May 2018
I am somewhat averse to working on 'vintage' machinery. 'Classic' is my cutoff point - something to do with the era I was born into I guess.
However, I understand machines and I respond to people, so sometimes when they ask for help and I can understand the problem I put my own preferences on hold.
Such was the case with Tommy's Blue Star. It had been biting his leg since he bought it because it had no decompressor fitted, but should have. 500cc singles could wound you just as well in the 1930's as they could in the 1960's, so I figured there wasn't much difference.
I had always liked the twin exhaust look of the Blue Star, but girder forks and sprung seats are a bit archaic for me. Not to mention exposed valve gear. But I guess that was par for the course back when this beastie set forth on its path of mayhem.
We had a decompressor which had been repaired, although it had not been fitted in our experience, so there would be some trial and error, but it all looked promising.
This bike had suffered some hot starting problems which my friend had decided was a sticking valve, but when I began to strip the valve gear I found that there was about 1/4" clearance on the exhaust valve adjuster. Something had occurred with the rocker arm versus pushrod relationship, so there was some machining done, plus a bit more to arrange the interference between the decompressor and the exhaust rocker arm.
The 'box' which housed the rockers and decompressor is not pictured but bolts on above the centre of the head, leaving the outer ends of the valves exposed to the world. Apparently one was supposed to carry an oil can and give the hot bits a wee squirt when pausing in the natural flow of things. I don't think this happened a lot, hence the concept that a valve may be sticking. Instead I got the impression that the carb was in trouble and occasionally flooding, so that later got some attention.
It went back together better than it came apart, plus with a working decompressor. That is the aim of the exercise after all. I was not excited by the process, but it made sense.
I suppose that is why I prefer to work on the bikes of my choice. They excite me, and that brings out my best work...