2017 txt gearbox noise

[SamAs]

Hi all, Ive recently got a 2017 txt racing 300 and it’s making a noise in the gearbox. There is a ticking noise that im assuming is the chain as it does this in time with the master link. But once I shift into 4th gear the box starts to whine like crazy. I know theyre straight cut gears but it sounds like a race car, it’s almost louder than the engine. I’ve been told that it’s a case of possibly bearings or something in the box but seen on an older post on here that the whine is “somewhat normal”

im just trying to figure out if I need to take the engine out or not as I’ve never done it before and dont want to do it if I don’t have to. But I want to do as much as I can myself to save money as the bike cost me a lot. 
 

thanks in advance for any help, I might end up taking it out soon anyway it’s just a bit daunting 

[RonH]

SamAs, I don’t think I’ll be much help to you but I have a 23 TXT 250 that does NOT whine when shifting to 4th. I think the engines are nearly the same as the 2017 but I could be wrong. I’m no mechanic and there are others on here that will have better judgement than I, but I simply wanted to let you know that in my experience, on my bike, there is no whine shifting to 4th. If there was I would be worried. So far, working on my own bike, I’ve found it’s simpler than I ever imagined to do it myself. If you’re mechanically inclined and have common sense, I’d say go for it on your own. Just review and follow what you find in the maintenance manual if you have it. I’m all about saving cash too. Good luck!

you can download the 2018 manual for free here: https://drive.google.com/drive/folders/1xOzbrZQDO_W_AxpjvHU1xJMOqfRsVfPJ

Edited Monday at 06:19 AM by RonH

[konrad]

4 hours ago, RonH said:

...you can download the 2018 manual for free here: https://drive.google.com/drive/folders/1xOzbrZQDO_W_AxpjvHU1xJMOqfRsVfPJ

That's a very nice manual!  Anyone learning to do maintenance on a trials bike (regardless of brand) would be well-advised to study it. 

Unfortunately, there is almost no content about the gearbox (see page 49).

[mcman56]

I was curious so looked at the manual.  It looks like the minimum piston clearance for the 250 is 0.050 and the maximum is 0.080.  What is the 0.100 "Assembly" number?

 

 

 

 

[konrad]

At first, I was going to say the "assembly" number is the service limit.  But viewing that table in the context of the other displacements, it makes no sense at all.  It's a horrible table!

[SamAs]

On 9/8/2025 at 11:59 AM, konrad said:

That's a very nice manual!  Anyone learning to do maintenance on a trials bike (regardless of brand) would be well-advised to study it. 

Unfortunately, there is almost no content about the gearbox (see page 49).

Hi, sorry about the jumping between posts I’ll try keep it on this one now, I’ve uploaded a video to YouTube in case you or anybody with either a similar issue or similar experience can listen to. Thanks in advance to anyone who gives it a listen and helps and hopefully this helps you too if you’re here for answers 🙂

hopefully it works. I should mention I’ve been told the clicking is a worn chain or sprockets so replacing the lot. 

Edited 19 hours ago by SamAs
Just the part about the chain at end

[zippy]

Check your rear wheel bearings for play.  I was in an event and had a horrible clicking noise, so much I thought something was wrong in the clutch / transmission. I went so far as to pull the clutch cover off in the paddock to investigate.

I found nothing, DNF the event. later discovered the rear wheel bearings were sloppy as all hell and was causing the rear sprocket to move out of alignment enough that the chain would "click" off the edge of the sprocket.

I couldn't really hear the whine, so I would say it's probably normal.  I can't remember if you state you changed gearbox oil or not, watch for tremendous amount of metal shavings or chunks on the drain magnet.  Some small gook type build up is normal.

[konrad]

I could not tell much from listening to your video at 1x, 0.75x, and 0.5x speed.  I think a better diagnostic would be to video the bike running on a stand in 4th (probably would have to load the motor by using the back brake) and slowly letting it rev.

Note that both 1st gear and 4th gear use three gear-pairs to transmit power though the box.  So the whine should be similar for 1st and 4th.

There is a large ratio change between 4th and 5th, and this will make a clunk and not be smooth.  The farther apart the ratios are, the more pronounced this will be.

Edited 8 hours ago by konrad

[SamAs]

2 hours ago, konrad said:

I could not tell much from listening to your video at 1x, 0.75x, and 0.5x speed.  I think a better diagnostic would be to video the bike running on a stand in 4th (probably would have to load the motor by using the back brake) and slowly letting it rev.

Note that both 1st gear and 4th gear use three gear-pairs to transmit power though the box.  So the whine should be similar for 1st and 4th.

There is a large ratio change between 4th and 5th, and this will make a clunk and not be smooth.  The farther apart the ratios are, the more pronounced this will be.

It may be nothing and just me being paranoid then, I’ll include a link to another video I have taken and if that doesn’t help I’ll try get one like you requested. Thank you for your help though

You can hear a kind of meshing noise on deceleration, as I say though it could be normal 

Edited 5 hours ago by SamAs

[faussy]

Minus the clicking, that sounds normal to me

[konrad]

The clicking sound is not normal.  But it seems the repetition rate is too slow to be something in the gearbox.  I'd look for something external like Zippy's problem first. 

Inspecting the drain oil is a good idea, but knowing the true history of the bike is more valuable.  Did the prior owner sell because there was debris in the drain oil?  Is there a chipped tooth somewhere?

Out of curiosity, I looked for gearbox parts.  It appears KTM is good about making GG parts available.  You can buy individual gears and even a complete transmission assembly (MT40000CT-CSV-1) for $840 USD.

https://trialssuperstore.com/products/gasgas-transmission-complete-19