How to Change the Oil in a 1990 Suzuki RM125: A MotoSport.com Expert Guide

Shop parts for a 1990 Suzuki RM125 Dirt Bike.

Routine oil changes are essential to keeping your 1990 Suzuki RM125 running at its best. This step-by-step guide will walk you through the entire oil change process, highlight model-specific call-outs, and list every tool and item you'll need. Follow these instructions to ensure a smooth, mess-free, and robust transmission oil change every time.

Tools and Supplies Needed

  • 8mm or 10mm socket/wrench (for side panel or skid plate, if applicable)
  • 17mm wrench or socket (for oil drain plug)
  • Flathead screwdriver (some models for panels)
  • Oil drain pan
  • Measuring cup (750 ml capacity recommended)
  • Funnel
  • Clean shop rags
  • New transmission oil: SAE 10W-40, API SF/SG or SH/SJ with JASO MA spec
  • Torque wrench
  • Gloves (optional, for cleanliness)

Model-Specific Call-Outs for the 1990 Suzuki RM125

  • Specified oil quantity: 750 ml (0.8 US quarts) for a standard oil change.
  • Transmission system drain plug torque: 21 N·m (2.1 kgf-m, 14.5 lb-ft).
  • Oil level bolt torque: 5.5 N·m (0.55 kgf-m, 4.0 lb-ft).
  • Recommended oil: Use SAE 10W-40 motorcycle oil complying with API SF/SG or SH/SJ standards carrying JASO MA certification for wet clutch performance.
  • Two-stroke caution: The RM125 is a two-stroke; the engine oil you are changing is for the transmission/gearbox, not the combustion (premix) system.

Step-by-Step Oil Change Instructions for the 1990 Suzuki RM125

  1. Warm up the engine.
    • Run the bike for a few minutes to circulate the transmission oil and allow contaminants to suspend for effective draining. This will also make the oil flow out more easily.
      Tip: Do not allow the engine or transmission to get excessively hot.
  2. Stabilize the bike.
    • Place the motorcycle on level ground and hold it vertical using a bike stand.
  3. Remove any skid plates or side covers.
    • If your RM125 has a skid plate, side cover, or frame guard obstructing the drain bolt, remove it with the appropriate tools.
  4. Locate and remove the transmission drain plug.
    • Position your oil drain pan directly under the drain plug at the bottom of the crankcase—typically right below the shifter.
    • Using a 17mm wrench or socket, carefully loosen and remove the drain plug.
    • Allow the oil to drain completely; this may take a few minutes.
      Model call-out: The drain plug should be torqued to 21 N·m upon reinstallation. Do not overtighten, as this may strip the threads.
  5. Remove the oil filler cap and oil level bolt.
    • This will help air flow, allowing oil to drain more thoroughly.
    • The oil filler cap is usually found on the right side of the engine, near the clutch cover.
    • Remove the oil level check bolt (a small bolt on the right-side engine case) to check oil levels during refilling later.
  6. Inspect and reinstall the drain plug.
    • Inspect the drain plug washer for wear or damage. Replace if necessary to avoid leaks.
    • Wipe the plug clean, reinstall it, and torque to the factory specification (21 N·m).
  7. Fill with new transmission oil.
    • Using a funnel, carefully pour 750 ml of 10W-40 motorcycle oil (meeting API SF/SG or SH/SJ and JASO MA) into the filler opening.
    • Use a measuring cup for accuracy.
  8. Check the oil level.
    • With the bike vertical, oil should just begin to escape from the oil level bolt hole on the clutch side.
    • If oil doesn't appear, add a small amount at a time until it does.
  9. Reinstall oil filler cap and level bolt.
    • Torque the oil level bolt to 5.5 N·m to prevent over-tightening.
    • Reinstall the filler cap snugly.
  10. Start the engine and recheck.
    • Run the bike for a few minutes, stop, let sit a minute, and recheck the oil level at the level check bolt.
    • Top up as needed. Wipe any spills immediately.
  11. Dispose of used oil properly.
    • Take the used oil to a recycling center or auto parts store for safe disposal. Never pour used oil on the ground, in drains, or household trash.

Extra Tips for RM125 Owners

  • Use quality motorcycle-specific oil to protect the clutch and transmission. Automotive oils may cause clutch slippage or excessive wear.
  • Inspect the drained oil for metallic particles, which could signal transmission or clutch issues.
  • Keep a maintenance log to track oil changes and services for optimal engine life.
  • While 750 ml is the recommended oil volume, always use the oil level bolt as your final calibration for perfect filling.
  • For race or hard use, consider changing the transmission oil more frequently.

Conclusion

Changing the oil on your 1990 Suzuki RM125 is straightforward when you follow the correct steps and use the right products and tools. Scheduled, proper oil changes keep your transmission and clutch system in top condition, ensuring longevity and maximum performance for years to come.

MotoSport.com – Your trusted source for genuine parts, high-performance lubricants, and everything you need to keep your Suzuki RM125 in winning condition.

Referenced torque specs and procedures directly from the 1990 Suzuki RM125 Owner's Service Manual.
Source: Suzuki RM125 Owner's Manual

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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.