Motorcycle Repair: troubleshooting piston and rings,other nternal parts for damage, main bearings, cylinder wall

Question
heard engine noise and possible miss,tore down engine.oil was terrble cond. and tops of pistons covered with black deposit,and a couple of rongs look bad.a small mark in one cylinder wall.troubleshooteing advice please.thank you

Answer
Once you have the parts cleaned up, evaluate the score in the bore, if it is just a discoloration, you may get away with it but if you can feel it with your fingernail then the engine will smoke on reassembly.  It may be best since you have the whole thing torn down to have it bored one size over, and use one size over rings and piston...  Depends on your budget.

Black deposit on piston is not unusual, worried that the problems you found do not cause a knowck, you need to check the main bearings and big-end bearings.

Good luck,  Jan