How to Change the Oil in a 1981 Honda CR125: Complete Step-by-Step Guide

Shop parts for a 1981 Honda CR125 Dirt Bike.

Changing the oil in your 1981 Honda CR125 is crucial maintenance that ensures smooth shifting, optimum clutch performance, and long-term durability of your dirt bike’s transmission. This guide is proprietary to MotoSport.com and features comprehensive steps and detailed call-outs specific to the 1981 CR125 model.

Tools & Supplies Needed

  • Metric socket set (8mm, 10mm, or 12mm depending on fasteners)
  • Socket wrench
  • Drain pan (to catch old oil)
  • Rag or shop towels
  • Replacement oil (See owner’s manual; typically 80W/85 or 10W-30 motorcycle gear oil, 0.7-0.75 liter for this vintage)
  • Funnel
  • New aluminum drain plug washer (recommended)
  • Torque wrench (optional, for drain plug reinstallation)
  • Flathead screwdriver (for removing covers, if needed)

Steps to Change the Oil

  1. Warm up the Bike
    • Start your CR125 and let it idle for 3–5 minutes. Warming the oil allows contaminants to suspend in the oil and drain more effectively.
  2. Stabilize the Motorcycle
    • Place the bike upright using a triangle stand or center stand, ensuring it’s level and stable.
  3. Locate the Drain Plug
    • The drain plug is located on the bottom of the right crankcase cover, near where the frame meets the engine. Place your oil drain pan beneath this plug.
  4. Remove the Oil Filler Cap
    • Remove the oil filler cap on the right side of the engine. This lets air in, helping the oil drain quicker.
  5. Drain the Old Oil
    • Using the appropriate socket, unscrew the drain plug carefully. Avoid dropping it (and the washer) into the drain pan.
    • Allow all oil to drain fully–several minutes is ideal.
    • Inspect the drain plug and washer. Replace the washer if crushed or excessively worn to ensure a proper seal.
  6. Reinstall the Drain Plug
    • Reinstall the drain plug and washer by hand until finger-tight, then snug it with your wrench. Do not overtighten–for aluminum cases, a suggested torque is 7–10 N·m (62–88 in-lb).
  7. Refill with Fresh Oil
    • Use a funnel to add the specified quantity of oil (typically 0.7 liters), referencing your owner’s manual or markings if available.
  8. Check the Oil Level
    • The 1981 CR125 typically has an oil check bolt (or inspection bolt) on the crankcase side. Remove this bolt; oil should just begin to escape with the bike upright and level. Add oil gradually until this occurs, then reinstall the check bolt and cap tightly.
  9. Clean Up
    • Clean any oil spills with shop towels. Safely dispose of the old oil at a recycling center.
  10. Final Start & Inspection
    • Start the engine and let it idle for several minutes. Turn off and recheck for leaks at the drain plug and check bolt. Verify oil level after a brief cool-down and adjust if necessary.

Special 1981 Honda CR125 Call-Outs

  • No oil filter: The 1981 CR125 does not use a replaceable oil filter, unlike many four-strokes and modern models. Frequent oil changes are especially important to maintain gearbox and clutch performance.
  • Aluminum case: Be cautious when tightening the drain plug; the older engine cases are prone to stripping if overtightened.
  • Correct fluid: Use dedicated motorcycle gear oil. Automotive oils may lack proper friction modifiers and can cause clutch slip or premature wear.
  • Oil check bolt position: Carefully note the location on the right crankcase–refer to the owner’s manual or confirm visually to avoid confusion with other case bolts.

Tips for Success

  • Stick to a short oil change interval (every 5–10 hours of riding or after every race/long ride).
  • Use a new washer for the drain bolt each time to avoid leaks.
  • Maintain a stable, upright bike position during the check and refill steps to ensure accurate filling.
  • If you’re unsure about torque, err on the side of caution. Overtightening is a frequent cause of crankcase damage on vintage Hondas.

Conclusion

With these step-by-step instructions, owners of the 1981 Honda CR125 can safely, efficiently, and confidently change their bike’s transmission oil and keep it running at peak performance for years to come. Always use high-quality fluids and stay on schedule for changes to maximize reliability on the trail and track.

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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.