Lost Sprocket Nut: Road Fix / Permanant Fix

[Reserector]

On my commute home, my cat went into permanent neutral.  I coasted into a parking lot and diagnosed the problem to be a lost front sprocket nut.  Not one to be easily defeated, I devised a plan to repair it and ride home.

I won't detail the whole ordeal, because it is a long story.  The fix is so simple, cheap and effective, however, that I want to share it here.  Keep this fix in mind in case this common failure happens to you.

Find a drink with a large cap.  (I walked to a nearby store and bought a Gatorade G2.)
Next,enjoy your drink as you walk back to the bike.
Hopefully you have the factory tool kit.  Using the medium size allen wrench and the spark plug wrench (for additional leverage) remove the cover screws.
Using the 10mm wrench, remove the shift arm and slide the cover off.
Using the 24mm wrench and the cheater pipe, loosen the rear axle nut.  Loosen the adjuster nuts and kick the wheel forward to put slack in the chain.

Put the front sprocket back on the shaft.

Using a pocket knife, carve most of the flange off of the bottle cap.  Start at the edge and work your way around as if peeling an apple.  Trim down in a spiral so you have good control.  Leave about 3/16 inch (4mm).
Find a place where you can lay the cap down and stab through it.  (A piece of wood, or a lawn.  not the seat.)  Or, better yet, spin your knife tip through it.  Just be careful not to bear much pressure, because that could lead to injury.
Enlarge the hole carefully.  Keep it centered.  Make it obviously too small by at least 1/8 inch (3mm)  Press it onto the shaft using the 24mm wrench.  Center the opening in the wrench over the cap and press hard.  The wrench will allow you to evenly apply a good deal of force.  The goal is to get a tight "stretch" fit.  The natural tension of the plastic will create a one-way push-nut of sorts.

Use a screwdriver to work the center portion onto the shaft as far as it will go.
Re-install the cover and shifter.  Readjust the chain.  Put your tools away and be on your way.   

How well does this hold?  Alarmingly well.  When I went to remove my bottle cap, It took a lot of screwdriver prying and a pair of channel lock pliers to get it off.  It was rediculous!

Here is my fix with some strips of duct tape added.  In hindsight, this was a waste of duct tape.  It was certainly the cap that held the sprocket on.  (Click the pic to enlarge the view.)



   

This cap will stay in my tool kit from now on.  You never know.....



   

My shaft threads would not allow the new nut to reach torque, so I snugged it as much as I dared, then tack welded the nut and spacer washer to the sprocket. The spacer is just to get the nut to where the threads are healthier.  I hope this holds up.  :/

My weld solution. I have a yamaha lock washer, but used a spacer in its place to get a stronger tack weld.



   

[dwinslow20]

You, sir, earned the prestigious Macgyver Award in my opinion!

Nice post! Maybe this should be added to the master "how to" list?

[bretb]

Res, you are fricken amazing! There is no way I would have come up with a gatorade cap or anything else for that matter other than a nut. I don't even thing the best mechanics I know would come up with something that ingenious.

Bret

[Reserector]

Thanks for the props.
Here's an update: The tack welded nut did not hold. The tack weld held fine, but the whole deal walked off the threads on my way to work this morning.
I coasted into a well-lit parking lot and opened it up. I took the sprocket off completely so I could break the tack weld by prying it apart. With the nut and washer removed, I reinstalled the sprocket with the G2 cap.

I rode the remaining 20 miles to work with no more problems.

My next move is to use either a snap ring, or a collar. I will update when I find a practical long-term solution.

[Reserector]

My plan is taking shape.  One of these should do the job. 



   

[bretb]

Good to hear you didn't have to buy a new Gatoraid. Are you going to submit this thread to one of the chick mags about use and reuse?

The c-clip would be a fix. What about just simply drilling a hole and lockwiring the nut? I don't know if there is a slot on the end of the shaft that is deep enough for the c-clip to hold. What my concern would be, and in no way questioning your MacGyver skills, is the nut already migrated loose with a tack welded nut. If the nut migrates again, it will stop at the c-clip, but be loose on the shaft and possibly cock itself.

[Reserector]

My plan was to start the engine and let the shaft turn as I cut a snap ring groove in it with a thin cut-off wheel.

I picked up some fresh 1/16" x 3" cut-off discs on my way home.  When mounted on my mandrel and spun up in the die grinder, I could see that the disc did not run very true.  I did a test groove on scrap and was not pleased with how wide and sloppy it looked.  With very little splined shaft prodtuding past the sproocket, this would simply grind away that margin if I tried to cut a groove freehand.

So I gave up. 





HA!  RIGHT!
So anyway, Plan B was to guide the cutter somehow.  I found that if I held it against a surface, it spun true.  I dug out an old sprocket that was the same thickness as my new-ish sprocket, and put it in place.  The sprocket kept the disc true, but I did not feel that I could turn the shaft with the engine now that a sprocket was in place.
As luck would have it, the cut-off wheel against the sprocket turned the shaft.  The air powered die grinder lacked the needed torque, so I put the cutter in my electric drill.  Now I was able to control the shaft speed by adjusting the pressure against the sprocket face. 



   

With a workable plan, I chose a snap ring that would seat against the bottom of the splines and still be removeable.  [7/8" I.D External retaining ring]
From there, I bagan cutting the groove a little at a time and test fitting the ring.



   



   

Once I reached the desired depth, I cleaned off the grinder grit, reassembled the chain and sprocket, and installed the sprocket with a yamaha lock washer and the new snap ring.

There is no side play, and The ring was a bit of a struggle to install because the groove is so deep.  I rode to work this morning with full confidence that this sprocket will not fall off on its own ever again.



   

[Riceburner]

Wow. Keep us updated as to the life of the snap ring in use.

[bretb]

Definetly keep us updated as to what you see and experience. I don't imagine you'd get any vibration from the c-clip on the shaft, but it is possible. Looks like a nice fit by the photo, more that 50% deep on the channel to the clip.

[Reserector]

As a reference, this repair was done at 61,200 miles.

Let me just add that I no longer dread changing front sprockets.

[Reserector]

Just a quick update;
I have not had a single issue since eliminating the sprocket nut and going to a snap ring.
What's more, I was looking at a buddy's Suzuki DR350 and saw that its front sprocket is held on the same way from the factory.  Further proof that this method works, even in off-road grit and mud.




   

[Reserector]

As a reference, this repair was done at 61,200 miles.

Let me just add that I no longer dread changing front sprockets.

Update: the cat is over 74,000 miles now. I just replaced chain and sprockets. The clip showed no signs of movement. These clips are a pain if you don't have a good pair of snap ring pliers, but it beats worrying about a nut loosening.

[tdah73]

I missed this thread 1st time around. Good work, Res. I've never had a problem with the stock bendy lock washer, but still a good work-around.

The goal is to get a tight "stretch" fit.

That's pretty much always the goal.

[Reserector]

Based on my observation and study of this failure, my hypothesis is this:
The sprocket splines wear slightly over time. This allows the nut and sprocket to move as a pair during acceleration/deceleration cycles.
The bendy washer prevents the nut from unscrewing, but allows it to vibrate as the slight rotation causes wear on the threads.
Once the threads have worn sufficiently, the nut will "walk" off the threads without rotating. once it falls off, the washer gladly follows.

I say this because 1.) it seems to happen to older, worn out chain and sprocket sets. If the sprocket and nut were replaced before spline wear set in, it would not have failed.
2.) I WELDED the sprocket, nut and washer together and they STILL CAME OFF. That (in my mind) proves that it does not have to rotate to come off the threads. It can vibrate off.

[Reserector]

Over 40,000 miles on this fix with no change or problems.

4,807 views
I read about sprocket nut problems on many other brands and models. I wonder if this has helped others.

[camnlo]

I thought for sure I had posted to this tread about my experience with the sprocket nut on my bike, but I seem to be mistaken... anyway, I bought my bike with about 25k on it and the chain and sprockets were in good shape so I didnt really look that closely at the sprocket nut at that time. Fast forward many miles later and the chain is wearing out and the sprokets are worn, I go to remove the front sprocket nut but it turns out the previous owner must have had a problem with it coming loose so he fixed it....permenantly,
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thats right spot welded that sucker in a couple spots and had some kind of collar around the treads. So to get the nut and welds and collar off I spent a couple days with my drimel and a cutting blade cutting it all off the shaft (it took about 3 days because my drimel is a rechargable battey type and it doesnt last very long). At this point I was thinking I might have to replace the output shaft but then I found this thread, I did mine almost exactly the same way you did except I didnt use the big washer, I cut the grove in the spline and have the clip against the sprocket, it has been at least 10k miles since then and have had no issue, I open it up and check it when I change my oil and it has never even looked loose. I have pulled it off a couple times just to see if it was bending or anything and it looks like new (once I wipe all the grime off of it)

[Reserector]

That's awful to do someone. I can understand welding it out of desperation, but to sell it without mentioning it is underhanded.

[Reserector]

Another related success story: http://www.yzf600r.reserector.com/thread...cket%2Bnut

[01YZF6]

Thanks Mark for your how to on the front sprocket fix!
Got to love the forums!!!
Saved my butt today for sure!

Took the bike for a test ride/final shakedown. Got 1/4 mile from the driveway and nothing...plenty of vroom but no goooo...
Pulled over and the chain was really loose and sagging. Pushed it home and took off the sprocket cover. No axle nut!!! The sprocket was hanging on the shaft. Air Dremel, retaining ring, and a few hail mary's to not f it up! Done!

So I managed to find the axle nut on the roadway too. Threads on but wont tighten down. I put it on with a new washer ring and blue loctite for good measure.

Reason #244 why the forums are priceless!

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[Reserector]

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