2008 KX125 Drivetrain

[ItsJuniorJ]

Hey Everyone!

 

After figuring out the electrical issues on the KX125, which I posted about the a couple of weeks ago, I’ve had another issue arise.

 

While running laps at the local track, to make sure the bike was doing everything it should, the rear wheel locked up and nearly sent the rider over the handle bars.

 

Opening up the right-side inner case and inspecting parts I found that the kick start gear had welded itself to the shaft.

 

My question: how could this happen?

 

I’ve just rebuild the engine with a new Vertex top-end, and this was the first “hard” ride after engine break in. The point here being that all fluids and internals were fresh, so what could cause so much heat to generate between the kick start gear/shaft to weld them together like this?

 

I’m genuinely confused?

 

 

 

[mlatour]

A misplaced lock ring or shim during re-assembly perhaps?

[turbo dan]

Poor lubrication.  I have seen this type of failure with ATF more than once, I no longer use it in these gearboxes.

What type of lube were you running?  Presumably the level was correct?

[ItsJuniorJ]

Poor lubrication.  I have seen this type of failure with ATF more than once, I no longer use it in these gearboxes.

What type of lube were you running?  Presumably the level was correct?

 

It was ATF!

 

I was to use it only for the initial run in and then change to the Liqui Moly gear oil I use in my KX250.

 

Lesson learned now, damn!

[ItsJuniorJ]

A misplaced lock ring or shim during re-assembly perhaps?

Everything was assembled as the manual directed actually. That, I can be 100% sure of.

[Motox367]

Yep lack of lubrication.  Riding mx should use oil 

[mlatour]

I wouldn't be too quick to blame ATF as other more high stressed components would have failed before this.

In the case of this KX, I'd first suspect the oil level rather than the type of oil.

 

Did you set the amount by the oil check bolt or, by adding the recommended volume?

Edited November 28, 2018 by mlatour

[turbo dan]

Rotella 15w40 is a good choice.

Hopefully this is the only part that took damage.  When my KDX200 chunked a tranny bearing I found a badly damaged first gear cog as well.  Similar type of damage, you could see that the gear had been overheating when it was freewheeling on the shaft.  That was my first gearbox failure with ATF.

Next one was my first 125 motor.  Same bearing chunked, oddly enough.  Input shaft, left side.  That gearbox was in decent shape other than the damage caused by the bearing coming apart but I found one of the gears on the output shaft had galled onto the shaft.  It hadn't locked up but it had to be hammered off of the shaft which destroyed the gear.  That was the second time I had issues with ATF.  Twice is enough for me.

[mlatour]

Dan, by memory from past topics,

by chance were those bikes on 40 hours gear box oil change intervals?

[turbo dan]

9 minutes ago, mlatour said:

Dan, by memory from past topics,

by chance were those bikes on 40 hours gear box oil change intervals?

Not remotely close.  I think you're thinking of somebody else.

[mlatour]

My mistake Dan, mixed you up another member.

Edited November 28, 2018 by mlatour

[turbo dan]

I do remember that thread.  Dude wasn't having any problems so whatever oil he was running was working.

Same for me.  Never had tranny problems with any other lube.  Run thousands of hours on numerous different bikes, many were clapped out when I got them.  I put tons more hours on all of them and I never had a single gearbox failure.  Traditionally I've run Bel Ray Gear Saver and Motul Transoil in two stroke gearboxes, lately I've been running Rotella since it's been working so well in my 600.  I still run Motul in my 250 but I like to spoil that bike.

[ItsJuniorJ]

Rotella 15w40 is a good choice.
Hopefully this is the only part that took damage.  When my KDX200 chunked a tranny bearing I found a badly damaged first gear cog as well.  Similar type of damage, you could see that the gear had been overheating when it was freewheeling on the shaft.  That was my first gearbox failure with ATF.
Next one was my first 125 motor.  Same bearing chunked, oddly enough.  Input shaft, left side.  That gearbox was in decent shape other than the damage caused by the bearing coming apart but I found one of the gears on the output shaft had galled onto the shaft.  It hadn't locked up but it had to be hammered off of the shaft which destroyed the gear.  That was the second time I had issues with ATF.  Twice is enough for me.

It was a friend who filled the oil, so I’ll check the amount they used, but I know it was ATF.

I do hope nothing else got too hot, but I know that nothing broke off internally to damage other parts.

I’ll get the new gear and shaft installed and run the bike with correct oil to see how it shifts, and go from there!

[ItsJuniorJ]

I wouldn't be too quick to blame ATF as other more high stressed components would have failed before this.
In the case of this KX, I'd first suspect the oil level rather than the type of oil.
 
Did you set the amount by the oil check bolt or, by adding the recommended volume?

I’ll drop the oil and check how much comes out. So far I only dropped the coolant because I checked the bike with it lay on its side.

[Motox367]

5 minutes ago, ItsJuniorJ said:

 

It was a friend who filled the oil, so I’ll check the amount they used, but I know it was ATF.

I do hope nothing else got too hot, but I know that nothing broke off internally to damage other parts.

I’ll get the new gear and shaft installed and run the bike with correct oil to see how it shifts, and go from there!

 

Take good look at the idler gear also . One in between that gear and clutch basket.  Make sure its not sloppy loose 

[ItsJuniorJ]

Take good look at the idler gear also . One in between that gear and clutch basket.  Make sure its not sloppy loose 

Sure thing! Thank you for the tips. If you have more then fire them in the thread when you have time!

[Motox367]

1 minute ago, ItsJuniorJ said:

 

Sure thing! Thank you for the tips. If you have more then fire them in the thread when you have time!

 

Those two things usually are what have problems with if run low on oil. Ive had engines come in that wont shift cause pinion gear seized to shaft but long as still shifting and no whining noises you're probably ok there ?

[ItsJuniorJ]

Those two things usually are what have problems with if run low on oil. Ive had engines come in that wont shift cause pinion gear seized to shaft but long as still shifting and no whining noises you're probably ok there [emoji846]

Got it! I’ll follow the pointers and see what comes back.

[Motox367]

2 minutes ago, ItsJuniorJ said:

 

Got it! I’ll follow the pointers and see what comes back.

 

Ya man ? also wouldn't hurt to check waterpump and powervalve bearings while have cove off

[ItsJuniorJ]

Ya man [emoji106] also wouldn't hurt to check waterpump and powervalve bearings while have cove off

I’ve added these to the “to-do-list”!