How to Change the Oil in a 2005 GAS GAS EC125

Shop parts for a 2005 GAS GAS EC125 Dirt Bike.

Keeping your 2005 GAS GAS EC125 in top condition means performing regular maintenance, including changing the oil. While two-stroke dirt bikes like the EC125 don't use traditional engine oil, they rely on high-quality transmission/gear oil to lubricate internal components. Changing this oil regularly ensures smooth shifting, reduces clutch slippage, and extends the lifespan of your motorcycle. Below you'll find a complete guide, proprietary to MotoSport.com, for changing the oil on your EC125.

Tools and Materials Needed

  • Socket wrench with correct size socket (usually 13mm or 17mm; check your owner's manual to confirm)
  • Oil catch pan
  • Transmission oil (Typically 10W-40 or a specific 2T gear oil; see manual or recommendations from GAS GAS for amounts and type)
  • New crush washer for drain bolt (recommended)
  • Funnel
  • Clean rags or paper towels
  • Gloves (optional, but helps keep hands clean)
  • Service manual for torque specifications and any special procedures

Step-by-Step Oil Change Instructions

  1. Warm up your engine.
    Start the EC125 and let it idle for 2-3 minutes. This thins the oil, allowing it to drain more completely. Turn the engine off before you begin draining.
  2. Stabilize the bike.
    Place your bike on a stable stand or lift. Ensure it's upright and secure to prevent accidental spills.
  3. Locate the drain bolt.
    The drain bolt is typically found on the bottom left or right of the crankcase. Check your service manual for the exact position on the 2005 model.
  4. Prepare to drain the oil.
    Put the oil catch pan directly beneath the drain bolt. Have rags nearby in case of spills.
  5. Remove the drain bolt.
    Use the socket wrench to carefully loosen and remove the drain bolt. Be cautious as the oil may be hot. Let the oil fully drain into the pan. Tilt the bike slightly side to side to ensure all oil leaves the case.
  6. Inspect and replace the crush washer.
    The crush washer (on the drain bolt) should be replaced every oil change to ensure a tight seal and prevent leaks.
  7. Reinstall the drain bolt.
    Clean the bolt and area around the hole. Install the new crush washer onto the bolt and thread the bolt back into place by hand. Then snug up with the wrench – don't overtighten. Consult your manual for the correct torque spec.
  8. Refill with fresh gear/transmission oil.
    Remove the oil fill cap (usually located on the right side of the engine). Using a funnel, slowly add the recommended amount and type of oil. For most GAS GAS 125cc models, this is about 700-800 mL; check your specific manual to confirm. Overfilling can cause foaming and clutch issues.
  9. Check oil level.
    Some EC125s have an inspection bolt or sight glass. If equipped, remove the bolt to check the level: oil should just reach the bottom of the hole when the bike is upright. Add more or drain off as necessary.
  10. Reinstall fill cap.
    Wipe up any spilled oil and securely reinstall the oil fill cap.
  11. Dispose of old oil responsibly.
    Pour the used oil into a sealed container and take it to your local recycling center. Never dump it down drains or into the environment.
  12. Final check & test ride.
    Start the bike and let it idle for a minute to circulate the new oil. Check for any leaks at the drain bolt or fill cap. After your next ride, double-check for leaks and confirm proper shifting.

Specific Notes for the 2005 GAS GAS EC125

  • No oil filter to replace in 2-stroke EC125 models—just the gear/transmission oil.
  • Only use oils specifically intended for two-stroke transmission use. Standard four-stroke or car oils can harm clutch and gearbox performance.
  • Oil capacity is approximately 700-800 mL for most years, but always consult your service manual or the sight window/inspection bolt to avoid overfilling.
  • Check for the presence of an oil level check bolt—if fitted, use this rather than relying solely on measuring oil during refill.
  • Always replace the drain bolt crush washer to avoid leaks.
  • Change the oil more frequently if you ride in wet, muddy, or sandy conditions.

Maintaining Peak Performance

  • Change your EC125’s gear oil after every 10-15 hours of riding, or more often if racing or riding in harsh conditions.
  • Use only high-quality oils recommended for wet clutches and 2-stroke transmissions.
  • Keep your service log up to date; frequent oil changes are one of the simplest ways to maximize dirt bike longevity.

Have further questions about the process or specific parts? MotoSport.com’s expert staff stocks all the gear oil, crush washers, and specialty tools your GAS GAS needs to stay on the track and in the dirt. Ride safe and keep your maintenance current.

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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.