Yamaha Thundercats
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Has your front sprocket fallen off??

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pale Has your front sprocket fallen off??

Post  hena-c on Thu Feb 28 2013, 16:02

Hi fellow Cat owners

I have been having a bit of an issue with the front sprocket on the cat... ie.. it disappears. I wondered if this was just an issue on my bike or it was a common theme, as i have heard of it before.. after a bit of research I find our fellow Yamaha owners have had the exact same problem. It turns out that it is a known problem with Yams, and there is a modified nut availiable..

I urge that you check your bike as soon as you can. I would hate for anyone to have the same issues as mine when the sprocket decides to jump off whilst doing... ahhem 60 mph up a hill...

If you have a look at this link it makes for some interesting reading

http://foc-u.co.uk/index.php?topic=2449.25

http://fazerowners.yuku.com/topic/5415/Lost-your-front-sprocket-and-washer?page=8#.US94g6LIbZ4

Basically the modified nut + washer comes as a kit. Part no. 90891-10124 The nut and washer come in the same packet. The nut is 12mm rather than the old 9mm nut

The output shaft can be an issue to. The thread can be damaged or worn and should be no less than
17.45mm dia. I've still to check mine...
I hold in my hand the modified nut and washer kit.. but i'm in the process of rebuilding the rear end.

Has anyone else come across this issue

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pale Re: Has your front sprocket fallen off??

Post  hena-c on Thu Feb 28 2013, 16:10

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pale Re: Has your front sprocket fallen off??

Post  YZFJohn on Thu Feb 28 2013, 17:03

My sprocket never came off in 20+K but the rider did! LMAO

Do they do a Modified Rider as well? stars
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pale Re: Has your front sprocket fallen off??

Post  Snowcat on Thu Feb 28 2013, 19:02

@YZFJohn wrote:My sprocket never came off in 20+K but the rider did! LMAO

Do they do a Modified Rider as well? stars

This has happened to Tomcom also I believe on 3 occasions LMAO
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pale Re: Has your front sprocket fallen off??

Post  SteveCat on Thu Feb 28 2013, 19:37

It is interesting that Yamaha haven't admitted the problem being on the Thundercat, not that really means anything.

Would be interesting for a mechy or engineer's view on the problem / possible resolution. The washer bent around the nut may play some part.
I've never had an issue (next time I go out, it'll fall off!!), but I've never changed the sprocket myself - maybe my mechy isn't as dozy as he looks.

Resisting the modified rider response
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pale Re: Has your front sprocket fallen off??

Post  bobh on Thu Feb 28 2013, 22:09

I've read (on Thumpertalk, US forum for offroad singles) of a similar problem affecting the Suzuki DRZ400. They suggest it's caused by the clearance of the sprocket on the shaft splines allowing the sprocket to move a tiny amount whenever the drive reverses, so gradually loosening the nut.

The cure suggested is to actually put some strong Loctite on the splines when you fit the sprocket, to prevent the rocking motion.

It's interesting that on the FZ6 (and presumably the R6 from which that's derived) the nut is actually locked to the shaft by peening a soft extension into a keyway-type groove in the shaft. Even so, when I did mine I put a drop of Loctite on as well, just for luck!

The fact that Yamaha changed the locking method does imply that they were probably aware that the tab washer method used on the 'Cat etc. was not 100% reliable.

Edit (after actually looking at the links posted by hena) - I see that the earlier R6 and FZ6 still had the old-style nut and washer, and had to be modified. It does seem strange that a problem like this, that could potentially result in a fatal accident, wasn't subject to a proper full recall.


Last edited by bobh on Thu Feb 28 2013, 22:24; edited 1 time in total (Reason for editing : New info.)
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pale Re: Has your front sprocket fallen off??

Post  Yammycat on Fri Mar 01 2013, 22:56

Ive not looked into this one, but from my experience with locking tabs and the washers - by rights there should be a flat surface on the washer, and also on the shaft that would prevent the washer from rotating, usually the top and side section of the washer would be then bent over one of the flats on the nut, preventing any movement of the nut, if it came loose.

In regards to the recall - sadly, vehicle manufacturers only recall vehicles with serious issues if the chances of any payout exceeding their set "limits" from insurance payouts, as usually it could cost less to pay out insurance, rather than recall vehicles to have them repaired. To be fair each manufacturer works different, but along the same lines - at the end of the day its all about the money.
the other time they recall is if enough customers complain to watchdog etc and then they have to take action as its national news.

just my 2p

cheers
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pale Re: Has your front sprocket fallen off??

Post  HEHORE on Sat Mar 02 2013, 01:49

Never had a problem with it undoing itself. Last time I had the chain changed it had locked on soo tight it was stuck no matter what it would not come off. Ended up having it cut off , it was only on there for 11 months , and sized solid !!
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pale Re: Has your front sprocket fallen off??

Post  stretchie_ on Mon Mar 18 2013, 15:06

Yep twice, not fun especially when over taking a car EEK

Only on the Thundercat though, never on another bike
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pale Re: Has your front sprocket fallen off??

Post  MevsyD on Mon Mar 18 2013, 20:11

This happened to me as well. I never mention it as I just put it down to experience but wow! Didn't realise how common this was?
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