Date: 17-01-22  Time: 19:58 pm

Author Topic: Loose front sprocket nut...  (Read 2347 times)

Fazero

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Loose front sprocket nut...
« on: 28 June 2021, 01:30:34 pm »
Hey there,
just wanna share with you the slight heart attack I got when I wanted to lube up the clutch actuation mechanism and found my front sprocket nut flopping around. It was hold on only by the washer.
For a brief second I saw myself tearing the engine apart 2 weeks before a big trip.
Luckily after some inspection there is no visible damage to the threads. Ordered the new nut and washer, some loctite and hopefully this will never happen again.
But still a little bad feeling to ride around with that issue back in my mind.


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Re: Loose front sprocket nut...
« Reply #1 on: 28 June 2021, 07:38:23 pm »
Looks like you caught it just in time
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Re: Loose front sprocket nut...
« Reply #2 on: 28 June 2021, 08:59:36 pm »
Good that you spotted it. It's an old issue that doesn't seem to have been mentioned for a good while.  Enjoy your big trip.

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Re: Loose front sprocket nut...
« Reply #3 on: 29 June 2021, 05:19:28 pm »
surely everyone has the new nut by know, lucky find as could have ended badly

Fazero

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Re: Loose front sprocket nut...
« Reply #4 on: 03 July 2021, 12:50:26 am »
Today the new 12mm nut arrived. Cleaned the threads, put some Loctite on there for my head and torqued to 70NM. Hope the problem is solved :rolleyes

b1k3rdude

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Re: Loose front sprocket nut...
« Reply #5 on: 03 July 2021, 08:58:34 am »
Ordered the new nut and washer, some loctite and hopefully this will never happen again.
As this seems to be a common issue and as we need this kind of info for the FAQ I would like to ask the community the following question -

b1k3rdude

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Re: Loose front sprocket nut...
« Reply #6 on: 03 July 2021, 09:00:59 am »
Today the new 12mm nut arrived. Cleaned the threads, put some Loctite on there for my head and torqued to 70NM. Hope the problem is solved :rolleyes
Looking at your photo it looks like the splines on the output-shaft are still in good condition, so the inner part of the washer should engage properly with it. just don't forget to bend up the tabe on the washer after you have tightened up the nut.

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Re: Loose front sprocket nut...
« Reply #7 on: 03 July 2021, 12:08:17 pm »
I am thinking 'Red Locktite' - Gnasher?

If it's Loctite go for 270 green, but you'll need to apply heat first to remove it. 

 
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b1k3rdude

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Re: Loose front sprocket nut...
« Reply #8 on: 03 July 2021, 01:32:11 pm »
If it's Loctite go for 270 green, but you'll need to apply heat first to remove it. 
I assume a normal butane torch can provide enough localised heat for this..?

And if 270 green is the best/extreme, what the next best that doesn't require a blowtorch..?

Gnasher

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Re: Loose front sprocket nut...
« Reply #9 on: 03 July 2021, 01:45:23 pm »
I assume a normal butane torch can provide enough localised heat for this..?

Yep a good torch will reach 600.

And if 270 green is the best/extreme, what the next best that doesn't require a blowtorch..?

There isn't one, you run the risk of the nut undoing.

The use of Loctite as a way to secure FZS600 nuts that haven't had the lay shaft replaced, is totally dependant on the thread being undamaged and the use of the tab washer.
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b1k3rdude

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Re: Loose front sprocket nut...
« Reply #10 on: 03 July 2021, 11:11:48 pm »
Fair enough.

Fazero

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Re: Loose front sprocket nut...
« Reply #11 on: 04 July 2021, 01:22:07 am »
I just used the normal blue Loctite. If this would ever loosen again I will probably go with Loctite 638.

Could you school me on the importance of the washer? Of course I bend it but it should be only an additional security or am I missing something?

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Re: Loose front sprocket nut...
« Reply #12 on: 04 July 2021, 10:16:05 am »
I just used the normal blue Loctite. If this would ever loosen again I will probably go with Loctite 638.

638 is not a thread locker it's for holding/bonding flat cylindrical components i.e. gears on shafts.

Could you school me on the importance of the washer? Of course I bend it but it should be only an additional security or am I missing something?

The washer is what is supposed to stop the nut undoing, not the Loctite.  The use of Loctite is a get around for a design flaw, to which there are two modifications, one redesigned nut, two redesigned (replacement) lay shaft.   Just the nut can work, but this is dependant on thread damage to the shaft.  Using just Loctite there's a high chance the nut will undo, using a lock/washer less so, but it can still undo, more so using 243 what was known as nut lock.

I would suggest you search on the site for sprocket nut and see what can happen.  They don't just undo and fall off they destroy the thread on the lay shaft  and the sprocket cover.  Replacing the lay shaft is a engine out split the casing job, plus the cost of the shaft, which the last I looked is no longer available new.   

I wouldn't advise using 243 or 638 but it's your choice, hopefully you'll get away with it.
« Last Edit: 04 July 2021, 10:51:04 am by Gnasher »
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Re: Loose front sprocket nut...
« Reply #13 on: 05 July 2021, 07:44:33 am »
That shadow looks like a tab washer was on there that hasn't been folded over.
Another one here for loctite 243.
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b1k3rdude

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Re: Loose front sprocket nut...
« Reply #14 on: 05 July 2021, 12:17:10 pm »
- That shadow looks like a tab washer was on there that hasn't been folded over.
- Another one here for loctite 243.
- Common mistake by people that dont know what they are doing.
- Gnasher has recommended Green 270

Gnasher

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Re: Loose front sprocket nut...
« Reply #15 on: 05 July 2021, 01:21:34 pm »
This is really old hat now and all the info is in the FZS600 folder.  The washer doesn't fail and will still be in place and bent over when the thread destroys itself, I mean destroys itself.   The bike will keep going, until it grinds it's way through the sprocket cover enough for the sprocket to fall off, the cover is what holds the nut on and interlocked with the lay shaft splines, driving the sprocket.  Once it's lose it will begin to wear away the lay shaft threads, it's doesn't take long before they're shot, even with some thread left the nut will not lock up even with Loctite 270.  You'll have to change the lay shaft.         

The Loctite application helps prevent I repeat HELPS the threads from destroying themselves due to a design flaw, it can still happen especially if you use 243 or nut lock as it was known.  I tried using it when this saga was first noticed, all still came lose using 243 it took anywhere between 2 - 6k but they all came lose.  Using 270 as far as I'm aware to date, none I did came lose, the bikes I tested this on were a mixture of despatch and everyday commuters all weather bikes, doing up 2k a week.  There's also a point where the threads are too worn even for 270.

It's up to you.           
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Re: Loose front sprocket nut...
« Reply #16 on: 05 July 2021, 08:19:07 pm »
- That shadow looks like a tab washer was on there that hasn't been folded over.
- Another one here for loctite 243.
- Common mistake by people that dont know what they are doing.
- Gnasher has recommended Green 270
Then I'm not surprised that sprocket nuts come undone.
Mine is staked but I don't trust that so I use a bit of loctite.
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Fazero

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Re: Loose front sprocket nut...
« Reply #17 on: 06 July 2021, 12:44:21 am »
For anyone who wonders:

The official Yamaha statement (Service Bulletin M2006-03, for FZ6 and R6, but the part numbers are the same):Use Loctite 620 and torque to 90NM with the new nut and washer...
So I was about right with 638 (choosed because of higher gap filling capabillites). Compared the data sheets and the 620 is better with higher temperatures.
« Last Edit: 06 July 2021, 12:56:16 am by Fazero »

Gnasher

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What version of Loctite to use on FZS600 front sprocket:
« Reply #18 on: 06 July 2021, 09:53:13 am »
As mentioned above all the info is here https://foc-u.co.uk/index.php?topic=92.0 back in the day what 19 odd yrs ago now, where did all that time go. As stated earlier 638 isn't a thread-lock neither is 620.  All Loctite thread-lock compounds start with 2 and their adhesives or retaining compounds start with 6.

Here's what retaining compounds do:

Here are link to the different loctite versions:

I remember talking to a chap in Yam tech dept at the time, asking why they'd chosen 620, the reply was to "fill the gaps in the thread"  I see, so why not use a thread-locker then? I used to know a fair few people who dealt with and knew personalities in Yams tech Dept back in the day, let's say their comments weren't gleaming and may answer why they picked the wrong product, who knows.         

What the bulletin doesn't tell you and Yamaha didn't want to face because of cost.  Is the the condition of the threads is vital, as that's where the problem is, machining tolerance, which is why some fail others don't.  Meaning the lay shaft on used bikes could well be screwed, beyond this fix.  In fact Yamaha did replace some shafts but all on the quiet, they didn't want a recall as it's a big and expensive job and are not alone in that approach. 

Many manufactures will only recall when there's no other option. e.g. good old Hotpoint and their dryers springs to mind. Bearing in mind not all bikes were affected, Yamaha wanted to avoid a recall and have a cheap a fix as possible and one that would kick the problem into the long grass, which it did.  If you slap on 620 and the threads are sufficiently worn, yours look worn, how much I can't say from a picture. It will still come loose, quite when is all dependant on how worn the lay shaft threads are, could be days, months even years depending on your mileage.     

What I do know is if you use 270 the chances of it undoing are reduced further, bearing in mind you had on idea the sprocket nut had come undone until you removed the cover and looked. It's also possible your chain has a good few tight spots by now too. 

The advice offered is to help you, it's up to you, if you use it.  Stick on 243, 638 or 620 even superglue if you wish, it's your bike and pocket. Best of luck with whatever option you choose.           

[I have cleaned up the post bit as this is very useful info and will link it in the FZS600 FAQ - bkd.]       
« Last Edit: 09 July 2021, 11:34:06 am by b1k3rdude »
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Re: Loose front sprocket nut...
« Reply #19 on: 13 September 2021, 08:56:38 pm »
If anyone needs the new nut and tab washer kit I have one sitting right beside me, I sold my 600 years ago now, kit no. is 90891-10124.Anyone near south cambs. is welcome to collect it or cover postage.
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Re: Loose front sprocket nut...
« Reply #20 on: 28 September 2021, 11:27:01 pm »
If anyone needs the new nut and tab washer kit I have one sitting right beside me, I sold my 600 years ago now, kit no. is 90891-10124.Anyone near south cambs. is welcome to collect it or cover postage.
Hello mate, have you still got this nut and tab washer kit?

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Re: Loose front sprocket nut...
« Reply #21 on: 30 September 2021, 01:47:27 pm »
Personal view
 
The sprocket nut is there to stop the sprocket sliding off the output shaft.
 
It doesn’t need to tighten flush with the sprocket to do this.
 
The output shaft is the fault on some of the fazers.  The grooves in some output shafts are cut a slightly too wide.
 
This allows the sprocket to move backwards and forwards on the shaft when placed under load or off load.
 
Because the nut is tight against the sprocket it continually rotates slightly on the threads… wearing them out.
 
The answer in my opinion is grind down the flange on the sprocket nut so that when it tightens on the shaft it is simply flush with the sprocket but does not tighten against it…. And put some grease on the sprocket to further ease the junction between the nut and sprocket. 
 
Therefore there is insufficient ‘grip’ between the sprocket and the nut to allow the sprocket to turn the nut.
 
In essence you want to tighten the nut up on the output shaft but not tighten it up against the sprocket.
« Last Edit: 30 September 2021, 01:54:26 pm by Paul »

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Re: Loose front sprocket nut...
« Reply #22 on: 30 September 2021, 03:16:28 pm »
Personal view
 
The sprocket nut is there to stop the sprocket sliding off the output shaft.
 
It doesn’t need to tighten flush with the sprocket to do this.
 
The output shaft is the fault on some of the fazers.  The grooves in some output shafts are cut a slightly too wide.
 
This allows the sprocket to move backwards and forwards on the shaft when placed under load or off load.
 
Because the nut is tight against the sprocket it continually rotates slightly on the threads… wearing them out.
 
The answer in my opinion is grind down the flange on the sprocket nut so that when it tightens on the shaft it is simply flush with the sprocket but does not tighten against it…. And put some grease on the sprocket to further ease the junction between the nut and sprocket. 
 
Therefore there is insufficient ‘grip’ between the sprocket and the nut to allow the sprocket to turn the nut.
 
In essence you want to tighten the nut up on the output shaft but not tighten it up against the sprocket.

Err no, on all counts.

The sprockets MUST not move in any direction or you get what's known as chatter, which is exactly what this issue was/is.  I've changed many back in the day, some the nut was still locked up tight, others there's was no nut left, the sprocket being held on by the chain tension.   The issue is the nut recess on some earlier nuts and the thread wasn't deep enough to lock against the sprocket and the layshaft shoulder when torqued up.  This enabled the sprocket to chatter and wear the nut facing, which in turn destroyed the nut due to it being softer than both the lay shaft and the sprocket.     
« Last Edit: 01 October 2021, 09:58:33 am by Gnasher »
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limax2

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Re: Loose front sprocket nut...
« Reply #23 on: 30 September 2021, 08:31:27 pm »
Just for interest this is a drawing I did and posted long ago on the sprocket nut topic. I've no information on the manufacturing tolerances but it will effect the clearances to a lesser or greater degree.

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Re: Loose front sprocket nut...
« Reply #24 on: 01 October 2021, 09:52:12 am »
If anyone needs the new nut and tab washer kit I have one sitting right beside me, I sold my 600 years ago now, kit no. is 90891-10124.Anyone near south cambs. is welcome to collect it or cover postage.
Hello mate, have you still got this nut and tab washer kit?
PM sent.
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