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

[m in sc]

there is a check valve but it would be impossible for it to get out you can see the nozzle on the intake, in the case, it was in place.

I would lean towards big rod bearing as well, but no sign of it coming apart, the rod play is basically nil beyond stock. as far as a main bearing, not sure, i replaced them in march last year.  its possible i had a defective one, but I get the feeling something just got left in the case and eventually got sucked in, maybe via the air filter track? 

there also was no abnormal noises leading up to it before the failure, both times. only after whatever is in there was bouncing around.

Im going to pull the motor out in a day or 2 and bring it home, set it on the bench and go thru it soon.

heres when i changed the main bearings 3/23


 

[m in sc]

either way, new piston, rings, etc on way wont show up till the end of the month. also going to helicoil the head studs since a few feel 'suspect' when torquing down. (never had a leak but it is 57 years old). this gives me a few weeks to invesitgate and rebuild any crank issues i might find. luckily the rest of the motor is tip top (trans, clutch, etc).

[rodneya]

Im kinda surprised you dont have it all stripped down yet.

[m in sc]

well, its at work at the moment in the warehouse. I'll pull the motor out in a few days, take the motor home and throw it on the bench. I just ordered a spare crank as well just in-case there's something really wrong w the one in it.   I have spare gasket sets already, etc. Ive had this bike 11 years or so, so it's def not going anywhere. 

[Striker1423]

I have to probably pull the head off the GT750 and put that massively oversized spare gasket I have in place of the cometic one since it's leaking again... But its cold in the garage and the house needs work. I will probably wait 'til  its good and warm in the spring or summer. Procrastination at its finest.

[m in sc]

pulled motor at lunch. going home tonight with the last batch of 2sw shirts (in box) I picked up on way in to work today.

 

[m in sc]

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.

we have a winner. rod bearing cage failed and was ejecting rollers.

[Dvsrd]

It is always great when you identify the problem!

I really would like to have a rotary valve single, BTW....
175 to 250 would be perfect.....

[m in sc]

i really like the kawi a lot, its a great engine design.

[Dvsrd]

i really like the kawi a lot, its a great engine design.

The only Kawasaki singles I ever worked on, is the KE/ KH100 models from late 70s to mid 80s. The only questionable design feature on those was that the LH end of the clutch shaft, and the RH end of the countershaft ran in Brass bushings, not ball or roller bearings. Is yours the same way?

[m in sc]

no, they are all ball bearings. Its interesting, the C2TR and C2SS 67-68-69 IMHO wa s away better motor design than the later ones.

the G3SS for example, was a turd motor design (by comparison). I mean, there's some weird stuff in my motor design wise,   but its a solid design.

[Dvsrd]

Oh, I had forgotten that the KE/KH 100 clutches were a little weak as well. Once you had got the engines to run real good, the clutch tended to slip...We were busy playing with porting and cutting the rotary valves back in the early 80s :)

[m in sc]

thats one thing they had in common, the 120s clutch is just trash. I actually found out that i could fit aftermarket clutch springs for a grom in mine and it helped, a lot. i have so many nos clutch frictions and steels for it its ridiculous. lol.

[m in sc]

pulled the old crank and the replacement ebay one apart as well, and replaced the rod bearing on the 'new' crank. the rod on the ebay one is def a replacement and looked great (left one in 4th pic). got it trued back up home but also brought it to work, to verify on a bigger lathe w 2 live centers. (my small one at home was fine but.. worth a double check)

[SoCal250]

  That old bearing is toast.
You're lucky to have access to all that equipment (press, lathe, etc.). Sure makes rebuilding a crank easier, faster, and cheaper