Tales from the classic world
Rick’s actions – and inactions – lead to a puzzling period with his Rex Acme
LAST MONTH I mentioned that the lack of power from my Blackburne ‘Scarlet Runner’ (Rick Rides...) was due to valve timing after the crank pinion slipped its (unkeyed) taper. This month, I went to fire up the 1923 Rex Acme and this time it was the other side; reverse shock from a backfire loosened the big outside flywheel, leaving it spinning uselessly on its crank taper. The wheel’s taper is worn and has been bodged with shim stock; it needs sorting but has held until now. As I re-tightened the nut, I made a mental note to check and nip it up occasionally – and maybe use an air rattle gun to get it really tight. Care is needed, as air power can twist a shaft in its flywheel, although Blackburne forged their shafts and crank webs in one piece, so it’s less risky. As it happened, I couldn’t find the right socket anyway.
Trying to start it a few days later, it wouldn’t go – and looking down, the valves weren’t moving. Dammit, obviously like the Runner, the crank pinion must be slipping. With the timing cover off, I turned the flywheel and yep – the crank pinion stopped moving when it met valve-spring resistance.
Strange that the pinion bolt was still tight – so tight in fact that reaching over the tank to hold the flywheel against the engine turning, it started to slip – had the taper really had it now? But no, I’d forgotten to fully tighten it.
WHO IS RICK?
Rick Parkington has been riding and fixing classic bikes for decades. He lives and fettles in a fully tooled up shed in his back garden.
Having removed the bolt there was another surprise, though – it took a puller to remove the pinion that was supposed to be loose – and worse still, unlike the Runner, it has a locating key that was undamaged. What? How could the pinion slip…? Oh, don’t say the shaft’s come loose in the crankweb? But how can it – it’s a one piece forging? Ah, unless the shaft wore out sometime and was replaced with a pressed in one. There was only one way to find out...
But before tearing it all apart to check this unlikely chance, I screwed a hex bolt into the end of the crank and, having secured the flywheel on the other side, applied heavy spanner force – including shock loading from a hide mallet. But the shaft didn’t budge. Something didn’t seem right...
Remember I said I had to tighten the flywheel nut earlier? Fool that I am, I’d gone off looking for that socket and got distracted, leaving the flywheel tight enough to turn the motor but not against resistance. It was the crank that stopped moving, not just the valves!
There’s two morals here. One: F
