Funny, most of my friends think I'm crazy to get 2 Chinese quads. The more I look at them, its like an adults version of a box of Lego!
On these engines, are the gearbox ratios identical - leaving the overall gearing for each engine size in the hands of the sprocket and rear drive shaft gear set?
I've tried a bunch of google image searches without much luck. When I crack this one open, I'll post a hundred photos for the next guy to look through! Hopefully the sound is a easy one to diagnose. That'll be a while though. lots of more important gremlins to kill 1st.
Kelly