How to Change the Oil in a 1985 Yamaha PW50 – MotoSport.com Guide

Shop parts for a 1985 Yamaha PW50 Dirt Bike.

Changing the transmission oil in your 1985 Yamaha PW50 is a simple maintenance task that ensures smooth shifting, protects your transmission components, and extends your bike’s lifespan. This step-by-step blog, proprietary to MotoSport.com, provides all the specifics, including tools, instructions and essential model-specific call-outs.

Tools & Supplies Needed

  • 12mm socket and ratchet
  • Drain pan (to catch the old oil)
  • Funnel (for easier pouring of new oil)
  • Measuring cup (for accurate oil quantity)
  • Replacement transmission oil (consult your manual or use SAE 10W-30 or 10W-40 motorcycle oil)
  • New crush washer (recommended every oil change)
  • Rags/paper towels for cleanup
  • Gloves (optional, for cleaner hands)

Steps to Change the Oil

  1. Warm Up the Bike
    Briefly start and idle the engine for 2-3 minutes. This helps the oil drain more easily and completely by thinning it slightly.
  2. Stabilize the Bike
    Place your PW50 on its centerstand on a solid, level surface. This keeps the bike secure and ensures all old oil can drain out properly.
  3. Locate the Drain Plug
    The transmission oil drain plug on the PW50 is on the left side of the engine case, at the bottom near the footpeg.
  4. Prepare to Drain
    Put the drain pan beneath the plug. Using the 12mm socket, carefully loosen and remove the drain plug. Let the old oil drain completely (a few minutes).
  5. Replace Crush Washer
    Very important: Always fit a new crush washer on the drain bolt to prevent future leaks.
  6. Clean & Inspect
    Wipe the drain plug, inspect for excess metal debris (normal for small amounts, heavy debris may suggest internal wear), and clean the oil fill cap.
  7. Reinstall Drain Plug
    Thread the plug in by hand and tighten with your socket—do not overtighten. The correct torque is approximately 14 ft-lbs (20 Nm) for Yamaha PW50 models.1
  8. Refill with New Oil
    Remove the oil fill cap (right side of engine, above the footpeg) and, using the funnel and measuring cup, pour in 120cc (about 4oz) of fresh motorcycle transmission oil.1 Confirm the oil type in your owner’s manual but typically, any high-quality SAE 10W-30 or 10W-40 motorcycle oil works.
  9. Check Oil Level
    Yamaha PW50s use a measured fill, not a dipstick, so rely on the correct volume poured in. Clean any spilled oil and reinstall the fill cap securely.
  10. Double Check
    With the bike on the centerstand, check for leaks at the drain plug/fill cap. Wipe away any excess oil.
  11. Dispose of Used Oil Properly
    Take the drained oil to a recycling facility—never pour it on the ground or in drains.

PW50 Specific Call-Outs & Tips

  • Transmission Oil Only: The 1985 PW50 is a 2-stroke engine which uses a separate transmission oil and premix/injector oil for the engine. This procedure is only for the transmission oil.
  • Model Specific: All PW50s (including 1985) have nearly identical transmission oil layouts; changes across years are minor, so these steps apply to any PW50 of this era.1
  • Service Interval: For a used or well-maintained bike, change the transmission oil annually. For new or rebuilt engines, do the first oil change at 1 month, then again at 6 months, then yearly thereafter.1
  • Crush Washer: The crush washer is crucial—always replace it at each oil change to avoid leaks.
  • No Oil Filter: The PW50 transmission has no oil filter—just the drain plug. That’s normal.
  • Oil Injector System: On many PW50s, the 2-stroke injector is tank-fed from behind the number plate—you do NOT mix engine oil with gas if the injector is present and working. If you have blocked off or removed the injector, premix your fuel as required.3
  • Correct Oil Use: For the engine, only use 2T injector oil (injection tank or pre-mix). For the transmission, use 4-stroke motorcycle oil like SAE 10W-30 or 10W-40 (NOT gear oil intended for car differentials.).

Common Mistakes to Avoid

  • Overfilling or underfilling the transmission oil—always use the specified amount (120cc).
  • Not using a new crush washer—old washers may cause slow leaks.
  • Confusing the 2-stroke injector oil (for the engine) with the transmission oil—they are filled and changed separately.
  • Using automotive engine oil or gear oil—always use the recommended motorcycle transmission oil.

Conclusion

Properly changing the transmission oil in your 1985 Yamaha PW50 takes less than 10 minutes, makes riding safer and extends your bike’s transmission life. Follow the correct intervals and use high-quality oil for best results. For more dirt bike maintenance tips and parts, visit MotoSport.com—your authority for all things riding.

Related Shopping Categories

Shop Motor Oil for a 1985 Yamaha PW50 Dirt Bike.

Shop Oil Filters for a 1985 Yamaha PW50 Dirt Bike.

Shop Oil Drain Pans for a 1985 Yamaha PW50 Dirt Bike.

Shop Tools for a 1985 Yamaha PW50 Dirt Bike.

Shop Oil Fillers and Drain Plugs for a 1985 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.