Deep inside my Martinsyde
With major progress on this eccentric motorcycle’s engine imminent, Rick reflects on its innards
My last mention of the Martinsyde was to own up to failing miserably in my attempts to weld the cracked crankcase. Well, just before Christmas word reached me that the new and improved casting is ready for collection at the foundry. Of course, that’s only the beginning of the story, the next step is machining it to fit and I hope to cover what goes into that in the near future but in the meantime, I have been marvelling at the work inside that gave a dear old vintage sidecar twin the power to destroy itself.
Originally my bike had been a ‘Quick Six’, the 736cc big brother to the standard 680 twin, the extra capacity coming from a longer stroke (96mm) crank. Since only one of these cranks survives, when specialist Chris Tait built my engine he had to find an alternative. By getting Alpha Bearings to make custom mainshafts to suit the Martinsyde crankcase, he was able to adapt a (97mm stroke) Harleydavidson 45 crank to fit, coincidentally side-stepping another Martinsyde issue – the high and tiny diameter gudgeon pin that hindered fitting alternative pistons. The Harley crank has a stronger big end and shorter rods with larger small ends that accommodate various pistons – mine are from a 250cc Triumph, giving 767cc.
To me, half the appeal of the Martinsyde is Chris Tait’s 70 years of dedication to promoting and improving this obscure and eccentric motorcycle and it’s a great honour to take up the challenge in his absence. Yes, I screwed up trying to repair that crankcase, but Chris did things he regretted – like chopping up the last surviving Quick Six to make a sprinter. I just wish he were alive to see us casting stronger crankcases, I don’t think he’d have dreamed this day would ever come.
‘I HAVE BEEN MARVELLING AT THE WORK INSIDE’
Rick’s Martinsyde engine has had a crankshaft swap which allows alternative pistons to be fitted
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.