Front sprocket issues again

[unfazed]

I own a FZS600 which I bought new in 2003 and now has 72000miles on the clock. 3 weeks ago my 5th sprocket nut failed, this time taking all but 2 threads on the shaft with it and the last 2 nuts were the modified nut, even though Yamaha were supposed to have fixed it in 2005. Dubious of the ‘repair’ at the time I tapped the holes in the 2003 sprocket cover to take the plate and damper from the 1998/1999 sprocket cover to prevent the sprocket falling on to the shaft and leaving me stranded again
Seriously pissed off I contacted Yamaha and under no circumstances would they do anything about it, not even supply me with a new shaft, head and base gaskets free of charge, for me to to replace it myself. They even suggested I spot weld the nut on.
I spoke to my bike guru friend and he recommended I cut a slot in the shaft and put a circlip on it or drill and tap a hole at the end of the shaft and put a washer and bolt on it to prevent the nut falling off. I did both as a sort of belt and braces job.
I uploaded what I did with some pictures and since I did not know where to put it I put it under
  Downloads » Manuals » FZS600 Fazer » How I fixed my Sprocket nut problem
Hope it helps

[Dead Eye]

Very extensive and well written, I'm sure it will be helpful to someone

[ade the blade]

good work that man...........fingers crossed it gives you many miles of worry-free riding 

[His Dudeness]

yeah nice work. you'll have to give us an update in a few months. i've heard this is a problem with a lot of Yamaha's not just the fazer

[unfazed]

Yes it appears to be mostly accross the yamaha 600 range, it appears to be a big issue also with the R6.
I don't remember hearing of it happening on the 1000 range.
I have covered over 1000 miles sinc I did the repair and it is still ok.
I will keep updating as I will be checking it every 1000 miles or so.

[marksfazer]

Excellent write up. Well worth doing considering most of us have experienced this problem.

Mark.

[darrsi]

What bothers me is the fact that it can be a very dangerous fault, rather than just some niggly issue.  :rolleyes

[unfazed]

Yes, I agree, the first time this happend to me in 2005 I was riding alone on a quite back road and powering out of a left hand bend when  I lost all drive. The sprocket had fallen onto the threads of the shaft.
Now if that had happened on a busy road or if I was overtaking, it could certainly have been a lot more serious.

[unfazed]

Just to update 1000 miles and still ok
No reply from Yamaha UK yet

[unfazed]

Yamaha UK replied and  this was the reply, It was along shot anyway being a different country
Thank you for your email, in relation to your Yamaha FZS600 Fazer.
Naturally we are sorry to hear of your concerns, which have been noted for our files.
We would in the circumstances, kindly suggest that you please re-establish contact with Danfay Ltd on telephone number +353 1 2859177, who being the official Importer and Distributor for Ireland, will be best placed to assist with your enquiry.
Whilst we thank you for taking the time to contact Yamaha Motor (UK) Ltd, we are sorry that we cannot be of any direct assistance.
I asked them for the contact details of Yamaha Europe which they sent me. I will try contacting them also

[His Dudeness]

in my experience danfay are alright at getting parts but they don't go beyond that. i think they're just importers i don't think they have any actual mechanics but they might be able to direct you on to someone else

[unfazed]

Absolutely no reply from Danfays to my email, will email again. There spares section might be good but their service and sales are crap
Fix still holding after 1300 miles

[Paul]

I reckon the reason why the problem with the front sprocket nut exists is as follows:

Minor play between the sprocket and shaft, likely due to shaft being machined with slightly larger grooves than needed.
Nut tightened up on the sprocket.
Sprocket moves fractionally back and forward, and because the nut is tight to it, so does the nut.
Nut threads wear out as do the shaft threads.

Possible solution:  Grind down the over-lap of the nut so it tightens up on the shaft and not on the sprocket.
In essence it should be flush with the sprocket but not tightening up against it.
Ideally make sure there's a layer of grease between nut and sprocket.

[unfazed]

Paul you might be right, I remember a few years ago a friend of mine put the modified nut on backwards after the first nut fell off, he was thinking along the same lines as you he used a 3 mm washer drilled out to fit over the splines between the nut an the tab washer to ensure the tabe washer could the located on the spines properly. There was about a 1 mm gap of play between the sprocket and the washer.
He always thought the nut should not be tight against the sprocket. I checked with him after reading the post and he never had the problem again. He still has the bike but cannot use it due to a back problem and there is 33000 miles and 2 sprockets with the same nut and tab washer.

[unfazed]

Frgot to add in the previous post that he put a rubber washer between the sprocket and the tabwasher

[Lumpy]

I reckon the reason why the problem with the front sprocket nut exists is as follows:

Minor play between the sprocket and shaft, likely due to shaft being machined with slightly larger grooves than needed.
Nut tightened up on the sprocket.
Sprocket moves fractionally back and forward, and because the nut is tight to it, so does the nut.
Nut threads wear out as do the shaft threads.

Possible solution:  Grind down the over-lap of the nut so it tightens up on the shaft and not on the sprocket.
In essence it should be flush with the sprocket but not tightening up against it.
Ideally make sure there's a layer of grease between nut and sprocket.

not an engineer are you  :lol

[Lawrence]

Paul you might be right, I remember a few years ago a friend of mine put the modified nut on backwards after the first nut fell off, he was thinking along the same lines as you he used a 3 mm washer drilled out to fit over the splines between the nut an the tab washer to ensure the tabe washer could the located on the spines properly. There was about a 1 mm gap of play between the sprocket and the washer.
He always thought the nut should not be tight against the sprocket. I checked with him after reading the post and he never had the problem again. He still has the bike but cannot use it due to a back problem and there is 33000 miles and 2 sprockets with the same nut and tab washer.

Hope his isn't like mine then, mine fell off at 33500  :lol

Certainly something to think about come sprocket change time.  The best option, regardless of whether the nut is tightened against the shaft or the sprocket, has got to be the circlip/bolt+washer or similar to stop the nut actually falling off if it does come loose.

[Lumpy]

Certainly something to think about come sprocket change time.  The best option, regardless of whether the nut is tightened against the shaft or the sprocket, has got to be the circlip/bolt+washer or similar to stop the nut actually falling off if it does come loose.

my TDM had a nylon collar to stop it coming off. Good idea. The sprocket isn't falling off whatever happens.

[unfazed]

Finally recieved a reply from Danfay, they have offered to give all the parts I require to replace the shaft at half price.

[His Dudeness]

well that's something at least. what are you going to do?