How to change the oil in a 1987 Kawasaki KX80 BIG WHEEL Dirt Bike

How to Change the Oil in a 1987 Kawasaki KX80 Big Wheel

Shop parts for a 1987 Kawasaki KX80 Big Wheel Dirt Bike.

Keeping your 1987 Kawasaki KX80 Big Wheel running strong means maintaining the right oil and performing regular oil changes. Follow this comprehensive MotoSport.com guide to change the transmission oil, including required tools, step-by-step process, and model-specific tips to keep your vintage two-stroke performing at its peak.

Tools & Supplies Needed

Socket wrench set (including 15mm or 17mm socket for the drain bolt – verify for your particular bike)
Drain pan
Clean rag
Funnel
Measuring cup or graduated oil container
Fresh transmission oil (Kawasaki recommends 10W-40 or equivalent two-stroke gear oil. Check your owner's manual for specification.)
Replacement crush washer for the drain bolt (optional but recommended)
Parts cleaning brush (for cleaning the drain bolt area if needed)
Torque wrench (recommended for reinstalling drain bolt)

Step-by-Step Oil Change Instructions

Warm up the engine
Start and run your KX80 for 2-3 minutes. This helps the oil flow more freely and brings out any contaminants suspended in the oil for a more effective change.
Place the bike on a stand
Ensure the motorcycle is upright and stable. A stand is strongly recommended for safety and proper leveling during drainage and refill.
Clean the area around the drain bolt
Use a parts cleaning brush and rag to remove any dirt or debris from the drain bolt and its surrounding area. This prevents contaminants from falling into the engine when the bolt is removed.
Remove the drain bolt
Position the drain pan beneath the transmission case. With the correct socket, slowly loosen and remove the drain bolt at the bottom of the right crankcase. Allow the oil to drain completely. Inspect the crush washer and replace it if damaged or flattened.
Inspect the old oil
Look at the drained oil for any metallic particles or excessive debris, which can indicate clutch or gearbox wear. Report or investigate abnormal findings.
Reinstall the drain bolt
Once the oil is fully drained, clean the drain bolt and its sealing surface. Install a new crush washer as needed. Thread the bolt in by hand, then tighten to the manufacturer-recommended torque specification (check your manual; overtightening may strip the threads).
- Tip for the 1987 KX80: Be careful not to overtighten—the aluminum case threads are relatively soft.
Add fresh oil
Using the measuring cup, pour in the correct amount of transmission oil for the 1987 KX80. Similar KX models from this era typically require around 700ml (23.6 oz), but always double-check your owner's manual or Clymer/Haynes guide for confirmation.
- Remove the transmission fill cap, insert the funnel, and slowly pour in the oil.
- Once full, reinstall and tighten the cap.
Check the oil level
Some KX80 models have a sight glass or a check bolt. Make sure the bike is upright and on a level surface. The oil should reach the level indicated by the sight glass or overflow gently from the check bolt (if equipped).
- If using a sight glass, the level should be at the halfway mark with the bike vertical.
Wipe up and inspect for leaks
Clean up any spills. Start the engine for a minute, shut it down, and recheck oil level and under the bike for leaks.
Dispose of old oil properly
Never dump used oil; take it to a local disposal site or auto parts store recycling program.

Model-Specific Callouts for the 1987 KX80 Big Wheel

Thread Strength: The crankcase is cast aluminum and the drain bolt threads can be easily stripped. Always start the bolt by hand and use a torque wrench if possible.
Oil Capacity: The correct oil capacity is typically 700ml for the transmission. Overfilling can cause clutch drag or foaming. Underfilling risks inadequate lubrication and gearbox damage.
Check for Sight Window: Some KX80 models have a small sight window near the clutch cover or a check bolt. If using the bolt, open it after filling – a small amount of oil should trickle out; otherwise, adjust the fill.
Oil Recommendation: Kawasaki's OEM recommendation is a high-quality motorcycle-specific 10W-40, but modern two-stroke transmission-specific oils are also suitable. Avoid using normal automotive engine oil, as it lacks the correct friction and clutch additives for wet clutches.
Regular Maintenance: Race and hard-use intervals often mean changing oil every few hours (every 3 rides or –7 hours for hard off-road use), especially with an older engine.

Common Issues & Tips

Don’t overtighten the drain bolt: Snapping or stripping the crankcase is an expensive and time-consuming repair.
Always check oil level with the bike upright: A slight tilt can give you a false reading.
Inspect oil for clutch material: Fine black particles can be a sign you’re due for a clutch inspection or replacement.
Use only motorcycle-specific oil: This extends clutch life and optimizes shifting feel.

Changing the transmission oil on your 1987 Kawasaki KX80 Big Wheel is a simple, essential part of keeping this classic dirt bike running smoothly. With fresh oil and a careful approach to maintenance, the legendary KX80 “Big Wheel” will keep tearing up the track for years to come.

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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.

How to change the oil in a 1987 Kawasaki KX80 BIG WHEEL Dirt Bike