Narrowing it down
Andy Wadman emailed for advice about the crank of the 500cc Triumph engine he’s just started building. He says it needs a regrind, but has two questions. First, the timing-side main bearing has some damage that he doesn’t think grinding will completely remove, and second he asks why
I think the width of the flywheel has been significantly reduced.
There’s two ways to look at nicks in bearing surfaces. On one hand, so long as the journal is ground smooth they can just be oil pockets that cause no harm, on the other they are ‘stress raisers’ that could propagate cracks. The alloy Tiger 100 engine in my TRIBSA scrambler has a crescent-shaped ding in the big-end journal from where it threw a rod when dad scrambled it in the late ’60s. I’ve taken a chance on that and so far, so good. With Andy’s timing-side journal it’s different; this is a main bearing and subject to less stress than a big-end (as well as being stronger), so as long as the damage doesn’t form a channel for oil to escape from the bearing I’d say it’s no problem.
I’d guess the flywheel has been narrowed to make the engine revvier. My old 5TA had a lightened wheel and was quick off the mark – but lacked torque compared to others. Mine was reduced in diameter; width is better because a large diameter, light flywheel has greater effect for its weight than a small, heavy one – that’s why Blackburne, Douglas, Moto Guzzi and others used big outside flywheels. By reducing width you minimise the loss of flywheel effect that was noticeable on my bike.
Well, it seems that the worst effects of the pandemic are behind us. I’m not so sure we have seen the end of this curious virus... by the time you read this, I guess we’ll know. But one thing we’ve all missed is riding our classic bikes – and what surprised me were people in club magazines saying they’d thought about a ‘shopping trip’, but didn’t think the police would be convinced if they were on a vintage bike.
Why pretend? I enjoyed a pleasant weekly ride on quiet roads to the butcher’s and supermarket on my 1936 Rudge. I would have been equally happy to take the 104-year-old Blackburne – it’s perfectly capable of the 20-mile round trip in any weather. It did at least that in a torrential downpour on last
‘I ENJOYED A WEEKLY RIDE TO THE BUTCHER’S AND THE SUPERMARKET’
year’s Ixion Run. I did my shopping by bike for years, but when you get a car you fall out of the habit; equipped with throwovers and tankbag, the Rudge carries a surprisingly large quantity of groceries and even my weekend beer didn’t get too boisterous over the bumps!
Why wouldn’t anybody seize the opportunity of a perfectly legitimate run out? If even owners’ clubs don’t regard their bikes as practical, it’s hardly surprising they can’t attract young members.
I’ve managed to live without a modern bike for my entire 40 years on the road. OK, I don’t have to do much motorway work – and if I did, I’d choose a classic from the motorway age, maybe an 850
Guzzi. But come on, local shopping?!
A Honda 50 can do it and so can anything else made in the 20th century – if it’s properly sorted and maintained. I’d say this has been a perfect time to get out on any classic bike and make it do what it was built for – work!