Two Stroke Motocross

Two Stroke Motocross Forum => Technical => Topic started by: rip2621 on February 10, 2013, 05:39:25 PM

Title: Strange crank problem
Post by: rip2621 on February 10, 2013, 05:39:25 PM

I've had a wet side main seal leak on my 03 YZ250 so I tore into it to replace the seal. I got the seal out and there's noticealbe play but it's not in the bearing - it's between the crank's shaft and inner bearing race. If I put a finger on the inner race it spins on the crankshaft.

I suppose the reason for the bad seal is this movement... It seem odd to me though. Shouldn't this be a tight or at least very snug fit?

Crank is tight but if I'm splitting the cases I might as well give it a complete rebuild. Just wondering about this movement. Anyone else see such a thing? I'd like to figure out why this happened. Bad main bearings beating the race to death perhaps?

Title: Strange crank problem
Post by: vetman on February 10, 2013, 07:43:09 PM

my thoughts are pretty similar the main bearings support all that pressure they are designed for it but in saying that your on a 10 yr old bike which may have never had a bottom end rebuild,and things do wear out.While its out take some measurements  i dont doubt theres folks on this forum how have more knowledge than methat can help but id look at rebuilding crank,mains, bigend etc

Title: Strange crank problem
Post by: moto867 on February 11, 2013, 04:51:52 AM

time for a new crank and main bearings.  i see it all the time on older cranks.  2 strokes have a press fit between crank and main bearing, over time the crank can wear and get loose and the only fix is to replace the crank.

Title: Strange crank problem
Post by: TMKIWI on February 11, 2013, 05:39:33 AM

New crank I am afraid.

Title: Strange crank problem
Post by: SachsGS on February 11, 2013, 04:39:00 PM

I've repaired YZ's of your year where the crank spun and seized in the inner bearing race. Might be the result of an earlier repair.

Title: Strange crank problem
Post by: rip2621 on February 11, 2013, 06:10:05 PM

Thanks for the input, guys.

I suspect that when I finish tearing it down, I will find really worn main bearings. I probably let that bottom end rattle I've been hearing for a year or so go too long. The bearing may have seized causing the race to spin on the shaft or just got beat hard and long enough to loosen and wear.

Good to hear it's not an isolated thing. I bought the motor used so don't know it's history but it appeared low hour and had no tool marks on any of the nuts or bolts.

If I find anything of interest when I get it apart I'll let y'all know.

I'm gonna replace the crank and mains with OE parts and send my top end to Eric Gore for the 295 treatment.

Title: Strange crank problem
Post by: ford832 on February 11, 2013, 07:21:02 PM

That sounds interesting.Post up a RR when you're done.