Performing seals
Brian Steers admits to going against his better judgement by buying a cilliers-engined bike. It’s a 1926 Royal Enfield 201, Enfield’s popular 225cc lightweight of the vintage era – but Brian’s has acquired a cilliers 9D twin-port motor somewhere along the road. This was cilliers 1930s/’40s 125cc hand-change three-speeder; being a cilliers lover myself, I know it’s a smashing little motor that probably makes a good conversion with decent torque and a top speed probably about the same as the Enfield motor. Despite himself, Brian agrees: “It’s actually quite a nice little thing, but it won’t fire up on the kickstart – although it bumps easily. I’ve cleaned out the simple carb, compression is good and although the Champion K7 plug could probably do with replacing, it has a great spark. Am I missing something?”
Well, what about primary compression, Brian? Typically, the first symptom of failing crank seals is poor starting and low-speed running, because the faster the engine runs the less the loss is felt. Think of it like pumping a punctured tyre – slow pumping does nothing, but if you pump fast enough you will overtake the leak and the tyre will inflate (until you stop, obviously). Compression is the same – at kickstart speed, a compression loss will be more troublesome than when running. Bump starts turn the engine much faster and for longer than a kick.
I think these engines had bronze crank seals which work perfectly well with these low-compression engines and and are easily replaced. But problems can arise if the bush has worn the crank itself, in which case new bush seals will be only a partial cure. If the seals are leaking, my guess would be that there will be black oil staining inside the primary chaincase and around the back of the magneto backplate. Parts for the engine should be readily available from cilliers Services (01384 265797).