How to Change the Oil in a 2018 GAS GAS TXT GP 125

Shop parts for a 2018 GAS GAS TXT GP 125 Dirt Bike.

Changing the oil in your 2018 GAS GAS TXT GP 125 is essential maintenance to keep your transmission running smoothly and extend the life of your clutch and gearbox. As a two-stroke trials bike, the TXT GP 125 uses premix fuel for engine lubrication, but it does require periodic gearbox/transmission oil changes. Follow these step-by-step instructions, including crucial call-outs specific to your model, to keep your GAS GAS performing at its peak.

Tools and Supplies Needed

  • Metric socket set (typically 8mm, 10mm, 13mm, 17mm sockets)
  • Ratcheting wrench
  • Flathead screwdriver
  • Oil catch pan
  • Rags or shop towels
  • Funnel
  • Torque wrench (optional, for drain plug)
  • Appropriate gear oil (consult owner's manual–specialist gear oils like GRO or 75W/80W are popular choices)
  • Replacement crush washer for drain plug (recommended)
  • Nitrile gloves (to keep hands clean)
  • Bike stand (for stability and access)

Pre-Change Preparation

  • Start the engine and let it run for 2-3 minutes. This warms the oil, reducing viscosity and helping contaminants drain out with the old oil.
  • Turn off the motorcycle and set it upright on a level surface using a bike stand.
  • If possible, wash the area around the drain and fill plugs to reduce contamination risk.

Step-by-Step Oil Change Process

  1. Remove Skid Plate (if equipped):
    • If your TXT GP 125 has a skid plate that blocks the drain plug, remove it first using the correct socket size.
  2. Locate the Oil Drain Plug:
    • Find the drain plug at the bottom of the engine case–typically a 13mm or 17mm hex bolt. The fill cap is usually on the right side engine cover, near the clutch actuator.
  3. Place Oil Catch Pan:
    • Position the oil catch pan under the drain plug to collect the old oil.
  4. Remove the Drain Plug:
    • Carefully loosen and remove the drain bolt with a ratchet. Allow oil to completely drain. Watch for the crush washer–replace it if damaged during removal.
  5. Inspect Oil and Plug:
    • Check the drained oil for metal particles or a milky appearance (which can indicate water intrusion). Clean the plug and threads thoroughly.
  6. Reinstall Drain Plug:
    • After draining, wipe any residue from the drain area. Install a new crush washer if available. Tighten the plug securely–do not overtighten, as the threads in the aluminum case can strip easily.
    • Call-out: Common on TXT GP models: stripped oil plugs from overtightening. Tighten just enough to snug without excessive force.
  7. Remove Fill Cap:
    • Use a flathead screwdriver or socket (depending on cap design) to remove the oil fill cap on the right engine case.
  8. Add Fresh Oil:
    • Place a funnel in the fill hole and pour in the recommended transmission oil. For the TXT GP 125, the typical capacity is ~400ml (check your owner's manual for the exact figure).
    • Use a specialist gear oil as recommended or a high-quality 75W/80W oil developed for two-stroke transmissions.
  9. Check Level:
    • Some TXT models have a sight glass or level check bolt–consult your manual. The correct level is usually when oil just reaches the bottom of the fill threads or weeps gently from the level bolt when the bike is upright.
  10. Reinstall Fill Cap:
    • With oil at the correct level, reinstall and tighten the fill cap. Wipe off any spilled oil.
  11. Test:
    • Start the engine and let it idle for 1-2 minutes to circulate the new oil. Check for leaks at the drain and fill plugs. Inspect the area after your next ride to ensure everything remains tight and dry.

Key Notes and Model-Specific Callouts

  • The 2018 GAS GAS TXT GP 125 is a two-stroke that uses premix fuel (gas and oil), but the transmission/clutch requires its own regular oil change .
  • Overtightening the drain plug is a common mistake–strip-outs are frequent due to the soft alloy case. Always use moderate torque or a torque wrench at manufacturer's specs if available .
  • Use only synthetic/semi-synthetic transmission oil (not standard engine oil or ATF). Specialist trials gear oils provide best clutch feel and protection .
  • If the bike's been submerged in water or ridden in very wet conditions, change the oil immediately after riding to prevent clutch/gear damage.
  • Always inspect both the old oil and the engine case for metal debris or oil cloudiness–these are early warning signs of mechanical wear.

Disposal and Final Tips

  • Dispose of used oil at an approved recycling center–never down the drain or in household trash.
  • Keep a maintenance log of oil change dates and types of oil used–helps with resale value and troubleshooting future issues.
  • MotoSport.com recommends changing transmission oil every 15-20 hours of riding or following especially harsh conditions for peak performance.

MotoSport.com Is Here to Help

For OEM parts, tools, oils, and unbeatable advice, MotoSport.com has everything you need to keep your GAS GAS TXT GP 125 in race-ready condition. Remember: regular transmission oil changes are the cheapest insurance for your bike's most critical components. Ride safe.

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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.