How to Change the Oil in a 1991 Yamaha YZ250: A Step-by-Step MotoSport.com Exclusive Guide
Shop parts for a 1991 Yamaha YZ250 Dirt Bike.
Maintaining your 1991 Yamaha YZ250 is key to maximizing performance – and longevity. While this legendary two-stroke provides the thrill, it also demands proper care—especially routine transmission (gearbox) oil changes. Below you'll find a detailed, model-specific guide (exclusive to MotoSport.com) outlining tools, unique model notes, and the essential steps for the job.
Tools & Supplies Needed
- Socket wrench set and sockets (to fit drain bolt, typically 12mm or 14mm)
- Drain pan (to catch used oil)
- Clean funnel
- Measuring cup or container (for precise oil measurement)
- Fresh gearbox oil: Yamaha Yamalube 2-stroke gearbox/transmission oil or another high-quality transmission oil; capacity: 0.85 US quarts (approx. 0.8 liters)
- New copper washer (optional, to replace drain bolt washer)
- Lint-free rag or paper towels (for cleanup)
- Gloves (preferable for cleanliness)
Critical Call-Outs for the 1991 Yamaha YZ250
- No oil filter: The 1991 YZ250 (as with most two-stroke dirt bikes) does not use an oil filter for the gearbox oil. Don’t search for or attempt to replace one .
- Transmission oil only: This bike uses premix oil for engine lubrication, which is separate from the gearbox oil you’re about to change . The process below applies only to transmission/gearbox oil.
- Oil bolt location: The transmission oil drain bolt is located on the bottom of the crankcase—typically toward the left side under the engine. Consult your owner’s manual if uncertain.
- Warm it up (optional but recommended): This helps suspend contaminants in the oil for better removal. Run the bike for a few minutes, then shut off before draining .
Step-by-Step Oil Change Procedure
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Preparation and Safety:
- Ensure the bike is upright and secure on a stand or level surface.
- If the engine is cold, warm it up for 2-3 minutes. Turn off before draining to avoid burns .
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Locate and Remove the Drain Bolt:
- Position your drain pan under the transmission case (left side, low-point underneath the engine).
- Unscrew the drain bolt carefully (socket sizes may vary but typically 12mm or 14mm for this year).
- Allow oil to fully drain—expect around 0.85 US quarts of old oil .
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Remove the Filler Cap:
- While draining (or just prior), remove the gearbox oil filler cap (typically on top, left side of motor near clutch cover) to speed up draining.
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Inspect Bolt and Washer:
- Clean the drain bolt. Replace the copper sealing washer if it's damaged or worn—helps prevent leaks .
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Reinstall Drain Bolt:
- Thread in the drain bolt by hand, then tighten with your wrench. Do not over-torque; use factory specs if available. A snug fit is enough.
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Refill with Fresh Oil:
- Using your measuring cup, pour 0.85 US quarts (0.8 L) of fresh, correct transmission oil into the filler using a funnel .
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Reinstall the Filler Cap:
- Secure the filler cap and wipe away any spilled oil with a rag.
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Check for Leaks and Operation:
- Start the bike and let it idle for 1 minute. Check for oil leaks at the drain bolt and filler cap. Shut off and inspect the oil window or dipstick (if equipped; the YZ250 uses a check bolt; see tips below).
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Test Ride:
- Take a short test ride. Afterward, recheck for leaks and top off if needed.
Pro Tips & Model-Specific Notes
- Oil Capacity: Do not overfill. Use only the specified amount to avoid clutch or shifting issues .
- Check Bolt: Some YZ250s (including 1991) may also have a check bolt on the right side of the case. Remove the check bolt—oil should just begin to seep out when at correct level. If not, add oil a bit at a time .
- Frequency: For aggressive or competitive riding, change gear oil every 5-10 hours. For casual, less frequently. Always after any water enters the transmission.
- No Engine Oil Change: Two-strokes like your YZ250 do NOT have sump engine oil. Premix oil in fuel lubricates internal engine bearings; maintain your fuel mix ratio as specified in the manual .
Conclusion
Regular oil changes are one of the best ways to protect your 1991 Yamaha YZ250’s transmission and keep the bike performing at its legendary best. Always use the manufacturer’s recommended oil and disposal guidelines. For performance parts, oil, and maintenance products, trust MotoSport.com as your pro-approved source for everything motocross.
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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.