General maintenance



  • Hi ! I’m going to do a small chronical of my bike so I can hopefully give you some info for my upcoming questions , so bear with me 🙂

    I bought a second hand Dt125r 1997 model, with 38K Kilometers on it at the time of the purchase.
    Since then i replaced the cylinder ( cause the old one was scored due to piston breaking at the edge ) , the piston and the small bearing. During the rebuild I noticed some rust on one side of the crankshaft flywheels ( the bike was not used for more than a year before I bought it ) , I cleaned it as best as I could . I don’t remember if I checked for big bearing play and if I did , I did it by feel and not found anything. Also I replaced the Mikuni vm26 that the bike came with due to physical damage ( previous owner mentioned the original carb got stolen and the vm26 was the replacement ) , with a Mikuni TM28ss from a donor bike I had laying around.
    Front and real brake discs got changed from the donor bike as well. The exhaust system is a DEP pipe , with an arrow silencer . I also serviced both the expansion pipe , de-carboned it and repainted it ( it was covered in rust ), and silencer.

    After the “rebuilt” the bike was used for one year with almost no issues , it has travelled 2300 km, mostly in city riding, including a 270km trip at 110km/h cruising speed for almost 2h ( with breaks in between so I can feel my a** again 😵 )

    Now to the point of this :

    • At 40k + kilometers, what should I check as maintenance ?

    • Is there some parts in the engine and the bike overall that I definitely need to replace or check ?

    • What is considered a weak point for these bikes ? Meaning , what's the first thing to probably fail ?

    Some issues I noticed over the year :

    • The carb overflows if you leave the tank valve open and park the bike , and the fueling feels to the rich side. Also if you snap the throttle from idling it bogs for a second before it revs up. For the carb , I’m going to order the needle and seat and the bowl gasket . Also probably buy an ultrasound cleaning machine and clean the carb with it.

    • There are some metallic ringing noises when riding , like if you leave some change in your car and they vibrate to the engine, but way more subtle.

    • The overall engine noise seems to take a higher frequency aggressively when the engine gets into the exhaust tuning rpm ( around 6500- 7500rpm ). You can hear the change between 5000 and 6500 clearly ( almost like a small supercharger gets activated after 6000 )

    • The front brake feels like it’s having two grip points as you press the lever, in low speeds the first “point” is enough to gently slow down but if you press a little more it grips suddenly harder. It’s like the breaking is not linear.

    • Back brake works smooth, but it has a long travel in the foot pedal till it becomes effective.
      That’s all I can think of right now. Ask me freely for more details.



  • @panmil92 the small supercharger would be your powervalve activating and also I suspect the metallic noise is also your powervalve bushing wearing out



  • Check your brake pads for wear and discs for grooves in them.

    I'd also suggest checking brake fluid and bleeding it out with fresh fluid. I'd hazard a guess at it never having new brake fluid since it was new.

    I'd change the gearbox oil in the bottom end as well, as it's often neglected and people fail to realise that their gearbox actually has separate oil in the bottom end. Do NOT use car oil. A lot of people say you can use ATF fluid or car engine oil, a load of nonsense it clogs your clutch plates up. Use Yamaha recommended oil from a dealer. £20-£30 for 5 litres of oil is better than £150-£200+ for new clutch plates. The drain plug is behind your rear brake pedal at the bottom of the engine.

    I also recommend double checking the oil feed is actually working, mine failed at 60MPH and demolished my engine. I went to premixing after that, but you get all the problems associated with premixing, such as dirty carb that needs cleaning regularly. If you ever do a overhaul, switch your oil feed pipes for clear ones. Also remember if you pull the pipes off your oil feed you need to run premix as it gets air in the lines.



  • @DTRLuke
    Thanks for the suggestions Luke ! Yes , the brake fluid hasn’t being changed by me for sure. The braking pads I replaced them with brand new, and the discs came from my donor bike and are also almost new regarding the thickness.
    Even though I checked them against a glass surface, I don’t have the equipment to check if they are bent.

    Regarding the oil in the gearbox, when I got the bike it was over-flowing, and had a really dark color and smelled like burned car oil, so I drained it and flushed the gearbox with some clean oil a couple of times. But to my ignorance , and since I followed the manual to the letter, I just replaced it with a generic car engine oil to the manual specs ….. I found out you should not do that , after almost a year later , so at this point I don’t know what to do with it. Should I completely replace the clutch plates ? Can I clean them somehow ?

    The autolube seems to be working on point, I never let the level drop too low, as not to introduce any bubbles in the system. It may actually be using a little more oil than necessary , as I see some deposits on the spark plug, but overall I need to refill it every 700Km if I remember correctly .



  • I have only ever used 5-30w car oil and never had issues. Had my DT nearly 10 years. The only time I've had issues is where I used Castrol Magnetec oil. Otherwise never missed a beat.



  • @Calum Good to hear. Since a never ridden a factory new DT I can't tell if there is a difference with this oil. Anyway since I know it now, if I ever replace the clutch discs I will make sure to get the correct oil. Any other tips regarding the maintenance? I always had a fear regarding the big end bearing and the crank ones..., how do I know if they need change ?



  • @panmil92 I don't recall there being any certain type of weak point. Fairly bullet proof motors.

    It's just general items. Bearings, bushes and seals.


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