Delighted to report the engine for my 1968 ISDT machine is now fully rebuilt. My good pal Pip Higham did the work to his usual high standard and I'm confident this motor will perform well. I've got two engines for this bike, the original 4speed unit (which production bikes were equipped with) and I've also got one of the ultra rare of 5 speed works engines. This is a particularly tricky project and so to keep things simple we decided to rebuild the production 4 speed engine which should be adequate for the long distance regolarita type events the bike will be used for. At some stage in the future I'll resurrect the works engine but for the time being it can stay under the bench along with all the other future headaches...
During the rebuild Pip unearthed some curious things about these unusual little motors and I thought I'd share the most interesting/important one here because if you've got one of these bikes in 150cc form or the American Eagle/ Garelli equivalent this info might be critical. The 150cc units can be identified by a spacer plate fitted under the barrel which helped provide the extra capacity. This spacer is the important bit.
The engine strip revealed excessive wear in the valve gear and so when Pip was carrying out final assembly the unit was spun up on the bench using an electric motor to drive the crank to check whether oil was getting to the parts it needed to. Sure enough no oil appeared to be getting through to the valve gear. After much head scratching the culprit was traced to the factory spacer plate which was masking the oil supply gallery from the crankcase to the barrel. I've got three of these blanking plates and they're all identical and they all block off the oil supply to the barrel and therefore it's probably safe to assume this is fault with the original manufacture. If you've got one of these motors I'd suggest it's vital to get this checked.
Pip's solution was to mill a groove into the spacer to allow the oil to travel up to the feed in the barrel and the pump now delivers a reassuringly healthy supply of oil to the valve gear.
During the rebuild Pip unearthed some curious things about these unusual little motors and I thought I'd share the most interesting/important one here because if you've got one of these bikes in 150cc form or the American Eagle/ Garelli equivalent this info might be critical. The 150cc units can be identified by a spacer plate fitted under the barrel which helped provide the extra capacity. This spacer is the important bit.
The engine strip revealed excessive wear in the valve gear and so when Pip was carrying out final assembly the unit was spun up on the bench using an electric motor to drive the crank to check whether oil was getting to the parts it needed to. Sure enough no oil appeared to be getting through to the valve gear. After much head scratching the culprit was traced to the factory spacer plate which was masking the oil supply gallery from the crankcase to the barrel. I've got three of these blanking plates and they're all identical and they all block off the oil supply to the barrel and therefore it's probably safe to assume this is fault with the original manufacture. If you've got one of these motors I'd suggest it's vital to get this checked.
Pip's solution was to mill a groove into the spacer to allow the oil to travel up to the feed in the barrel and the pump now delivers a reassuringly healthy supply of oil to the valve gear.
