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.

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.

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.

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.

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

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

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.

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.

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.

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

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.👍

Wrist pin clip fell out is my first thought

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.

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.

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!

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!"

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

Great diagnostics video as usual . Thanks !

I have learned a lot already. Thanks 2vintage.

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.

Thanks for the vod !

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"

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.

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.

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.

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!

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

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!!

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

I could conceraningly hear it knocking when you started it up

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

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

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

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

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

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

Love your content Keep up the good work

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

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

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

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

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

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.

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

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

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

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.

Been looking forward to this one .

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

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

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

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

Last summer I bought a YFZ450 from a guy. Had the same exact thing happen to him. Web around the wrist pin let go. I don't know why but I got it cheap lol. Sourced OEM crank, cylinder and a Wossner piston with anodizing - actually starting the rebuild this weekend. It should be good to go after I'm done with it. I have nothing against Wiesco, I just decided Wossner - took a while to come in. Still going to split the cases and clean, replace all the bearings so long as I'm in there - be new when done.

Great Chanel Great build 🙏🖤

Vertex cast piston, Italian engineering =)

I thought that sound when it locked up was familiar. 1985 Sears Point Raceway. AFM Formula Singles class race. just finished turn 8A and flopped the bike over for 8B at the same time up shifted and that same sound happened. The connecting rod let go and engine locked up tight in a fraction of a second. The rest of the seconds was the sound of me sanding down my leathers sliding down the track. You'll never forget that sound Joe. Sorry for the crappy luck.

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

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

I totally agree. The way the piston was broken on one side and the connecting rod was bent. And only one wrist pin clip was found in the engine

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

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?

Excellent tear down video

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.

Exactly What I came here to say! Spot on!

Bravo, you get to put someone's puzzle together

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

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

Good teardown, I suspect failure was HYDROLOCK your evidence was there you picked up on it but didn't see that as your issue. Coolant got into the cylinder, bad gasket ? Looking forward to the rebuild. Keep up the good work.

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

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.

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

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????

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

I had a wrist pin come out on a 1965 BMW R-27. Didn't bend the connecting rod but the wrist pin cut two 68mm long transfer ports (not good in a four stroke). Anyway, I got away with a cylinder, wrist pin, two clips and a piston pin. Funny thing is that it ran me home (150 miles) and just kept getting slower and smokier. This happened in 1970, so parts were readily available at the Sacramento BMW dealer..

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

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

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.

Joe great video 👍. It had to be the clip wasn't fully seated. I've seen this before. Please tell Vinny my mom said hi. 👍

Cant wait to watch rebuild Mark

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

I thought the same as everyone else about the snap ring not being in its groove right. How to grenade a motor 101.

Happy Days Joe Has Posted 🔥🔥🔥

Man, you're a cool cucumber, Joe! It has to be frustrating when, while all if not most of your repairs are fruitful and work, to have to trust someone else's. I mean, If I were you, I'd be like, "If anyone other than the Japanese factory worker who assembled this bike has touched it (besides ME of course), I'm OUT!

New valves and seals, your good on head.

That's a shame, gotta really look at the head, those guides and the surrounding casting have taken a hit, you probably won't know for sure until you start the lap the new valves if the head is still good, that sucks Joe, good luck with it, looking forward to seeing how this plays out

you have been lucky for awhile something had to go wrong sometime.😵

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.

I’m sorry this happened to you, however it is a treat to see your troubleshooting skills in action. You talk us through from the beginning then reassess as more information becomes available. Kind of like Sherlock Holmes searching for clues at the scene of a crime. Sooner or later, you will find the bad guy. Well done!

Well that sucks. There was more damage than ive seen before with the clip coming off but ive also seen it a lot worse so be happy the case didnt get messed up too.

Hay Joe hope you and your family are all fit and well I think someone forgot to put a c clip or circlip clip on the piston pin or dungeon pin how you want to say it but it dose that sort of damage when a clip is missing Bad learning curve for anyone to have Keep up the educational videos.

Like watching an I Do Cars video except its a cycle engine! What awesome carnage!

If it sounds like trash don’t continue to run it!! Hahah. Love your videos!!

I agree with everyone else someone was in a big hurry putting that engine back together.. & failed to do it correctly.! wow too bad.! looked like a nice bike.!

nah.... that'll Hone out 😳😂... Lucky there wasn't total collateral damage, cases and all.... *thinking positive*