front sprcket gone ???

[fireyphoenix1...]

riding the bike home today i heard a weird noise then lost all drive at first i thought the clutch had gone and pushed the bike home on the way i noticed the chain was really slack so i was hopeing it had just jumped off the sprocket
when i got the bike home i stripped the front sprocket cover off i found the front sprocket was completely gone no marks on the chain or the inside of the cover
i have been back to where the bike broke down with friends and found no pieces of it its like it just vanished the only thing i can think is when the bike was serviced about 100 miles ago the mechanic incorrectly fitted the cirlip holding the sprocket on .bikes being picked up and the guy better fix it or im reporting him

my question is this

does any one know how the hell this can happen as everyone i have spoken to says they have never heard of anything like this

fife
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2014 Aprillia dorsoduro 750 factory.

[Blau Zedong]

It can happen, especially on the sprocket type which is held on by a tab washer and two M6 bolts. Incompetent assembly is the cause.
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18:54:48 Rob Fzs: jews don't give away stuff for free

18:54:59 Rob Fzs: unless its their clothes/ hair/ golden teeth

[weasley]

It's a known issue on the Thundercat for the sprocket nut to unwind and eventually come off, although the sprocket usually stays in the sprocket cover.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[Marmalade]

Was the sprocket replaced when serviced?
Wouldn't be touched otherwise.
Have you tried walking the route you pushed the bike home, sprocket might have come off but not actually fallen out until on the way home, more than likely it's embedded in the side of someone's head, think how fast that thing spins.
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[Pete.]

As above, there's no reason to touch it in a service - unless you had a new one fitted. don't blame the fitter you just had some bad luck.

What bike is it anyway?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[.Bishbash.]

Wow, that's unlucky it came off completely. I did have this once, thought the same as you, the clutch had gone etc. But my sprocket was still there.

Luckily they are cheap
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Current bike - GSX-R1000 k8

[andym]

Same thing happened to me quite recently, although I was told it was the clutch or shaft had gone, it was only after posting on here (and stripping the bike down to get at the clutch), did I find it was probably the front sprocket... Luckily the sprocket, washer and nut were all still sitting in the casing.

Because me and a friend replaced the chain and sprockets I put it down to I hadn't tightened up the nut enough. So with the bike on the ground and both brakes applied I tightened it up as much as the weight of the bike would allow and made a mental note to check it after 2 weeks... I checked it yesterday and the nut had started working itself loose again... so if it does it again I'll be using a splash of locktite on there

Anyway as already mentioned walk back the way you came and see if you can find the parts... may want to walk back further than where the bike broke down though as the nut (if it has one), could have come off a couple of miles before the sprocket finally let go.

[fireyphoenix1...]

me and a friend walked the route twice yesterday no joy not a sign of it
Yes the bike had a new chain and sprocket kit fitted about 100 miles ago i had checked the bike over before going for a ride chain was just oiled and the tension was correct . its a baimo RSR 125 over 11000 km on the clock with no mechanical issues so im rather annoyed that its playing up right after a full service and having the perishables replaced
the mechanics picking the bike up in the morning

ah well my das soon then i can get my honda
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2014 Aprillia dorsoduro 750 factory.

[fireyphoenix1...]

bike in the garage the lock ring had disintergrated with the sprocket
mechanic found a few very small fragments that i hadnt spotted

its being put down to a faulty component and repaired for free
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2014 Aprillia dorsoduro 750 factory.

[Cognitive_Faux]

yup happened to me too on my old thundercat.

isnt there a lock tab nut under there that gets twisted?
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bike theory (pass) bike test (pass)(4 minors) car theory (pass) car test (pass)(1 minor!!!)
cb125t->sr125->expressII50->xlr125->GS550L & GS550E->XBR500 'chop'->YZF600R->FZS600->GSF650->fantic 212cc->gsf650->kwak GT750->VFR750 ->
HGV class 2 (pass)

[fireyphoenix1...]

couldnt see one when the sprocket kit was swaped out
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2014 Aprillia dorsoduro 750 factory.