the mystery debris in the motor. (kawi 120) wtf

[m in sc]

So, my 67 kawasaki C2TR last week was being ridden, and out of nowhere, started stalling  and then just died. I go tit fired back up on the side of the road but def could hear 'something' in the motor bouncing around. figured for sure a chunk of piston broke off or a ring failed. Nope. pulled top end down, and while this piston had seen better days, there were no immediate failures except obviously SOMETHING got int he crankcases. I rebuilt the crank last year, well, the outer bearings. I have at least 150 miles on it since then, and found this. (see pics). prior it ran absolutely excellent all year.   whatever got in there was def metal, and the rod and wristpin bearings were fine as well. so, i had a spare ready to go top-end for it, so flushed out crankcases, looked in there with a borescope,  checked the exhaust and the carb and intake area, and found nothing. reassembled with spare top end, and it did the same thing inside of 2 minutes running.    no idea WHATS in there, but def taking the motor out and splitting motor see what the hell is going on. ive never had this happen and not been able to find it, especially on a single.    
 

[rearwheelslider]

My bike in the past had a crank bearing cage that was letting go over time. Looked very similar to this, pecking the piston and cylinder head.

[m in sc]

Im wondering, maybe. the crank bearings are brand new so while possible, unlikely but ive seen weirder things.

[Kawtriplefreak]

Damn

[747drvr]

does the rotary valve have any damage?? can't remember if it has needle bearings or not, but whatever caused that was hard metal!!!

[m in sc]

nope. i checked the disc thru the window in the crankcase  and didnt see any damage. I agree, def metal. Id swear it was a 2-3mm ball bearing by the marks it left,  but there's nothing that size in the crankcase or intake. its a fkn mystery as to what it actually is. i mean, i'll find it. one way or another. 

[Striker1423]

My snowmobile had plastic bearing cages and those exploded when I blew it up. Looked like crack all over the place. But, that won't be the case here...

I'd double-check that rotary valve Mark. I had a hole in the middle of mine on my sled once. I mean directly in the middle of the plate. Probably explained the weird sputtering the motor did at low revs. Looked like it wore through somehow. Probably had a bearing going out on the rotary shaft and it had too much play. Or, the 2t oil quit for a while to the plate, plate was warped. Who knows.

[m in sc]

beats me. the disc is right on the crank so i doubt thats it, and its a fiber material to boot. its a simple motor so tearing into it is pretty easy. soon, because its bugging the shit out of me.   

[747drvr]

i know you have probably looked already, but is all the ceramic still on the plug?? that ceramic is really hard and could cause some issues!!

[m in sc]

yes, still there. i thought the ground strap might have come off actually. nope plug ok

[1976RD400C]

Something with the air filter/air box come apart??

[Daytona1]

Man that sucks!Wrecking 2 top ends hurts. Been there with 2 Moto-villa's in the late 80s. Nice bikes never seen any before or after my 2. It was the Lower rod bearing and cage. Lost a bultaco pursang 175 after but stopped after the first top end. 

[SoCal250]

Ouch, that hurts. That sucks Mark. I'm interested to find out what turns up as the culprit.

[teazer]

I'd speculate that it's a big end cage starting to break up. It could be a main bearing cage failing, but more likely it's a big end.

[Dvsrd]

nope. i checked the disc thru the window in the crankcase  and didnt see any damage. I agree, def metal. Id swear it was a 2-3mm ball bearing by the marks it left,  but there's nothing that size in the crankcase or intake. its a fkn mystery as to what it actually is. i mean, i'll find it. one way or another. 

Are there any check valve balls in a separate lube system?