Technical sheet, recommended fluids and engineering specifications for the secondary transmission system
The secondary transmission kit — popularly known as the ratio — is the mechanical assembly responsible for transferring the driving force from the engine to the rear wheel. Composed of pinion, crown and chain, this system requires constant preventive interventions. The lack of cleaning and technical lubrication accelerates friction between metal links and gear teeth, compromising the motorcycle’s directional stability and drastically reducing the durability of spare parts.
Factory parameters, recommended fluids and clearance measurement
To ensure the structural integrity of the system, the rider must follow strict metrology and lubrication standards. Preventive maintenance is based on three essential numerical indicators: mileage, voltage measurement and oil specification.
Lubrication interval: The application of fluids must occur every 500 kilometers driven. In conditions of severe use under rain, dirt or sand roads, the procedure must be carried out immediately after washing;
Approved fluids: The owner’s manual generally recommends the use of SAE 80 or 90 transmission oil. As a practical and efficient alternative for everyday life, the use of synthetic lubricants in spray form is accepted, preferably formulated with PTFE (Teflon), which guarantee greater adherence to the seals (O-rings) and prevent splashing on the wheel;
Chain tension (slack): The chain cannot be stretched to the extreme. The standard specification requires a vertical clearance of 25 to 35 millimeters, measured with a ruler or tape measure in the center of the lower portion of the chain, exactly between the sprocket and the crown;
Tightening torque: When completing the adjustment of the rear axle, closing requires the use of a torque wrench. On low-displacement utility motorcycles, the main nut requires around 49 to 88 Nm of torque, depending on the model, to prevent the bearings from locking or the wheel loosening in motion.
Signs of wear and failure to drive alerts
Unlike electronic systems that issue failure alerts on the instrument panel, the relationship kit manifests the end of its useful life physically and acoustically. Early identification of these symptoms prevents sudden chain breakage while riding.
The main indicator of imminent mechanical failure is the successive metallic clicks, noticed especially during starts or gear reductions. This noise indicates that the chain rollers are no longer fitting perfectly and are starting to ride on the gears.
Visually, the component exhibits severe fatigue when the crown teeth become pointed, taking on an asymmetrical and sharp shape, similar to shark fins. Furthermore, if the driver needs to adjust the axle play at increasingly shorter intervals (every 200 or 300 kilometers), it means that the metal has yielded and lost its elastic retention capacity, requiring total replacement.
Inspection and cleaning procedure in the workshop
Correct hygiene requires precision and the use of non-aggressive chemicals, ensuring that abrasive dirt is removed without damaging the system seals.
1. Degreasing and solid waste removal
With the motorcycle suspended and leveled on a central stand, apply a specific degreaser for chains or regular kerosene. Never use gasoline, corrosive solvents or high pressure washers, as these agents destroy the rubber seals (O-rings), expelling the permanent factory lubrication. Use a soft bristle brush to scrub all surfaces of the links, the ring gear and the pinion area.
2. Rinse and completely dry the system
After removing old grease and asphalt debris, rinse the assembly with clean water at low pressure. Before applying the new product, it is mandatory to dry the relationship completely using a microfiber cloth or compressed air. Wet metal repels oil molecules, nullifying the effectiveness of lubrication.
3. Tension Adjustment and Wheel Alignment
Before lubricating, loosen the rear axle nut and use the adjusting nuts (turnbuckles) to calibrate the gap between 25 and 35 millimeters. Check the reference marks engraved on both sides of the scale to ensure the rear wheel is perfectly aligned. Then, tighten the main nut to the force required in the manual.
4. Millimetric application of the lubricating fluid
With the rear wheel rotating freely, apply SAE 90 oil or synthetic spray directing the jet exclusively towards the inside of the chain, exactly over the junction of the retainers and the contact rollers. Wait about 15 minutes before starting the motorcycle so that the solvents evaporate and the lubricant anchors in the metals.
Expected service life and assembly replacement budget
The financial viability of the system directly depends on the driver’s preventive discipline. An original transmission kit, operating under rigorous cleaning and lubrication every five hundred kilometers, can achieve 30,000 to 40,000 kilometers of useful life. On the other hand, severe use with negligence reduces this margin to less than 15,000 kilometers.
When it comes to replacement, the auto parts market provides components made from SAE 1045 alloy steel, which deliver excellent resistance to traction and thermal fatigue. Repair costs fluctuate considerably depending on engine size and part technology.
For utility and urban motorcycles with 160 cc, a complete ratio kit with seal costs, on average, R$ 130 to R$ 280. For trail models with 300 cc, the price of the parts (reinforced chain, crown and sprocket) ranges between R$ 450 and R$ 680. To this value, is added the specialized labor of the mechanical workshop, valued at around R$ 80 to R$150 for a complete replacement and axle alignment.
Postponing the change creates severe mechanical risks to the pilot’s physical integrity. When a worn chain breaks at high speed, it acts like a steel whip and can strike and puncture the engine block (crankcase), causing an immediate oil leak onto the track. In the worst case scenario, the twisted links tend to jam in the pinion and instantly lock the rear wheel, resulting in uncontrollable skidding and potentially lethal accidents on highways. The metrological rigor in the maintenance of this component transcends financial care, being the absolute foundation of road safety in two-wheeled vehicles.
