How to Change the Oil in a 2014 Yamaha YZ125

Shop parts for a 2014 Yamaha YZ125 Dirt Bike.

Changing the transmission (gearbox) oil in your 2014 Yamaha YZ125 is a straightforward but essential job to maintain peak clutch and gearbox performance. Below you’ll find all the tools you need, step-by-step instructions, expert MotoSport.com tips, and important call-outs specific to the Yamaha YZ125.

Tools and Materials Needed

  • Drain pan – Catches used oil as it drains out
  • Funnel (preferably long spout) – Reaches under the exhaust to fill oil without making a mess
  • Ratchet and 12mm socket – Removes the transmission drain bolt
  • Measuring cup or graduated oil jug – Ensures the proper refill amount
  • 4mm Allen wrench – Used for the oil check (level) bolt
  • Clean rag or shop towels – Cleans up any drips or spills
  • Replacement drain bolt washer (recommended) – Helps seal the drain bolt and prevent leaks
  • High-quality 10W-40 wet clutch compatible transmission oil – 0.69 US quarts (660 ml) capacity

Step-by-Step Guide to Changing Your YZ125 Oil

  1. Preparation
    • Warm up your engine for a few minutes. This helps the oil flow freely and ensures more contaminated oil drains out. Shut off the engine before starting work.
    • Place your bike upright on a level surface or a work stand. Make sure it’s secure and not leaning.
  2. Drain the Old Oil
    • Locate the 12mm drain bolt under the crankcase (bottom of the engine).
    • Put your drain pan directly beneath the bolt to catch the old oil.
    • Remove the drain bolt with your ratchet and socket. Allow the oil to fully drain.
    • Inspect the old oil for metallic particles or discoloration, which could indicate clutch or gearbox wear.
  3. Replace the Drain Bolt and Washer
    • Replace the drain bolt washer if available. This is an inexpensive part that aids in sealing and prevents stripping the casing threads.
    • Tighten the drain bolt with the 12mm socket and ratchet. Tighten to 14 ft-lbs (18 N·m) of torque for a safe seal and to avoid damaging the threads.
  4. Add New Oil
    • Remove the oil fill cap, which is located on the engine’s right side near the clutch cover. It can be hard to reach underneath the exhaust, so use a long spout funnel.
    • Using your measuring cup, pour 0.69 US quarts (660 ml) of 10W-40 motorcycle oil into the engine slowly. This avoids overflowing and possible spillage.
    • Replace the oil fill cap securely.
  5. Check the Oil Level
    • Some YZ125 models have a small “check bolt” secured by a 4mm Allen wrench near the clutch cover. After adding oil, briefly remove this bolt: if oil lightly seeps out, your bike is not overfilled and at the correct level. If not, add small amounts of oil until it does.
    • Replace the check bolt and tighten gently.
  6. Final Steps
    • Wipe up any oil residue with a clean rag.
    • Dispose of old oil responsibly according to local regulations—MotoSport.com encourages recycling used oil at an authorized collection center.

Specific Owner Call-Outs for the 2014 Yamaha YZ125

  • The YZ125 uses a separate gearbox oil system—do not confuse this with premix oil for the fuel; only use 10W-40 (or similar) formulated for wet clutches in the gearbox.
  • The oil fill port can be difficult to access due to the exhaust; a long, narrow funnel is highly recommended to prevent mess.
  • Do not overfill: excessive oil can cause clutch drag and shifting problems. Stick to the manufacturer’s recommended capacity of 660 ml.
  • A crushed or damaged drain bolt washer is a common source of leaks. Replace this washer at every oil change.
  • Torque specs are crucial: Over-tightening the drain bolt can strip engine case threads.
  • If you see any leaks around side covers or the drain bolt after an oil change, replace gaskets or washers promptly to prevent future damage or mess.

Conclusion

Changing the oil on your 2014 Yamaha YZ125 is a quick task that pays off with smooth performance and extended transmission life. Always use fresh, high-quality motorcycle oil and replace washers and gaskets as needed. Regular gearbox oil changes, as recommended by MotoSport.com, keep your YZ125 race-ready after every ride.

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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.