Countershaft sprocket shaft splines repair?

[Chuck78]

Looking for some knowledge from experienced machinists, as I know we have two resident machinists on here who are fairly active...

Being that the '89-'06 200/220 transmission output shafts are NLA, & the shaft splines are getting more & more worn on most bikes, I was wondering if someone could enlighten us on how one could potentially weld up and machine then harden the repair area for a proper spline restoration?


Would a particular steel alloy of filler rod be recommended for TIG welding the affected area?

A horizontal mill with a dividing head fixture would certainly be the tool used to machine down the area back to stock. I've got some antique manual mills (1946 Atlas MFB horizontal mill! Enco 1980's round column vertical mill, 1959 South Bend Heavy 10L lathe),but need a dividing head aka Atlas Indexing Centers still... I'm just an amateur that makes good use of the lathe & vertical mill with DIY hobbyist projects...

Once machined down, how does one properly harden the steel repair area? Heat up red hot to a certain temp and quench in _____???

Is the original finish a nitrided finish? Or just a result of a case hardening process?

It's useable but less than perfect, but something like this pictured is about the best one can expect from most random eBay countershafts (1 of my 3 is far worse than this):

Screenshot_20250310-182837.png (1.06 MiB) Viewed 1076 times

After reading some pinion gear spline repair postings on the Practical Machinist forum, although it may not be the ultimate repair as strong as the original shaft and easy repair would be to clean, degrees, bake for additional cleaning, degrease again, and use some silicon bronze MIG wire on the splined area that is worn, to build it up and then very easily machine it down without having to cut into the original hardened material....
I'd definitely feel more confident in the repair process doing that myself, but skeptical on how long the silicon-bronze filler would hold up.


https://www.practicalmachinist.com/foru ... st-3498321

I'd considered making a spline engagement add-on adapter piece by cutting down another sprocket and removing the entire outer toothed portion, just leaving the center hub, and machining a recess into one side of it against the splines so that you could slide it onto the end of the shaft after the sprocket has been installed as original with the snap ring, & the recess machined into this piece would allow it to fit tight against the other sprocket with the snap ring nesting into the recess cut. Then drill & tap 2 or 3 holes from this new outboard spline engagement piece and bolt it to the actual sprocket.
Perhaps a combination of the silicon-bronze repair and this would perhaps have a chance of lasting through several top ends but might necessitate more frequent bottom end tear-downs.
A TIG welded repair with proper machining and hardening would probably be the best bet? Perhaps with the right filler, hardening would not be required? I would imagine it is hardened to some extent from the factory, although hardening significantly would introduce the potential for the shaft just to sheer under extreme loads.

Lastly, as an alternative method to keep running a worn out shaft spline, I found that I believe it was a 1983 KX500 sprocket uses the same splines but has a flange that extends further inboard, and can be used after cutting down the seal bushing sleeve collar piece appropriately, as this will engage splines that are further in than what the OEM sprocket ever used.
That also fits a couple years of KX and KDX 250 models. It is a scarce part though.

[kdxdazz]

Silicon bronze is very soft and wouldn't last 2 minutes, just throwing ideas out there, there's a lot of Pakistani YouTube videos than show spline and gear repair, maybe check from the video what kind of rod they are using, even though our parts are very small compared to what they do you could take the stick rod,remove the flux and use it as a Tig filler rod, I would also add in pre and post heat, I work for a hydraulic company, the cylinders and shafts are made of 4140, when welding we preheat to 200 degrees Celsius then wrap in a fire blanket for slow cooling, they are then machined and sent for nitriding,
I've done quite a few Kickstarter repairs and I use Allen keys as filler material for the repair, incredibly hard if Tig welded quickly due to the quench effect
Another option would be to weld with regular Tig filler wire then DIY case hardening which is quite easy with a forge
But having said all this to rebuild your engine and install the repaired shaft and it may or may not work is a big headache
I've used the kx500 sprocket with great success , I would be inclined to go this direction
Have you tried the loctite 660 fix ? I've tried it on 2 of my kdx's , 1 worked well, the other one didn't but maybe I didn't clean it well enough, I'm in Australia now so will try the loctite fix on my kdx here as the shaft is slightly worn, I think the trick to the loctite fix besides being clean is when installing the sprocket, hold it in the turned direction of travel, that way it's hard up against the splines

[kdxdazz]

Yet another option, there are companies in Bangkok which makes shafts for the Kawasaki kr150 engine which is loosely based in the kdx E series engine,they use the same 6 splines but in a smaller diameter, maybe we could start a goodfundme for the development of new kdx shafts

[Kawibunga]

I'd lean towards building from new. Creating a new manufacturing drawing would not be the problem (I'll add that to my list!). The question would be is there enough demand to build and sell 20 of them, as that's about the qty you'd need to build to bring the price out of the "prototype" machining range into the "production" range.....

I'd have to educate myself on metric spline specs and callouts though....... option B would be to just fake it and draw it all in inches. Which would actually be easier up here, as even though Canada has been metric since 1970, the vast majority of the manufacturing (in Alberta anyway) is all spec'd in inches..... but I digress