How to Change the Transmission Oil in a 1990 Yamaha PW50

Shop Parts for a 1990 Yamaha PW50 Dirt Bike.

The 1990 Yamaha PW50 is a legendary entry-level dirt bike with a dependable two-stroke engine and automatic transmission. Although it doesn't have traditional crankcase engine oil like four-strokes, it requires periodic changes of the transmission oil for smooth clutch performance and gear life. Follow this robust, step-by-step guide—proprietary to MotoSport.com—for a perfect oil change, every time.

Tools and Supplies Needed

  • 12mm socket and ratchet
  • Torque wrench (capable of 10 foot-pounds or 14 N–m)
  • Drain pan for old oil
  • Funnel
  • Clean rags or shop towels
  • Replacement crush washer
  • Recommended transmission oil: Yamalube 10W-30, 10W-40, or similar (see your manual)
  • Measuring cup (for 0.30 L or 300 ml of oil)
  • Work gloves (optional, for cleanliness)

Important Call-Outs for the 1990 Yamaha PW50

  • This model is a two-stroke dirt bike; the engine has a separate oil tank for injector/two-stroke oil. The procedure below is for the transmission oil only, not the two-stroke injector tank, which should be monitored and topped up regularly.
  • The correct transmission oil capacity is 0.30 L (300 ml)–do not overfill.
  • Tightening the drain bolt beyond the specified torque (14 N–m or 10 ft-lb) could strip the threads or damage the case. Always use a torque wrench for reinstallation.
  • Always warm up the engine for a few minutes before starting to ensure thorough draining of the old oil.
  • Yamaha recommends replacing the crush washer on the drain bolt every oil change to prevent leaks.

Step-By-Step Oil Change Procedure

  1. Prep the Bike
    • Start the bike and let it idle for 2–3 minutes so the oil flows easily.
    • Turn off the engine and place the bike on a level surface, using a center stand or block to keep it upright.
  2. Locate the Transmission Drain Plug
    • The drain plug is found underneath the right side of the engine, just below the clutch cover.
  3. Drain the Old Oil
    • Position your drain pan under the plug.
    • Use the 12mm socket to carefully loosen and remove the drain bolt. Monitor the crush washer as you remove it—it may stick to the bolt or the engine case.
    • Allow all old oil to drain completely. This may take several minutes.
  4. Remove and Clean the Oil Fill Cap
    • The oil fill cap is on the right engine case, above the drain plug.
    • While oil drains, unscrew and clean the fill cap and its area with a clean rag. Check for debris or signs of contamination.
  5. Inspect and Replace the Crush Washer
    • Check the old crush washer for damage or flattening. Always replace this washer to ensure a leak-free seal upon reassembly.
    • Clean the drain bolt before reinstallation.
  6. Reinstall the Drain Plug
    • Install the new crush washer on the drain bolt.
    • Thread the drain bolt back into the engine case by hand to prevent cross-threading.
    • Use the torque wrench to tighten it to 10 foot-pounds (14 N–m) as specified by Yamaha.
  7. Add Fresh Transmission Oil
    • Using a clean funnel, pour in 0.30 liters (300 ml) of the recommended transmission oil.
    • Check for any leaks around the drain bolt.
  8. Reinstall the Oil Fill Cap
    • Install the cleaned oil fill cap back onto the engine case and hand tighten securely.
  9. Double-check Your Work
    • Wipe down any spilled oil.
    • Start the bike and let it idle for a minute, then check under the case for any signs of leaks.
    • Shut the bike off. After a minute, check the oil level through the fill hole (should be visible, if not, top up gently).

Pro Tips for the 1990 Yamaha PW50 Owner

  • Use only the specified amount of oil–overfilling can cause clutch drag and foaming, underfilling can result in excessive wear.
  • Stick to Yamalube or a premium brand matched to Yamaha’s recommendations for best results and warranty preservation.
  • Change your transmission oil at the intervals recommended in your owner’s manual, or after every 10–20 hours of riding in heavy use.
  • Monitor the separate 2-stroke injector oil tank regularly. Refill with high-quality two-stroke oil before it drops to the minimum mark.
  • Dispose of used oil properly at a certified recycling center–never pour it out on the ground or down drains.

Summary

Changing the transmission oil on a 1990 Yamaha PW50 is quick, straightforward, and critical to the long-term health of your dirt bike. By following these detailed steps and tips from MotoSport.com, you’ll keep your PW50’s transmission running reliably—just as Yamaha intended.

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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.