How to Change the Oil in a 1989 Yamaha YZ125

Shop parts for a 1989 Yamaha YZ125 Dirt Bike.

  • Tools and Materials Needed:
    • Drain pan
    • 12mm hex or socket wrench
    • 4mm Allen wrench (for oil check bolt)
    • Funnel (preferably long and narrow)
    • Measuring cup
    • Engine oil – recommended 10W40 wet clutch protection oil (synthetic preferred)
    • New crush washer for drain bolt
    • Rags or shop towels
    • Motorcycle stand or level ground area
  • Specific Model Considerations for 1989 Yamaha YZ125:
    • The YZ125 is a 2-stroke dirt bike requiring premixed fuel and oil for the engine; the "engine oil" in this procedure refers to the gearbox or transmission oil inside the crankcase.
    • Use Yamaha—s recommended oil type or an equivalent synthetic 10W40 oil suitable for wet clutches.
    • The drain bolt uses a 12mm hex socket, and it is critical to replace the crush washer to prevent leaks.
    • The bike should be level to ensure accurate oil drainage and filling.
    • Run the engine for a few minutes before draining to warm up the oil for better flow.
    • The oil capacity is approximately 0.69 quarts (660 ml), so accurate measurement is important.
    • Check the oil level via the check bolt and adjust accordingly to avoid overfilling.
    • Tighten drain bolt to around 14 foot-pounds torque–a torque wrench is recommended if available.

Step-by-Step Procedure:

  1. Prepare the Bike and Workspace:
    • Place the bike on a stable, level surface or motorcycle stand to keep it upright and steady.
    • Start the engine and let it idle for 3-5 minutes. This warms the oil to allow easier draining.
    • Turn off the engine and allow 1-2 minutes for the oil to settle.
  2. Drain the Old Oil:
    • Place the drain pan beneath the oil drain bolt located under the crankcase on the left side.
    • Using the 12mm hex socket, carefully remove the drain bolt. Old oil will start draining out; allow all the oil to completely drain.
    • Inspect the drain bolt crush washer; replace it with a new washer to ensure proper sealing when reinstalled.
    • Once fully drained, reinstall the drain bolt and hand tighten, then torque to 14 ft-lbs.
  3. Refill with Fresh Oil:
    • Remove the oil fill cap located on the right side of the crankcase–this can be unscrewed by hand or with an appropriate tool.
    • Measure out approximately 660 ml (0.69 quarts) of fresh 10W40 synthetic wet clutch oil using the measuring cup.
    • Using a long, narrow funnel, slowly pour the oil into the filler hole, making sure not to spill or overfill (the bike—s exhaust pipes lie close, so tipping carefully is vital).
    • To confirm the correct oil level, remove the oil check bolt (4mm Allen) located near the engine. If oil trickles out, the level is correct; if not, add a little more oil and check again.
    • Reinstall and tighten the oil fill cap and check bolt securely.
  4. Final Checks and Clean Up:
    • Wipe off any spilled oil around the drain and fill bolts with a clean rag.
    • Start the engine for a minute to circulate fresh oil and check for leaks at the drain bolt.
    • Turn off the engine and inspect again; re-torque bolts if necessary.
    • Properly dispose of used oil according to local regulations.

Additional Tips:

  • Oil changes for the 1989 Yamaha YZ125 gearbox should be done regularly, typically every 10-15 hours of riding or as recommended in the owner's manual.
  • Always use the recommended oil type for your 2-stroke dirt bike to protect transmission gears and clutch function.
  • Check the tightness of all fasteners related to the engine and frame, as vibrations can loosen these over time.
  • If you are replacing the piston, ring, or gears, note that a break-in period with half throttle is necessary to ensure proper seating of new parts.

Changing the oil on a 1989 Yamaha YZ125 is a straightforward maintenance task that can save your bike from costly repairs if done properly. Following these steps and using the correct tools and fluids will keep your YZ125 running smoothly and reliably for many rides to come.

Related Shopping Categories

Shop Motor Oil for a 1989 Yamaha YZ125 Dirt Bike.

Shop Oil Filters for a 1989 Yamaha YZ125 Dirt Bike.

Shop Oil Drain Pans for a 1989 Yamaha YZ125 Dirt Bike.

Shop Tools for a 1989 Yamaha YZ125 Dirt Bike.

Shop Oil Fillers and Drain Plugs for a 1989 Yamaha YZ125 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.