaky petrol tap lad? I'm reminded of Chug-a-Bug my M20, that too had a leaky petrol tap, and the petrol cleaned off all the crud from the dynamo. Then dumped it all on the copper strips on the round thing in the dynamo, that spins to make the leccy. Hope that's not too technical for you?
Hey Morgan, I know the burnt-out exhaust valve problem well, because many years ago I had a chair on another M21 and it used to burn out exhaust valves like there's no tomorrow. But I loved that outfit.
I have learned that old Brit bikes are like used race bikes, best to strip the engine/gearbox at least down to the last nut and bolt and rebuild to the best standard you can achieve. A major gasoline leak inside a house would concern me, fuel/air explosives are best left to the military.