How to Change the Transmission Oil in a 1979 Honda CR250

Shop parts for a 1979 Honda CR250 Dirt Bike.

Changing the transmission oil on your 1979 Honda CR250 is an essential maintenance task that ensures smooth shifting and extends the life of the transmission components. This how-to guide from MotoSport.com covers all tools required, outlines each step for the task, and details important model-specific notes you should be aware of to protect your vintage dirt bike.

Tools and Supplies Needed

  • 17mm socket (for the drain bolt)
  • Socket wrench
  • Oil drain pan
  • Funnel
  • Transmission oil (10W-40 or Maxima MTL, as recommended for 2-stroke transmissions)
  • Measurement cup (to ensure accurate oil quantity)
  • New sealing washer for the drain bolt
  • Clean rags
  • Protective gloves

Preparation

  • Start the bike and let it idle for 2-3 minutes. This warms up the transmission oil, allowing it to drain more completely and helps suspend particulates for removal.
  • Shut the engine off and place the bike upright on a level surface, using a center stand, triangle stand, or have someone help hold the bike steady.

Step-by-Step Oil Change Process

  1. Remove the Oil Filler Cap
    Locate the oil filler cap on the right crankcase cover, and unscrew it. This step allows the oil to drain more easily by reducing vacuum inside the case.
  2. Position the Drain Pan
    Place your oil drain pan directly below the transmission's oil drain bolt to catch old fluid.
  3. Remove the Drain Bolt
    Use the 17mm socket and wrench to unscrew the oil drain bolt located underneath the crankcase. Allow all the oil to drain into the pan. Be patient and let gravity do its job—this may take several minutes.
  4. Inspect and Clean the Drain Bolt
    Wipe the drain bolt clean. Many CR250 drain bolts have a magnetic tip designed to trap metallic debris; clean off any particles or metal shavings you find.
  5. Replace the Sealing Washer and Drain Bolt
    Install a new sealing washer on the bolt for best sealing performance, then reinstall the bolt. Tighten firmly but do not overtighten to avoid damaging the aluminum threads (spec torque: approximately 21 lbf·ft or 29 N·m for later CR250s–for the 1979 model, hand snug plus a solid tweak is appropriate if no torque wrench is available).
  6. Measure and Add New Oil
    Using your measurement cup (such as a Ratio Rite), pour in the recommended quantity of fresh transmission oil. For older CR250s, the typical fill is around 650-700 ml (0.69 US quart), but always consult your service manual or check the sight glass/inspection bolt on the engine case.
  7. Check Proper Oil Level
    Some CR250s feature a check bolt. Remove it (usually on the right crankcase above the drain bolt) and check if oil flows out when the bike is upright and level. A slow trickle means the oil level is correct; otherwise, add more in small increments.
  8. Reinstall Oil Filler Cap and Check for Leaks
    Replace the oil filler cap and wipe up any spillage. Start the engine again for a few minutes, then inspect around the drain bolt and filler cap for leaks.
  9. Dispose of Old Oil Responsibly
    Pour the used oil into a sealed container and take it to a proper recycling facility according to local regulations. Never pour oil down the drain or onto the ground.

Important Model-Specific Notes for the 1979 Honda CR250

  • The 1979 CR250’s transmission uses separate oil from the two-stroke pre-mix in the fuel. Never pour engine oil into the fuel tank–the tank runs premix only (typically 32:1 gasoline/oil ratio; consult owner’s manual for specifics).
  • Use only motorcycle-specific gear or transmission oil, not car engine oil. Aftermarket manual or Honda’s own transmission oil are excellent choices to protect clutch and gear components, and to ensure proper clutch function.
  • This model’s drain bolt and filler cap are threaded into aluminum. Use appropriate care when reinstalling bolts and avoid overtightening to prevent stripping threads–a common issue on vintage Hondas.
  • There is no disposable oil filter to replace on this model—just drain and refill.

Tips to Avoid Mistakes

  • Warm oil drains more completely–always warm up the engine first.
  • Level the bike before checking or adding oil. Being off-kilter can lead to overfilling or underfilling.
  • Check for leaks after your first ride following the change.
  • Document service intervals in a logbook to help track maintenance and assist if you ever sell or rebuild the bike.

Perform this maintenance regularly for the best performance and longevity from your classic Honda CR250. For parts, oils, tools, and more in-depth guides, trust MotoSport.com to keep your ride in top shape.

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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.