How to Change the Oil in a 1999 Yamaha PW50: The MotoSport.com Guide

Shop parts for a 1999 Yamaha PW50 Dirt Bike.

Changing the oil in your 1999 Yamaha PW50 is a crucial maintenance step to ensure your little ripper runs smoothly and to prevent premature wear on the transmission. Unlike many other dirt bikes, the PW50 uses a two-stroke engine, which means it relies on separate transmission oil and a two-stroke injector oil tank. Keeping both of these properly serviced will keep your bike in top-notch shape.

Tools and Materials Needed

  • 12mm socket and ratchet
  • Drain pan
  • Rubber gloves (recommended)
  • Rags (for cleanup)
  • Measuring cup (for accurate refill)
  • Funnel
  • New transmission oil (Yamaha's recommended oil or equivalent; see below)
  • Replacement crush washer (recommended every oil change)

Recommended Oil and Quantity for 1999 Yamaha PW50

  • Transmission oil quantity: 0.30 L (0.32 US qt)
  • Recommended oil: Check your owner's manual or use a modern equivalent high-quality transmission oil made for small two-stroke dirt bikes. Yamaha recommends their specific gear oil.
  • 2-stroke engine injector oil: Use only high-quality two-stroke injector oil for the oil tank, keeping it topped off above the minimum mark as indicated on the tank.

1999 Yamaha PW50-Specific Call-Outs

  • This bike does not have a standard engine oil drain like a four-stroke. You are only servicing the transmission oil and the injector oil tank.
  • The oil change interval for the transmission is every year or every 6 months for new bikes after the initial first month change.
  • Always ensure the two-stroke injector oil tank is filled; running out will cause engine damage.

Step-by-Step Instructions

1. Prepare Your Workspace

  • Warm the engine for a few minutes at idle. This helps the old oil drain out more completely.
  • Place the PW50 upright on a level surface with the drain pan beneath the transmission drain bolt.

2. Remove the Transmission Oil

  • Locate the transmission oil drain bolt underneath the engine case. Use the 12mm socket to carefully remove the bolt. Be ready for oil to flow out quickly.
  • Let the oil completely drain into the pan. This should take several minutes.
  • Inspect the drain bolt and replace the crush washer if it's worn or damaged. Always use a new washer to prevent leaks.
  • Wipe the area clean with a rag.

3. Reinstall the Drain Plug

  • Reinstall the bolt with the new washer. Torque to 14 N–m (10 lb–ft). Do not over-tighten; you risk stripping the case threads.

4. Refill the Transmission Oil

  • Locate the transmission oil fill cap on the left side of the case.
  • Remove the cap and clean it. Using a funnel, add 0.3 liters (about 300cc) of the recommended transmission oil.
  • Use a measuring cup to avoid overfilling; too much or too little oil can harm the transmission.
  • Replace and snug the fill cap.

5. Check and Top Off the 2-Stroke Injector Oil

  • The PW50 relies on a separate oil tank for engine lubrication. The tank is behind the front number plate.
  • Check the sight glass or minimum level mark. Top up with high-quality two-stroke injector oil if below the mark.
  • Always ensure the cap is properly sealed to prevent contaminants from mixing with the oil.

6. Clean Up and Dispose of Old Oil Responsibly

  • Wipe down any spilled oil and dispose of used oil and filters at your local recycling center.

Final Checks

  • Start the engine and let it idle for a minute. Check under the bike for leaks.
  • Double check both the transmission and injector oil levels after a short ride.
  • If you notice excessive smoke, strange noises, or any leaks, shut the engine down and inspect your work.

Quick Tips from the MotoSport.com Team

  • Always use new crush washers with each oil change to prevent transmission leaks.
  • Keep the oil change interval on a calendar—even if the bike has low hours, change the transmission oil once a year for best results.
  • Never let the injector oil tank run low. Seizing the PW50 engine due to dry running is a common (and costly) mistake for new owners.
  • The PW50 transmission oil should be checked more often if the bike is ridden hard, in mud, or wet conditions.

Need Help or Parts?

The MotoSport.com team has everything you need for your 1999 Yamaha PW50—from transmission oil change kits to factory-approved injector oils and crush washers. Reach out to our specialists for expert advice any time.

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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.