socalmike_cb72
'80 Honda CB900C; '72 Honda CB350; '65 Honda C102
A few days ago I blew the piston on a cb350 and I want to get a better understanding of what could have caused it. Dropping about $500 into getting it fixed, and want to prevent it from happening again of course.
Here's a bit of background to the incident. This was the first time the bike was on the highway since the rebuild. Everything on the bike was redone except for the motor. Motor previously had great compression, so did not tear it apart. Was riding for about 15 minutes, 80 mph at the time when the left side went out. At the exact moment of power loss, first there was about 10 seconds of minor loss of power (20%), then suddenly left side went out completely and blowing smoke.
I'm not sure exactly what went wrong. One suspicion was that it was just too hot for it since it was near full throttle and maybe running lean. Main jets were reduced to 45 mains (from 50 mains). A different suspicion was the the exhaust might have been too restrictive as they are essentially straight pipes with a baffle inside. The baffle has holes in it, but restricts down to 1/2. Lastly after tearing the engine apart, the timing tensioner is all tore to shreds, but the valves show no signs of damage from hitting the piston.
So anyways, again, my guess is it's one of these:
-Overheated. Piston sized, and blew out piston
-Worn Tensioner. Threw off timing, and valve knocked out piston.
-Restrictive Exhaust. Pressure blew hole in piston.
New wiseco 66mm 10.5:1 compression pistons, gasket kit, and KA tensioner are already ordered. Plan to rebuild this next week.
Here's a bit of background to the incident. This was the first time the bike was on the highway since the rebuild. Everything on the bike was redone except for the motor. Motor previously had great compression, so did not tear it apart. Was riding for about 15 minutes, 80 mph at the time when the left side went out. At the exact moment of power loss, first there was about 10 seconds of minor loss of power (20%), then suddenly left side went out completely and blowing smoke.
I'm not sure exactly what went wrong. One suspicion was that it was just too hot for it since it was near full throttle and maybe running lean. Main jets were reduced to 45 mains (from 50 mains). A different suspicion was the the exhaust might have been too restrictive as they are essentially straight pipes with a baffle inside. The baffle has holes in it, but restricts down to 1/2. Lastly after tearing the engine apart, the timing tensioner is all tore to shreds, but the valves show no signs of damage from hitting the piston.
So anyways, again, my guess is it's one of these:
-Overheated. Piston sized, and blew out piston
-Worn Tensioner. Threw off timing, and valve knocked out piston.
-Restrictive Exhaust. Pressure blew hole in piston.
New wiseco 66mm 10.5:1 compression pistons, gasket kit, and KA tensioner are already ordered. Plan to rebuild this next week.