Why would lower connecting rod bearing fail?

[fauxamish]

My friend's Blaster quit running and I offered to try and fix it for him. I have a 400ex and have rebuilt the engine several times, so I figured I could do this. I took the top end off the motor and discovered that the lower bearing on the connecting rod at the crank is seized. It'll still move, but it is super stiff. I am planning on replacing the crank, but I don't want this to happen again.

I don't know a whole lot about 2 strokes, but I do know that the oil that is mixed in the gas lubricates the piston and the crank. Would running lean cause this? Or improper oil/gas ratio?

Also, is there anything I need to know about splitting the cases? I requested the Clymer from the library, but I don't want to order the crank if this is going to be something I need special tools for.

Thanks

[Dualstroke]

The lower bearing could have seized formultiple reasons.Lack of lubrication,lean condition,lots of hours and no maintenance,etc. You can inspect it once you are in there and see hwat you can find.The crank usually will have some blueing to it from the heat treating at the factory.Working on blaster motors are relatively easy with all the tools.You will need a flywheel puller,crank puller or crank removal tool,crank installer,clutch holding tool, and just metric sockets etc etc. You can always improvise if need be but the right tools make it alot easier.A manual will help you out immensely but once you do one the rest comes easy.I would also suggest getting a block off kit and blocking off the oil injection and just pre mixing the gas to 32:1 ratio.

[fauxamish]

I'm guessing I should be able to pop the cases apart, just like on the 400ex ("persuading" them with a rubber mallet, etc). Since I am replacing the crank, can I just press the old one out? As for putting the new crank in, if I heat the bearing a little with a torch and put the crank in the freezer for a while, I should be able to get it installed right?

I'm not worried about the clutch, I"ll just use an impact wrench to get the nut on and off (works great on 400ex) and I'll get a bolt from Fastenal for the flywheel. Anything I am missing?

[greenmachine70]

lack of lurication, raw fuel

[fearlessfred]

sanding the motor will kill the crank . in other words the air filter has come off or not oiled and or it has not seal up good.the signs off sanding will be on the piston and cylinder walls.the top end could of been freshen up before you got to it and you may not see it. i have seen two strokes piston seize from no oil in the gas and the crank be alright and i have also seen sanded motors with a fresh top end seized with in an hour

[fearlessfred]

oh yea,im not disagreeing with anyone elses answers, just adding another one

[headache]

you can get the blasters cases split without any special tools Except a flywheel puller. the cases will come apart fine if you are careful with screwdrivers and a hammer. Just be easy. I've split one twice. you can get crank out with a rubber mallet and put the new one in the same way.. the lower rod bearing probably just failed from age. what year is it?

[fauxamish]

I've gotten the cases split and crank removed. My buddy said it was from the late 80's, so I'm going with old age for the failure. The new crank comes tomorrow, so hopefully it will be up and running in a couple days.

Thanks everyone