Topic: What's up with my pistons?

[zachiepie]

1982 cb650sc that was running very rough and powerless. The second cylinder wasn't firing but it was getting a spark. I had cleaned the carb and tore down the motor looking for problems. The pictures of the pistons are really the only thing I found. You can see the wear on the sides and a strange pattern on the piston head. I thought the head might be bad, but the shop I took it to said it was fine. Where do I go next? Piston rings?

[bryanj]

Looks like it was running with no air filter to me

[HondaMan]

It's hard to tell much from those pictures, but the #1 and #2 pistons show some minor leakage past the rings on the intake side of the pistons. This isn't causing the trouble you mention, though. That sort of trouble is more often carb- or spark-related issues.

[zachiepie]

Thanks for the tips! I also did a compression test and all 4 cylinders were low at about 60. I checked compression while tapping the valves and there was little increase (5 ish). Does that give a bit more info?

[lrutt]

You should have done a little more troubleshooting while all together. A little oil in the cylinders then throttle WOT would have given a clue on compression. A quick valve adjust and another run might have shown something different. At this stage, you are looking at checking bore and making a decision on just doing rings, cleaning up valves, putting it back together and checking the real problem, carbs and / or ignition.

[05c50]

Thanks for the tips! I also did a compression test and all 4 cylinders were low at about 60. I checked compression while tapping the valves and there was little increase (5 ish). Does that give a bit more info?

If all four were at 60, I doubt that it would run at all. My guess is that you have a faulty compression tester or did the test incorrectly. I'm afraid at this point, your test could be considered inconclusive, but the fact that all were even (60) is actually a good sign.

.......Paul

[BomberMann650]

#3 has some wear that would need addressed.  Check the wrist pin fitment while its apart. 
Honing and new rings are worth it.