Front Sprocket

[andybesy]

Hello Folks,

Firstly just to quickly introduce myself: I'm Andy and I've recently become the proud owner of a 2002 FZS 600 Fazer. My first big bike and I absolutely love it. So pleased I chose the Fazer.

Anyway, having been reading these forums I've become aware of the problems many people have reported with the front sprocket nut.

I'm a little concerned about this and would like to begin by checking my own bike to see if the nut is secure.

My question for now is: does the cover to the front sprocket require a gasket seal? Or can I safely remove this at home and have a quick peak?

It's been a long time since I've done any motor mechanics so please consider me an amateur. Is this something I can check myself?

Also any hints on what I should look for to confirm if it's OK or has old/new part appreciated.

All the best, Andy

[darrsi]

Don't need gasket, and if you weren't told the nut has been changed, then it ain't.......buy the 12mm version, NOT the 9mm! 

[andybesy]

OK great, thanks Darrsi.


I'll open it up and investigate, and get a 12mm nut put on there.


I'm also going to measure the size of the spindle as I read on another thread if it's greater than 17mm then it's not affected.


It's just that I'm doing a lot of touring and all the time I'm cruising down the motorway I'm thinking "what if...". Just need to put my mind at rest.


Thanks for your help.


Andy

[Paul]

If the nut is secure and you're not intending changing the front sprocket I'd leave it where it is.
 
If the bike has never had a front sprocket change and the nut hasn't been affected by sprocket chatter (and as far as I can tell most bikes aren't affected) then you will find that the nut is very tight and difficult to undo.
 
First time I changed the front sprocket I ended up using a 240V impact driver.  I think it cost around £45.00 from Machine Mart.
In any event it worked a treat, but don't use one to tighten the nut up unless it has torque settings.
 
When I put a new sprocket on I used 'bearing fit' on the output shaft splines and locktite on the nut along and a smear of grease between the tab washer and the sprocket.
 
 
If there is a problem with the nut and it's not tight, consider this:
 
I reckon the reason why the problem with the front sprocket nut exists is as follows:
 
Minor play between the sprocket and shaft, due to shaft or sprocket being machined out of tolerance.
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 / security washer / sprocket.
 

 

[Lawrence]

If the nut is secure and you're not intending changing the front sprocket I'd leave it where it is.

Having been in this situation, followed by the nut falling off I'd say change it.  New 12mm nut, threadlock, tab washer and then some (bad) welding is now holding mine on but I'm still paranoid about it.  Will be checking it daily (every 120 miles) for the next week or so, then will add it to me weekly jobs.

[Paul]

To Lawrence
 
To Lawrence:
 
You're making me paranoid now.
 
My bikes done 67,800 and I'm on my third front sprocket, and I've never experienced a problem.
 
And I've only ever met one person who this sprocket issue has happened to.
 
When it next comes time to change the front sprocket I'm going to do the grinding down the over-lap bit and just tighten it on the shaft.
 
 

[darrsi]

Everyone should have the new nut fitted, as it's a known problem and there's no point in finding out the hard way if you have a dodgy one or not, for the sake of a few quid?

[Paul]

To Darrsi
 
But is it the fault of the nut or the fault of the fit between the sprocket and the shaft?
 
I reckon from what I've read here the fault lies in the fit between the sprocket and the shaft.
 
So even if you put a 12mm nut on it's only going to make a difference if the friction between the nut and the saft is greater than the friction between the nut/washer and the sprocket.
 
Admittedly a large nut with more threads should produce more friction, but whether it will be enough or not appears unknown.
 
 
 
 
 
 
 
 

[phillywilly]

how often - i.e roughly how many chain renews do you have to replace sprockets , i know you change them when the teeth start wearing , but on ebay it seems most new chains are sold with sprockets .
this is the first bike ive owned so never had the pleasure of chains/sprockets, but has anyone out there got any experience of how many chains they,ve gon through in relation to sprockets ?

[Paul]

To Phillywilly
 
The usual procedure is to replace a chain and sprocket set.
 
That means both front and rear sprockets and the chain.

[richfzs]

Always replace the front sprocket, when fitting a new chain - the attached shows the price to pay if you don't. That was a feccing stressful ride back from Assen, with the chain tightened up so it got some purchase on the sprocket 

I've heard it said you can get away with chains to one rear sprocket, but really, why would you risk it, given the relative cost of the rear sprocket compared with chain and FS?

I learnt the lesson the hard way...

[darrsi]

@Paul, i've not heard or read of one bike going wrong with the 12mm nut 

[Paul]

I don't reckon it's the nut, I reckon its the tolerance between the shaft and sprocket.
 
I believe that if the friction between the sprocket and the nut - via the washer, is greater than that between the nut and the shaft the nut will move on the shaft and wear out the threads (mainly on the nut, because its not been hardened). So if the sprocket moves fractionally, the nut will move fractionally, and hence wear its threads out.
 
And all that said having spent 67,800 miles on 2001 Fazer without experiencing any problems at all, I think that I may well try and demonstrate a solution, to which for me; at least has not been a problem.
 
 
 

[Lawrence]

I thought the problem was more the sprocket falling onto the shaft and buggering the threads up (what mine did, but thankfully it wasn't completely knackered) rather than the nut moving and wearing the threads out?

[Paul]

To Lawrence
 
There's no way in God's sweet mother earth that the nut can come undone given the fact its tightened up and has a tab washer on it, unless something causes it to move repeatedly on the threads.
 
A 12mm nut presumably has more threads in contact with the shaft than the original nut.
Therefore there should be more frictional resistance between the threads and the shaft than was previously the case.
 
Neverthelss the issue cannot be the size of the nut, it has be what is causing the nut to loosen.
 
And from everything I've read I reckon its sprocket chatter.
The sprocket is fractionally too small for the shaft, or the splines of the shaft are fractionally too small for the sprocket.
 
If the frictional resistance between the nut and the sprocket is greater than between the nut and the shaft (via the threads) and you have a small amount of movement in the sprocket, it will move the nut continually on the threads as you put the bike on and off load .
 
Ultimately the threads on the nut (because its softer than the shaft which is likely hardened) will wear out.
 
The end product is the nut wears out and comes loose.
 
Look at the nut, it's recessed where it tightens to the sprocket.
Why put a recess in it?
Unless it's there to lessen the frictional resistance between the nut and the sprocket (less contact area).
 
Up to press everything I've read points to the issue of sprocket chatter and the nut being tightened against the sprocket.
Hence the proposed remedy of tightening the nut against the shaft as opposed to the sprocket.
 
The only thing that f***ing nut has to do is keep the sprocket on. And something is causing it to loosen when it shouldn't.
I reckon it's sprocket chatter and the nut being very tight against the sprocket. 
 
If memory serves: on the old hondas the nut never tightened against the sprocket.
 
 
 
 
 
 
 
 
 
 

[Lawrence]

Im not arguing that and I understand what your'e saying, what I meant was that the damage to the threads isn't from the nut but from the sprocket spinning on them.  Mine were flattened off although running the new nut on a bit at a time cleaned them up and they were ok to use again.  I'd like to have seen the condition of the old nut but it's probably somewhere up the A12.

[unfazed]

See Post on Front sprocket issues again