pay your respects - 23' YZ250 engine failure

ELECTRICAL FOR SURE

Cold weather and running lean. 

Mike is a man of few words, but when he does speak it’s usually important. 😉

To his point, you would have thought the OP would have chimed in already but he’s probably trying to find a rebuild kit that is still in the manufacturing stages. lol

This right here!

Been detonating for some time by the looks, which always leads to a failure eventually, whether it’s the piston, ring, electrode falling off, or locating pin as in this case.

Br8eix 

I forgot my login in password!
I was cleaning up my home office desk and found the post-it note I wrote it on over the weekend. 

IT’S ON NOW!!! 🤣

Got too hot from not being rich enough. Combustion temps are hottest around stoichiometric ratio ~14.7:1. Not technically "lean", just not rich enough to achieve necessary fuel cooling at WOT. Piston failed near the exhaust port (as is typical) due to seizing and high heat. I'm guessing what many are assuming is the ring gap in the wrong spot is actually a broken edge of the ring, which happened due to no longer having top ring land support and catching the bad spot in the cylinder. I assume the majority of the damage is from the debris rather than just detonation pitting.

A bummer for sure, but I bet it's happened to most of us here who have ridden a two stroke aggressively, so don't feel too bad

Whoever rebuilds that motor have them check the ignition timing with a degree wheel and make sure its on point.  We had a few 23' YZ250's up here in CT that were banging out of the box on straight C12..timing was off on them.  May not be the case here but it would not hurt to do it.

Good luck-J

Same thing happened to us on our 2013.  Predetonation using pump gas.  Happened at 18 hours..  After a bucket of money we went 50/50 races gas/93 octan and problem was solved.   Yamaha support stuck to the manual - top end every 10 hours, we're sorry.

While rebuilding recommend you measure your squish and get the head cut to preferred .050 or whatever it is, sure quite a few folks still do this. We're running pump, with no issues with a pretty good rider and some flordia sand.

My 21 has been a little knock prone out of the box. It was angry in FL at high load/temp as well. is there a rule of thumb on jetting for colder weather you'd be willing to share?

Who did your head work?

But here's the thing now one is talking about...this guy can fix this for around $500, based on the parts shown. Try to replace the same components on a Four-stroke and it will cost $2500+.

What does the spark plug look like?  It probably got beat up too but I would like to see it. If it did end up running so lean I would suspect an air leak vs fuel or jetting. You guys are looking at what a shop goes through to determine a failure on a engine. 

Has anyone seen this type of failure on a fuel injected 4t? Yes 2 strokes are generally cheaper to rebuild, but they take a better mechanic/tuner to keep from blowing up too.

I'm with you on the blown head gasket...that amount of lean is usually an air leak. Did the bike ever have trouble coming back to idle? 

You're correct to a point. The solution is to just put in larger jets that are $5 and take 5-10 minutes to change.  Not bagging on the OP but 30 degrees is very cold to not change the jetting and he knows now.  I used to ride my old yz at an indoor facility in winter (in the north east) and definitely would have blown it up if I didn't richen it up.   Sorry for your loss, OP!

Here's who did mine.  He does great work!  I don't know about the newer YZ250 but I know the older ones had too much clearance in the squish area. Mine had .085" with all OEM parts used.

yz-head (rb-designs.com)

+1 on the ignition.

May not have been the cause but still 100% worth getting it properly set. A friend of mine got a YZ250 brand new in 2017, the stator came completely loose within a few hours. Seems to be a common issue with YZ's from new

Get ‘em Mike! Show them that now they have awakened the beast!!😂

sorry to hear about this....i know how much this sucks for you as and as a fellow rider i feel you pain.  I have a YZ250 as well and the local motor guy around here (TZR Motorsports) tells me to run 50/50 pump/ race gas so you're good there.  I go up on the main jet one size as well.  These motors are not as bulletproof as you would think.  The transmission indent thing happens around 60 hours from my experience.

Don’t believe stock jetting will cause that level of a lean condition…

I had this happen and it turned out there was a small gap (defect) in sealing the cases causing it to suck in air making it lean

Somewhere/somehow the engine is getting excess air… crank seal another possible culprit

I wasn’t thinking lean but more so sucking a little coolant, creating steam/heat, that ended up causing the breaking down/melting of the piston lleading to ring failure. 2 stokes often detonate with no harm to the piston. Something caused the dimples or wash away of certain spots on top of the piston. The eventual loose debris is what caused all the ping marks. Had a CR do this about a year and looked identical. Albeit a consistent Southern Cal weather day where the bike had been running fine, running lean was not a factor. My 2 cents of course. Anyway, sucks for the OP and his new bike. Hope it goes back together well and can get back on it soon. 

Awesome, heard good things about him but the site stated he was done doing it when i was interested last. Glad to know it's on again!

Tom Morgan 295cc kit.

Your numbers are quite a bit off. Just sayin'

I'd like this twice if i could.