How to Change the Oil in a 1991 Honda CT70

Shop parts for a 1991 Honda CT70 Dirt Bike.

Changing the oil in your 1991 Honda CT70 is an important part of routine maintenance that keeps your mini bike running smoothly and extends its lifespan. Below, find a proprietary MotoSport.com guide with step-by-step instructions, a list of required tools, and essential model-specific information.

Tools and Supplies Needed

  • 17mm socket or wrench (for the drain bolt)
  • Oil drain pan
  • Funnel (recommended for clean pouring)
  • Paper towels or rags
  • Gloves (optional, but keeps hands clean)
  • New engine oil (typically SAE-10W40, but always check your owner's manual for confirmation)
  • Measuring cup (to ensure proper oil quantity)

Step-by-Step Instructions

  1. Warm Up the Engine
    • Start the CT70 and let it idle for 2-3 minutes. Warm oil flows better and helps remove more contaminants when drained. Safety tip: Do not skip this step.
  2. Locate the Drain Plug
    • The drain bolt is located underneath the engine, accessible through a hole in the skid plate. Use the 17mm socket wrench to remove it.
      On the CT70, the drain bolt is facing downward and can be identified easily when looking under the engine.
      Place your oil pan directly underneath to catch all the oil.
      Be sure not to confuse the drain bolt with other nearby bolts. Only remove the bolt centered under the motor with direct access through the plate .
  3. Remove the Oil Filler Cap
    • To allow oil to drain out faster, unscrew the oil filler cap (located on the right side of the engine) before pulling the drain plug. This allows airflow for smoother draining .
  4. Drain the Oil
    • Let the oil flow completely into the oil pan. This usually takes several minutes. For best results, slightly tilt the bike upright to ensure all oil drains.
  5. Inspect and Clean the Drain Bolt
    • Check the drain bolt and its sealing washer for damage or excess grime. Wipe them clean with a rag or paper towel. If the washer looks worn, replace it to prevent leaks.
  6. Reinstall the Drain Bolt
    • Thread the drain bolt back by hand first to avoid cross-threading; then snug it down with the 17mm wrench. Do not overtighten—just firm enough to compress the washer and prevent leaks. Overtightening can strip the oil pan threads .
  7. Add New Oil
    • Using a funnel, pour in fresh engine oil. The recommended capacity for the 1991 Honda CT70 is approximately 0.8 liters (about 0.85 US quarts). Double-check your owner's manual for the exact amount if uncertain .
  8. Check Oil Level
    • Insert the dipstick without screwing it in. The oil should be between the minimum and maximum marks on the dipstick. Add oil a little at a time if needed to reach the correct level. Avoid overfilling as this can cause engine damage .
  9. Reinstall Oil Filler Cap
    • Once the oil level is correct, screw the oil filler cap back on snugly by hand.
  10. Start and Inspect
    • Start the engine and let it idle for a minute. Check for any oil leaks from the drain plug or filler cap. Turn off the bike, let it sit for 2-3 minutes, and re-check the oil level. Top off if necessary.

1991 Honda CT70 Model-Specific Tips and Call-Outs

  • Drain Bolt Size is 17mm: Many modern bikes use different sizes, but the 1991 CT70's drain bolt is 17mm, so double-check your toolkit before starting .
  • Recommended Oil Type: Use non-synthetic SAE-10W40 motorcycle oil rated for wet clutches unless you have modified your engine. Some synthetic oils can cause clutch slippage on older designs .
  • Oil Filter Screen: The CT70 does not use a replaceable oil filter, but it does have a mesh screen inside. Every few oil changes, remove and clean this screen by accessing it under the clutch cover. If you've never checked it, plan to inspect and clean the screen during your next engine maintenance .
  • Watch for Paint and Decals: Avoid spilling oil on painted surfaces or original decals. Wipe up splashes immediately to avoid stains or peeling.
  • Dispose of Used Oil Properly: Never pour used oil down the drain or on the ground. Take it to a designated recycling center or auto parts retailer for proper disposal.

How Often Should You Change the Oil?

  • It's typically recommended to change the oil every 600 miles or at least once per riding season. If you ride hard, perform frequent short trips, or operate in dusty conditions, change oil more often. Always change oil after buying a used bike, especially if maintenance history is unknown .

Final Thoughts

Oil changes on a 1991 Honda CT70 are simple and quick when you have the right tools and follow the correct steps. Whether you're a lifelong rider or new to vintage mini bikes, basic maintenance like this will help keep your Honda running for years to come. Keep your owner's manual on hand for specific recommendations, and always use quality oil and parts for best results .

This guide is proprietary content exclusively for MotoSport.com. If you have further questions about your CT70 or other classic Honda models, contact MotoSport.com's customer service or check the detailed factory manuals for more in-depth instructions specific to your bike.

Related Shopping Categories

Shop Motor Oil for a 1991 Honda CT70 Dirt Bike.

Shop Oil Filters for a 1991 Honda CT70 Dirt Bike.

Shop Oil Drain Pans for a 1991 Honda CT70 Dirt Bike.

Shop Tools for a 1991 Honda CT70 Dirt Bike.

Shop Oil Fillers and Drain Plugs for a 1991 Honda CT70 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.