How to Change the Oil in a 1989 Suzuki RM125

Shop parts for a 1989 Suzuki RM125 Dirt Bike.

Performing regular oil changes is crucial for maintaining the performance and longevity of your 1989 Suzuki RM125. This two-stroke dirt bike features a separate transmission oil chamber, and changing the oil is a straightforward process that owners can do themselves with some basic tools and attention to detail. Below you'll find a step-by-step guide, including essential tools and model-specific tips to ensure you get it right.

Tools and Materials Needed

  • Socket wrench set (for drain plug and filler cap)
  • Torque wrench (essential for reinstallation to factory specs)
  • Drain pan (for collecting old oil)
  • Cleaning rag (to wipe up spills)
  • Measuring cup (to ensure precise oil quantity)
  • SAE 10W-40 oil with an API SF/SG (or SH/SJ with JASO MA) rating
  • New crush washer for the drain plug (recommended but optional)
  • Gloves for protection

Preparation

  • Start by warming up your engine for a few minutes—this helps the oil drain easily and completely as it reduces viscosity and brings contaminants into suspension.
  • Turn off the motorcycle and allow it to sit for about 3 minutes, so the oil can settle in the transmission.
  • Place the bike on a level surface and securely hold it in a vertical (upright) position. Use a stand if possible for additional stability.

Step-by-Step Oil Change Instructions

  1. Locate the drain plug and filler cap:
    • The drain plug is located at the bottom of the transmission case. Have your drain pan positioned underneath to catch old oil.
    • The filler cap is typically found on the right side of the engine, above the clutch cover.
  2. Remove the filler cap:
    • This step allows the oil to drain more freely by preventing a vacuum in the case.
  3. Drain the old oil:
    • Use the socket wrench to carefully remove the drain plug. Be cautious—the oil may be hot.
    • Allow the oil to drain thoroughly. You can gently tilt the bike from side to side to ensure complete drainage.
  4. Inspect the drain plug and replace washer:
    • Clean the drain plug and inspect the threads and crush washer. Replace the washer if worn to prevent leaks.
  5. Reinstall the drain plug:
    • Install the drain plug by hand first to prevent cross-threading, then use your torque wrench to tighten it to 21 N–m (2.1 kgf-m, 14.5 lb-ft) for the 1989 RM125.
  6. Add new oil:
    • Pour in 750 ml (0.8 US qt or 0.7 Imp qt) of SAE 10W-40 oil that meets API SF/SG (or SH/SJ with JASO MA) specifications.
    • Use a measuring cup for precision—overfilling can increase crankcase pressure and cause leaks; underfilling risks inadequate lubrication.
  7. Replace and tighten the filler cap:
    • Install the filler cap and tighten it by hand, then finish with the torque wrench to 5.5 N–m (0.55 kgf-m, 4.0 lb-ft).
  8. Check oil level:
    • Hold the bike upright and check for leaks. Run the engine briefly, shut it off, and wait about 3 minutes for the oil to settle. Check the oil level through the inspection bolt or level sight if equipped.

Model-Specific Notes for the 1989 Suzuki RM125

  • Two-Stroke Transmission:
    • The 1989 RM125 is a two-stroke motorcycle; don’t confuse the transmission (gearbox) oil with the premix oil used for the fuel. The procedure above is for the gearbox oil only.
  • Specified Oil and Volume:
    • Always use SAE 10W-40 with an API SF/SG or SH/SJ with JASO MA rating. Using the wrong oil type can lead to clutch slippage or excessive wear.
    • The correct volume is especially important—0.75 liters (750 ml) after a standard change, and 0.8 liters (800 ml) after a full overhaul.
  • Torque Specifications Matter:
    • Both the drain plug and filler cap require proper torquing to avoid stripping threads or causing leaks: 21 N–m for the drain plug, 5.5 N–m for the filler cap.
  • Disposal of Oil:
    • Take used oil to a recycling center or auto parts shop that accepts waste oil—never dump it on the ground or in the trash.
  • Frequent Changes:
    • If riding in sandy, wet, or racing conditions, change your oil more frequently, as debris and moisture can contaminate transmission oil faster.

Common Mistakes to Avoid

  • Forgetting to reinstall the drain plug before adding new oil.
  • Over-tightening drain or filler plugs, which can strip threads in the aluminum case.
  • Using automotive engine oil not rated for wet clutch motorcycles.
  • Not using a torque wrench—hand tightening leads to inconsistent results.

Conclusion

Changing the oil in your 1989 Suzuki RM125 is a key part of owning and maintaining a dirt bike. By using the correct oil, following torque settings, and carefully measuring, you’ll keep your machine running smoothly for years of performance on the track or trail.

This guide is proprietary to MotoSport.com and tailored for RM125 riders who demand reliability and precision in their maintenance routine.

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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.