Motorcycle Repair: About piston and rings, stroke cycle engines, air screw

Question
Hi..Im from Malaysia, own a 2 stroke Yamaha 125cc bike...my questions are :-
1.Is it normal for 2 stroker's engine sound very noisy (rings noise i think) after 5 months of usage (mileage=10k)
2.My usual practice is to replace the rings only not the piston, is this a correct way?
3.Can innacurate carb setting & jetting lead to instant piston & rings damage.(factory set my air screw 1/2 turn only!)

Need your advise...regards  

Answer
Hi Zaldanzig,

Q:  "...Is it normal for 2 stroker's engine sound very noisy (rings noise i think) after 5 months of usage (mileage=10k)?"

A:  Yes, two-stroke cycle engines may make noises. I doubt the rings are the source of the noise. Rings are compressed and have little space in their grooves for movement. Engine failure would be imminent if a ring were defective as suspected.

Q:  "...My usual practice is to replace the rings only not the piston, is this a correct way?

A:  You can get by with replacing only the rings sometimes. It depends upon the amount of wear/defects to related parts. Measure related parts to learn the amount of wear and if amount of wear is within service limits. Replace piston, rings, and refinish the cylinder bore as necessary.

Measure cylinder compression and perform a leak-down test to determine the sealing properties of the engine/combustion chamber(s).


Q:  "...Can innacurate carb setting & jetting lead to instant piston & rings damage.(factory set my air screw 1/2 turn only!!!)

A:  I dodubt the air screw setting would cause a lack of lubrication to the cylinder and crankshaft. It may affect the throttle response, engine idle, and low RPM performance.

Check out a book titled: The Two Stroke Tuner's Handbook. This as a good resource. Although much of the material in this book is scientific, it has a wealth of information above and beyond the service manual.

Respectfully,
Mark Shively