Post Master General
Join Date: Apr 2012
Location: Bowling Green, VA
I Ride: '09 ZX6R
Two stroke engines fire every time the piston approaches top dead center. Twice as often as a four stroke. No valves. Very simple, extremely light, and they produce a lot more smog than a 4 stroke. No valve train means the engine is much more compact. Power is very roughly equivalent to near twice the 4 stroke displacement.
The fuel\air mix is pulled in through a port in the cylinder wall, and exits another port. That's two fairly large holes in the cylinder wall. That beats up the rings much more quickly than a four stroke does. Also blows a lot of rich mixture out the exhaust....
Because the cylinder gets doused in the un-burned fuel, it rinses away the crankcase oil that would lubricate the rings. 2 strokes require oil in the fuel to lube those rings. Some bikes do this automatically, metering oil for you. Many more require you to pre-mix it before you fill the fuel tank.
All that fuel washing away oil films is tough on plain pressure fed bearings.... 2 strokes by and large use roller bearings instead. Roller bearings wear more quickly than plain bearings will.
All of that means long term ownership should include learning to replace rings and roller bearings -- not anywhere near as critical for a kid's tiddler mini bike as it would be on a full blown race bike.
"Basic stuff fellas. Use your head for something other than to break your next fall."