the seller who rebuilt it, forgot to fully install the wrist pin retaining clip, the wrist pin worked its way out, got caught on the bottom of the cylinder bending the connecting rod and cracking the piston. that is why only half of the piston is cracked off

After watching this entirely, I'm willing to bet that one of the wrist pin clips wasn't fully seated. Whoever rebuilt this engine forgot to listen for the snap.

Before I looked at the comments I had come to the exact same conclusion that the wrist pin clip had not been installed on the one side. I'll wager that you won't find any evidence of the second clip in the motor. Thanks for your content, I love it

That result is every motor enthusiast's worst nightmare. Good diagnosis and video! Looking forward to watching the rebuild.

All these 4-stroke MX bikes are throwaway engines. Part it out and cut your losses, Joe.

That sound of a four stroke seizing is as fear inducing as the thought of erectile dysfunction.

Wrist pin clip fell out is my first thought

You can see on the bottom right side of cylinder wall where the Piston pin scraped and caused piston to break. Like others have said it looks like the wrist pin clip wasn't installed all the way and fell off causing pin to slide out catching cylinder wall and or just caused piston pin journal to break.

I could conceraningly hear it knocking when you started it up

I've owned motorcycles all my life and I have never seen that happen before !!!!!! Just because it's new doesn't name that is a good part !!

Here's why I always double-check customer work. Admittedly, finding a misplaced wrist pin clip would've been impossible to see without a complete teardown, which I likely wouldn't have done, so I would've had the same result as Joe. I always hated dealing with other people's lack of mechanical knowledge.

I agree with other commenters the wrist pin was likely floating in there before you even got the bike started. Enjoy the videos, great work.

From the last video, there were 50 professional small engine builders that declared "but the timing chain is slapping the case", "Im deaf in both eyes, and blind in my left ear, and my hearing eye dog told me the timing chain was on upside down!"

Had bent rod situation about a year ago, could find parts, European junk. Heated rod a bit, used the press and got it back straight as an arrow. Ran fine after, still running today!! Crazy, was a hail Mary but it frkn worked. Setting up to straighten was the pain.

Great video, with lots of learning moments. 😭No riding today. Keep working on the problem, your patience and skills are amazing.

The crank is from Hot rods. I rebuild a yz250f and the rod had the same id system. If you search for hot rods connecting rod 616 you’ll find visibly identical cranks for the crf250r.

Looks like a clip popped out and the pin slid to one side and hit the cylinder and bent the rod.

If I had to guess the E clip came off and let the pin slide over to the wall and break one ear. Or maybe there was only one E clip. I am 67 years old and have been working on motorcycles for 55 years.And I still learn stuff from you all the time. Keep up the good work. And I wish when I was young I would have had the job you do.👍

Im 49 this is why i prefer simple two stroke engines no timing chains or camshafts. 👍🇺🇸

I can tell you what happened with 100% certainty as I have seen this before what happened was whoever rebuilt it either forgot to put one of the wrist pin clips in or it wasn't put in correctly the pin walked its way out of the one pin bore and then once that happens there's so much stress on the one side of the pin bore it will break and bend the rod at the same time as the load is only on one side of the rod bending it with 100% certainty that is absolutely what happened there clearly someone put it together that did not know what they were doing

No question, first failure was piston pin retaining clip coming loose

The real carnage starts around the 27:00 mark for those impatient to know.

Clip was not put in all the way and it fell out and the the wrist pin backed out. Then Boom.

It didn't "let go 2 seconds into the ride" it was already letting go before you even swung a leg over it. Im still amazed that you got on the bike and then thrased it when the knock was so clear to hear it was ridiculous. Had you had an once of mechanical sympathy you could maybe have saved it.

when it let go i definently thought the timing chain broke, thats pretty crazy.Thanks for the videos love how you break things down!!!

WOW! What a blow up! Joe, you should do you next video on this bike on how fast you can rebuilt a motor. No talking, just getting at it. That would be fun to watch.

It's nice to read these comments, which seem to be 100% accurate on the reason the engine failed. It's unfortunate when a newly rebuilt engine fails in such a short amount of time. But, knowing why it happened is priceless knowledge. Love and appreciate your content.

FYI, Something I'm sure you know. Top end rebuilds only you need to pull the engine out flush out down inside the crank area with diesel fuel. Work the crank by hand really well (for a few minutes) Turn engine upside down, continue working the crank (round and round) Both directions too. Blow out wit air well Repeat Repeat Repeat Get all metal chunks, spers, flakes out This is a must Good work

You should have probably checked the other guys work before starting it. He apparently did not have a clue what he was doing!

Thanks for the vod !

Hey Joe I want to say I’ve been watching your videos since you were at 100k subs you’ve come a very long way but very worth it you deserve everything you’ve achieved I learn something from almost every video keep it up! 500k on the way!

Great diagnostics video as usual . Thanks !

If you don't have a borescope camera yet, it's time to get one. 🙂

Never trust some one's engine rebuild. I learned from years of experience working at a dealer ship.

wrist pin clip wasnt snapped in !!! YOU GOT LUCKY !!! engine immediately stopped instead of metal chunks taking out the cases and everything else!! 😃👍👍👍👍👍👍👍👍

I have learned a lot already. Thanks 2vintage.

I must say, if this happened to my bike (and I have one of that vintage), I think I'd be inclined to just scrap it and save all the bother. However, it's great to see someone with more patience and enthusiasm at work.

Vertex cast piston, Italian engineering =)

Dude, you're deep down in the bones a real work horse. You could take 3 months off and I'd still be here playing catch up on videos. haha

Wow! I did not expect it to let loose like that. I thought the timing chain broke, but man was I wrong.

Great tear down. I’d love to see the research you do to find good replacement parts. Might make a good filler video for those looking to do their own repair.

On one hand its insane how much damage can that little circlip do. I have never heard about this happening in a 4 stroke. On the other hand thats why you should not ride with the engine sounding like a coffee grinder.

Excellent video, this was really interesting to watch. Bummer on the carnage in that motor, what a mess. Thanks for the video loving the content.

I have watched your videos for a long time and enjoy them. Thank you. I've never seen a piston give away like that. So like the other grease monkeys I say it has to be the wrist pin clip was not installed. Good job again my friend.

Love your content Keep up the good work

Other guy forgot to put a clip in the wrist pin...

Excellent tear down video

I've seen this before. They either forgot one or both of the wrist pin 35:45 clips. Or did not get the clip properly into the groove. When the wrist pin slides over it puts all the stress on one eyelet of the bottom of the piston and that's why it broke.

What a video! You have a great attitude as well towards seeing something that can be devastating. I hope you had the funds to rebuild it because at this point you would have a new engine that would last many years. I sure hope I can find a video of you putting it back together

Props to you for putting Humpty Dumpty back together again. Ditto, like many other commenters I would also run away from someone else's rebuild, now you are depending on their level of skills. "I have all these unnecessary parts leftover"

What a lot of damage from what is likely misinstalled wrist pin clip. Sadly, the cost of parts to repair makes this not such a good deal.

Been looking forward to this one .

Great stuff and I’d agree re the gudgen pin (as we Brits call it ) came loose after the circlip came loose . I have seen a piston loose like this when riding Enfield in the Himalayas . On one that was running rough the crown of the piston had broken away from the body of the piston !! It ran badly but was fixed by putting a new piston in . Those bikes are tough , which is what you need in those remote areas . Love your stuff

When someone says they "rebuilt" an engine but it won't start you can bet it was done wrong! So, when you hear rebuilt you should tear the whole thing down to make sure it was done right or ....learn the hard way that it wasn't.

Great Chanel Great build 🙏🖤

😂I predicted the wrist pin in some manner ❤ I was close! Great videos Joe and as always keep it up

I watched the last video on this but the start on this for you bro blew me away bro.

You're like a surgeon with that motor . Nice work.

I was not expecting that. That was crazy

I never seen that happen, that is such a bummer. I would change the main bearings too, just to be sure. Great video again, Big Up!

Jkjk love your vids and constant content brother keep up the good work

That’s amazing I’ve never seen that kind of failure before.

Bravo, you get to put someone's puzzle together

Early four stroke MXers> HAND GRENADE and not cheap to fix

This is why they say that 99% of people can’t build a motor lol

Would be interesting to see what the ring end gap was. Maybe it caused the piston to seize in the bore when the engine heated up?

I knew right away from the first video that the thingamabob next ro the whatchacallit broke rightaway buuutttt i didn't say anything because i didn't want to be a know-it-all.Love your videos Joe!!

great video as always. Joe, dont what your "day job" is but it must be a good one. these things are pricey to fix.

The crf250 send and mend series.... Stuff happens. Looking forward to the rebuild Joe !

Cant wait to watch rebuild Mark

Yup..... retainer didn't seat and the pin walked out enough have the load all on the broke side. Good stuff!!

New rod, piston, cylinder, and valves. Clean it up good, lap in new valves and put it all back together and should be fine. Good video

Happy Days Joe Has Posted 🔥🔥🔥

Ohh that was another gold turn of events. It sucks to happen to you, but makes for a great video. Crazy stuff. Reminds me of exploding Piston.

Great autopsy joe as usual,but all I keep thinking about is my desire for that elsinore in the background! Cheers 🍻

Thanks for the vids goes to show that sometime we win, and sometimes we lose.

Hey Joe where goin with that gun in your hand. In my best jimi hendrix voice 😢

Looks like the wrist pin clip wasn't in place or popped off on one side.

Exactly What I came here to say! Spot on!

Agree. Piston pin clip/s came out. Seen that before. Cylinder tells the story

WOW!! Quite a mess there, Joe! I think I'd agree with jeredalmedia 1880-the wrist pin clip didn't seat on that one side. You have to pay attention to the small details, which will save your attention from being distracted by the disaster to follow, if you don't.

first i am studying to be a mechanic I live in greece so sorry for the bad English so what probably happened was piston bend the valve and then probably because of the high rpm piston gave in and broke that's a nightmare it was a fresh rebuild so something was wrong from the first place from the rebuild re last owner did its only a guess. nice video tho its nice watching video with clean explanations keep up from me I love you videos

People saying the previous owner didn't install the retaining clip, he did, if he can rebuild it himself he knows about a retaining clip...but he probably put it in vertically or it accidentally spun enough which allowed it to expand and pop out while under pressure... turn it the opposite way and it'll only get tighter while under pressure. I've seen many clips pop off because of improper install. It doesn't help when the bike is idling to the absolute moon before ever giving it throttle, on a brand new engine with no heat cycles. It's far better for no idle at all and just leave the throttle open enough to keep it from stalling, than it is idling like that... turn it to where it doesn't idle, then turn the screw just enough until its just on this side of stalling, you do not need a high idle. It sounded terrible before it ever grenaded. He revs the piss out of everything, doesn't matter if it's new or not, cold start or hot, just wide open continous blips or idling super high while also giving it wide open blips. I've yet to hear a properly tuned crisp 2 stroke on the channel, yet every time, "it sounds perfect" noooo... I either hear it being way too rich or detonating. Like this he said sounded great, no it didn't. He's a great mechanic and good at diagnosing issues, without a doubt, but jetting and knowing what a properly tuned bike sounds like is not it.. jetting from a piece of paper will get you in the ball park, the fine tuning is done by ear.

Just a idea for you. Buy you a shipping container to keep your toys in at home. It's far cheaper then buying a building and lasts longer then anything you could purchase to store your things. They go for very good deals and that includes shipping them to your home. Plus you won't have to worry about storage fees and all your things will be at home at hands reach. Just a suggestion that will pay off in the long run and I have gotten one for 2500 with it being shipped to my home. So something to think about buddy.

I think the casting on the piston where it attaches to the rod failed because it didn't let loose until you tried to ride it so when it had a load on it is when that part failed. You can tell Joe has rebuilt so many motors he can take them apart and know where every gear goes. When this bike is rebuilt its going to be a good one. Hope he can get 3k for it when he sells it to make some money for all that work.

Wow, I am FLOORED!!! Lesson LEARNED!!!!

It looks like all of us agree. The clevis ring was not fully seated.

super cool video, but on what platform do you look to find a good bike to buy??

Tuff luck on this one but could have been so much worse. Great job brother keep it up

Wow! Nice necropsy!👍

"What the hell happened here" I tell you Joe, you revved it to the moon when the engine made knocking sounds so loud you could hear it wearing ear mufflers.

Soon as you started it in the field I could hear it knocking like a madman. It was letting go but you rode it & finished it off

Totally agree, c clip on wrist pin

Man, i really like your videos... It really pushs to work on my bikes! I have a suggestion regarding the title of the videos... Why don't you put the name of the bike or At Least if its part 1or 2????

Good troubleshooting Joe! Personally I’d rather jump off a bridge than work on a early CRF or YZF

Wrist pin clip for the win! 🙂

Yup! I was gonna say wrist pin clip, had to be it!

Think its sp tools makes a adapter to put on you extensions and sockets for hammering on so you don't trash them. It's pretty cool.

Piston wrist pin clip was most likely not fully seated and caused the failure.

Hey Joe, did you find one or two wrist pin clips? I saw just one in the crank case. Thank you.