My simple Front Sprocket Fix

[packie]

yep. new nut, washer and sprocket.


My guess is that the dimensions of the nut/shaft are wrong (design flaw) so that the nut is just slightly too big and when hot (expanded) can jump threads

Now you know why I did my simple fix. Thats serious sh!t, but i'm not surprised. When I torqued my new nut up...I found that at about 60nms it felt like the nut was going to strip or jump it's threads as you put it. I went as far as I could go, but I don't trust their nuts one bit....not with my life, anyway. I used stronger wire but might do a proper job and put a "stopper" on the end of the shaft like "unfazed" did.

[Dead Eye]

I forget who, but someone did post up that this is exactly why the nut fails. Its due to a manufacturer defect where Yamaha failed to produce output shafts of the correct diameter. I can't remember the exact sizes at the moment, but anything less would cause the threads to strip / skip etc causing the nut to eventually fail. Correctly sized output shafts typical have no faults at all from what I've gathered.

Mine torqued up to 90Nm the other day with no issue or iffy feeling so its definitely worth keeping an eye on yours. Also, I believe 70Nm was originally recommended for the old nut, but Yamaha revised this to 90Nm for the new 12mm nut

[pointer2null]

I check it from time to time and in the six year or so I've had the bike the worst it's been it about one or two turns loose.
Still pretty shite though. You'd have though Yam would produce an undersized nut to match the bad shafts

[packie]

I check it from time to time and in the six year or so I've had the bike the worst it's been it about one or two turns loose.
Still pretty shite though. You'd have though Yam would produce an undersized nut to match the bad shafts

You'd be damn sure if it was a new bike there would have been a recall and the whole shaft replaced. They relented and gave "Unfazed" the whole set of parts to sort out himself.

What I would be worried about in your case is this....if it's constantly jumping the threads, eventually one day all the rubbing of the threads on the nut from skipping over the harder threads on the shaft might wear the threads on the nut so much that there will be no more bite to cling onto the shaft and you might have a total catastrophic failure before you get the chance for your next check-up.

I would liken your nut working a little loose constantly as to being like a warning sign to you...you know...like when you get a little pain every now and again in your chest and you keep saying to yourself "sure a heart attack couldn't possibly happen to me...i'll be grand once I constantly keep an eye on things". Well life don't work that way. Disaster could strike at an instant without you even knowing.

I had those type of small warning signs but took heed and got checked out and discovered I had a mild heart attack and I never even knew it!! They didn't even know it in the hospital after two ECGs as it never showed up. It was that mild a heart attack. It only showed up in my bloods and they discovered two badly blocked arteries after an angiogram. That was 6 years ago and I don't think I would be conversing to you now if I didn't take heed to the warning signs that my body was telling me and let those arteries block up further. Your bike is telling you the same thing....that all is not well down there. Your choice, your life.

See "Unfazed" download for his fix and the damage it caused his nut and shaft over time. I was talking to him personally and his whole sprocket dropped off, but he was haunted that he was at a near standstill.

[pointer2null]

I understand what you're saying. One of the reasons I'm not too owrried is on both the sprocket nuts I've had they both seem to undo one/two threads worth but then never seem to get any worse. It seem like when the pressure is reduced there isn't enough deformation in the thread to allow it to jump again.
In order not to tempt fate though, I will check it this Saturday.

[pointer2null]

Just looked at the wire fix again and I'm not sure that would even have an effect. The wire holds the nut to the sprocket right? If it's the sprocket thats forcing the nut over the threads then the wire will just keep the sprocket against the nut as the pair of them work their way off the shaft. (assuming the forces don't stretch/snap the wire).
One foccer used to put a spot weld on the sprocket and grind it off when it needed removing.

[Dead Eye]

I understand what you're saying. One of the reasons I'm not too owrried is on both the sprocket nuts I've had they both seem to undo one/two threads worth but then never seem to get any worse. It seem like when the pressure is reduced there isn't enough deformation in the thread to allow it to jump again.
In order not to tempt fate though, I will check it this Saturday.

This could be that over time, the vibrations and force on the first few threads (when the nut is tight) has caused them to wear. Once the pressure is off the nut and its moved on to some better quality threads, it stops moving... still not a good sign though

[packie]

Just looked at the wire fix again and I'm not sure that would even have an effect. The wire holds the nut to the sprocket right? If it's the sprocket thats forcing the nut over the threads then the wire will just keep the sprocket against the nut as the pair of them work their way off the shaft. (assuming the forces don't stretch/snap the wire).
One foccer used to put a spot weld on the sprocket and grind it off when it needed removing.

It's not the sprocket thats forcing the nut off. I lost mine nut and tab washer and was driving around for 1200 miles unaware of the fact with the sprocket still in place doing up to speed of 100mph. If the sprocket was on a forced outward journey, it would have come off too. The sprocket stayed on due to just a tiny little bit of rust which created a flimst bond. I was able to pull the sprocket off by hand easy enough when I changed my chain and sprockets. So there are no abnormal forces pushing outwards from the sprocket onto the nut.

One posters theory (which I attend to agree with) is that because the nut or shaft is isn't the right size and that there is some play between the two, the nut is vibrating to and fro and the threads are eventually getting damaged and stripping from all the rubbing with the shaft. And the shaft threads are getting damaged too. Your nut has just found a new set of decent threads on the shaft to latch onto. In time, it's possible that they will fail too and so on and so on.

That is why my wire job will do the trick. It's there to keep the nut in position. It can't work it's way outward anymore. On top of that, the wire that is on my sprocket takes a fair bit of force to cut through it with a sharp  pliers. So it is pretty tough enough to handle anything that might want to travel outwards even with a bit of excessive force.

Finally, as I stated elsewhere, I'm not advocating to have anyone to do it my way. I just posted this as a simple fix that I'm confident will work. Find another way like the spot weld or tapping the centre of the shaft to take a nut and large washer like "Unfazed" did. But for God's sake man, do something. Last year I have a horrendus fall at only 20mph and the damage to my body was appaling even with all my gear on. So just imagine if yer bike should lock up solid at 50-60mph and the consequences. Don't say you haven't been warned...not just by me, but by what your nut and shaft is doing at the moment.

[Dead Eye]

packie, are you not worried that the nut will pull the sprocket off now? Don't kill me, I'm just thinking aloud ^^

If it is the nut just vibrating off by itself, then nothing in theory will stop it from doing so bar extra resistance / grip to the output shaft. So, potentially, now that the nut is secured to the sprocket, as it comes lose, it will pull the sprocket with it, rather than the sprocket holding the nut in place... I'm not saying it will happen, its just something that crossed my mind - there may well be something I haven't considered which prevents this.

[pointer2null]

I can't imagine that the nut is simply vibrating off (the thread would need to be non existent at that point). I suspect that the socket is "bouncing" back and forth (left to right) and impacting the nut, forcing it off the drive shaft. The only reason the sprocket doesn't follow it immediately is that the chain holds it in line. Also with a high tension on the chain it will act to pull the front sprocket into line with the rear sprocket.  It would be interesting to see a breakdown of speed, sprocket alignment and engine mount condition (loose or soft mounts would allow the engine to rotate anti clockwise, when viewed from above, under load changing the alignment of the two sprockets) on bikes that have lost the sprocket.

[darrsi]

Random idea, but what about using P.T.F.E. tape on the threads before tightening up the nut?  :think
You know the white stuff that plumbers use to waterproof pipe joints.
Surely that would take away the vibration, and fill any possible imperfections of the thread making the nut more difficult to move?

[packie]

Random idea, but what about using P.T.F.E. tape on the threads before tightening up the nut?  :think
You know the white stuff that plumbers use to waterproof pipe joints.
Surely that would take away the vibration, and fill any possible imperfections of the thread making the nut more difficult to move?

.....a better idea.....don't use a nut at all!  :eek

Seriously!!....while I was waiting for my nut to arrive I needed the bike because I couldn't be arsed to take my Bandit out of dry drock.. So what I did was, on the shaft I put a very very tightened Jubilee Clip that you use for hoses ect. I tell ya one thing, I should have just left it there and saved myself £11 on a nut. It was rock solid and a bas!a%d to get off when my nut did arrive. I rather have that than going around with a dodgy nut loosening every so often.

[stevierst]

Hell fire packie, you should be on the engineering design team with ideas like that.

Sent from my HTC One X using Tapatalk 2

[Fazerider]

Random idea, but what about using P.T.F.E. tape on the threads before tightening up the nut?  :think
You know the white stuff that plumbers use to waterproof pipe joints.
Surely that would take away the vibration, and fill any possible imperfections of the thread making the nut more difficult to move?

:rollin

[darrsi]

[quote author=darrsi link=topic=6468.msg60761#msg60761 date=1362063855]
Random idea, but what about using P.T.F.E. tape on the threads before tightening up the nut?  :think
You know the white stuff that plumbers use to waterproof pipe joints.
Surely that would take away the vibration, and fill any possible imperfections of the thread making the nut more difficult to move?

:rollin
[/quote]


What's so funny?  :rolleyes

[Fazerider]

[quote author=Fazerider link=topic=6468.msg60781#msg60781 date=1362078067]
[quote author=darrsi link=topic=6468.msg60761#msg60761 date=1362063855]
Random idea, but what about using P.T.F.E. tape on the threads before tightening up the nut?  :think
You know the white stuff that plumbers use to waterproof pipe joints.
Surely that would take away the vibration, and fill any possible imperfections of the thread making the nut more difficult to move?

:rollin
[/quote]
What's so funny?  :rolleyes
[/quote]
Sorry, assumed you were joking.
PTFE, being the slipperiest substance on earth, is pretty much the opposite of threadlock.

[His Dudeness]

packie, are you not worried that the nut will pull the sprocket off now? Don't kill me, I'm just thinking aloud ^^

If it is the nut just vibrating off by itself, then nothing in theory will stop it from doing so bar extra resistance / grip to the output shaft. So, potentially, now that the nut is secured to the sprocket, as it comes lose, it will pull the sprocket with it, rather than the sprocket holding the nut in place... I'm not saying it will happen, its just something that crossed my mind - there may well be something I haven't considered which prevents this.

killed by a 5 page answer :lol

[His Dudeness]

[quote author=darrsi link=topic=6468.msg60783#msg60783 date=1362078605]
[quote author=Fazerider link=topic=6468.msg60781#msg60781 date=1362078067]
[quote author=darrsi link=topic=6468.msg60761#msg60761 date=1362063855]
Random idea, but what about using P.T.F.E. tape on the threads before tightening up the nut?  :think
You know the white stuff that plumbers use to waterproof pipe joints.
Surely that would take away the vibration, and fill any possible imperfections of the thread making the nut more difficult to move?

:rollin
[/quote]
What's so funny?  :rolleyes
[/quote]
Sorry, assumed you were joking.
PTFE, being the slipperiest substance on earth, is pretty much the opposite of threadlock.
[/quote]

wrong! banana skins are the slipperiest substance on earth :lol

[Dead Eye]

[quote author=darrsi link=topic=6468.msg60783#msg60783 date=1362078605]
[quote author=Fazerider link=topic=6468.msg60781#msg60781 date=1362078067]
[quote author=darrsi link=topic=6468.msg60761#msg60761 date=1362063855]
Random idea, but what about using P.T.F.E. tape on the threads before tightening up the nut?  :think
You know the white stuff that plumbers use to waterproof pipe joints.
Surely that would take away the vibration, and fill any possible imperfections of the thread making the nut more difficult to move?

:rollin
[/quote]
What's so funny?  :rolleyes
[/quote]
Sorry, assumed you were joking.
PTFE, being the slipperiest substance on earth, is pretty much the opposite of threadlock.
[/quote]

Unfortunately true and backed up by wiki (granted not the MOST accurate source, but still)

"PTFE has one of the lowest coefficients of friction against any solid."
http://en.wikipedia.org/wiki/PTFE

[darrsi]

It's not something that i use but just thought i was adding a possible idea to solve the issue.


But obviously i've made a huge mistake and must apologise unreservedly for sounding like a dumb foccer!  :moon