Bad Crank cause a seized Piston?

[j_blaster]

I just rebuilt the top end of the blaster, broke it in correctly. No problems. Then took it out for a real ride at the ORV park and after about 20 minutes of easy riding it sieized the piston. Spark plug was not lean, matter of fact, it was running a little rich/dark on the plug.

Tore open the top end to find the siezed piston and also found the crank has some play at the top side to side.

Can a bad crank sieze a piston. I run 44:1 premix, plugged up the oil injection tube so no air into the carb (pump is still running, however). What am I missing???

 

[Kyleblaster]

I dont think it can i never heard of thAt before i heard of no oil and the piston hiting the head that it that sound weird what you decribe

 

[specialized7]

try running 32:1 that might have been your problem.

 

[Blown 97 GT]

44:1 might be your problem, that is a little lean... I just had the same thing happen to me actually. My new piston/rings etc should be here this week. I just rebuilt it with no probs then rode for abt 15 min and it fried. Took it to yamaha shop and we put in a new crank seal cuz they think it was leaking. It was only 12 bucks so i did it. It my blaster still sputters and wont idle after this new top end, they are doing a leak down test to find out the problem hopefully!

 

[Blown 97 GT]

Wait, 44:1 is rich sorry! anyways the mix shouldnt be your prob... What main jet do you run? Airbox lid on or off?

 

[Blown 97 GT]

Also, i'm pretty sure a LITTLE side to side play in the crank is ok, just not alot and not up and down play.

 

[03blasteryfs03]

well u might have got a bad gasket or sometin and got a air box and its not the premix caus ei run 100:1 ya thats rite 100:1 no smoke and never blown fried or stuck anything

 

[j_blaster]

I'm running a 230 main, airlid on (with holes in it) with Uni filter. It's piped with FMF Fatty. I think I agree with everyone that the crank couldn't cause this, so it must be an air leak somewhere. I'm also going to replace the crankshaft seals in case I've got a leak in there, and I think I'll run a leak test before I run it again.