Wasted crank bearings

[irk_miller]

Looking for opinions are what to look for and where to go next.  I have an RD350 I converted to LC a few years back that has seen about 5k miles.  It's been running flawlessly the entire time, until it suddenly decided to waste the crank bearings two days ago.  I haven't cracked the bottom end apart just yet, but the top end is in wonderful shape with visible crosshatch on the cylinder walls and everything measuring in spec. Ed Toomey rebuilt this crank three years ago, so I am really surprised this happened.  There is no visible rust on the crank and no indication so far that coolant got to it.  I didn't get to put a lot of miles on the bike this summer, so it sat more than it ran. Are there specific signs I should look for, besides rust, that would indicate coolant or moisture getting to the bearings? It has always passed regular pressure tests, so I never expected anything out of the ordinary. Anything else that would cause the bearing to let loose all of a sudden?  Is this just one of those things that happens sometimes?  I'm not wanting to pay another grand to have this crank rebuilt, so I am thinking of going with a Vitos crank.  Seems like they are quality part.

[m in sc]

i put a vitos in my hybrid,  zero issues.  no idea why it went on yours. on mine weights came loose 2x, and I rebuilt it both times myself. 1st crank i had in it got wiped out during a top end blowup back around 2011. so im on my 4th crank and its def been fine. but this is over 22 years of hard thrashing

[1976RD400C]

Are you talking the main bearings or the lower rod bearings or both?

[m in sc]

if its the main bearing, is it the drive side? if so, look at the interaction between the primary gear and the clutch

[irk_miller]

How does this even happen?

[m in sc]

50+ year old metal fatigue. yikes

[85RZwade]

holy shit 

[RDnuTZ]

https://vitosperformance.com/products/rd350-vito-s-performance-yamaha-crank-crankshaft-stock-size-oem-replacement-new?_pos=3&_psq=cranks&_psid=0a953f0ad&_ss=e

 

[irk_miller]

holy shit 

It's wild.    In all my years (I'm 55), even with 2t sleds, No one I know personally has seen anything like this. I was sure it wiped the bearing on the ignition side, so I went ahead and posted before I cracked open the bottom end.

[m in sc]

ive seen a few sheared triple cranks and a broken daytona crank

[1976RD400C]

I had that happen once also. 

[irk_miller]

Sucks it happened to anyone else, but at least I'm not alone. Curious if there is simply a point where these cranks can't be rebuilt anymore and putting them through a press contributes to their demise.  Not at all suggesting bad craftsmanship on the rebuild, but more that the process created fractures that led to what happened. My first reaction when I pulled it apart was that a bearing froze, but that didn't happen.  The bike ran normally until it suddenly didn't. 

[1976RD400C]

The 400 Daytona crank is known to have not been hardened as much as the other 400's and those are the ones that break most often. I think it might just be old age and hard use doing it. Maybe also if the crank gets out of true it stresses it more in the middle. 

[sav0r (CL MotoTech)]

I'd think more hardening would lead to more failures like seen here. You need ductility. Surface hardening is a factor in that break, or if it was, it's where the stress riser started.

Either way, this one was cycled out.

[Dvsrd]

Stock alternator? Ported engine/ chambers?
The heavy stock rotor combined with higher rpm would cause more problematic crank dynamics, from what I understand.
TZ's had much lighter rotors...