How to change the oil in a 1991 Honda CR125 Dirt Bike

How to Change the Oil in a 1991 Honda CR125: A Step-by-Step Guide for MotoSport.com

Tools and Supplies Needed

• 17mm socket or box wrench
• Oil drain pan
• Funnel
• New transmission (gear) oil–check your owner’s manual for recommended oil type and amount
• Replacement crush washer or sealing washer for the drain bolt (recommended)
• Clean rags
• Torque wrench (optional, but ideal for correct reinstallation torque)
• Stand or triangle stand to hold bike upright
• Replacement oil level/inspection bolt (optional, if existing is worn or damaged)

Preparation: What to Know Before You Begin

• CR125s use separate oil for the transmission and clutch, not engine oil.
• Warm up the engine for 1–2 minutes before draining. Warm oil flows better and drains out more contaminants, yielding a cleaner flush and refill—
• The 1991 Honda CR125’s drain bolt is typically a 17mm bolt located at the bottom of the right engine case. The fill plug and oil level bolt (sometimes combined) are on the clutch side case cover.

Step-by-Step: How to Change the Oil on a 1991 Honda CR125

1. Warm up the Bike:
   • Start your CR125 and let it idle for about 1–2 minutes.
   • This helps suspend contaminants and allows for a more complete oil drain.
2. Stabilize the Bike:
   • Turn off the engine and place the bike on a stand so it is upright and steady.
3. Remove the Oil Check/Fill Plug:
   • Locate the oil fill/check plug (typically on the right clutch cover) and remove it to allow air in for smoother draining.
4. Place the Oil Drain Pan:
   • Position the pan directly under the 17mm oil drain bolt at the bottom of the right engine case.
5. Remove the Drain Bolt:
   • Carefully loosen the 17mm drain bolt and let the old oil flow into the pan.
   • Be cautious: Oil may be hot. Look for the crush washer—replace it if worn.
6. Allow Oil to Drain Completely:
   • Wait several minutes to let all the oil and contaminants drain out.
   • You can gently rock the bike for a more thorough drain, but keep it upright.
7. Reinstall the Drain Bolt and Washer:
   • Clean the bolt and threads. Install a new crush washer if needed.
   • Hand-tighten, then torque to manufacturer’s spec (do not overtighten, as the case is aluminum).
8. Pour in New Oil:
   • Using a funnel, pour the recommended quantity and type of oil into the fill hole. For most 1991 Honda CR125s, this is usually around 650–700ml but always verify with your owner’s manual or fill to the specified level at the oil check screw.
9. Check Oil Level:
   • Wait a few minutes for oil to settle. With the bike level, check the oil level at the inspection hole or via the level bolt if equipped.
   • Add oil slowly if needed until it starts to seep out at the specified level port, then reinstall the level bolt.
10. Reinstall the Fill Plug and Clean Up:
    • Wipe away any drips. Reinstall the fill/check plug snugly but not overtightened.
11. Dispose of Oil Safely:
    • Take your used oil to a recycling center or auto store that accepts waste oil—never dump oil outdoors.

CR125 Model-Specific Tips and Call-outs

• 1991 Honda CR125:
  • The 1991 model’s transmission case is aluminum; avoid overtightening drain or fill bolts to prevent stripping threads—
  • The correct oil capacity is critical—overfilling may cause excessive clutch drag, while underfilling risks gearbox failure.
  • The oil should be changed after every 2–5 hours of riding in demanding conditions for optimal clutch and transmission life.
  • No oil filter to replace on this two-stroke; simply changing the oil is sufficient unless you notice metallic debris or abnormal contamination.

Maintenance Schedule and Oil Recommendation

• Use a quality transmission/gear oil specified for 2-stroke motocross bikes (10W-30, 10W-40, or manufacturer-recommended non-friction modified oil).
• Check oil for color and contamination at each change—milky or very dark oil may indicate water intrusion or clutch wear.
• Always use the correct oil type—engine oil for 4-strokes, gear oil for 2-stroke transmissions.

Conclusion

• Changing the oil on your 1991 Honda CR125 is fast, straightforward, and protects your motocross investment. With the right tools and a careful approach, you’ll keep your CR125 running at full throttle for seasons to come.

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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.