How to Change the Oil in a 1981 Yamaha PW50

Shop parts for a 1981 Yamaha PW50 Dirt Bike.

Changing the transmission oil in your 1981 Yamaha PW50 is a straightforward maintenance task that extends the life of your dirt bike and keeps it running smoothly. Although the PW50 features a 2-stroke engine—which means the engine itself is lubricated by injector oil—there is still a separate transmission oil that should be replaced regularly. Below, MotoSport.com provides a proprietary, step-by-step guide tailored specifically for this classic mini dirt bike.

Tools and Supplies Needed

  • 12mm socket and ratchet
  • Oil drain pan
  • Funnel
  • Measuring cup (with metric markings for precise volume)
  • Fresh transmission oil (see below for type and quantity)
  • New crush washer for the drain bolt
  • Rags or shop towels
  • Gloves (recommended)

Recommended Oil Type and Quantity

  • Transmission Oil Quantity:– 0.30 L (0.32 US qt, 0.26 Imp qt)
  • Recommended Transmission Oil:– Yamalube or other high-quality gear/transmission oil as specified in your owner's manual

Specific Notes for the 1981 Yamaha PW50

  • The transmission oil is separate from the 2-stroke injector oil. Always check and maintain both fluid levels.
  • Torque spec for the transmission oil drain bolt is 14 Nm (10 lb·ft).
  • Check for leaks around the drain bolt after completing the oil change, as classic models are more prone to weeping seals.

Step-by-Step Oil Change Procedure

  1. Warm up the engine.
    Let the PW50 idle for 1-2 minutes. This warms the oil and allows it to drain out more thoroughly.
    Do not overheat. A brief run is all that’s needed.
  2. Prepare your workspace.
    Place the bike on a level surface and secure it using a bike stand if available. Slide your oil drain pan under the transmission case beneath the left side of the bike.
  3. Remove the drain bolt.
    Using your 12mm socket, carefully loosen and remove the transmission drain bolt. Allow the old oil to drain completely into your pan.
    While draining, inspect the oil color and consistency. Milky or dark fluid may indicate contaminants or water ingress and could signal a need for further inspection.
  4. Replace the crush washer.
    Whenever you remove the drain bolt, always use a new crush washer. This ensures a leak-proof seal when the bolt is reinstalled.
  5. Reinstall the drain bolt.
    Once the oil has fully drained, wipe off the drain area and bolt. Insert the bolt with a fresh crush washer and tighten to 14 Nm (10 lb·ft) with your socket. Do not overtighten to avoid stripping the casing.
  6. Remove the oil fill cap.
    The fill cap is typically located higher up on the left case. Remove the cap and clean any debris from the area to prevent contamination.
  7. Add fresh transmission oil.
    Use your funnel and pour in 0.30 liters (300 ml) of the recommended gear/transmission oil. A measuring cup helps ensure accuracy.
    Overfilling can cause leakage and transmission drag. Underfilling may result in premature wear.
  8. Reinstall the fill cap.
    Tighten the cap securely by hand.
  9. Check for leaks.
    Gently wipe any spills. Start the engine and let the bike sit for a minute. Inspect the drain bolt area for signs of oil seeping.
  10. Dispose of used oil responsibly.
    Never pour oil onto the ground or into household drains. Bring it to a local recycling center or automotive shop that accepts used oil.

Additional Tips for the 1981 PW50

  • The PW50 uses a 2-stroke oil tank for engine lubrication. Check and refill this regularly with premium 2-stroke injector oil, separate from the transmission oil. The tank is behind the front number plate and should never be allowed to run low.
  • If your PW50 has been sitting for many months or you ride in muddy, wet conditions, consider more frequent oil changes and check your gaskets and seals regularly for leaks.
  • For new engines, perform an initial oil change after the first month, again at six months, and thereafter annually as general maintenance, unless otherwise specified by usage intensity.

Final Checks

  • Test ride your bike for a few minutes, then recheck the drain bolt and fill cap for any leaks.
  • Stay up-to-date on your maintenance schedule to keep your 1981 Yamaha PW50 running smooth for years to come.

This MotoSport.com guide ensures your vintage Yamaha PW50 gets the best care possible. For all your service parts and step-by-step instructions, keep MotoSport.com bookmarked for future DIY tasks.

Related Shopping Categories

Shop Motor Oil for a 1981 Yamaha PW50 Dirt Bike.

Shop Oil Filters for a 1981 Yamaha PW50 Dirt Bike.

Shop Oil Drain Pans for a 1981 Yamaha PW50 Dirt Bike.

Shop Tools for a 1981 Yamaha PW50 Dirt Bike.

Shop Oil Fillers and Drain Plugs for a 1981 Yamaha PW50 Dirt Bike.

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.