Countershaft threads stripped

[johnkol]

I went to replace the CS sprocket on my WR250R, and the nut would not turn. Using a breaker bar I was able to turn it, but then realised it was not unthreading.

It appears that the threads have stripped (aftermarket sprocket installed by previous owner), so what are my options now?

1. Dremel the nut out at the flat cut-outs of the CS, then use a thread file to fix the threads (or may have to use a die to re-thread).
2. Take it to a machine shop where other options may be available?
3. Any other ideas?

Here's what it looks like:

 

[augustiron]

Are you sure you are not turning the CS?
I usually leave the chain on and use the rear brake to hold it while I unscrew the nut.
Are you sure of LH or RH threads?

If ok on both points, ok to carefully grind the nut then punch it off. If you are lucky, just the nut threads failed. If the CS is stripped. Well, pull out your wallet.

 

[stangmx13]

its not uncommon on the internet to find ppl that have welded the nut on because they don't want to split the cases and replace the countershaft.

nut still looks peened somewhat. I wouldn't be surprised if you were just turning the engine and/or slipping the clutch.

 

[thedub]

What method are you using to hold the countershaft still while you turn the nut without the chain on?

 

[Rumbo Sur]

My first thought was that it's a left hand thread??? ... and you tried to loosen it going wrong direction? Possible?

Hopefully a machinist can use a die tool to clean up the threads on the shaft and re-use it.

Hope it can be saved, good luck!

If it's frozen, next time try a 50 50 mix of Acetone and ATF. Does a good job freeing up frozen/corroded/rusted fasteners. Soak over night. Way better than
Liquid Wrench and many others.

 

[johnkol]

What method are you using to hold the countershaft still while you turn the nut without the chain on?

I usually leave the chain on and use the rear brake to hold it while I unscrew the nut.
Are you sure of LH or RH threads?

That's exactly what I did; with chain on, I stomped on the rear brake and tried to unthread the nut. After encountering so much resistance, I tried RH, but there was no difference; that was when I knew the threads were stripped.

I removed the chain in anticipation of using this sprocket tool that I have on order.

nut still looks peened somewhat. I wouldn't be surprised if you were just turning the engine and/or slipping the clutch.

I completely removed the peening before attempting to turn the nut; the flange was still mangled in a couple of places, but it is relatively soft metal, so I do not expect it to provide much resistance.

This picture shows the state of the flange a little better:

If ok on both points, ok to carefully grind the nut then punch it off. If you are lucky, just the nut threads failed. If the CS is stripped. Well, pull out your wallet.

You mean split the cases to replace CS? I was hoping that a machinist would be able to add some material (even JB Weld), and re-thread with a die. There are no significant lateral forces on this nut, so this should be sufficient for keeping the sprocket in its place.

 

[Tri750]

I would take a Dremel with a cutoff wheel and cut the nut off at the slot at 12:00 o' clock .
Once it's off, assess.
Order or buy a few nuts now.
If it has to go to a shop, choose one familiar with motorcycles.
When fixed, replace the seal, o-ring if one present.
And keep the extra nuts in your tool box.
If they are the "pinched" or dimpled nuts, they are intended to be used once.

 

[afm199]

Use impact wrench next time

 

[Enchanter]

I don't see evidence of the nut or shaft (gigiddy) stripping. As was pointed out previously, I too suspect that the output shaft was turning. Put the chain back on and put a 2x4 between the spokes of the wheel and resting on the swingarm. Try again.

 

[afm199]

I don't see evidence of the nut or shaft (gigiddy) stripping. As was pointed out previously, I too suspect that the output shaft was turning. Put the chain back on and put a 2x4 between the spokes of the wheel and resting on the swingarm. Try again.

 

[auntiebling]

i'll +1 for trying again. instead of relying on the brake and your coordination (kinda hard to mash the brake while simultaneously reefing on the breaker bar and apply 100% effort to both) put something in the rear wheel to jam it against the swingarm. think 2x4, but that'll probably be too big. ratchet straps or rope would likely work as well once you get all the slack out.

the threads adjacent to the slot in the countershaft don't look buggered, or covered in shavings, which would likely be the case if the nut stripped.

putting a little heat on the nut, as accurately as possible so countershaft stays as cold as possible, would also help. a small butane torch would work well, something like this
https://www.amazon.com/GiBot-Culina...8&qid=1526747266&sr=8-3&keywords=butane+torch

if you have a propane plumbers torch it'll probably heat everything up which isn't all that helpful and could damage seals. hot to the touch is all you need. not red or anywhere near it.

 

[mototireguy]

Impact gun might be the magic sauce.

 

[ST Guy]

But BEFORE cranking on it any more, know for sure which way to turn it. 'Hard to say from the pix, but it looks like a right hand thread so turn it counterclockwise.

And heat up the nut some before cranking on it. Do NOT get it red hot!

 

[johnkol]

I don't see evidence of the nut or shaft (gigiddy) stripping. As was pointed out previously, I too suspect that the output shaft was turning.

You guys were right: the countershaft was turning, which means that there was nothing wrong with the threads, but that means something worse -- there is something wrong with the CS splines:

and the corresponding sprocket splines:

How on earth was the bike working without a problem? And why was the spline shearing split between the CS splines and the sprocket splines?

And the bigger question, what do I do next? I put on a new sprocket, and it engages the CS splines that are still in good condition, but how long will these last?

Any idea how much it would be for a shop to split the cases in order to replace the countershaft?

 

[buellistic]

Maybe a spacer issue or the wrong sprocket..
File it clean and check it with the right sprocket And spacer..

 

[ST Guy]

I wonder if the sprocket was installed the wrong way.

 

[seadog]

Glad to see you were able to remove the sprocket. Last one I did had a sprocket that could go on either way, but only one way was the correct orientation.

If it were mine; I'd probably weld the sprocket on so I could ride the bike this summer and plan on rebuilding it this winter. If you go this route make sure the weld ground is attached to the counter shaft not the engine or frame. You'll pass welding current through the bearings = no bueno.

I don't know how much a shop would charge but it would be cheaper if you could remove the engine and bring that in.

 

[johnkol]

I wonder if the sprocket was installed the wrong way.

Hmmm, the sprocket has a flat side and a grooved side; it was installed with the flat side towards the engine, which I think is correct.

In any case, I tried it with the grooved side towards the engine, and it seems to make no difference with respect to its position relative to the countershaft.

Maybe a spacer issue or the wrong sprocket..
File it clean and check it with the right sprocket And spacer..

From the parts diagram the spacer appears to be the correct one.

I removed the spacer and tried a new sprocket -- and there was no difference on how far the sprocket would go, which means that the sprocket correctly engages the splines.

One thing that I found odd was how little force I had to apply to remove the CS nut; the specs call for 69 ft-lbs of torque, and the nut was certainly not torqued that much. I'm thinking that maybe Yamaha relies on the spacers and the excessive torque to take up most of the forces on the CS sprocket, so if the nut is lightly torqued there is excessive pressure on the splines and they fail.

 

[stangmx13]

The similar nut on my R6 loosens all the time even when torqued correctly. That’s y it gets peened and safety wired on my bike. It’s such a bad design. The M10 (iirc) bolt on my CBR is half the torque, is ez to work on, and doesn’t come loose ever.

I wonder if the prev owner ran the bike without the nut peened. It loosened, the sprocket moved over, and riding on it destroyed half the splines. Then they tightened everything without replacing the sprocket.

 

[johnkol]

The similar nut on my R6 loosens all the time even when torqued correctly. That’s y it gets peened and safety wired on my bike. It’s such a bad design. The M10 (iirc) bolt on my CBR is half the torque, is ez to work on, and doesn’t come loose ever.

I wonder if the prev owner ran the bike without the nut peened. It loosened, the sprocket moved over, and riding on it destroyed half the splines. Then they tightened everything without replacing the sprocket.

I have a CBR too, so I know what you're talking about. Yes, the Honda design is much better.

The nut was not peened at the cutouts; it was smashed a bit, which may indicate that some effort was put to secure it, but was not done correctly. The scenario you describe seems plausible.

If it were mine; I'd probably weld the sprocket on so I could ride the bike this summer and plan on rebuilding it this winter.

I am not going that route. I have a CBR that I can ride instead, so it is not essential that I get the WRR ready for the summer season -- although it would be great if I could so because I had been planning a Utah trip.

I have been watching some RMATVMC videos on splitting the cases, and it looks doable, so I'll either do that, or give the engine to Thumper Racing for a stroker crank and in the process ask them to replace the countershaft.

The question now is, if I were to put a new sprocket on and torque it correctly, how long will the rest of the splines withstand the load on them?