How to Change the Oil in a 1985 Yamaha YZ490

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Changing the oil in your 1985 Yamaha YZ490 is a core maintenance task that prolongs engine life and ensures peak performance, especially for a classic two-stroke dirt bike like the YZ490. While two-stroke engines like the YZ490 do not have a separate engine oil reservoir (since oil is mixed into the fuel), the transmission oil still requires regular changing to maintain crisp shifts and clutch longevity. Below, you'll find a step-by-step guide, call-outs unique to this model, and a comprehensive list of tools and materials you'll need for the job.

Tools and Supplies Needed

  • Socket set (with metric sockets, especially 8mm and 12mm)
  • Ratchet and/or wrench set
  • Drain pan (large enough to catch all old oil)
  • Funnel
  • Clean rags or shop towels
  • Fresh transmission oil – typically 10W-30 or 10W-40 non-energy-conserving oil (check your manual for specifics)
  • Measuring cup or ratio cup (for accurate oil measurement)
  • New crush washer (for the drain bolt, optional but recommended)
  • Safety gloves (optional, for cleaner hands)

1985 YZ490-Specific Call-Outs

  • The YZ490 is a two-stroke—There is no engine oil to change–only the transmission oil.
  • This model uses a right-side fill plug above the clutch cover and a drain plug on the bottom of the engine case.
  • Recommended transmission oil capacity is about 750cc (0.75L), but always refer to your manual or measure the amount when draining to confirm.
  • Always check for leaks around the drain and fill plugs after service to avoid damage from low oil levels.
  • The crush washer on the drain bolt should be inspected and replaced as needed for a tight seal.

Step-by-Step: Changing the Transmission Oil

  1. Warm Up the Engine
    • Start the engine and let it run for a few minutes. This warms the oil, allowing it to drain more thoroughly.
    • Warning: Do not let it get too hot; just warm enough for fluidity.
  2. Secure the Bike
    • Shut off the engine and place the bike on a stand so it’s upright and secure.
  3. Locate the Drain Plug
    • The drain plug is on the bottom of the right side engine case (check under the shifter).
  4. Drain the Old Oil
    • Place the drain pan underneath, then use the correct socket (usually 12mm) to remove the drain bolt.
    • Allow all oil to drain out. Tilt the bike slightly side to side if needed for complete drainage.
  5. Inspect and Clean
    • Clean the drain bolt and inspect the washer/crush washer. Replace if damaged or flattened.
    • Check drained oil for any metal shavings; a small amount is normal, but excessive debris could indicate internal wear.
  6. Replace the Drain Plug
    • Reinstall the drain bolt with the washer. Tighten to manufacturer’s specs (do not over-tighten; typical spec is around 10–15 lb-ft).
  7. Add Fresh Oil
    • Remove the oil fill plug (on the right side above the clutch cover).
    • Using a funnel, pour in the correct type and amount of oil (approximately 750cc or 0.75L, or as specified in your manual).
    • If you lost track, pour roughly the same amount as what was drained, and check the level via the inspection bolt if present.
  8. Secure and Clean Up
    • Reinstall the fill plug and wipe any spilled oil.
    • Start the bike and let it idle for a few minutes, then check for leaks at the bolts and plugs.
    • Double-check the oil level and top off if necessary.

Additional Tips and Model-Specific Advice

  • This year and model YZ490 does not use an oil filter—transmission oil only.
  • Use high-quality oil designed for wet clutches for best clutch feel and longevity.
  • Routinely inspect drain and fill threads for damage; these older magnesium cases can strip easily if over-torqued.
  • The oil change interval should be around every 5–10 hours of use, or after every couple of rides in harsh or muddy conditions.
  • If the bike has sat for a long period or after a rebuild, consider flushing the transmission with a small amount of inexpensive oil, running briefly, and draining to remove any residual debris.

About Mixing Oil for Fuel (Model Note)

  • The transmission oil is separate from the oil that is pre-mixed with gasoline.
  • For the fuel/oil ratio, base it on your riding style—ratios from 20:1 (heavy use, more protection, slightly more smoke) to 40:1 (lighter use, less smoke) are used; 32:1 is a common starting point, but always refer to the best practice or your manual for preference and engine condition.

Maintaining the transmission oil on your 1985 YZ490 is an easy, satisfying job that keeps your classic Yamaha running strong. Done regularly, it will save you from costly repairs and lost track time. For all your OEM or performance parts needs, trust MotoSport.com for the best in dirt bike maintenance and upgrades.

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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.