250-500cc bottom end shelf life?

i know its another one of 'those' questions but deep down i know you blokes love answering them! got nearly 180 hours(approx) on engine. was planning on doing another top end & leaving it till 300 hours before it gets split. thoughts? i know its rider/maintenance dependent but how many hours do you guys reckon is safe? will check rod play next top end(around 20 hours time) but what else should i look for aside from noises that shouldnt be being made? 32:1 full syn, 98 octane, clean filter all the time. im heavier than normal but only B grade type rider. fair bit of WOT but generally slower single track type riding. cheers ladies & gents

My husky 125 and 250 2 strokes went 4 full years over 5,000 miles of expert class racing before i replaced the rod bearings

My 95/96 WR360 has had two bottom end rebuilds in 12 years that l've owned it..all due to lean seizures caused by airleak and bad jetting.
I've had the barrel replated once and about to do another replate or go down the C type piston (just on that wear limit).
Overall, it's a 2 stroke, keep the airfilter clean, jetting sweet, quality oil and the bottom end can last (depending on your riding) quite a long time.

I have approx 300hrs on my 300 and the bottom end is still tight. Just put the first top end on it.

That is awesome! I just got a lot more confidence in my bike after reading that.

Several hundred hours on my weekly practice wr250-just did the rod after 6 years-it was pitted on the big end and showing movement- very strong bottom end; but not forever

its had 1 already & about to do a second in a coupla months time. usual speedo dramas so id reckon it has about 7000km on it. is it just rod/main bearings that get replaced generally or rod/crank/whole shebang? cylinder needs replating so ill get that sorted. am thinking ill bite the bullet & post the cylinder stateside to powerflow as its cheaper to post it there & back than get it done in OZ(& no doubt a better job!). anyone recommend these guys or anyone else? seems easy as they sell wossner piston kits so can match it to the piston & post the lot back! clutch & gearbox still seems solid so hopefully everything will hold out to 300 hours. mates 09 300exc shat itself bigtime at about 250 hours so im startin to get a little paranoid is all

how many hours mate?

Lot of guys from DBW send their cylinders over to powerseal which is cheaper than doing it locally. If you have to change the bearings on the connecting rod, you might as well get a quote from them as the whole crank needs to be shipped over (weight of postage the key $$ factor) in order to be split and bearings replaced and the crank to be trued.
If you are doing the top end, check for up & down play on the rod, if there is a hint of movement then it's time for a bottom end rebuild and rod bearings need to be replaced, if you can push the fly wheel up/down or feel any movement, then bottom end rebuild with new main bearings and seals - if there is no movement then don't worry about it, do the top end and recheck after another 180hrs on the piston or your next topend
Generally, you don't need to touch the bottom end unless you've shattered a piston, main seal leaks, sunk the bike in muddy water or ANY movement (up/down on the rod and flywheel side to side) so the reality is that most rod bearings can last hundreds of hours before they need to be replaced.
PS. Buy an hour meter rather than go by kilometres.

Depends how it is ridden. I'd personally be cringing after 150 hours and downright afraid after 200. Always cheaper to rebuild a sound bottom end than a blown-up one.

I ride with a guy on a Ktm 300 and at 20k mark he finally rebuilt bottom end. These modern two strokes are so good I now double my 300 as a duel sport bike and am hardly worried at the 1500 ish mark. Bike is still super tight.

Sorry - I do not have an hour meter-two oem pistons worn right out, showing the port marks beaten into them- rev it to the moon- 2nd gear rounded right off[it's the 'B' bike]

My 2006 CR 125 went almost 5 full years of desert racing won 2 National # 1 plates one in the regular 125 expert class and one in the over 50 expert class.then after 5 years had george at uptite replace the crank bearings.Then george put it back together using the original clutch yes the original clutch the cylinder is still stock bore also
The bike is still ridden and I would race again if I needed to but we have a 2008 CR 165 and the 300 now

yeah got hour meter on from after first top end, has 75 hours on it. guesstimated 100 hours on first top end goin off mates hour meter who i ride with & km travelled which was around 4000km(average about 40km/h). bikes had a couple of drinks through breathers(before re-routing!) & drain hole of airbox(bit of foam stopped that!) but never sunk. normally check rod play but didnt know about flywheel play, cheers mate