What Causes Wrist Pin Bearings To Fail?

[RUNMYTA]

Last week I got my 99 shee out and was just play riding in the yard. I got of her and let her sit and idle for about 2 min. I get back on pull out easy and she locks up tight as a drum!!!

 

I tear her down and the wrist pin bearing had came apart and jammed a needle bearing on each side piston trashing the left cylinder! What is unique is that the rod is tight and looks new where the pin goes. I am guessing faulty bearing?? I redone the topend about 2 years ago, but only have 20 -25 hours of riding on her. I don't race her anymore, just play riding or letting the little woman tag alone on it.

 

Yammy dealer say that he thinks that it wasn't getting enough oil???? I run Motol 800 @ 40:1. What do you guys think might have caused this?? I want to make sure that I cover all basis before i sink a ton of money in and it go booom again!! Thanks,MIKE

[Banchetta]

the rod is tight??? Lower bearings are siezed also??

[NYUK]

motul 800 is a good oil even at 40 to 1. if no other bearings were seized i would say bad bearing.if the other bearings show signs of seizure.could have been an air leak or some kind of lean condition.

[RUNMYTA]

Banchetta,

The rod bearings are fine. I guess what I was trying to say is that the wrist pin whole is still tight and shows no signs of being worn. I figured if the wrist pin bearing had been going bad over a period of time the slack would damage the wrist pin hole. Mike

[blk02banshee]

a backfire, severe detonation, or a foreign object in the combustion chamber could possibly damage the bearing, but I'm gonna say it was'nt getting the oil it needed, although 40:1 SHOULD be enough oil.

[merlin7]

You may find the small end eye on the rod is oval this will cause bearing to fail.

Even though the bearing may feel tight get it checked by someone with the correct equipment, a Vernier gauge will NOT do.

If worn only new rods will cure it.

 

Merlin7