Casting around for refinement
The cases for Rick’s Martinsyde Sprint bike have arrived, but there’s plenty more work to do yet...
Remember a while back I mentioned an unfortunate disaster involving my vintage Martinsyde sprint bike’s crankcase? Well, at last we have the raw castings to make a new and improved set.
These cases have been cast in a superior grade of aluminium to the originals and heat treated; plus they have additional buttresses to support the main bearing. Chris Tait, the bike’s creator, had such reinforcement welded onto the original crankcases but as you can see, a fire ten years ago rendered these unusable and the standard ones I’ve been using to date cracked around the main bearing after some spirited riding.
Looking at the dimension of the Harley 45 flywheel Chris fitted, my mate Bruce Hazelgrove (who sorted out the casting) reckons we don’t need to bore out so much material from the inside of the cases as on the originals, so they will actually be thicker. The only issue there, on a total-loss lubrication engine, is that the crankcases are essentially a (minimal) wet sump design, so Bruce is going to offset the machining to provide increased flywheel clearance at the bottom, where there is no real loading, giving a reasonably capacious oil sump. Unfortunately this is all going to cost. The crankcase castings already set me back £500 for the pair and the machining job is complicated, well beyond the resources of my ability and machinery – and that’ll be more expense. But at the moment the bike is way too powerful for its bottom end. There were two options: ride it slower or cough up for quality crankcases. As far as I’m concerned, there was nothing to discuss.
‘THE MACHINING JOB IS COMPLICATED, BEYOND MY RESOURCES AND ABILITY’