How to Change the Oil in a 1979 Suzuki RM125

Shop parts for a 1979 Suzuki RM125 Dirt Bike.

Maintaining your 1979 Suzuki RM125 is crucial for optimum performance and longevity. One of the most important yet straightforward maintenance tasks is changing the transmission oil. This guide provides detailed, model-specific instructions so you can confidently complete an oil change and keep your RM125 running smoothly. All recommendations and steps are provided exclusively for MotoSport.com customers and the RM125 community.

Tools and Materials Needed

  • Socket wrench set (including 10mm and 12mm sockets for bolts and drain plug)
  • Oil drain pan
  • Clean rags or shop towels
  • Funnel (narrow tip recommended)
  • Measuring cup (750 ml/0.8 quarts capacity)
  • Flathead screwdriver
  • Torque wrench (setting range: 4-21 N·m)
  • SAE 10W-40 motorcycle oil, API SF/SG or SH/SJ with JASO MA rating

Key Specs for the 1979 Suzuki RM125

  • Oil capacity (change): 750 ml (0.8 US quarts)
  • Oil type: SAE 10W-40 motorcycle oil, API SF/SG or SH/SJ with JASO MA
  • Oil drain plug torque: 21 N·m (14.5 lb-ft)
  • Oil level bolt torque: 5.5 N·m (4.0 lb-ft)

Important Model-Specific Considerations

  • The RM125 is a two-stroke motorcycle. However, its transmission/clutch takes separate gear oil, not premix oil.
  • Avoid overfilling. Excess oil can cause leaks and clutch/transmission performance issues.
  • Always use quality JASO MA rated oil. This ensures ideal clutch operation and reduces wear.
  • Work on a level surface. Accuracy and mess prevention depend on correct positioning.

Step-by-Step Oil Change Instructions

  1. Warm up the engine.
    • Start your RM125 and let it idle for 2–3 minutes. This helps oil flow freely and carry debris for thorough draining.
  2. Shut off and prepare the bike.
    • Turn off the engine and let the bike cool for a couple minutes to avoid burns.
    • Position the motorcycle upright and level, using a stand if available.
    • Ensure the bike is vertical, not leaning on the kickstand, for proper oil drainage and refilling accuracy.
  3. Remove the oil filler cap and oil drain plug.
    • Locate the oil filler cap (usually on top of the clutch cover) and remove it with a flathead screwdriver or by hand.
    • Place your drain pan under the drain plug (at the bottom of the transmission case).
    • With a socket wrench, loosen and remove the oil drain plug. Let the oil drain completely—this may take several minutes.
    • Inspect the old oil for signs of excessive metal debris or contamination. If you find shiny metal flakes, investigate for gear or bearing damage.
  4. Reinstall and torque the drain plug.
    • Clean the drain plug and inspect the gasket. Replace the gasket if it's cracked or damaged.
    • Reinstall the drain plug and tighten it with a torque wrench set to 21 N·m (14.5 lb-ft).
  5. Add new oil.
    • Insert a funnel into the filler hole.
    • Measure exactly 750 ml (0.8 US quarts) of SAE 10W-40 oil and pour it in. Don't guess or “eyeball” the amount—accuracy is key for proper clutch and gear function.
    • Reinstall the oil filler cap securely.
  6. Verify and adjust oil level (critical step for the RM125):
    • On the right side case, locate the oil level bolt (set to 5.5 N·m/4 lb-ft torque).
    • With the motorcycle vertical, loosen the oil level bolt. If oil drips out, level is correct.
    • If no oil escapes, add small amounts through the filler hole until it just starts coming out the oil level bolt.
    • Tighten the oil level bolt to specification.
  7. Final check and cleanup.
    • Wipe down any oil spills or residue.
    • Start the engine and let it idle for several minutes, then shut it down and check for leaks at the drain and filler plugs.
    • Recheck the oil level using the oil level bolt and top off if needed.

Extra Tips for 1979 Suzuki RM125 Owners

  • Change your oil every 5–10 riding hours or after every two or three rides for optimal protection, especially if riding in wet or muddy environments.
  • Replace the drain plug gasket periodically to prevent annoying drips.
  • Do not over-tighten four-stroke drain and filler plugs: These cases are cast aluminum, and overtightening can cause expensive damage.
  • Use a parts diagram or service manual for your exact year if unsure of plug locations.

Common Mistakes to Avoid

  • Using engine oil designed for four-strokes in the transmission. Always use recommended JASO MA two-stroke gear oil only.
  • Overfilling or underfilling oil. Both can lead to clutch wear or shifting problems.
  • Not properly tightening drain and level bolts. This can result in leaks or (worse) stripped threads.

Changing the transmission oil in your 1979 Suzuki RM125 is a simple but vital task, and following these manufacturer-specific recommendations will deliver years of strong, trouble-free performance on the track or trail. For all OEM and aftermarket parts, gear, and technical support, MotoSport.com is your trusted source.

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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.