Shattered C/S sprocket

FWYT
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FWYT
Edited Date/Time 5/10/2020 5:02pm
Asking for a friend. (No, really!!)

Ever seen this? Theories?

YZ 250F. Not sure on the sprocket brand though, knowing them, it is a reputable brand.

The lad said the nut was tight and the lock washer folded over.
Washer, nut and that missing piece are nowhere to be found. Those three pieces were recovered.

Is it possible a rock got in there just right and demo'd the sprocket? Could then the chain running over the nut in the counterclockwise direction back off the nut since there would be no tension on the lock washer ?

The counter shaft is a little banged up, but is thought to be repairable.

Luckily, it did not send the lad into a yard sale.





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Titanium
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Titanium 5/7/2020 6:51pm
5/7/2020 6:51pm
That sprocket was trashed before it shattered...Should have been replaced a long time ago. looks like an older pro taper or something, glad no one was hurt!
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Falcon
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Falcon 5/7/2020 6:56pm
5/7/2020 6:56pm
Odds are that the chain was just loose enough to allow the perfect rock to go between it and the chain. It sucked up the foreign material and somehow the sprocket was weaker than the chain. I can't imagine the chain derailing, loosening the countershaft nut, and breaking the sprocket all at the same time.
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FWYT
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FWYT 5/7/2020 7:08pm
5/7/2020 7:08pm
Falcon wrote:
Odds are that the chain was just loose enough to allow the perfect rock to go between it and the chain. It sucked up the foreign...
Odds are that the chain was just loose enough to allow the perfect rock to go between it and the chain. It sucked up the foreign material and somehow the sprocket was weaker than the chain. I can't imagine the chain derailing, loosening the countershaft nut, and breaking the sprocket all at the same time.
No, my thought was, like yours, the sprocket broke, THEN the nut came off as the chain was sliding over
it in a CCW direction.

It's all whacked, for sure!

Where's the "sprocket bolts" comments? Cuz this is next level!! hahahah
FWYT
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FWYT 5/7/2020 7:15pm
5/7/2020 7:15pm
Titanium wrote:
That sprocket was trashed before it shattered...Should have been replaced a long time ago. looks like an older pro taper or something, glad no one was...
That sprocket was trashed before it shattered...Should have been replaced a long time ago. looks like an older pro taper or something, glad no one was hurt!
OK, but what was the coup de grâce? It came apart strictly from being worn?
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Sprew
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Sprew 5/7/2020 9:49pm
5/7/2020 9:49pm
That sprocket is in tatters. 😛
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lowbudget83 5/7/2020 10:21pm
5/7/2020 10:21pm
Titanium wrote:
That sprocket was trashed before it shattered...Should have been replaced a long time ago. looks like an older pro taper or something, glad no one was...
That sprocket was trashed before it shattered...Should have been replaced a long time ago. looks like an older pro taper or something, glad no one was hurt!
It´s been well used, but far from thrashed IMO.

This shouldn´t be the cause of the fail... Could´ve been very expensive.
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inthebadboycorner 5/8/2020 12:21am
5/8/2020 12:21am Edited Date/Time 5/8/2020 12:23am
The counterparts sprocket takes a lot of abuse, all that torque on 9 or so teeth with such a small base circle, or whatever I'm trying to say.
The owner needs to inspect closer when cleaning and lubeing.
As the others have mentioned, luckily the cases were saved.
Lastander
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Lastander 5/8/2020 12:26am
5/8/2020 12:26am
I had this happen to me about 12 years ago, brand new sprocket, last lap, second to last corner, freak accident due to a rock
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FWYT
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FWYT 5/8/2020 6:59am
5/8/2020 6:59am
Lastander wrote:
I had this happen to me about 12 years ago, brand new sprocket, last lap, second to last corner, freak accident due to a rock
Thank you.
Falcon
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Falcon 5/8/2020 8:20am
5/8/2020 8:20am
Sprew wrote:
That sprocket is in tatters. 😛
Nice quote, Mick. Wink
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hubbardmx50
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hubbardmx50 5/8/2020 8:32am
5/8/2020 8:32am Edited Date/Time 5/8/2020 8:37am
Looks like a JT self cleaning countershaft sprocket. This has me worried because I just put one on my bike last weekend, lol.Silly

Edit: I see Pro Taper and Renthal's have the holes too. Very likely it was a rock.
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ktmdan
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ktmdan 5/8/2020 9:45am
5/8/2020 9:45am
Was it bolted on to spec?
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FWYT
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FWYT 5/8/2020 10:17am
5/8/2020 10:17am
ktmdan wrote:
Was it bolted on to spec?
According to the lad, yes, with lockwasher tab folded over.
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Snapper
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Snapper 5/8/2020 10:45am
5/8/2020 10:45am
ktmdan wrote:
Was it bolted on to spec?
FWYT wrote:
According to the lad, yes, with lockwasher tab folded over.
I don't understand. If the sprocket broke, how would the nut and washer disappear or is the threads on the shaft ruined where the nut was forced off?
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MZ193
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MZ193 5/8/2020 10:52am
5/8/2020 10:52am
Once my chain went byebye, it destroyed my sprocket and also the right carter.
Nowadays im only buying ek/did chains, renthal sprockets and change them every 25/30 hours on a 250f.
No o-ring shit.
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bh
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bh 5/8/2020 12:13pm
5/8/2020 12:13pm
My guess would be a rock or the chain was too tight or both. Sprocket looks fine to me.
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HighPlainsSquid 5/8/2020 12:56pm
5/8/2020 12:56pm
Whew!!!! My first response was "a broken C/S sprocket??!!! That's gotta HURT!!! What bone attaches to it? Where IS the C/S sprocket, anyway??"

Took me all morning to get up the courage to click on the thread.

Oh. "Spr-ocket!!! Not SOCK-et. Doh."
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FWYT
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FWYT 5/8/2020 1:07pm
5/8/2020 1:07pm
ktmdan wrote:
Was it bolted on to spec?
FWYT wrote:
According to the lad, yes, with lockwasher tab folded over.
Snapper wrote:
I don't understand. If the sprocket broke, how would the nut and washer disappear or is the threads on the shaft ruined where the nut was...
I don't understand. If the sprocket broke, how would the nut and washer disappear or is the threads on the shaft ruined where the nut was forced off?
The idea being, that somehow the sprocket grenades, then the tension on the lock washer is released, no longer holding the nut, and then the chain spins the nut off as it is travelling in a counterclockwise direction. The threads on the counter shaft were OK, but a little mangled up towards the inside where the chain had run across it.

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FWYT
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FWYT 5/8/2020 1:31pm
5/8/2020 1:31pm
MZ193 wrote:
Once my chain went byebye, it destroyed my sprocket and also the right carter. Nowadays im only buying ek/did chains, renthal sprockets and change them every...
Once my chain went byebye, it destroyed my sprocket and also the right carter.
Nowadays im only buying ek/did chains, renthal sprockets and change them every 25/30 hours on a 250f.
No o-ring shit.
Yes, I asked that question as well. But apparently the chain is OK.
FWYT
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FWYT 5/8/2020 1:32pm
5/8/2020 1:32pm
HighPlainsSquid wrote:
Whew!!!! My first response was "a broken C/S sprocket??!!! That's gotta HURT!!! What bone attaches to it? Where IS the C/S sprocket, anyway??" Took me all...
Whew!!!! My first response was "a broken C/S sprocket??!!! That's gotta HURT!!! What bone attaches to it? Where IS the C/S sprocket, anyway??"

Took me all morning to get up the courage to click on the thread.

Oh. "Spr-ocket!!! Not SOCK-et. Doh."
LaughingLaughingLaughing

And again, luckily, no injuries in this incident. Because obviously that could have been very very bad.
1
dirtwalker 5/8/2020 10:30pm
5/8/2020 10:30pm
Could be a few causes such as rock damage. From a materials perspective could be connected to the quality (“cleanliness” is the word) of the steel (typical relates to trace elements some of which you want and some you dont), or heat treating processes. Or a combination of the chemistry and heat treatment.
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Vet57
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Vet57 5/9/2020 1:35am
5/9/2020 1:35am
Sprew wrote:
That sprocket is in tatters. 😛
Falcon wrote:
Nice quote, Mick. Wink
Shadoobie...
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CG118
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CG118 5/9/2020 7:08pm
5/9/2020 7:08pm
Shattered shattered.....
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RbR
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RbR 5/10/2020 9:02am
5/10/2020 9:02am
'clean' breaks indicated Metal was over-hard. This can result from incorrect heat treatment, post quench, if the metal is not tempered at the correct temperature or correct soak time. Alternatively, metal can become brittle from repeated stress, referred to as work-hardening.

Looks like a heat treatment problem to me.
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Sprew
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Sprew 5/10/2020 9:37am
5/10/2020 9:37am
Heat treatment or case harden. Work hardening would be more localized. Teeth usually round over before the structure fails. They live a hard life.

I can’t give it away on 7th avenue.
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PFitzG38
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PFitzG38 5/10/2020 10:14am
5/10/2020 10:14am
Bummer, obviously you won't be able to repair that without the missing piece.
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ti473
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ti473 5/10/2020 4:54pm
5/10/2020 4:54pm
PFitzG38 wrote:
Bummer, obviously you won't be able to repair that without the missing piece.
well thank God for 3D printers!
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