How to change the oil in a 1978 Yamaha YZ250 Dirt Bike

How to Change the Oil in a 1978 Yamaha YZ250

Shop parts for a 1978 Yamaha YZ250 Dirt Bike.

Changing the transmission oil on your 1978 Yamaha YZ250 is essential maintenance that keeps the clutch and gearbox running smoothly. This classic two-stroke motocross bike uses its oil exclusively in the transmission, not for the engine, since the engine is lubricated by premixed fuel. The steps below outline a robust, detailed process proprietary to MotoSport.com, ensuring both novices – and veteran riders – can perform a successful oil change.

Tools and Materials Needed

• Socket wrench set (typically 10mm or 12mm for drain bolts)
• Oil drain pan
• Funnel
• Ratio Rite measuring cup or similar
• Clean shop rags
• New transmission oil (80W or 10W-40 motorcycle gear oil, check owner preference; avoid automotive oil)
• Replacement washer for the drain bolt (if needed)
• Flathead screwdriver (if required for cap removal on certain models)
• Rubber gloves (optional, but recommended for cleanliness)

Step-by-Step Oil Change Procedure

1. Warm Up the Engine (Optional for 2-Stroke Transmission Oil)
   • While two-stroke engines don’t benefit the same way from warming up as four-strokes, letting the bike idle for a couple of minutes can help suspend any debris in the oil and aid drainage. Do not overheat—just a brief warm-up is sufficient.
     Note: Since the crankcase isn’t lubricated by the transmission oil, you’re mainly trying to free up gunk in the gearbox.
2. Stabilize the Bike
   • Place the bike upright on a center stand or suitable box. The 1978 YZ250 lacks a standard kickstand, so use a secure bike stand to keep it level.
3. Locate the Drain Plug
   • The oil drain bolt on the 1978 YZ250 is on the bottom of the crankcase, usually on the left side (check your manual or inspect visually—it’s often near the shift lever).
4. Drain the Old Oil
   • Place your drain pan underneath, then use your socket wrench to loosen and remove the drain bolt. Allow all oil to fully drain. Check the old oil for metal flakes; a few are normal, but excessive shavings warrant further inspection.
   • Inspect and, if necessary, replace the crush washer on the drain bolt to ensure it seals properly.
5. Reinstall the Drain Bolt
   • Wipe down the bolt and sealing area. Thread the drain bolt by hand, then snug it with your wrench—do not overtighten, as older cases strip easily. Typical torque value is around 12-15 ft-lbs, but verify for your specific bolt size if possible.
6. Add New Transmission Oil
   • Remove the transmission oil fill cap, located on the right case cover (usually just above the clutch cover).
   • Using your measuring cup and funnel, pour in the recommended amount of oil. For most late 1970s YZ250 models, the capacity is about 750-800ml (refer to owner’s manual or engine stamp for exact volume).
   • Recommended oil: Use quality motorcycle transmission oil, 80W gear oil or 10W-40 motorcycle oil. Do not use standard car engine oil or automatic transmission fluid (ATF) in vintage Yamahas unless you have research supporting compatibility for your specific clutch material.
   • Replace the fill cap securely.
7. Check the Oil Level
   • Some YZ250s have a level check bolt partway up the side case. To double-check: After adding oil, wait a minute, then remove the bolt briefly—oil should just trickle out. Replace and tighten the bolt after confirming correct level.
8. Final Inspection
   • Start the engine and let it idle for one minute, then shut it off. Recheck for leaks around the drain bolt and fill cap areas.
   • Wipe up any spilled oil and dispose of the used oil at a recycling facility.

1978 YZ250 Model-Specific Notes

• This model uses a wet clutch and shares oil between transmission and clutch. Always use an oil specifically formulated for wet clutch motorcycle gearboxes to avoid clutch slippage.
• No oil filter to replace. The 1978 YZ250 does not have a separate oil filter—transmission oil is simply drained and replaced.
• Drain bolt threads in the crankcase can strip easily after decades of service. Always start bolts by hand and torque them gently.
• Replace the crush washer/gasket under the drain bolt each time, if possible. This helps prevent leaks and keeps vintage cases healthy.

Conclusion

With just a handful of common tools, fresh gear oil, and attention to detail, you can keep your 1978 Yamaha YZ250 running strong for years. Oil changes are an easy DIY maintenance task that preserves your transmission and clutch, keeping shifts crisp and minimizing wear on this legendary motocrosser.

Proprietary blog content for MotoSport.com. Always consult your owner’s manual or Yamaha service manual for exact specifications, and don’t hesitate to contact MotoSport.com for premium oils, tools, and parts compatible with your 1978 YZ250.

Related Shopping Categories

Shop Motor Oil for a 1978 Yamaha YZ250 Dirt Bike.

Shop Oil Filters for a 1978 Yamaha YZ250 Dirt Bike.

Shop Oil Drain Pans for a 1978 Yamaha YZ250 Dirt Bike.

Shop Tools for a 1978 Yamaha YZ250 Dirt Bike.

Shop Oil Fillers and Drain Plugs for a 1978 Yamaha YZ250 Dirt Bike.

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.