How to Change the Oil in a 1979 Yamaha YZ250: Your Definitive Guide

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Regular oil changes are crucial for the longevity and performance of your 1979 Yamaha YZ250. While two-stroke engines like the YZ250 use premix oil with gasoline for top-end and crank lubrication, the transmission still requires separate oil changes. Follow these expert-backed steps to keep your vintage YZ250 running strong, along with important model-specific notes every owner should know.

Tools and Supplies Needed

  • Socket wrench set (8mm or 12mm socket is typical, verify for 1979 model)
  • Drain pan
  • Funnel
  • Ratio Rite measuring cup or equivalent
  • Fresh transmission oil (Yamalube or a high-quality 2-stroke transmission oil, viscosity often 80W or as per manual)
  • Clean rags or paper towels
  • Gloves (optional)

Preparation and Important Notes

  • Warm up the bike briefly to help the oil flow out smoothly. Just a few minutes at idle is sufficient.
  • Place the bike on a level surface with an upright stand for proper draining and refill accuracy.
  • Double-check your manual (if available) for the exact oil type and amount for the 1979 model. As a typical baseline, the YZ250 transmission uses around 750ml to 800ml of oil, but verify for your particular year.
  • No oil filter on this two-stroke — the oil change is straightforward compared to four-stroke models.
  • Do NOT overtighten the drain or fill plugs. “Snug, not tight” is the rule to avoid stripping the threads or cracking the case.

Step-by-Step Oil Change Process

  • Warm-Up: Start your engine and let it idle for 2–3 minutes. This helps the transmission oil to drain out more completely when warm. Shut off the engine before starting.
  • Remove the skid plate (if equipped): If your 1979 YZ250 has a skid plate, remove it with the appropriate sockets to access the drain bolt.
  • Position the drain pan: Place your oil drain pan directly under the engine's transmission case drain bolt.
  • Loosen and remove the drain bolt: Using a socket wrench, carefully loosen and remove the transmission drain bolt (typically on the lower right side of the case). Let the oil fully drain into your pan. Inspect the oil for excessive metal shavings, as these may indicate internal wear.
  • Inspect and clean the drain bolt: Clean the threads and magnet (if equipped) on the drain bolt. Inspect the sealing washer; replace if damaged.
  • Reinstall the drain bolt: Once oil stops seeping, install the clean drain bolt. Tighten carefully to “snug”—typically about 12 ft-lb, but confirm the 1979 YZ250 spec. Do NOT over-tighten to avoid damaging the threads or case.
  • Refill with new oil: Using your funnel and measured cup, pour the specified quantity and type of transmission oil into the fill port (usually on the right side, higher up the case). Reference for the YZ250 is about 750ml–800ml of 80W transmission oil, but check your owner's manual or service book for the precise fill level for the 1979 model. Too much or too little oil can affect clutch and gear performance.
    Note: If your YZ250 does not have a fill-level check window or bolt, use the measuring cup for an accurate fill.
  • Install the fill cap: Put the fill cap back on and tighten “snug.” Again, no need to over-torque; hand tight is sufficient.
  • Wipe up spills and reinstall skid plate (if applicable): Clean any residual oil, and replace the skid plate if you removed one.
  • Confirm operation: Start the bike and briefly idle. Check for leaks around the drain and fill bolts. If any leaks are present, shut off the bike and snug the bolts gently as needed.

1979 YZ250 Owner-Specific Tips

  • Vintage YZ special attention: Old gaskets or washers may be brittle or missing. Check and replace as necessary to prevent leaks.
  • Thread wear: Transmission case threads may be more worn on older models. Be extra cautious not to cross-thread or overtighten bolts.
  • No oil filter or screen: The 1979 YZ250 transmission has no filter—cleaning the case and using the proper oil becomes even more critical.
  • Limited fill marking: Some vintage YZ250s use a “level bolt” on the clutch cover to verify proper fill. If equipped, remove this bolt when filling; once oil begins to weep from the hole, the proper level is reached. If not, rely strictly on volume filled.
  • Use oil rated for wet clutches: Always use an oil designed for 2-stroke transmissions and wet clutch compatibility to avoid clutch slippage or drag.

Finishing Up

  • Dispose of used oil responsibly at an authorized recycling location.
  • Keep a maintenance log including the type and amount of oil used, and the date for next service tracking.

Maintaining your 1979 Yamaha YZ250 is simple yet essential. Paying extra attention to proper procedures and vintage-specific issues will keep your classic running strong for years to come.

This guide is proprietary to MotoSport.com. For more DIY dirt bike maintenance, visit us again.

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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.