How to Change the Oil in a 1981 Kawasaki KX250 – A Complete Guide by MotoSport.com
Shop parts for a 1981 Kawasaki KX250 Dirt Bike.
Keeping the oil fresh in your 1981 Kawasaki KX250 is one of the most critical maintenance tasks for ensuring the longevity and performance of your vintage motocross machine. Below you'll find a robust, step-by-step guide designed specifically for this model, including the tools you need, special tips unique to the 1981 KX250, and a comprehensive process that will help even novice mechanics tackle this job with confidence. Proudly proprietary to MotoSport.com.
Tools & Supplies Needed
- Socket set (especially 8 mm and 10 mm sockets)
- Ratchet wrench
- Drain pan
- Funnel
- Rags or shop towels
- Replacement oil – For the 1981 KX250, use high-quality 80W gear/transmission oil for the gearbox (2-stroke, no engine oil in crankcase). Gearbox capacity: approximately 750-800mL (Always check your owner's manual if you have it, and verify on the clutch cover or case markings)
- New drain plug crush washer (if necessary)
- Gloves (optional but recommended)
Essential Call-Outs for the 1981 KX250
- No oil filter. The 1981 KX250 is a two-stroke; you are changing only the transmission oil, not engine oil. There is no oil filter to replace.
- Watch oil level markings. Unlike modern four-strokes, there’s no sight glass; the correct level is often measured via a small check bolt or by removing the fill cap and checking if oil is just at the threads with the bike upright.
- Clutch cover design. Always be careful not to over-tighten the drain or fill plug; these aluminum cases can strip with too much force.
- Use the proper oil. Do NOT use engine oil; only use the recommended gearbox/transmission oil for two-stroke dirt bikes.
Step-by-Step Oil Change Procedure
-
Warm the Motorcycle Up
- Start the KX250 and let it idle for 2-3 minutes to warm the transmission oil. This helps the oil drain more completely by lowering its viscosity.
-
Stabilize the Bike
- Place the bike securely on a stand or have a helper hold it upright. The 1981 KX250 does not have a center stand; a flat, stable motocross stand is best.
-
Locate the Drain Plug
- The oil drain plug is found on the underside of the right side engine case, typically under the clutch area. Have your drain pan ready beneath this spot.
-
Remove the Drain Plug
- Using the correct socket (usually 10 mm), slowly loosen and remove the drain plug. Be cautious, as the oil may be hot.
- Allow all old oil to fully drain out. Inspect the drain plug for metal shavings or debris – a small amount is normal, but large pieces can indicate internal wear.
-
Replace the Crush Washer (If Equipped)
- Inspect the drain plug washer and replace it if it’s flattened or damaged to prevent leaks.
- Clean the plug thoroughly before reinstalling.
-
Reinstall the Plug
- Install the drain plug by hand to avoid cross-threading, then snug it down with your wrench. Do not over-tighten – typically 7-10 ft-lbs is sufficient for these plugs. Overtightening can crack the case.
-
Add New Oil
- Remove the gearbox oil fill plug/cap, located on the right side cover, usually above the clutch area. Using a funnel, add new 80W transmission oil slowly.
- For the 1981 KX250, pour in 750-800mL (see manual or case marking).
-
Set the Correct Oil Level
- Some models have a check bolt (located slightly below the fill opening) – remove it; when oil just begins to weep out the check bolt hole, the level is correct. If not, oil should be just below the lower threads of the fill hole with the bike upright and level.
-
Install Fill Cap & Clean Up
- Once filled to correct level, reinstall the fill cap and clean any oil residue from engine cases.
-
Run and Check for Leaks
- Start the motorcycle and let it idle for two minutes. Shut off and restabilize the bike, then check for leaks at the drain plug and fill area.
- Top off oil if necessary after a short ride.
Pro Tips for First-Time KX250 Owners
- Transmission oil color: Fresh oil is light-gold or amber. If drained oil is milky, it may indicate water intrusion (bad crank seal/gasket).
- Drain interval: For motocross use, change every 5-10 hours of riding or after every race weekend.
- Never substitute: Only use high-quality gear/transmission oil—engine oil can cause clutch slippage and excess wear in two-stroke gearboxes.
Consistent oil changes are the easiest way to keep your 1981 Kawasaki KX250 shifting strong and the clutch operating smoothly. Have fun wrenching, and see you on the track.
Related Shopping Categories
Shop Motor Oil for a 1981 Kawasaki KX250 Dirt Bike.
Shop Oil Filters for a 1981 Kawasaki KX250 Dirt Bike.
Shop Oil Drain Pans for a 1981 Kawasaki KX250 Dirt Bike.
Shop Tools for a 1981 Kawasaki KX250 Dirt Bike.
Shop Oil Fillers and Drain Plugs for a 1981 Kawasaki KX250 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.