Modern Vespa

can an overheating engine ruin a crank bearing? i've got this incessant whirring from the flyside after running hot from a clogged carb a few months back. doesn't seem to really have detrimental effect other than bugging me, but i went out and bought new crank bearings. thought i'd check here first before tearing it down.

edit: et3

The heat itself shouldn't do much damage, but whatever was causing your motor to overheat (lack of lubrication) could cause damage to it. Unfortunately, if you are having noise from that area, you should check it out anyway. A bad crank bearing, if left unchecked, can lead to some pretty bad damage to crank, rotary pad, stator, flywheel, etc. All expensive parts.

crank is shot.

What was it, out of curiosity? Bad big end bearing ?

Yeah, what crank and where did it fail?

I've had two Mazz longstrokers fail me - one on the Cannonball (big end bearing just went to shit) and the one I replaced on the C'ball failed soon after (one end of the crank web worked itself about 4mm off the big end bearing)

i'm not sure what crank it is. it's whatever was in this et3 when i got it. pretty sure it's either just the original or a stock replacement.

honestly i'm not sure what problem occurred first, but i AM pretty sure the problems compounded each other. bad flyside bearing, which i installed new earlier this year (both sides new, actually)...and the crank. the rod had way too much play, which wasn't the case when i built the engine earlier this year. there was some evidence of rotary pad contact, and some odd bluing (heat related?) on one of the counterbalancers on the outermost edge where the rotary pad lives. i'll see if i can get some pics with my crappy phone camera.

first came the whirring after overheating a few months back. like i said, didn't affect running quality, so i said fuckit. then a couple weeks ago the plastic fan piece on brand new hp4 flywheel flew apart. approximately 30-45 degrees of it missing. i chocked it up to high rpms and maybe a hairline crack since i discovered a hairline crack on my new fan as well, but it could have been high rpms + vibration. only ran the bike a few days, and gingerly, before new fan arrived and installed. ran bike at typical aaron-rpms then, and felt a bad vibration immediately. then i knew it was game over.

so the old crank was indeed stock. noted the piaggio logo on it. the new crank is mazuchelli. i was dismayed to see that the maz crank has a shorter and shallower intake duration...using my eyeballing powers, appears to be roughly 3-4% less, but the shallowness is what really bugs me. sho' nuff, i lost a lot of giddyup. may have to jet down, but i don't think i'm getting that old kick in the ass back.

good news is that the original problem is solved.