Date: 29-03-24  Time: 11:45 am

Author Topic: Sprocket Nut  (Read 5673 times)

crickleymal

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Sprocket Nut
« on: 01 April 2015, 04:40:43 pm »
I see from the Articles Section that there is or was a problem with the front sprocket nut. I have no idea whether anything has been done to my bike so I was thinking as a precautionary measure of buying a nut and locking tab from Wemoto as they're only a fiver. I presume the Wemoto nut is ok?
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bandit

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Re: Sprocket Nut
« Reply #1 on: 01 April 2015, 06:06:17 pm »
Yes that is the correct one.

rhinoeli

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Re: Sprocket Nut
« Reply #2 on: 01 April 2015, 06:17:42 pm »
If no problems, I would wait for the chain/sprocket change service. Problems arise when someone overtightens the nut. Mine have the narrower nut with over 80000 kms and 2 sprocket replacements. No problems yet.

unfazed

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Re: Sprocket Nut
« Reply #3 on: 01 April 2015, 07:58:21 pm »
If no problems, I would wait for the chain/sprocket change service. Problems arise when someone overtightens the nut. Mine have the narrower nut with over 80000 kms and 2 sprocket replacements. No problems yet.


Over tightening the nut has nothing whatsoever to do with it. :wall

The problem is quality control at the factory, the diameter of some output shafts were smaller than the minimum 17.5mm and the nuts were only gripping the edge of the threads, which caused fretting (A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force.") and the vibration eventually caused the threads and tab washer to wear and the result being the nut falling off. Replacing the nut with the 12mm nut and tightening it to 80Nm or 90Nm maybe more reduces the fretting, but does not completely resolve it as the only cure is replacing the shaft. After some major issues with Yamaha with the problem, they eventually at 71000 miles relented to sell me all the parts I required to repair the problem at half price. While this was ongoing I tried a different approach which has worked and is still working after 12000 miles. The solution I devised is on the forum here http://foc-u.co.uk/index.php?action=downloads;sa=view;down=43 
The new shaft I now have if I ever decide to install it is 17.82mm and the nut is tight going on it, compared to my original being 17.2, but nowhere the minimum 17.5mm.

YamFazFan

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Re: Sprocket Nut
« Reply #4 on: 01 April 2015, 08:41:26 pm »
If no problems, I would wait for the chain/sprocket change service. Problems arise when someone overtightens the nut. Mine have the narrower nut with over 80000 kms and 2 sprocket replacements. No problems yet.


Over tightening the nut has nothing whatsoever to do with it. :wall

The problem is quality control at the factory, the diameter of some output shafts were smaller than the minimum 17.5mm and the nuts were only gripping the edge of the threads, which caused fretting (A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force.") and the vibration eventually caused the threads and tab washer to wear and the result being the nut falling off. Replacing the nut with the 12mm nut and tightening it to 80Nm or 90Nm maybe more reduces the fretting, but does not completely resolve it as the only cure is replacing the shaft. After some major issues with Yamaha with the problem, they eventually at 71000 miles relented to sell me all the parts I required to repair the problem at half price. While this was ongoing I tried a different approach which has worked and is still working after 12000 miles. The solution I devised is on the forum here http://foc-u.co.uk/index.php?action=downloads;sa=view;down=43 
The new shaft I now have if I ever decide to install it is 17.82mm and the nut is tight going on it, compared to my original being 17.2, but nowhere the minimum 17.5mm.


Do you know if the threads in the upgraded nut are larger than the threads in the original nut (ie so they engage deeper with the threads on the shaft), or is the only difference the extra 3mm width of the nut?.
Thanks.

unfazed

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Re: Sprocket Nut
« Reply #5 on: 01 April 2015, 08:58:39 pm »
As far as I can make out the nut is standard and the only real difference is the thickness and the torque setting was higher.

I fitted the damper and cover from a 99 sprocket cover and 12mm nut to stop the nut falling off the shaft and leaving me stranded when the sprocket came off the splines like it did the first time it happened.



crickleymal

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Re: Sprocket Nut
« Reply #6 on: 02 April 2015, 08:45:02 am »
What about some loctite on the thread as an extra precaution?
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bandit

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Re: Sprocket Nut
« Reply #7 on: 02 April 2015, 09:03:20 am »
I used Blue Loctite as easier to remove than using the red stuff.

fazersharp

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Re: Sprocket Nut
« Reply #8 on: 02 April 2015, 09:05:46 am »
Here you are ---- some stuff about the NM and threadloc http://foc-u.co.uk/index.php/topic,14924.msg169123.html#msg169123
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fazersharp

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Re: Sprocket Nut
« Reply #9 on: 02 April 2015, 09:29:43 am »
So this has re-ignited in my head a debate I was having here a while ago its all here http://foc-u.co.uk/index.php/topic,9920.msg102281.html#msg102281 if you can be arsed.

But in a nutshell I rang my local dealer about this and they then rang yamaha with my reg and vin number and they came back saying that 98s are not affected by the issue, I then attempted to find via this forum a 98 owner running the original sprocket and nut with the issue and could not find any and now we have crickleymal  running a 98 with no problems and also rhinoeli running a 98 and thin nut with no problems, so I still can not find a 98 owner with the problem (running and untouched OEM sprocket)

I have a theory
If the problem is the wrong sized shaft then could it be that the bike was first made in 97/98 at a low rate and then when it really took off, production was stepped up and extra shaft making machines were drafted in to cope with demand and its these ones that were not made to the correct spec which then got fitted onto the later models. But also at the same time the original factory with the correct spec were still producing correct ones so during the production run some later bikes did have the correct spec shaft like all 98s.

Discus !!

Edit --- I should add that I do have an upgraded 12mm nut sitting on my shelf and do monitor the oem one.
« Last Edit: 02 April 2015, 09:35:06 am by fazersharp »
I don't do rain or threat there of. dry rider only with no shame.

crickleymal

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Re: Sprocket Nut
« Reply #10 on: 02 April 2015, 10:08:49 am »
To be fair I don't know whether or not I have a problem  :rolleyes . The bike's only done 15k and I don't know whether the chain has been changed or anything. No idea whether it's gone back on a recall either.
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fazersharp

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Re: Sprocket Nut
« Reply #11 on: 02 April 2015, 10:13:57 am »
There was no recall and I would guess at 15k you are still on OEM --- as am I with 16k
I don't do rain or threat there of. dry rider only with no shame.

unfazed

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Re: Sprocket Nut
« Reply #12 on: 02 April 2015, 05:21:18 pm »
The worst affected were the Foxeyes and the first of the fuel injected FZs
« Last Edit: 02 April 2015, 05:22:34 pm by unfazed »

limax2

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Re: Sprocket Nut
« Reply #13 on: 02 April 2015, 06:11:36 pm »


Do you know if the threads in the upgraded nut are larger than the threads in the original nut (ie so they engage deeper with the threads on the shaft), or is the only difference the extra 3mm width of the nut?.
Thanks.


I think the thread in the nut is the same size on diameter but with greater length of engagement.
Here is a drawing that I did long ago, (and has cropped up on this and other sites since), which shows the difference.



YamFazFan

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Re: Sprocket Nut
« Reply #14 on: 02 April 2015, 08:07:34 pm »
To be fair I don't know whether or not I have a problem  :rolleyes . The bike's only done 15k and I don't know whether the chain has been changed or anything. No idea whether it's gone back on a recall either.

For a quick check without taking the sprocket cover off, if you crouch down alongside the rear wheel and shine the beam of a torch along the chain run to behind the sprocket cover (takes a little while to manoeuvre yourself to the perfect position) you can get a pretty good view of the nut. If you can see any shaft thread/s beyond the end of the nut, chances are you have the original 9mm thick nut.