I am new to posting to the forum but reading old posts has helped me a lot, thank you all.
I have a 70 A65 L that I recently acquired as a project. This is my first BSA. The engine was supposedly refreshed by the previous owner. Not sure exactly what that involved or what his level of expertise and attention to detail were, but I have the old bearings, valves, springs, rings in spare parts box so I am assuming at least that much. Has AMAL
930s and I just installed a Boyer
mk 4 setup. New battery
and wiring harness.
I had it running really well, but had only ridden it half a block at a time while I was working out brakes, clutch, timing and carb adjustments. The other day I decided to take it out for a little longer ride (a few miles, at around 45mph), and it was running great out and back until I got to my driveway, at which point there was a terrible metallic ping followed by what sounded like metallic grinding sound in proportion to engine speed. For the short trip up the driveway it was popping and backfiring on what sounded like every other cylinder, and I shut it down immediately.
I am concerned about a spun bearing based on the awful sound of it. However after reading some posts and checking some things, the following is what I found:
When I lever on the crank end at the stator nut using the footpeg for leverage, I get no appreciable movement on any of the 6 faces.
When I put a stick into the spark plug hole and push on the piston as I spin the engine, there is no binding, catching or dropping on either cylinder.
The crank rotates by hand smoothly and without making the terrible grinding noise I heard at the end of the previous ride.
I drained the oil at the sump plate and there are no metal flakes in it., or on the magnetic plug. It was new oil and I could see clearly through it with no glitter.
When I used the kickstart lever to rotate the engine, it has a point maybe every 180 degrees that feels very stiff, as with very high compression all of a sudden.
Of course after just having gotten it into rideable condition I am not really excited to do a complete teardown, but if it is a bearing or the like I would prefer not to completely grenade the engine. I suppose it was lucky that at least it happened in my driveway and not on the main road.
I would appreciate any further investigation you would suggest before I start disassembly.
Thanks for your time.