The Yamaha NMAX155 employs a continuously variable transmission (CVT) system. Separate from the engine at the rear is a rear gearbox, which reduces speed and increases torque via a set of gears before ultimately transmitting power to the rear wheel. The oil within this gearbox is the subject of this article—transmission oil.
Regular replacement ensures adequate lubrication of gears and bearings, reduces wear and operational noise, and guarantees smooth, efficient power delivery. The recommended replacement interval is every 4,000-6,000 kilometers or annually.
Preparation and Safety Precautions
Required Tools and Materials:
1. Engine Oil: API-certified SG grade or higher SAE 10W-30 or 10W-40 four-stroke motorcycle oil. Ensure the oil bottle specifies suitability for “wet clutches.” Approximately 0.13 liters required.
2. Tools:
· 8mm T-wrench or socket (for drain plug and fill plug)
· 12mm box wrench or socket (for removing exhaust tailpipe bolts if necessary)
· Torque wrench (highly recommended)
· Funnel and hose (for easier filling)
· Oil collection container
· Gloves, work light, cleaning cloth
Important Notes:
· Position the vehicle on a flat, stable surface.
· Start the engine and let it idle for 2-3 minutes to warm the transmission oil, improving its flow for complete draining.
· Turn off the engine and engage the center stand.
Standard Operating Procedure (Eight-Step Method)
Step 1: Locate and Clean
· Locate the gearbox positioned at the rear of the engine, to the left of the rear wheel. You will see a drain plug at the bottom and a fill/check plug on the upper side.
· Thoroughly clean the drain plug, fill plug, and surrounding areas with a clean cloth and spray to prevent contaminants from entering the housing during disassembly.
Step 2: Remove Exhaust Tailpipe (if necessary)
· On certain model years of the NMAX155, the exhaust tailpipe may partially obstruct the filler plug, preventing direct tool access.
· Using a 12mm wrench, remove the two bolts securing the exhaust tailpipe.
· Carefully push the tailpipe forward and lift it off, taking care not to damage the gasket. This step significantly increases working space.
Step 3: Position the Oil Drain Pan
· Place the oil drain pan directly beneath the oil drain plug.
Step 4: Remove the Oil Drain Plug
· Using an 8mm T-wrench, loosen and remove the oil drain plug by turning it counterclockwise.
· Caution: Be aware that the initial oil flow may come out at an angle.
· Allow the oil to drain completely until only a slow drip remains. This process may take 5-10 minutes.
Step 5: Clean and Install the Drain Plug (Critical Torque Step)
1. Wipe the old seal ring on the drain plug clean with a clean cloth. Inspect the seal ring for aging or damage. Replace with a new seal ring if any issues are found.
2. Hand-tighten the drain plug (with seal ring) into the threaded hole, ensuring no misalignment.
3. Using a torque wrench, tighten to the standard torque: 23 N·m.
· If a torque wrench is unavailable, proceed with extreme caution. Tighten until it feels snug—never use excessive force, as this can easily damage the aluminum alloy housing threads.
Step 6: Add New Oil
1. Using an 8mm wrench, remove the fill/check plug located on the upper side of the gearbox.
2. Connect a hose to a funnel and insert the hose end into the fill port.
3. Slowly pour approximately 0.13 liters of new oil into the gearbox. Proceed patiently due to the small fill opening.
4. Stop adding oil when it feels full or begins overflowing from the fill port.
Step 7: Check Oil Level (Critical!)
· Standard oil level check method: Do NOT screw in the filler plug!
· Keep the vehicle upright on the main stand.
· At this point, the oil should be right at the lowest edge of the filler hole, about to overflow. This is the perfect level.
· Important: If the level is too low, top up until it overflows; if too high, let it drain naturally to the standard position. Overfilling is strictly prohibited!
Step 8: Reassembly and Final Checks
1. After confirming correct oil level, clean the filler hole threads.
2. Install a new seal (also strongly recommended), then hand-tighten the filler plug.
3. Using a torque wrench, tighten the filler plug to the standard torque: 23 N·m.
4. Reinstall the exhaust tailpipe (if previously removed) and tighten its mounting bolts.
5. Start the engine and allow the rear wheels to spin freely for a moment to circulate the new oil within the gearbox.
6. After shutting off the engine, recheck for any signs of leakage at the drain plug and filler plug locations.
Key Points and Expert Advice
· Torque is paramount: 23 N·m of torque is critical for aluminum cases. Over-loosening causes oil leaks, while over-tightening strips threads, leading to extremely high repair costs.
· Seals are essential: We strongly recommend replacing both aluminum seals on the screws during every oil change. This is the most cost-effective way to prevent leaks.
· Better Low Than High: Slightly low fluid levels cause far less harm than overfilling. Excess oil creates excessive internal pressure, damaging seals and forcing oil onto rear brake discs—a major safety hazard leading to brake failure!
· Oil selection: Always use motorcycle-specific oil. Friction modifiers in automotive oil may cause wet clutches to slip.
· Disposal of old oil: Collect used oil in a sealed container and deliver it to a designated waste oil recycling center.
Conclusion:
Changing the transmission fluid in your NMAX155 is a simple yet meticulous maintenance task. By following this standard procedure, you'll not only save on labor costs but also deepen your understanding of your beloved vehicle through hands-on care, gaining a sense of accomplishment and peace of mind.
Now, grab your tools and restore your NMAX155's drivetrain to its smooth, quiet operation!
