Front sprocket nut. Broken thread?

[chris-seed]

I can't tell if there should be more thread on the rod than this. I have lost two sprocket nuts over the passed 2 weeks and have just bought another one to fit. The nut spins on the rod to a certain point, then goes tight and then slack again. Is the thread busted? And what are my options now?





Thanks
Chris

[pefrey]

Those threads look shot. I don't know if the threads are supposed to go all the way to the splines. If you don't have a tap and die set that big, bring it to a shop or machine shop (with a new sprocket so they can measure the correct thread pitch) and see if they can fix it.

[willandrip]

From the photo;

Cheap/ill fitting sprocket ( bet it is JT) is too thin, allowing the sprocket to slide back and forth on the splines.

Space it off the c/cases using one lockwasher.
Use another correct lockwasher on the nut side.
Uprate the nut using one from an R6.
Use locktite on the (clean threads.)

Do not try to keep torqing it up to spec if it is tightening then going slack; all you are doing is destroying what little threads are left.

The nut is m18 ; cannot remember if 1.25 or 1.0 pitch ( pretty sure 1.25mm)

Read the posts in a topic about 10 or 11 previous to this.

I had saved much,much worse shafts than that. !

[pefrey]

And clean your chain.

[chris-seed]

Cheers guys.

What's special about the R6 front sprocket nut? Is it wider than the FRZ nut?

I've ordered a new sprocket (a Sunstar one) and the plan was to weld the nut in place this week. I'm a bit worried about the space in between the nut and the washer (the bit where there doesn't seem to be any thread). I don't mind welding the nut in place but if I can salvage the shaft without doing any welding then that would be nice.

[willandrip]

The R6 nut is wider and hence more threads.
The part of the shaft without threads is correct and as manufactured.
Are you using the correct lockwasher? you do not mention it .

I would not weld that shaft; but if you do , only the locknut to the very end of it.

Have a google of pics of ;Talon
Renthal
Afam
gearbox sprockets and compare with JT, Sunstar and the other plain pressed out ,cheap sprockets.
You will notice straight away the difference in quality.

[willandrip]

There is a technical drawing of the new nut compared to the old one ; halfway down this link.

http://foc-u.co.uk/?topic=92.0

[chris-seed]

Excellent. Thanks for the help guys. I've ordered an R6 sprocket nut. As far as I'm aware I am using the correct locknut. I have 2 FZR 600 locknuts to suit a 1989 bike which mine is.

I'll see if I can get away without welding. The new nut should help a lot. Also the chain was very slack, there was over 2 inches of travel in the chain. This meant that I was able to slide the sprocket off the drive shaft with my hands. I've tightened the chain now and I can no longer move the sprocket by hand. So I'm guessing that this will help too.

I'll let you know how I get on with the new parts. Hopefully no welding will be needed.

Thanks again for the help.

[rcaircraftnut]

You could also use a second nut to lock against the first nut if there are enough threads. I do this on all my 4 stroke model airplane engines to hold the props on as they have a tendency to kick back ant through nuts in the grass where you can't find em, .

[chris-seed]

A quick update:

Ive put on an R6 sprocket nut, a new 14tooth sprocket and tightened the chain, as it was really loose before. I've used blue threadlock on the sprocket but and the but tightened up really well. I had cleaned the thread on the drive shaft a bit beforehand so maybe this helped. Its strange because the R6 sprocket but that I received seemed to be identical to the FZR sprocket but. Weird. Took the bike for a short test drive and all seemed well.

I'll be riding it for an hour or so tomorrow so we'll see if it all holds up.

I also added a small amount of metal epoxy paste to the end of the sprocket but just so that I could measure to see if the but comes undone at all. No welding needed.

Now for an oil change and a brand new chain.