Scooterotica

Why can't cranks be built using tapers and woodkeys on the pins and webs(a la flywheel taper)? Bolt them together with a recessed nut and bolt and surely no more crank twisting problems.
Thoughts?

Price I guess , more parts more to go wrong , not much room around the pin for other things , balancing issues , im happy to tig weld mine

dirtyhandslopez wrote:Why can't cranks be built using tapers and woodkeys on the pins and webs(a la flywheel taper)? Bolt them together with a recessed nut and bolt and surely no more crank twisting problems.
Thoughts?

That's going to need a fair bit of additional engineering to allow for fitting a puller to break the taper when the bearing needs to be changed. For OE applications, so long as the interference fit is as intended then the press fit is a completely viable solution.....it's when we start feking about with the poor things that it starts to go wrong

Tapers were the abomination of most old knacker brit bikes. Eventually they would twist as you increased the power.
Plus they were a bugger to assemble.
I'm not sure many (if any) had keyways as it would a) make assembly even more difficult, b) be a permanent stress raiser.

Most people making replacement cranks for go faster old bikes use a parallel pin. Modern production methods and equipment and improved detail design mean they hold together well.
Phil Pearson http://www.bsagoldstar.co.uk/price_list/price_list.htm note £875, or ABSAF http://www.absaf.nl/index.php?content=p ... selector=5 for BSA Gold Stars
Greg Sommerton for JAP Vtwins http://www.eurospares.com/greg.html

Works Norton went one better and produce one piece cranks for Manx's at £1400 each. A whole engine is £11500. All their engine parts are CAD/CAM, no castings.
Andy Molnar is similar in price, although his are built up.
Actually, considering the number of parts, and quality of execution, not to mention the days required to assemble one correctly, add to the fact they are truly raceworthy/potential race winners straight out the box, almost seems a bargain compared to some of the Lammies we've read about on here.

All the above are bought from the guys making them, there are no middlemen and wholesalers creaming off the profit.
None are cheap, perhaps the reason lambretta cranks twist may have something to do with the economics.

Re Coasters comments, absolutely true. And there are only so many split and re-presses in there in the first place, however good.

The best current answer is to start saving for one of the uber casings with thicker, larger diameter cranks.