Motorcycle Engine Motorcycle engines work the same way that car engines do. They consist of pistons, a cylinder block and a head, which contains the valve train. The pistons move up and down in the cylinder block, driven by explosions of a fuel-air mixture that has been ignited by a spark. Valves open and close to allow the fuel-air mixture to enter the combustion chamber. As the pistons move up and down, they turn a crankshaft, which transforms the energy from the pistons into rotary motion. The rotational force of the crankshaft is transmitted, via the transmission, to the rear wheel of the motorcycle. Motorcycle engines are generally classified by one of three characteristics: the number of cylinders they possess, the capacity of their combustion chambers or the number of strokes in their power cycles. Valvoline Technical Services Page 1
Motor Cycle Oil Cylinders Motorcycle engines can have one or multi cylinders. But in India, we have mostly single cylinder engine for motor cycle. For years, the V-twin design was the engine of choice for motorcycle engineers in America, Europe and Japan. The V-twin gets its name from the fact that the two cylinders form a V shape, such as the classic Harley-Davidson V-twin. Capacity The size of the combustion chamber in a motorcycle engine is directly related to its power output. The upper limit is about 1500 cubic centimeters (cc), while the lower limit is about 50 cc. In India, we have mostly 100 cc and 125 ccc engine. The lower capacity engine are usually found on small motorcycles (mopeds). 2- Stroke Engine A two-stroke (or 2T) engine is much simpler in offer ease of maintenancee for bikers. design. They have a better power-to-weight ratio and Two-stroke engines do not have inlet and exhaust valves, the flow of gases is controlled by the channels in the cylinder blocks. Therefore, this design can result in high fuel consumption and incomplete combustion. 2 Stroke Engine 4 Stroke Engine Because of the nature of the inefficient combustion and that the lubricating oil is fed into the combustion chamber with the fuel, more carbon deposits are formed. These deposits, mainly unburned fuel and oil, gather at the exhaust port and the piston-ring grooves. Valvoline Technicc al Serv ices Page 2
Motor Cycle Oil Compared to a 4-stroke (4T) engine, the 2-stroke (2T) offers several advantages as mentioned below : Higher specific output: One power stroke per revolution Higher power-to-weight ratio Smaller engine size (for the smaller capacity) Fewer moving parts, simpler construction & cheaper to produce Easy to maintain Similarly the 2T Engine has some disadvantages compared to 4T Engine. The downside of 2T engine are: High fuel consumption Emits more pollution- high HC, CO and particulates 2T engine may not last as long as a 4T, due to the lack of higher wear rate Unburnt 2T oil can clog up exhaust port & muffler and needs frequent maintenance, e.g. decarburizing Noisy operation a dedicated lubrication system- Normally engine oil in 2T engine is burnt along with fuel and produces higher exhaust emissions, Hence 2T engine based motor cycle can manufactured in India currently for on road applications. 2T engines are however used for smaller out board motors. Motorcycle Transmission A motorcycle engine can create an enormous amount of power, which must be delivered to the wheels of the vehicle in a controllable way. The motorcycle transmission delivers power to the rear wheel through a series of structures that include the gearset, the clutch and the drive system. Valvoline Technicc al Serv ices Page 3
Gear Set A gear set is a set of gears that enable a rider to move from a complete stop to a cruising speed. Transmissions on motorcycles typically have four to six gears, although small bikes may have as few as two. The gears are engaged by shifting a lever, which moves shifting forks inside the transmission. Clutch The job of a clutch is to engage and disengage power from the engine crankshaft to the transmission. Without the clutch, the only way to stop the wheels from turning would be to turn off the engine -- an impractical solution in any kind of motorized vehicle. The clutch is a series of spring-loaded plates that, when pressed together, connect the transmission to the crankshaft. When a rider wants to shift gears, he uses the clutch to disconnect the transmission from the crankshaft. Once the new gear is selected, he uses the clutch to re establish the connection.. There are three basic ways to transmit engine power to the rear wheel of a motorcycle: chain, belt or shaft. Chain final-drive systems are by far the most common. In this system, a sprocket mounted to the output shaft (i.e., the shaft in the transmission) is connected to a sprocket attached to the rear wheel of the motorcycle by a metal chain. When the transmission turns the smaller front sprocket, power is transmitted along the chain to the larger rear sprocket, which then turns the rear wheel. This type of system must be lubricated and adjusted, and the chain stretches and the sprockets wear, requiring periodic replacements. Valvoline Technical Services Page 4
The Friction Drive The friction drive is another transmission found in some motorcycles. A friction drive is a type of continuously variable transmission, or CVT, in which the variation in gear ratios comes about as a disc connected to the engine (the driving disc) rotates across the face of a second disc connected to the rear wheel (the driven disc). By varying the radius of the contact point between the two disc surfaces, different gears can be achieved. Continuously variable transmissions have a long history of use in motorized vehicles, with variable friction transmissions appearing in motorcycles in the early 1900s. Belt drives are an alternative to chain drives. Early motorcycles often used leather belts, which could be tensioned to give traction using a spring-loaded pulley and hand lever. Leather belts often slipped, especially in wet weather, so they were abandoned for other materials and designs. By the 1980s, advances in materials made belt final-drive systems viable again. Today's belts are made of cogged rubber and operate much the same way as metal chains. Unlike metal chains, they don't require lubrication or cleaning solvents. Shaft final-drives are sometimes used. This system transmits power to the rear wheel via a drive shaft. Shaft drives are popular because they are convenient and don't require as much maintenance as chain-based systems. However, shaft drives are heavier and sometimes cause unwanted motion, called shaft jacking, in the rear of the motorcycle. LUBRICANT FOR TWO WHEELER Due to hardware difference, the requirement of lubricant for 2T engine and 4T engine is entirely different. Let s discuss the lubricant requirement for both type of 2 wheeler engine. Valvoline Technical Services Page 5
Motor Cycle Oil Lubricant for 2-Stroke Engine Lubrication of a two-stroke petrol engine is quite different from that of a four-stroke engine, as it is not possible to have separatee lubricating oil sump. Hence a two-stroke petrol engine is always lubricated by a petrol & oil (lubricant) mixture. The lubricating oil is mixed with petrol in suitable proportion as per the manufacturer's recommendation. In the latest generation Two-stroke engines, the lubricating oil is directly injected by an accurate metering device from a separate tank into the petrol in quantities dependent on the speed and load of the engine. When the petrol mixture enters the crankcase, because of the high temperatures prevailing, the petrol fraction vaporizes leaving a thin oil film of lubricant on the crankcase, cylinder walls, crankshaft and bearings. The primary equirement of two-stroke enginee oil is its ability to readily mix with petrol and burn without leaving too much ash. The oil should reduce engine wear, spark plug fouling, combustion chamber deposits, piston ring sticking, exhaust port blocking and silencer deposits. In addition the oil should have the ability to keep the engine clean at high engine operating temperatures and prevent bearing corrosion at lean oil-fuel ratios. Lubricant for 4-Stroke Engine Four stroke two wheelers have a different lubrication requirement than a two stroke two wheeler since it does not use the Petrol mixed with lubricating oil. These engines are like the four stroke engines used in Cars. A separate Oil sump in the enginee lubricates the various moving parts in the engine. The main differences between the four stroke Engine in a Two Wheeler and in a Car are: Two wheeler Engines in India are mostly Single Cylinder Engines where as Car engines are multi cylinder (3 or 4 or 6 cylinder engines). Specific power output (kw/litre) of 2 wheeler engine is much higher compare to 4 wheeler engine because of lower swept volume for 2 wheeler engine, though the power output (kw) of 4 wheeler engine is more compare to 2 wheeler engine. Specific Powe er Output Com mparison (kw( w/l) Ferrari F50 KTM LC4 620 Harley Davidson FLHT EI. GI. Std. Ducati 748 S.P.S. 81 (4.7L) 57 (0.6L) 333 (1.3L) 103 (0.7L) Yamaha YZF-R6 Suzuki GSX-R600 Kawasaki ZX-60R Honda CBR 600F 147 (0.6L) 130 (0.6L) 132 (0.6L) 128 (0.6L) Valvoline Technicc al Serv ices Page 6
Therefore 2 wheeler engine components are under severe stress compared to 4 wheeler engine components. The RPM of 2 wheeler engine is almost double compared to 4 wheeler engine which leads engine oil under severe shear stress. Output Ratio (kw / Litre) 147 132 118 102 88 Bike engine operates at higher engine speed (rpm at higher engine speed (rpm- revolution per minute) Motorcycle 74 Pas s enger 59 Car Bikes operate at a 44 higher rpm, higher temperature and 29 stresses than the car engine 15 2000 4000 6000 8000 10000 12000 14000 16000 Engine Speed (rpm) The acceleration of 2 wheeler engine is very high compare to 4 wheeler engines, and it put enormous stress on 2 wheeler engine components. Bike Engine Operate at Higher Acceleration Most of the Engines in two wheeler are air-cooled engines where as Car engines are Water cooled Engines. The air drag across the engines as the vehicle moves cools the engines in two wheeler. Valvoline Technical Services Page 7
In two wheeler, the Engine, the wet clutch and the Gear trains are housed in a single unit and lubricated by the same oil where as in a car, Engine, Clutch and gearboxes are separate unit and lubricated by separate oils. All Parts are Lubricated by One Oil Chain Drive Multiple Wet Clutch Assembly Final Shaft Crankshaft Transmission Gear The sump size of 2 wheeler engines is smaller compare to 4 wheeler engines, and on the other hand the same oil is using to protect engine, wet clutch and transmission system, therefore 2 wheeler engine oil is experiencing tremendous stress. The oil stress factor for motorcycle oil is around 4 times higher compare to car engine oil. The calculation details are given below for your understanding: Now the lubrication requirement for all three components, i.e., engine, transmission system and wet clutch in 2 wheeler is entirely different. 1. The engine requires good cleaning property, mild anti-wear property and lower frictional characteristic to achieve fuel economy. The modern engine oil is having substantial amount of friction modifier which provides fuel economy by reducing coefficient of friction. 2. Transmission system require high AW (Anti-Wear)/ EP (Extreme Pressure) property and extremely good shear resistant VM (Viscosity Modifier). The AW additive is generally Phosphorus based and modern engine equipped with after treatment devices (Catalyst) to reduce engine emission requires lower Phosphorus level to extend Catalyst life as Phosphorus has poisonous effect on catalyst. The VM in MCO (Motor Cycle Oil) is also experiencing severe shear stress in transmission system, therefore high quality, highly shear resistant VM is selected for formulating MCO. 3. Similarly, the wet clutch has separate requirement as far as lubrication is concerned. The function of clutch is to engage and disengage engine from transmission system, therefore frictional characteristic is the most important for lubricating oil. Now oil with friction modifier is not the right choice for wet clutch lubrication, as it causes clutch slippages and leads to clutch breakage. Valvoline Technical Services Page 8
These differences in Engine configuration demands a separate quality of Oil for use in four stroke Engines in two wheeler. The air cooled Engines suffers the most in terms cooling efficiency wherein the vehicles running at slow speed, such as city driving condition, leading to higher Engine operating temperature compared to a car Engines where the Engine is cooled by the coolant leading to more or less constant operating Temperature irrespective of the Speed of the Vehicle. The air cooling facility of 2 wheeler engine causes its oil to run 1.5 to 3 times hotter than a water-cooled 4 wheeler engine. This higher operating temperature encountered demands oils with very high thermal and Oxidation stability and also higher viscosity grades. To achieve higher & higher fuel economy in a Car Engine, the oils are formulated with friction modifier additive which reduce the friction drastically between moving parts in Engines. However use of this oil in a Two Wheeler, which has a wet clutch incorporated in the Engine, will cause starter clutch slippage (Engine start failure) and also Poor running due to higher engine stall speeds.to overcome this the Oil for four stroke two wheeler Engine demands controlled friction characteristics as specified by the JASO (Japanese Automotive Standards Organization). Major performance requirements for two-stroke engines are- Performance 2 Storke Piston cleanliness (ring & groove) Oxidation control Cold sludge prevention Mechanical stability - Anti-wear performance Anti-foaming Corrosion prevention Combustion quality Ash forming tendency - least, - Best For air-cooled two-stroke engines, lubricating oil performance is classified according to API, JASO & ISO Air-cooled engines: API TA, TB and TC are the oldest performance categories for two-stroke aircooled engines, although API TC has been the most prevalent and demanded category. At present, the API TC detergency test is run using previously used cylinders and slightly oversize pistons because Yamaha no longer provides the test parts. Also, new low-ash reference oil is being used instead of the original ashless oil because the ashless oil had experienced hot ring sticking problems over the last decade. Only a limited number of test parts are available for the API TC detergency test. In 1994, the Japanese Automobile Standards Organization (JASO) defined a specification that describes three quality levels for low-ash air-cooled two-cycle engine oils: FA, FB, and FC. Lubricant performance is assessed according to four performance criteria: detergency, lubricity, exhaust blocking, and smoke. Performance of candidate oil is rated against that of Valvoline Technical Services Page 9
reference oil. The thrust of the JASO specification is the low-smoke requirement, which is especially stringent for the FC performance category. This requirement arises from the need to alleviate smoke problems in Asian cities. JASO FC will be the predominant performance level. JASO Two-Cycle Index1 Ratings Parameter FA FB FC Detergency Index 80 min 85 min 95 min Lubricity Index 90 min 95 min 95 min Initial Torque Index 98 min 98 min 98 min Smoke Index 30 min 45 min 85 min Exhaust Blocking 40 min 45 min 90 min Index Viscometric Requirements Viscosity 6.5 cst @ 100C min Flash point 70C min. (PMCC) Ash 0.25 mass% max. Major performance requirements for four-stroke engines are - Performance 4 Storke Piston cleanliness (ring & groove) Oxidation control Cold sludge prevention Mechanical stability Anti-wear performance Anti-foaming Corrosion prevention Combustion quality Ash forming tendency - - least, - Best Traditionally, four-stroke motorcycles used oils designed for spark-ignited four-stroke passenger car engines. However, due to the inclusion of fuel economy requirements in the latest API Categories, many oils have been formulated to contain friction modifiers. In a motorcycle wet-clutch application, these additives cause clutch slip and power loss. Therefore, JASO established new specifications for four-stroke motorcycle oils. In addition to API categories SH to SN, the oils are classified according to their frictional characteristics as determined in an SAE #2 test procedure defined by JASO. Valvoline Technical Services Page 10
These specifications are outlined below. Four-stroke motorcycle OEMs may specify either MA of MB oils for their engines. JASO introduced the MA and MB specification to distinguish between friction modified and non friction modified engine oils. Most four-stroke motorcycles with wet clutches need a JASO MA oil. JASO MB grade oils are classified as the lowest friction oils among motorcycle fourcycle oils. They are not to be used where a JASO MA grade oil is required. JASO MB oils are normally recommended for Scooters where in the Clutch System is dry. Performance Classification Standards Required for JASO Four-Stroke Motorcycle Oils Standard Classification API SH, SJ, SL, SM, SN and possible new future classification Performance and Standard Indexes of Four-Stroke Motorcycle Oils (JASO T 904-11) Valvoline Technical Services Page 11
Significance of Friction Indices Dynamic Friction Index (DFI): Measure of clutch feel and how progressively power transfers under slipping conditions Static Friction Index (SFI): Measure of breakaway resistance to slip under high torque Stop Time Index (STI): Measure of how quickly the clutch engages Valvoline Technical Services Page 12