Does the motorcycle feel like it is slipping? Are there loud noises coming from the primary? These conditions generally point towards an issue with the clutch or compensator drive. These problems can be fixed sometimes with a simple adjustment. The clutch cable can have so much slack the clutch is chattering every time the engine is running. A lack of lubricant can also cause overheating and wear problems in the clutch. The first step is to inspect.
On some motorcycle models an inspection cover can be removed to see the condition of the clutch and primary chain. This would be an excellent place to start. Some motorcycles use a derby cover to inspect the clutch and adjust it, others adjust from the side of the engine. In order to remove and inspect a clutch, it usually will need to be completely unadjusted and loosened.
Clutches on motorcycles work with plates in a basket. The basket holds the clutch plates and friction discs. There are usually springs and pushrods to make all this work. When an engine is running and the clutch handle is squeezed, the spring(s) is/are compressed and the discs and friction plates kind of slip past each other. This causes the engine to spin freely of the transmission so that there is no connection between the two. However – the friction plates lose their grip and springs can sag over time. This is the time when a clutch overhaul is needed.
Accessing the clutch can require some engine disassembly. First drain the clutch lubricant. A drain plug under the clutch is usually how this is done. On some bikes the oiling system is connected, so you will have to drain the motorcycle’s oil. On a sport bike type motorcycle, the clutch just has a cover that is usually retained with a few bolts. Once they are removed, the cover should come off with ease. On a cruiser type motorcycle, the clutch is located within a primary case. Again it is held with perimeter bolts and removed from the side of the engine. The clutch will be exposed once the cover is removed.
Clutch replacement usually means you are changing the fiction discs, metal plates, springs and maybe a stretched cable. A nut holds a spring which is on a stud that holds all of the discs and plates in place. A special tool is usually required to depress the clutch springs so that the nuts that hold them on can be loosened and removed. This tool can sometimes just be made with a piece of flat stock steel drilled across two spring studs that hold the clutch down. The nuts can be removed and the springs taken off. The plates will slide out and new plates can be reinstalled. Some require pre-lube before installation.
Once the plates are in place, the springs will need to be depressed with the special tool and nuts reinstalled with lock washers or thread locker. Torque to manufacturer specifications. Make sure no springs are binding and that everything seems to be moving freely. A new clutch cable may need to be installed as well. These are usually attached to a clutch releasing mechanism. It can be spring loaded. An adjuster on the cable should give enough slack to slide the cable end from the handle bar lever. It can then be removed from the engine side as well. Reinstall in the reverse order. Lube the clutch cable with cable lubricant. If the motorcycle uses a hydraulic mechanism, no replacement should be necessary.
Once the clutch is installed and inspected the clutch cover or primary case can be reinstalled. A new gasket may need to be installed if the system is enclosed in oil. The perimeter bolts should be torqued to manufacturer specifications and lubrication should be added if necessary. The clutch cable can be adjusted. The motorcycle should be tested at low speeds to make sure the clutch is fully engaging and disengaging. Once broken in, it should provide a smooth and torquey ride.