Thread: 50cc or 80cc
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Old 10-10-2009, 03:28 PM
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2door 2door is offline
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Default Re: 50cc or 80cc

I probably shouldn't comment here because I only have the bigger engines but I will say that they are all as different as night and day. Two of them are from the same vendor and one from another source. The engines, outwardly, are identical. No difference that the eye can discern. The difference is how they run. One, the oldest, and by the way, the most expensive, will top out at about 24mph with my skinny 140 pound butt parked on it and a 44T sprocket. The next oldest runs a little better and has almost no vibration. It pulls through a 41T and is faster on the flats. Then we have the third one. It simply hauls. Vibrates like a, well, a vibrator, and will pull me from a dead stop, no pedaling and also running a 41T, has a confirmed top speed of 34. (I hate to say that 'cause it will surely start something) Nevertheless, it does run good.
So...I was curious. "What is the difference between these three engines?" I asked myself. Same bore, same stroke, same carburetor, ignition, fuel, etc. What's so special about this one engine that makes it run circles around the other two.
Ignition Timing. I made an adapter to fit my automotive cam degree wheel and used it to check magneto rotor (magnet) position relative to the coil based on piston position or top dead center, TDC.
The best running engine is a full 2 degrees advanced over the next best one and 3 degress over the weakest engine. My conclusion: The factory cuts the keyway in the crankshaft that positions the magnet roughly, or, 'in the ballpark' one, two three or possibly more degress difference probably isn't much in the Chinese version of quality control, but it apparently has a huge impact on the way an engine performs.
Anyone else ever taken a look at magnet position, timing, on their engines?
This discussion has been up before but there were never any real conclusions or confirmations so I'm relighting the fire.
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