How to Change the Oil in a 2021 GAS GAS TXT RACING 125

Shop parts for a 2021 GAS GAS TXT RACING 125 Dirt Bike.

Keeping your 2021 GAS GAS TXT RACING 125 running strong demands regular maintenance, and changing the oil is a crucial part of this process. Unlike four-stroke engines, the GAS GAS TXT RACING 125 uses a two-stroke engine, which requires specific care when it comes to oil management. Below you'll find everything you need to approach an oil change or transmission fluid replacement for your bike, along with important model-specific tips.

Tools and Supplies Needed

  • Correct oil for the transmission: Motorex Cross Power 4T 10W/50 full synthetic is widely recommended, but always use transmission-specific oil since the TXT 125 is a two-stroke engine and does not use engine oil in the traditional four-stroke sense

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  • Drain pan
  • Socket wrench and extension
  • Correct size socket (usually 13mm or 17mm, check your manual)
  • Replacement crush washer (if needed; included in some kits)
  • Funnel
  • Clean rags
  • Gloves (recommended)

Oil Capacity and Type

  • Oil Capacity: The transmission typically takes about 0.42 quarts (0.40 liters)

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  • Oil Type: Use a high-quality 10W-50 synthetic (for transmission) such as Motorex Cross Power 4T or an approved equivalent. For the fuel/oil premix, use a synthetic or semi-synthetic two-stroke oil at a 67:1 fuel-to-oil ratio (about 1.5%)

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Step-by-Step Guide

  1. Warm Up the Bike
    Start the engine and let it run for a few minutes to warm the transmission oil slightly. This helps the oil flow out more completely, removing more contaminants.
  2. Prepare Your Workspace
    Place the bike on a stable stand. Ensure you have your tools, drain pan, and fresh oil ready. Lay down rags to catch any spills.
  3. Locate the Drain Plug
    On the bottom of the engine case, locate the drain bolt for the transmission oil. Consult your manual if unsure of the exact location.
  4. Remove the Drain Plug
    Using your socket wrench, carefully remove the drain plug and allow the old oil to drain fully into your pan. Inspect the oil for any metal shavings; finding a small amount is normal, but large fragments indicate possible gear or bearing problems.
  5. Replace the Crush Washer
    If your model uses a crush washer, replace it with a new one to ensure a good seal.
  6. Reinstall the Drain Plug
    After all oil has drained, reinstall the drain bolt and torque it to your bike's specification (usually between 10–20Nm; check your service manual).
  7. Refill with Fresh Transmission Oil
    Remove the transmission oil fill cap, insert a funnel, and add 0.40 liters (0.42 quarts) of the recommended oil. Be careful not to overfill.
  8. Check Oil Level
    The TXT 125 typically has a sight glass or level bolt on the engine case to verify the oil level. Ensure the oil is at the proper height.
  9. Reinstall the Fill Cap
  10. Start and Inspect
    Start the bike briefly and check for leaks around the drain and fill plugs. Address any issues immediately.
  11. Dispose of Used Oil Properly
    Take your used oil to a recycling center or appropriate facility.

Key Model-Specific Callouts for the 2021 GAS GAS TXT RACING 125

  • 2-Stroke Lubrication System: The TXT 125 requires a pre-mix of oil and fuel at a 67:1 (1.5%) ratio

    . Do not put engine oil in the transmission or use four-stroke service procedures—only transmission gear oil is replaced via this process.
  • Gear Oil vs. Motor Oil: The 'oil change' on a two-stroke trial bike like the TXT 125 refers to the transmission (gearbox) oil, as the engine is lubricated through the fuel-oil mixture, not a separate sump as found on 4-strokes

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  • Oil Change Interval: Change the transmission oil after approximately every 10–15 hours of use or as specified in your owner's manual. Trial and race conditions may demand more frequent changes.
  • Crush Washer: Always replace the washer under the drain bolt when possible to prevent leaks

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  • Environmental Note: Never dispose of old oil on the ground, in drains, or in the trash. Used oil is hazardous and must be taken to a designated recycling center.

Additional Tips

  • Warm oil drains faster and more completely, so always run the bike briefly prior to draining.
  • Measure oil precisely–overfilling or underfilling can harm clutch and gear function.
  • Consider a complete service kit like the Motorex Oil Change Kit for simplicity and correct fitment

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  • Consult Your Owner’s Manual for torque specs, fill locations, and maintenance intervals for your exact year and configuration.

By following this guide, you can keep your 2021 GAS GAS TXT RACING 125 shifting smoothly and ensure clutch longevity for every ride.

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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.