How to Change the Oil in a 1977 Yamaha YZ80 – A Complete MotoSport.com Guide

Shop Parts for a 1977 Yamaha YZ80 Dirt Bike.

Changing the gearbox oil on your vintage 1977 Yamaha YZ80 is a straightforward but vital maintenance task to ensure smooth operation and longevity of this classic two-stroke dirt bike. Below you’ll find everything you need to know, from the required tools to model-specific tips, so you can get your YZ80 back on the trail in peak condition.

Tools and Supplies Needed

  • 10mm wrench/spanner (for drain bolt removal)
  • Torque wrench (recommended for precise tightening)
  • Oil drain pan
  • Funnel
  • Measuring jug (to accurately measure oil volume)
  • Clean rags (for cleanup)
  • New oil (use high quality two-stroke transmission oil; see below for specification)
  • New drain plug gasket/crush washer (original Yamaha part number: 4F4-14766-00-00 for 14mm plug, or superseded from 137-15353-00-00)

Recommended Oil and Quantity

  • Oil type: High-quality 2-stroke gearbox/transmission oil (use a product suitable for vintage Yamaha transmissions such as Motul Transoil or Yamalube Transoil)
  • Oil quantity: 550 ml for Yamaha YZ80 engines of this era

Step-By-Step Instructions

  1. Warm up the engine (optional): Start and run the motorcycle for a few minutes. Warm oil drains faster and more completely. Turn off the engine and allow it to cool just enough so you don’t burn yourself.
  2. Position the bike: Stand the bike upright on a stable, level surface—use a bike stand if available.
  3. Locate the drain bolt: On the 1977 YZ80, the drain plug is located on the bottom of the engine case, near the shift lever and right below the transmission area.
  4. Place drain pan underneath: Position your oil catch pan directly under the drain bolt to avoid spills.
  5. Remove drain bolt: Using a 10mm wrench, loosen and remove the drain bolt.
    Tip: Have a rag handy as oil will flow out quickly.
  6. Fully drain the oil: Allow oil to flow until it slows to a drip. Gently tilt the bike to the right to help expel the last bit of old oil.
  7. Inspect and replace the gasket: Remove the old crush washer or gasket from the plug and replace with a new Yamaha drain plug gasket (ID 14.5mm, OD 21mm). This ensures a tight seal and prevents leaks.
  8. Clean and reinstall drain bolt: Wipe the drain bolt and area clean. Thread the bolt in by hand, then snug it up with the wrench.
    IMPORTANT: Do not overtighten. If you have a torque wrench, tighten to 10 Newton-meters. Too loose can cause leaks; too tight can damage your crankcase.
  9. Add fresh oil: Remove the transmission filler cap (typically on the right side of the engine, above the kick start). Use your measuring jug and funnel to pour in 550 ml of the recommended gearbox oil.
  10. Replace filler cap: Screw the cap back on finger-tight.
  11. Clean up: Wipe away any spilled oil.
  12. Run and check for leaks: Start the motorcycle and let it idle for a few minutes. Inspect around the drain bolt and filler cap for leaks, tightening as necessary.

1977 Yamaha YZ80 Specific Call-Outs

  • Crush Washer is Essential: The 1977 YZ80 uses a crush washer between the drain bolt and crankcase for a proper oil seal. Using the correct size (Yamaha 4F4-14766-00-00) prevents leaks and crankcase damage.
  • Oil Measurement: Do not guess oil volume—overfilling can cause drag, underfilling leads to rapid gear and bearing wear. Always use a measuring jug for 550 ml.
  • Vintage Oil Recommendations: While modern oils are better, make sure to use one compatible with older seal materials and gearboxes. Avoid automotive motor oils—use only 2-stroke transmission/gearbox oil.
  • Tightening: Be careful when reinstalling the drain bolt. Aluminum cases on vintage bikes strip threads more easily than newer models—always torque correctly.

Key Maintenance Tips for Longevity

  • Change the oil regularly. For the 1977 YZ80, every 5–10 hours of riding or after every couple races is a good rule of thumb.
  • Always inspect drained oil. Look for water contamination (milky color) or metal fragments—both can indicate other mechanical issues.
  • Check for leaks after every oil change. Take the time to re-torque and inspect all bolts after your first ride.
  • Keep extra gaskets on hand. Vintage parts can be harder to source, so stock up for smooth, uninterrupted riding.

Proper maintenance makes all the difference. With these steps specific to the 1977 Yamaha YZ80, you’ll keep your bike in top shape and enjoy many more years on the track or trail.

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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.