250-500cc urgent help needed please, WR300 seized

Hi guys,
what a sad morning..was going for 6am ride to local trail. getting to the trail requires 2 miles on 60mph... 30 seconds in to the ride on the hwy, engine quit. no crash and pushed the bike home..

tear down revealed seizure and to me engine looks bone dry... hour meter is at 50 hours, but I see that there is B piston there!!!

so details, 09 Wr300, Lectron carb. yesterday I was playing with the carb and adjusting power jet to riches setting (2 turns out (was too rich, no power) and dialing back to 1 3/4 from full in) for richest good power setting.

any ideas what could have caused this? as my engine is on the way to the shop..

four corners seizure... piston expanded too fast in the bore and damage ensued. Were the radiators full? Were the head o-rings intact? Lastly, did you do anything to deal with the (potentially) leaking reed intake?

If your cylinder isn't too beat up then I've got a OEM 'C' sized piston kit I'll make you a deal on.

Radiators were full.. I must have gunned it before it was fully warmed up, but chock was off.

orings are fine. intake was sealed. will post pic of the plug.. but as you can see, head is very very clean..

any why was there B size piston to begin with?

93 Exon gas with 50:1 Amzoil interceptor mixture.

Man I cringe every time someone says they run 50:1 or less. I know guys do it and have no issues, but "not in my engines, thank you". It's not a leaf blower. That said I'm sure it's not the cause, but oil is your barrier......

Wash on the piston looks awfully lean. Probably a partial-throttle thing with the needle, not just the power jet setting. When you look down in the crankcase between the crank webs, is there a little oil pooled in the bottom?

Unfortunately our trail bikes don't do well on highways at constant sustained speeds. They're designed for constant variable throttle. Your worst load on motor was on highway where lubrication was critical. If you plan other sustained long pulls like that I would suggest using more oil. I've torn down a well jetted Honda CR250 and it ran 50:1 for a year. Bottom of crank was dry - no residual oil build up. You want that there for oddities like your hwy run. I'm using 32:1 but that sure don't mean I'm fast!

More than likely you have a B cylinder. The difference between pistons is so small it is not the problem anyway.

here is the plug.. $500 repair bill and 2-3 weeks to think about meaning of life and all...

good clean fresh fuel and I do measure mixture very carefully with error on more oil side.
I was playing with the Lectron and adjusting power jet to richest setting (2 turns out (was too rich, no power) and dialing back to 1 3/4 from full in) for richest good power setting..still that plug looks lean and engine is really dry '

so fracking pissed...

yeah..reed block is sealed fine and is in great condition..I have around 10 hours on the Lectron, and ran it on 1 1/2 PJ setting. it always runs just fine and starts really nice. this week, one of the local dudes told me that it sounds lean so I tried to adjust PJ to richer setting and 2 turns out was way 2 rich.., no power at all, so I settled on 1 3/4 thinking that richer is better for the engine and I was not looking for most power possible and bike still had good response and all..

so this morning, i set out for a ride at 6am, so I started riding as soon as I started the engine. 1/2 block to traffic light. another 60 seconds waiting for light to change and than onramp to highway.. flat out to get to 60mph fast. 30 seconds later...kaboom.. so total, no more than 2 minutes of running engine.

dealer said "cold seize".. because piston is damaged on all 4 sides...


could this really be cold seizure? I've never even heard this term before..

So it seized after a hard run, but was at partial throttle when it happened. Cold sieze does look like that, but it isn't the only way to get a four-corner. It can happen anytime the piston temp spikes abnormally. A lean mixture can spike the piston temp and cause it. Plug looks leaner than I feel safe with mine (100% throttle probably 40-60% of the time) but isn't way off and can't be trusted as an indicator at all throttle openings. Piston wash looks lean. Probably is lean at partial throttle, possibly a setting, possibly debris or a drop of water in the bowl. I'd pull the carb bowl without draining it/letting it spill, and see what you've got. You'll want to take it off anyway to check/reseal the reedblock area.

Thanks guys. No water for sure in clear bowl. Using downtime to restore bike to new condition. Basically stripped down to frame.

Or I should just go buy new husky or Gasgas...

60 mph in a WR!? What gearing are you running?

I suspect that going 60 mph after 60 second of warmup is the root cause. How much oil is pooled in the bottom end?

stock gearing i think..
according to GPS, I hit 68mph on 1:35 in to the ride...whatta idiot i am!!! expensive lesson learned

donno how much oil was at the bottom end, engine is at Bobs now (central Jersey cycles) but it was not much at all..i was thinking that things looks rather dry to me... but that again, by the time i took it apart I did kick it few dozen times..I though i lost ignition in the beginning..and was checking for spark

my 300 is plated but I am leery of open sustained rds but have done lots of 60 mph stuff reluctantly. When I do it I always roll on and off throttle. Never just hold it open. Run 40-1 with lectron. Never any problems

I was not just open, I got up to speed, rolled off and on and bam..

It's just 2 mile stretch of open road, I've done it before on hot bike no issues.

Oh well..sucks to be me right now...long weekend and no bike