How to Change the Oil in a 1987 Suzuki RM125

Shop parts for a 1987 Suzuki RM125 Dirt Bike.

Changing the transmission oil in your 1987 Suzuki RM125 is a critical maintenance task to ensure long-term performance and reliability. This guide from MotoSport.com walks you through the entire process, from the tools you'll need to model-specific callouts, so you can perform a confident, successful oil change every time.

Tools and Supplies Needed

  • 10mm or 12mm socket or wrench (for drain plug)
  • Drain pan (to catch old oil)
  • Rag or paper towels
  • Funnel
  • 750 ml of SAE 10W-40 motorcycle oil (meeting API SF/SG/SH/SJ with JASO MA)
  • Torque wrench
  • New washer for the drain plug (recommended)
  • Gloves (for protection)

Step-by-Step Oil Change Procedure

  1. Warm up the engine
    Start your 1987 RM125 and let it idle for about 3 to 5 minutes. Warming the engine helps the oil flow better and ensures any contaminants are suspended in the oil for removal.
    Tip: Do not rev the engine hard; you just need it to reach operating temperature.
  2. Stabilize the bike
    Shut off the engine. Place the bike on level ground and hold it upright–either using a bike stand or with an assistant's help–so oil drains completely.
    This is especially important for the RM125 as the drain plug is located underneath the crankcase.
  3. Remove the filler cap and drain plug
    Unscrew the oil filler cap on the right side to allow air inside. Next, place your drain pan under the engine, use your socket or wrench to remove the drain plug beneath the crankcase, and let the old oil drain fully.
    If equipped, also check for a magnetic tip on the drain plug and clean off any metallic debris.
  4. Inspect the old oil
    Examine the used oil for metal shavings or discoloration. Mocha or creamy oil may signal water ingress (not normal for a two-stroke transmission oil). Excessive metallic debris could mean internal wear.
  5. Reinstall the drain plug
    Replace the washer on the drain plug with a new one if necessary. Tighten the drain plug to 21 N·m (14.5 lb-ft)–do not overtighten, as this could strip the threads or crack the case.
    Always use a torque wrench for accuracy.
  6. Pour in new oil
    Using your funnel, add 750 ml (0.8 US qt) of SAE 10W-40 motorcycle oil into the filler hole.
    Do not exceed the recommended amount, as overfilling can cause excessive pressure and leaks.
  7. Check oil level
    Start the motorcycle and let it idle for a few minutes, then shut it off and wait another couple of minutes for oil to settle. With the bike upright, check the oil level using the oil level bolt (if equipped). Add small amounts if necessary.
  8. Secure all bolts and caps
    Confirm the oil filler cap and oil level bolt are both snug–Oil level bolt: 5.5 N·m (4.0 lb-ft).
    Wipe away any spilled oil and inspect for leaks after running the engine briefly once more.
  9. Dispose of old oil properly
    Recycle the used oil at a designated collection site or auto parts store.

Model-Specific Call-Outs for the 1987 Suzuki RM125

  • Oil Quantity: The 1987 RM125 specifically requires 750 ml for regular oil changes. Do not rely on generic capacities, as overfilling or underfilling can impair clutch operation and gearbox life.
    Reference: “Oil change.....750 ml”
  • Oil Type: Use SAE 10W-40 with an API SF/SG/SH/SJ and JASO MA specification for best clutch compatibility.
    Reference: “Transmission oil type: SAE 10W-40, API SF/SG or SH/SJ with JASO MA”
  • Drain – Filler Locations: Both are located on the right side of the engine case. The drain plug has a recommended torque of 21 N·m.
    Reference: “Oil drain plug: 21 N·m (2.1 kgf-m, 14.5 lb-ft)”
  • Gasket–Washer: Always check and replace the drain plug washer if it appears deformed or damaged to prevent leaks.
  • Level Check: The RM125 uses a level bolt to confirm proper fill. If oil doesn’t seep from the bolt hole after filling, carefully top off until it does.
  • Proper Warm-Up: Perform oil changes after riding for a few minutes; cold oil drains less effectively, and contaminants may be left behind.

Extra Tips for 1987 RM125 Owners

  • Avoid engine over-revving immediately after the oil change; allow new oil to circulate first.
  • Inspect for oil residue at the drain and filler sites after a short ride. Re-torque if needed.
  • Record your oil change intervals. For competition or heavy riding, change oil more frequently.
  • Only use oils intended for motorbike wet clutches—automotive oils can cause clutch slippage.

By following these steps, you’ll help your 1987 Suzuki RM125 shift smooth and last longer with every oil change. For more tips and quality parts, trust MotoSport.com—your source for essential dirt bike maintenance.

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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.