I purchased a 66cc chinese motor in Australia about 12 months ago. I put it in my backpack (weighs about 9kg) and travelled home to Africa. My Schwinn sierra is a great bike & I didn't want to butcher it so I purchased a 2nd hand mtb for about $35USD. I mounted the motor on the bike.By the way I have about 20 years experience in motor bikes, have supercharged a 50cc four stroke, made expansion chambers using the water method ,had fancy cams ground ,ported 2 strokes, bored out liners etc. etc. The motor lasted about 2-5 RPM before seizing up!!
I stripped it to find a loose woodruffe key (spelling?) inside the crankcase wedged between the case & the crankshaft !!! It didn't belong anywhere it was just a loose key.
Whilst stripping the motor -using wooden drifts to knock the crank out of the housing I managed to cock up the threads for the 1st time in my life - on both side of the crankshaft!. I was bitterly dissapointed in this piece of chinese rubbish. I rebuilt the motor-using a very strange imperial set of crankshaft seals which were only single lipped & not a true labyrinth seal (nothing else available).
I was also dissapointed that it was a bushed motor....
anyway, after a careful re-assembly & run in I am surprised at how well it runs! Yes I saw the ports didn't match, the piston didnt uncover the inlet port fully,the exhaust port os badly cleaned up,there was no dowels in the case or barrel,the gaskets are rubbish etc. Yet it starts great, runs at full throttle easily & willingly produces a full usable power.
Yes the gaskets weep, but overall I'm surprised at how the motor seems to be doing it's job.
I know in the old days with car motors they expected a 20% loss on hp between the blue prints & the final product.
My question is... Is it really worth the porting etc discussed on the forum. Its NOT a high performance motor- & NEVER will be. Why can't someone just make a proper version rather than try & fix up an inheritinaly flawed design. Its not actually flawed its just detuned... for the sake of the quality of the material, the tolerances, etc.
I have lots of russian model aircraft engines. Designed like a ferrari with the tolerances of a ford & the materials of a wheel barrow.....
Is it worth it?
Cheers Simon
I stripped it to find a loose woodruffe key (spelling?) inside the crankcase wedged between the case & the crankshaft !!! It didn't belong anywhere it was just a loose key.
Whilst stripping the motor -using wooden drifts to knock the crank out of the housing I managed to cock up the threads for the 1st time in my life - on both side of the crankshaft!. I was bitterly dissapointed in this piece of chinese rubbish. I rebuilt the motor-using a very strange imperial set of crankshaft seals which were only single lipped & not a true labyrinth seal (nothing else available).
I was also dissapointed that it was a bushed motor....
anyway, after a careful re-assembly & run in I am surprised at how well it runs! Yes I saw the ports didn't match, the piston didnt uncover the inlet port fully,the exhaust port os badly cleaned up,there was no dowels in the case or barrel,the gaskets are rubbish etc. Yet it starts great, runs at full throttle easily & willingly produces a full usable power.
Yes the gaskets weep, but overall I'm surprised at how the motor seems to be doing it's job.
I know in the old days with car motors they expected a 20% loss on hp between the blue prints & the final product.
My question is... Is it really worth the porting etc discussed on the forum. Its NOT a high performance motor- & NEVER will be. Why can't someone just make a proper version rather than try & fix up an inheritinaly flawed design. Its not actually flawed its just detuned... for the sake of the quality of the material, the tolerances, etc.
I have lots of russian model aircraft engines. Designed like a ferrari with the tolerances of a ford & the materials of a wheel barrow.....
Is it worth it?
Cheers Simon
