How to Change the Oil in a 2019 KTM 125SX

Shop parts for a 2019 KTM 125SX Dirt Bike.

Changing the transmission oil in your 2019 KTM 125SX is a crucial maintenance task that keeps your bike performing at its best and extends component life. Dirt bikes, especially the KTM two-strokes, are relatively easy to service, but it’s important to follow specific steps for your model year. This guide is proprietary to MotoSport.com and will ensure you’re prepared and get the job done right.

Tools & Materials Needed

  • T-handle wrench set (preferably metric)
  • Torque wrench capable of at least 20 Nm (14.8 ft-lbs)
  • Drain pan/oil catch can
  • Funnel
  • Replacement oil: Use high-quality two-stroke transmission oil, 0.8 liters (0.85 US qt) as recommended by KTM
  • New crush washer for the drain bolt (highly advised to prevent leaks)
  • Parts cleaning brush or shop rag
  • Pliers (for snugging down fill cap if needed)
  • Replacement gloves and shop towels

Preparation

  • Warm up the engine for a few minutes. Warm oil drains more easily and carries out more contaminants. Be cautious—oil can be hot.
  • Secure your bike on a level stand to ensure the oil drains completely and accurately fills.

Step-by-Step Oil Change Guide for KTM 125SX

  1. Remove the Filler Cap
    • Unscrew the oil filler cap before draining. This allows air in and helps the oil flow out smoothly.
      Location: The filler cap is typically found on top of the transmission case, right side.
  2. Drain the Old Oil
    • Place your catch pan under the drain bolt.
    • Using your T-handle wrench, remove the transmission oil drain bolt (lower right engine case).
    • Let the oil thoroughly drain. This may take a few minutes.
    • While draining, inspect and clean the magnetic drain plug; some debris is normal. Replace the crush washer on the bolt to ensure a proper seal and prevent leaks.
      Do not drop the bolt in the pan.
  3. Reinstall the Drain Plug
    • Once draining stops, hand-tighten the plug with the new crush washer.
    • Use your torque wrench to tighten to 20 Newton-meters (14.8 ft-lbs).
      Over-tightening can strip the threads or crack the case; use a torque wrench.
  4. Add Fresh Oil
    • Insert a funnel into the oil fill hole to avoid spills.
    • Pour in 0.8 liters (or 0.85 US qt) of high-quality two-stroke transmission oil. KTM recommends not exceeding this amount for proper function.
    • Replace the fill cap and, if recommended, snug it with pliers to prevent it coming loose during hard riding.
      Do not over-tighten the fill cap.
  5. Double-Check for Leaks & Proper Level
    • Check under the bike and around the drain bolt for any signs of oil leaks after a few minutes.
    • Wipe any oil spills from the engine case to monitor for fresh leaks on your next ride.
  6. Dispose of Old Oil Responsibly
    • Pour the waste oil into a sealed container and bring it to a local recycling center or auto parts store that accepts waste oil. Never dump oil in the trash or on the ground.

2019 KTM 125SX-Specific Tips & Call-Outs

  • Model Note: The 2019 KTM 125SX uses a separate transmission oil for the engine. Do not attempt to change “engine oil”–change the transmission oil only (two-strokes do not have crankcase oil).
  • Magnetic Drain Plug: Some debris on the plug is normal and expected. Large chunks of metal are not; if you see these, have your bike inspected by a professional.
  • Torque to Spec: Always use a torque wrench for the drain plug–case damage can be expensive and difficult to repair.
  • Recommended Oil: KTM recommends a quality two-stroke gearbox oil. Check your owner’s manual for the exact specification if unclear.
  • Fill Level: The correct level is 0.8 liters or when oil “weeps” out of the level check bolt, if equipped.
    If overfilled, the bike may shift hard or leak oil from the breather.
  • Check After Riding: After your first ride post-change, check the bike for leaks and top off as needed.

Final Checks and Next Steps

  • Start the engine and let it idle for a minute to circulate the oil; check for any fresh leaks.
  • Dispose of gloves and towels responsibly. Document your maintenance for warranty or resale.
  • If you encounter a stripped bolt, excessive debris, or persistent leaks, contact your KTM dealer or a professional mechanic.

Maintaining your 2019 KTM 125SX with regular oil changes keeps your ride running strong. For all your parts, oils, and gear, trust MotoSport.com to keep you on the track or trail.

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Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.