Motorcycle Primary Drive
Primary Drive Basics
a motorcylce primary drive serves to transfer rotation, generated from the engine, to the clutch. One pulley, or sprocket, of the primary drive is connected to the crankshaft, while the other is connected to the clutch assembly. A belt or chain is used to transfer rotation from one pulley, or sprocket to the other.
Motorcycle Chain Drives
Motorcycle chain drives are the older of the two drive types, but are still standard issue on most off-the-shelf motorcycles. A tensioned chain is used, along with two sprockets, to transfer power from the engine to the clutch. The chain is enclosed in a housing comprised of an inner primary cover (the inboard half of the housing) and an outer primary cover. The two halves of the housings are sealed together, with a gasket, in order to protect the chain and create a reservoir for the lubricant. The clutch assembly is also housed in the the primary drive housing.
The enclosed chain drive drive provides quieter operation and is ideal for higher torque applications. Primary chain drives are comparatively narrower than belt drive drives. The tensioned chain, requires routine adjustment and constant lubrication. Chains are susceptible to mechanical failures (broken links, for instance) and should be inspected regularly. Spare links and hand tools can be carried by the rider and repairs may be possible should the chain fail.
Primary Belt Drives
Motorcycle belt drives systems have grown in popularity. They are readily available and can be seen on today's custom choppers for both performance and aesthetic reasons.Because the belt requires no lubrication, primary belt drives can be configured in either open or enclosed configurations. Belt widths can vary from 1 1/2 to 3 inches. Belt drives used pulleys, instead of sprockets, to transfer the power.
Enclosed belt drives use have both inner oand outer covers, much like chain drives. In some cases, enclosed belt drives can be directly substituted for chain drives. Enclosed primary belt drives are narrower than open belt drives. Since all the moving parts are enclosed, the belt, pulleys, and clutch assembly are protected from debris and the rider, in turn, protected from them. Enclosed motorcycle belt drives are susceptible to heat build-up, and they should be inspected regularly for cracks and wear.
Open belt drives use an inner primary shield and an outer primary shield or support to keep the assembly from flexing. Belts for these drives can be as wide as three inches and are seen on many custom choppers, especially pro-street customs. Wider bets are better suited for high horsepower applications. If not mated appropriately, belts will "skip" or slip if too much power is applied. Open primary belt drives tend to be a bit noisier than enclosed belt drives, and there is an inherent risk associated with being exposed to moving parts. Care should be given to keep loose clothing, and body parts, away from the drive and guards are available to reduce this risk. Drive belts should be inspected for damage, cracking and wear before every ride, since the belts are exposed to road debris.
The chart below gives a quick comparison between the two motorcycle primary drive types and some of the pros and cons of each.