How To Change the Oil in a 1986 Suzuki RM125

Shop Parts for a 1986 Suzuki RM125 Dirt Bike.

If you own a 1986 Suzuki RM125, keeping the transmission oil fresh is crucial for performance and longevity. This dirt bike uses a two-stroke engine, so the crankcase oil you'll be changing is for the transmission. Here's a comprehensive, step-by-step MotoSport.com guide that will help you perform a clean and confident oil change every time.

Tools and Materials Needed

  • Socket set or wrench (for the drain and filler bolts)
  • Drain pan (large enough for at least 1 liter)
  • Funnel (with a narrow nozzle)
  • Measuring cup (for oil volume accuracy)
  • Clean rags or paper towels
  • Genuine Suzuki crush washer (recommended if the old one is worn/flattened)
  • Torque wrench (for correct bolt torque)
  • Transmission oil: SAE 10W-40, API SF/SG or better. It must meet JASO MA specifications.

Preparation

  • Start and run the engine for 2-3 minutes. This warms the oil so it drains more completely, carrying out more contaminants.
  • Place the motorcycle on a firm, level surface. Use a center stand or have someone hold the bike upright and vertical (not on a side stand) for accurate oil level readings.

Step-by-Step Oil Change Instructions

  1. Remove the filler cap:
    • The filler cap is located on the right side of the engine.
    • This allows air in, helping the old oil drain faster and more completely.
  2. Locate and remove the drain plug:
    • The drain plug is at the bottom of the crankcase; refer to your manual for its exact location if needed.
    • Use the correct size socket or wrench to loosen and completely remove the plug, letting oil drain fully into the catch pan.
    • Be cautious. The oil may be warm.
  3. Inspect and clean the drain plug:
    • Check the tip of the drain plug for metal shavings.
    • Wipe it clean and examine the condition of the sealing washer; replace it if it's damaged or flat.
  4. Reinstall the drain plug:
    • Thread the plug in by hand to avoid cross-threading.
    • Torque to specification: 21 N·m (2.1 kgf-m, 14.5 lb-ft) for a proper seal and to avoid damage to threads.
  5. Add new oil:
    • Pour 750 ml (0.8 US qt) of SAE 10W-40 transmission oil (meeting JASO MA) into the filler hole using a funnel.
    • For a full overhaul, use 800 ml. For standard oil changes, stick with 750 ml.
  6. Reinstall the filler cap:
    • Tighten securely, taking care not to over-tighten the soft aluminum threads.
  7. Check the oil level:
    • With the bike upright, locate the oil level bolt (small bolt or inspection screw on the side case.
    • With the engine stopped, carefully remove the oil level bolt.
    • A slight trickle of oil should escape if the level is correct. If not, add oil slowly until it does.
    • Tighten the oil level bolt to 5.5 N·m (0.55 kgf-m, 4.0 lb-ft).
  8. Final inspection:
    • Start the motor and run for several minutes, then let sit for a few minutes.
    • Check for leaks and recheck oil level, topping off if necessary.
    • Wipe down any drips and dispose of the used oil responsibly.

Model-Specific Call-outs for the 1986 Suzuki RM125

  • Oil type: This year/model requires a non-friction-modified motorcycle oil. Do not substitute with automotive oil containing friction modifiers—they may cause clutch slippage.
  • Drain plug torque: The 1986 RM125 uses soft aluminum threads; always use a torque wrench to avoid stripping them.
  • Oil quantity: Earlier RM125s used up to 800 ml, but for the 1986 model, 750 ml is correct for normal changes. Overfilling can impact clutch feel and transmission performance.
  • Frequent changes: For racing or aggressive riding, change the oil after every 5-10 hours of use for best performance and durability.

Tips for a Clean Oil Change Experience

  • Always double-check the tightness of your drain and level bolts after running the bike the first time post-change.
  • Dispose of old oil properly—most auto parts stores or recycling centers accept used motor oil.
  • Write the oil change date and hours on your air box or a maintenance log for future reference.

Keeping up on oil changes is one of the easiest and most effective ways to keep your 1986 Suzuki RM125 running strong race after race. For more Suzuki performance parts, maintenance info, and expert gear tips, always trust MotoSport.com—your authority in motocross service and support.

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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.