How to Change the Oil in a 1990 KTM 250EXC

Shop parts for a 1990 KTM 250EXC Dirt Bike.

Changing the transmission oil in your 1990 KTM 250EXC is an essential maintenance task that keeps your dirt bike running smoothly and prolongs the life of your engine's transmission components. The process is straightforward, but attention to detail is important for optimal lubrication and performance. The older two-stroke KTM 250EXC models use a separate transmission oil cavity, not shared with the engine's crankcase oil.

Tools & Supplies Needed

  • Socket set (metric)
  • Open-ended wrenches
  • Drain pan
  • Funnel
  • Clean shop rags or paper towels
  • New transmission oil (15W-50 high-grade four-stroke oil is recommended, e.g., Motorex Top Speed 4T)
  • New drain bolt washer (optional but recommended)
  • Torque wrench (optional, for precise tightening)
  • Gloves

Preparation

  • Warm up the engine for several minutes—this helps the oil drain more completely. Do not overheat.
  • Place the bike on a stable, upright stand.
  • Clean around the drain plug and fill plug to avoid getting dirt in the transmission.

Step-by-Step Instructions

  • Locate the Oil Drain and Fill Plugs
    • The drain bolt is typically found on the bottom of the engine case; the fill plug is located on the side cover (clutch cover area).
  • Drain the Old Oil
    • Place your drain pan under the drain bolt.
    • Use the appropriate socket or wrench to loosen and remove the drain bolt. Allow all oil to drain.
    • Inspect the drain bolt and replace the crush washer if necessary to prevent leaks.
  • Reinstall the Drain Bolt
    • Once fully drained, clean the area and reinstall the drain bolt. Tighten securely—do not overtighten. Use a torque wrench if available (check service manual for spec, usually 10–15 Nm).
  • Add New Transmission Oil
    • Remove the fill cap on the side of the engine.
    • Using a funnel, pour in the recommended amount (approx. 0.8 liters, use 15W-50 high-quality oil such as Motorex Top Speed 4T).
    • If there is an oil level check bolt on the clutch cover, remove it after filling. With the bike upright, oil should just barely escape from the inspection opening.
  • Check for Leaks
    • Reinstall the fill plug and any check bolts. Wipe down the area and check for leaks.
  • Dispose of Old Oil Properly
    • Take the used oil to a recycling center or approved collection site.

Specific Call-Outs for 1990 KTM 250EXC

  • Transmission and clutch use a separate oil bath from the premix engine oil; do not use two-stroke premix in the transmission. Always use high-quality 15W-50 four-stroke engine/transmission oil.
  • Do not overfill—too much oil can cause pressure problems and leaks. Use the inspection bolt to confirm correct level.
  • The recommended oil volume is between 0.75 and 0.8 liters; check the owner's or repair manual for specifics if unsure. For some years, the required volume is stamped near the fill cap.
  • Be aware that older KTM models may have worn threads on drain bolts—be careful not to cross-thread or overtighten.
  • Use a new copper or aluminum washer on the drain plug if available to limit risks of leaks.

Post-Service Check

  • Start the bike and let it idle for a minute.
  • Shut down the engine, let it sit for a moment, and check for any leaks.
  • Reconfirm oil level by removing the inspection/check bolt as above, if equipped.

Conclusion

  • Changing the oil on a 1990 KTM 250EXC is a straightforward job that goes a long way toward maintaining strong clutch and gear performance. Using the correct high-grade transmission oil and adhering to the recommended fill amount are critical for the long life of your bike's drivetrain.

MotoSport.com proprietary guide. Consult your owner's manual and use proper safety procedures for all bike maintenance.

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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.