Piston gone!

b wizzQ: I’ve had my BWS for five years now with no problems at all and, it’s still the best scooter ever made, even though Yamaha has stopped making them now.

Recently a ‘pop’ noise came from the engine and it locked the back wheel, which obviously means it’s seized! I had no idea why until I discovered the main jet was blocked with some sticky stuff, which is congealed fuel, I presume.

So I took off the head and barrel to discover the piston had a hole in it but the crankshaft assembly was covered and sprayed in aluminium debris, great!

The reason I’m writing is, I’ve asked many people how, or should I, clean out this mess. Some say just wash it out with petrol and rebuild the top end, others say split the crankcases and rebuilt the entire motor with new bearings and con-rod assembly. So what do you recommend?


A: We’ve seen riders blow up these engines whilst racing, and they just wash the engine out with petrol and ‘stick’ a new piston in, which isn’t really ideal for longevity.

If you use it a lot one way is to take out the whole rear end/engine and wash the engine/crankcase out with paraffin. We’d recommend removing the two crank seals and fitting new ones afterwards so you can get inside the bearings and finally wash out with petrol. Keep doing this until no debris comes out and rebuild with new parts and gaskets, then you should be good to go.










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