whats the chances of it living???

[danimal95]

on my 250r i have a fresh top end,just a stock overbore,and it runs very strong,it is actually faster than my friends TRX250R with a 310 kit.anyhow i have a 310 kit i have been contemplating putting in it but i am concerned about the rod letting go if i do.i hhave heard alot on this board about guys doing big bores and much sooner than later the rod gives out.however i would have thought that with the fresh stock displacement rebuil that if the rod bearings where weak it would have already let go?so my question is should i do the big bore kit now or wait till it needs a new top end and have a new rod put in it at that point?

[Dirtcrasher]

Just ask yourself how many hours are on that bottom end....

I always use 2 top ends for every 1 bottom end rebuild, 3 top ends at the very most.

If that case has never been split, then it's time to do so. That 250R motor is one of the simplest motors out there. And, if there are hours on it, I bet you'll find countershaft bearing and holder wear, or loose/broken mounting bolts and a notched clutch basket.

If you have 300$ or so, I'd tear into the bottom end myself if it is has a fair amount of hours on it. Many of these 22 yo ATC's have the original bottom end, hows that for reliability!!

Waiting till it blows up is asking to ruin the case or tranny or worse, a complete explosion!!

The best mechanic I ever knew explained to me that 2 strokes that are running there fastest are usually ready to blow up. Everything inside is so loose and worn that it revs even faster than a tight motor - that made sense to me.

Just my .02c

[masonryman13]

I was on the last bore for my cylinder-- 0.80 over stock-- it only ran @ 6 hrs, on & off, when in the middle of a BIG jump(40 ft table-top), big for me, the rod bearing went. And believe me, it was running FAST. So, now i am learning the process of splitting the cases, replacing whole crank assembly, and other bearings. Also, I get to fix the cylinder, buy another piston, plus enjoy the down time-NOT- b/c I didnt just replace the bearings first. Plus, the landing hurt like HELL. I didnt pull in the clutch lol, lol. So, yes, I would fix it right if I were you...

[Erics350x]

I'd wait till the next time it needed a rebuild

[danimal95]

thanks for the replie,i have about 12-17 hours on this current rebuild w/o any problems,but i think you guys are right,before i pu th 310 kit in i will definatley do the crank and rod bearings

[300rman]

thanks for the replie,i have about 12-17 hours on this current rebuild w/o any problems,but i think you guys are right,before i pu th 310 kit in i will definatley do the crank and rod bearings

definitely the cheaper way to go. just remember, you will have to send the crank out to get the rod kit installed.

for a bigbore kit, i would go with a HOTRODS rod for added strength.

[danimal95]

your reading my mind