This topic has been beat to death!!. No matter what is said theres people who believe just because its a "yamaha" it doesnt need rings, well nothing could be further from reality, sure.... they will run along just fine and show you no problems with alot of miles on them, but ANY brand 2 stroke engine will have blow by and not be making the power it did when the rings were sealing and not letting blow by escape into the crankcase.
You see a 2 stroke engine pistons and rings takes a beating, they get pounded 2 times more then a 4 stroke does. Theres no valves, camshafts, etc to wear in one, the piston is your valve, it is what opens and closes the ports, the rings must seal off the ports from one another and they also stabilize the piston in the bore, this is how the rings aid in piston wear. When the rings begin to lose their tensile strength they lose thier tension and begin to destabilize the piston, this leads to blow by escaping past the rings to the fresh intake charge below in the case. It also allows the piston to rock back and forth in the bore, this leads to skirt wear and skirt breakage if let go long enuff.
Why is the blow by problem important? because heat is the number one enemy of a 2 stroke engine, if you dont think so,.... then take your sled for a ride across the field this summer when its 50-60 degrees out, and see how fast it will run, do the same run when its in the 20-30 degree range.......why was it slower???, because heat makes a 2 stroke run richer, and richer is less power output plain and simple, this is how the blow by affects the engine, it heats up the fresh cooler inlet charges below, not to mention its not pure anymore either, theres now some exhaust mixed in it. Another thing that happens is the negative pulse thats returned by your pipe is weaker because the positive pulse is not as strong exiting the pipe, because you lost some of its energy below the rings into the case.
a 2 stroke engine makes more power then a 4 stroke of the same size, they are also half the weight of a 4 stroke but theres a reason we dont have 2 stroke cars, they need piston ring maintance done on a regular basis to keep them running clean and up to its power potential!! Can you imagine having your car taken to the local dealership every 3000 miles for a ring change, every 8000 miles for new topend??
you guys have to make your own decisions on what to do with your engines, if ya wanna run em to 10,000 miles and not do anything, go ahead, but when ya cant seem to get the speed you used to out of the old machine, I would begin looking at the piston and rings!!!!
Just because its a yamaha means nothing as to the miles it can be ridden without proper maintenance!!
