What would cause a bad crank bearing?

[canuckjgc]

What could cause a bad crank bearing on a 2 stroke? Looking at a mid-90's Yamaha Enduro (which is supposed to be made extra tough) that had a bad crank bearing, but everything has been rebuilt and runs great. No real history on it though - just curious what might cause this?

 

[Philster]

Re: What would cause a bad crank bearing?

Dirt, heat or wear. There are other more elaborate ways, but these would be biggies.

Engine was run very hot and the weakest bearing gave way and suffered the most. Cheap oil was used and not the more expensive, higher-end stuff (maybe in conjunction with running hot).

All out wear and tear from hours and a history of someone running it hot, using cheap oil, etc.

One or a combo of all these is most likely.

"everything has been rebuilt" ? Are you eluding to an entire engine rebuild which replaces all the moving parts?

 

[canuckjgc]

Re: What would cause a bad crank bearing?

Given that it is an enduro which is often commercially used, I'm thinking wear maybe. Bearings, seals, pistons rings replaced. Should I pass on this thing? Or is it theoretically good for a number more years?

 

[Sea Rider]

Re: What would cause a bad crank bearing?

If that engine has lubrication pipes with check valves inside them and are broken, loosing lubricant or with clogged check valve, could be blamed for improper bearing lubrication.

Happy Boating

 

[Frank Acampora]

Re: What would cause a bad crank bearing?

Unless I were getting a VERY good deal I think I might walk away from that one. If that engine has roller bearings that ride directly on the crank like most other outboards and the bearing damaged the crank, service life will be shortened. If however it has a multiple piece crank and the bearing and crank parts were replace it would be OK. Problem is you don't know and EVERY engine runs great---until you buy it. Again, I think I would keep looking.