How to Change the Oil in a 1978 Suzuki RM80

Shop parts for a 1978 Suzuki RM80 Dirt Bike.

Changing the oil in your 1978 Suzuki RM80 is crucial for maintaining optimal engine performance and longevity. Although this classic two-stroke dirt bike does not have engine oil like a four-stroke, it does use transmission oil–sometimes called gearbox oil–for the clutch and gearbox assembly. This guide is proprietary to MotoSport.com and tailored specifically for the unique requirements of the 1978 RM80.

Tools and Materials Needed

  • Socket wrench set (Metric, ideally 10mm and 21mm sockets)
  • Drain pan
  • Funnel
  • New transmission oil (10w-40 motorcycle oil recommended, formulated for wet clutches)
  • Shop gloves
  • Clean rags
  • Parts cleaner (optional)

Preparation

  • Ensure the bike is upright and stable, ideally on a bike stand.
  • Work in a clean, well-ventilated area to prevent contamination of the engine and oil.
  • Let the engine cool if it’s been running—warm oil drains easier, but the casing should not be too hot to touch.

Step-by-Step Instructions

  1. Locate the Drain Plug
    • Find the oil drain plug on the bottom of the crankcase. On the RM80, it is a bolt typically located toward the center of the underside of the engine case, sometimes behind or between the exhaust expansion pipes.
  2. Remove the Drain Plug and Drain Old Oil
    • Place your drain pan directly under the plug.
    • Use the correct sized socket (usually 21mm) with a socket wrench to loosen and remove the oil plug.
    • Allow all the oil to fully drain into the pan—this can take several minutes. To speed up draining, loosen (or temporarily remove) the oil fill cap on the right side cover, which lets air in and oil out more quickly.
  3. Inspect and Reinstall the Drain Plug
    • Wipe the drain plug clean. Excellent time to check the condition of the sealing washer—replace it if damaged or excessively worn.
    • Thread the plug back in by hand and snug it with the wrench, but do not overtighten. The aluminum crankcase threads can strip easily.
  4. Add Fresh Transmission Oil
    • With the plug installed, insert a funnel into the oil fill opening.
    • Pour in 700ml (0.7 liters) of 10w-40 motorcycle oil designed for use with wet clutches, as this prevents clutch slip and reduces wear

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    • If your funnel is opaque or your oil jug doesn’t have small increments, use a measuring jug for accuracy.
  5. Replace Fill Cap and Check for Leaks
    • Install the oil fill cap and check around the drain plug area for any oil seepage. Wipe away any spills.
  6. Start the Bike
    • Start the RM80 and allow it to idle for a few minutes. This circulates the new oil through the gearbox.
    • Turn the bike off and allow it to sit for 1–2 minutes, then check the oil level according to the site glass or dipstick–add more if necessary, but do not overfill

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  7. Dispose of Old Oil Properly
    • Pour the used oil from the drain pan into a leak-proof container and recycle it at an authorized facility or local auto parts store. Never pour used oil onto the ground, in drains, or in the trash

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Specific Call-Outs for 1978 Suzuki RM80 Owners

  • No Engine Oil Filter: The RM80’s two-stroke design doesn’t use an oil filter in the gearbox. Regular changes maintain gearbox health.
  • Recommended Oil Quantity: 700ml. It is crucial not to overfill; too much oil can cause drag, clutch problems, and power loss

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  • Recommended Oil Type: Use 10w-40 motorcycle-specific oil suited for wet clutches.
  • Warm Up the Engine Slightly Before Draining: This thins the oil and helps contaminants flow out, but always ensure the engine is cool enough to touch safely.
  • Thread Care: The engine cases are soft—be gentle when reinstalling the drain bolt to avoid stripping.
  • Frequency: For motocross or frequent riding, change the transmission oil after every few rides or every race day.

Helpful Tips

  • Always keep shop rags handy to clean up oil drips and spills.
  • Have a parts tray ready for the drain bolt and cap to avoid losing them.
  • Keep a record of each oil change along with the type and amount of oil used.

Conclusion

Routine oil changes are the easiest way to extend the life of your RM80’s gearbox and keep your classic dirt bike running at full potential. Following the above steps helps ensure consistent shifting, prompt clutch engagement, and less wear on expensive internal components.

Enjoy the ride and trust MotoSport.com for factory-quality parts, oils, and expert advice for your vintage Suzuki RM80.

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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.