Motorcycle Repair: 1998 Yamaha PW80 Broken Rings, bikebandit com, bike bandit

Question
My Sons 1998 Yamaha PW80 piston rings are broken. The Piston has  some deep gouges on one side in the ring grove area that run vertically. They are about 1/4 wide and about 3/4" long.The pins in the ring grooves are both in place. There are no marks or scratches at all on the cylinder wall. The exhaust port inside the cylinder has a rough burred edge.On disassembly after removing the Cylinder head the Piston could be twisted back and forth about 1/16".The rod needle bearing on the wrist pin was intack but seemed to have some excessive play.The rod rotates freely with the crankshaft.
My question is this: What caused the rings to break? Does the engine case have to be completely split apart to remove the piston rod from the crankshaft?If so any tips that will aid with disassembly?  I a hoping to be able to just replace the piston,wrist pin, rings, and rod bearings and smooth up the rough edge on the exhaust port.what do you recomend? Thanks for your help! Bigcarpontiac@aol.com  

Answer
Hi Mark,

Q:  "...What caused the rings to break?"

A:  I suspect the worn parts caused the burr and/or caused a ring to snag the burr and break.


Q:  "...Does the engine case have to be completely split apart to remove the piston rod from the crankshaft?If so any tips that will aid with disassembly?

A:  I refer you to get a copy of the service manual. Review the procedures involved. The cases need to be split to access the connecting rod big end, if necessary.

Visit "www.bikebandit.com" or "www.yamaha-motor.com" to view parts michrofiche. Compare parts prices at Bike Bandit.


Q:  "...I a hoping to be able to just replace the piston,wrist pin, rings, and rod bearings and smooth up the rough edge on the exhaust port. what do you recomend?"

A:  Measure cylinder, rod ends, wrist pin, etc.. for wear. Replace parts that are worn out of service limits or that are otherwise defective.

I think your plan of repair is the right approach. Measuring engine parts will tell the integrity of parts. Replace or repair worn parts accordingly. For best results, work and measure accurately and patiently.

There are websites dedicated to the PW50/80. They are great respources for parts and tech advice. Serach internet using PW80 keyword combinations to see the website links.

Respectfully,
Mark Shively