Another Stripped Counter shaft :(

[Drezza]

Hi,


Bought a 2002 FZS600 last month, was praying that I wouldn't be one of the unlucky ones with a stripped countershaft, but looks like I am 


I removed the front sprocket cover last week and was relieved to see no welded nut, and the sprocket was still there, so I assumed it was all fine. However after replacing the sprocket for a new one and tightening it back up, it would tighten a small amount, and then loosen again, so I'm lucky it didn't come off over the last 400 miles I've done.
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The threads on the shaft look shot, so I'm not sure if re-threading would work?


I'm thinking I may as well weld the nut to the shaft, would I have to weld the full circumference of the nut, or would some spot welds suffice?


I'd like to be able to grind it off and replace in the future if possible.


Also, will a garage be likely to weld this for me, or would it be classed as unsafe? 

[HydrocarbonPrimate]

If I was you I'd find a good tig welder, He / she might be able to run beads around the shaft thread to build it up and then re-thread it

[Drezza]

If I was you I'd find a good tig welder, He / she might be able to run beads around the shaft thread to build it up and then re-thread it

Has this ever been done before? I'd be worried about not being able to get the nut on again if it couldn't be threaded.

[joebloggs]

Not sure if this good idea or not but how about a grub screw provided you managed to get the nut torqued up the grub screw would prevent it backing off

[Fazerider]

A couple of decent spots should be sufficient.
Coincidentally, I changed my sprocket this afternoon… angle grinder to cut the old welds and clean up the end of the shaft, new sprocket, old nut back on which tightened up just enough to clamp the sprocket firmly and a couple of fresh welds and it should all stay put.


Nice idea to build up the shaft and then cut a fresh thread, you could actually choose a pitch suitable for the job. I doubt it could be done in-situ though, that much welding would probably get the shaft hot enough to roast the oil seal.

[Bretty]

Could you not drill down the centre of the shaft (using progressively larger drills). Then tap a thread in it. Then (with a load of loctite) refit and nip up the new nut and retain it with a big washer with hex screw down the middle of the shaft, again with loctite?


Just thinking out loud. I refitted the gearbox in my bike last Xmas. It cost me £100 in parts, gaskets and fluids and a three day weekend.

[Fazerider]

Could you not drill down the centre of the shaft (using progressively larger drills). Then tap a thread in it. Then (with a load of loctite) refit and nip up the new nut and retain it with a big washer with hex screw down the middle of the shaft, again with loctite?

Yes, someone on here (Unfazed?) did this a while back, though I can't find the post at the moment.
It certainly looked neater, it'd be interesting know how well it's held up.

[Bretty]

In my head it seems like a good idea...
but also in my head these sprocket nuts shouldn't be failing or require such high torques as they are under no load?!?!

[Drezza]

In my head it seems like a good idea...
but also in my head these sprocket nuts shouldn't be failing or require such high torques as they are under no load?!?!

Yeah that does make me wonder, perhaps if Yamaha used a reverse thread, then the nut wouldn't spin off?

[fazersharp]

In my head it seems like a good idea...
but also in my head these sprocket nuts shouldn't be failing or require such high torques as they are under no load?!?!

Yeah that does make me wonder, perhaps if Yamaha used a reverse thread, then the nut wouldn't spin off?

The reason for it is that some bikes were produced with very slightly undersized (diameter) output shafts and t is Russian rulet as which one you have got. 

[Bretty]

...The reason for it is that some bikes were produced with very slightly undersized (diameter) output shafts...

I've heard this said before. If this is true, does anyone know what diameter it should measure so we could check?

[Fazerider]

...The reason for it is that some bikes were produced with very slightly undersized (diameter) output shafts...

I've heard this said before. If this is true, does anyone know what diameter it should measure so we could check?

Yes, I've seen the same claim many times, though all from the same source and it is only a theory.
17.8 mm is the typical diameter measured across the threads, Yamaha say to change the shaft if it's less than 17.5 mm. I've not heard of anyone measuring theirs and finding it undersize unless it's previously been battered to death by a loose nut and/or sprocket. Shafts being manufactured undersized will remain a myth until that happens.


The nut is of such soft steel that the threads on the shaft often survive it coming loose. The real damage is done if the nut falls off the end of the shaft, then the sprocket can move onto the threaded portion and chew it up. Later Fazers are at much greater risk of this because they lack the damper plate on the inside of the sprocket cover which tends to prevent a loose nut, particularly the 12mm one, from falling off the end of the shaft.


Earlier Fazers also had the factory nut put on with a ridiculously strong threadlock, anyone who's undone one can tell you that it requires a very long lever, a lot of force and it sounds like a gunshot when it finally lets  go. I was convinced I'd broken something!


The nut doesn't necessarily rotate to become loose. Several times when it's happened to me the washer was still engaged with both the nut and the splines meaning the nut has managed to "hop" a thread. There has also been excessive wear on the inside edge of the sprocket and I suspect the sideways hammering from the chain might be the cause of the nut becoming loose in those cases.

[Drezza]

So how would my threads become worn if the nut had aways been on the shaft? My only thought is that it was manufactured under size.

[Fazerider]

So how would my threads become worn if the nut had aways been on the shaft? My only thought is that it was manufactured under size.

How do you know it's never come off? And have you measured the shaft?

[daviee]

mabe thats why the bike was sold because it happened and was patched up , i would go with the spot welds and tbh it will out last the bike if done properly and can be done plenty of times when you need to change the sprockets

[HydrocarbonPrimate]

A couple of decent spots should be sufficient.
Coincidentally, I changed my sprocket this afternoon… angle grinder to cut the old welds and clean up the end of the shaft, new sprocket, old nut back on which tightened up just enough to clamp the sprocket firmly and a couple of fresh welds and it should all stay put.


Nice idea to build up the shaft and then cut a fresh thread, you could actually choose a pitch suitable for the job. I doubt it could be done in-situ though, that much welding would probably get the shaft hot enough to roast the oil seal.

oil seal would be a concern,
is there much shaft sticking out with the sprocket removed, like enough to get a wet rag around it?


 

[unfazed]

Could you not drill down the centre of the shaft (using progressively larger drills). Then tap a thread in it. Then (with a load of loctite) refit and nip up the new nut and retain it with a big washer with hex screw down the middle of the shaft, again with loctite?

Yes, someone on here (Unfazed?) did this a while back, though I can't find the post at the moment.
It certainly looked neater, it'd be interesting know how well it's held up.

Check the downloads, http://foc-u.co.uk/index.php?action=downloads;sa=view;down=43  I uploaded the file of how I did it. A bit of a belt and braces job, used a circlip and a bolt with a washer. 16000 mile on it since I did it. Change the sprocket at 12000 miles and replaced the circlip, it still running like a clock.

[Drezza]

Thanks guys, think I'll just weld the nut on with two tack-welds for the time being if the local garage will do that. If not I will probably try the circlip and bolt method.

[daviee]

Could you not drill down the centre of the shaft (using progressively larger drills). Then tap a thread in it. Then (with a load of loctite) refit and nip up the new nut and retain it with a big washer with hex screw down the middle of the shaft, again with loctite?

Yes, someone on here (Unfazed?) did this a while back, though I can't find the post at the moment.
It certainly looked neater, it'd be interesting know how well it's held up.

Check the downloads, http://foc-u.co.uk/index.php?action=downloads;sa=view;down=43  I uploaded the file of how I did it. A bit of a belt and braces job, used a circlip and a bolt with a washer. 16000 mile on it since I did it. Change the sprocket at 12000 miles and replaced the circlip, it still running like a clock.

thats a nice job and tbh more than adequate on my cbr 600 all that holds the sprocket on is an m6 and washer so i cant see no reason why it would fail 

[Drezza]

So I've got this far... 15mm Circlip on like what was done in that PDF. Does the circlip look seated correctly here?





Also, tried drilling the shaft with a Bosch HSS drill, wouldn't even touch it. Do I need to get something like a cobalt bit?


Thanks!

[daviee]

looks good i would go with cobalt drills  as the shaft will be hardened

[Bretty]

Yes it'll be hard as foc. And you'll want a few bits as you might need to start small and work up in sizes.

[unfazed]

Circlip looks fine.
I used a very high quality HSS bit, but with slow speed with a variable speed drill.
The shaft is case hardened and using a slow speed it will get through the case hardening.
If the speed is to high it will over heats and destroy the bit.

[Drezza]

All reassuring to hear thanks guys!


I have ordered a 3.5 cobalt drill bit so hopefully that will work, I'd imagine once I've broken through the case hardened surface then it should be much easier. (touch wood). 


Will keep you updated.

[daviee]

should once you get past it slowly slowly catchy monkey lol