YZ250 bottom end life

I have an 05 YZ260 that I use for woods riding/racing. I have put about 2000 miles on the bike since I bought it used two years ago. :lol: I have replaced the top end a few times but I have never done anything to the bottom end. I have checked the crank bearings for free play on the flywheel side and I don't feel any. Typically how long does the bottom end last? Any input would be appreciated:thumbsup:

Singletrak

There is no definitive answer to this. A dune bike help WFO all the time wont last as long as a woods bike ridden constantly on the pilot circuit.

I'll split my cases at 200hrs of run time (per hour meter) and inspect gears and replace the crank.

I ride tight woods 80% of the time and dunes, desert & track the other 20%.

He's right, there's no set answer.

I put 100 hours on my bike and then decided to do the lower end. Had an unknown number of hours when I bought it. Everything looked great. My plan is doing top ends every 50 and the lower end at 200 hrs.

I too am a ~80% single track rider.

Id just run it till she blows...there really is no middle ground on the big end bearings, and the side bearings typically don't go out.

You can get a lot of hours out it for sure on a 250, they are underloaded stock.

A 125 is another story!

How would one know it's time to change the bottom-end?

While doing the top-end, might as well just inspect the bottom for any movements, sideways and up?

Thanks.

The people that know me in this forum know that I have broke everything on a YZ250 that can possibly break. Between two different 06 YZ250's (from what I can quickly remember) I have tore up the trans about 6 times, cracked and broke about 4 pistons, wore out a shift drum, smoked clutches and eaten a basket, snapped a fork spring, burnt a stator, worn out a water pump seal, worn out a rear hub, tons of wheel and suspension bearings and other small things here and there....

Anyway, what I'm getting at is out of these two bikes neither of them ever showed any wear or any indication of wear in the crank bearings or rod bearings. I think this is one of the YZ250's strenths. I'm confident in the YZ's crank.

wish i could say that i am confident in the yz's crank..... my bike has eaten 2 cranks in two years pistons being ok but thats just my bike p.o.s im trying to get a newer yz the one i ahve is a lemon

wish i could say that i am confident in the yz's crank..... my bike has eaten 2 cranks in two years pistons being ok but thats just my bike p.o.s im trying to get a newer yz the one i ahve is a lemon

If it was a lemon it'd be destroying parts, breaking down, and being a POS 7 years ago when it was still new. There has to be a reason for killing 2 cranks in 2 years.

  • How did the cranks fail? Main bearings? Lower rod bearing?
  • What premix ratio do you run?
  • What is your air filter service interval?
  • How were the crankcase halves pressed/drawn together?
  • Has one of the crankcase halves been replaced, but not the other?

my yz has approx 8,000 trail miles on it and the original crank is still tight.

depends on how hard u ride and how well u maintain it

I opt for the 200 hr change. @$180 it is good value and insurance.

If it was a lemon it'd be destroying parts, breaking down, and being a POS 7 years ago when it was still new. There has to be a reason for killing 2 cranks in 2 years.

  • How did the cranks fail? Main bearings? Lower rod bearing?
  • What premix ratio do you run?
  • What is your air filter service interval?
  • How were the crankcase halves pressed/drawn together?
  • Has one of the crankcase halves been replaced, but not the other?

yes true however im thinking the previous owner may have crashed it hard on a rock or something as the clutch cover housing looked as if it had a crack in it at one point and was fixed with some sort of apoxy or something any way to answer your questions....

the first crank was the stuffers melted and seized the connecting rod and destoryed the lower rod bearing (over heating? lack of oil?)

the second crank had one of the main bearings beleived to be the right side fused to the crank shaft

I run 32:1 which i later found out i was mixing at 40:1:banghead:

cleaned air filter every couple weeks when i dont ride it that often or after every long race day

i beleive my dad and myself put the cases together the first time and im pretty sure we did it way wrong as we just used a rubber hammer and as evenly as we could hit them together (my money is on this :worthy: )

and i dont think the cases have ever been replaced atleast not since i have owned the bike since 2007

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