Kawasaki motorcycle clutch troubleshooting?

Clutch Operation Faulty

Clutch Slipping:

No clutch lever play
Friction plate worn or warped
Steel plate worn or warped
Clutch spring broken or weak
Clutch release mechanism trouble
Clutch hub or housing unevenly worn
Clutch inner cable catching

Clutch Not Disengaging Properly:

Clutch lever play excessive
Clutch plate warped or too rough
Clutch spring compression uneven
Engine oil deteriorated
Engine oil viscosity too high
Engine oil level too high
Clutch housing frozen on drive shaft
Clutch release mechanism trouble
Clutch hub locknut loose

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Definitions

Pressure Plate – The moving part of the clutch assembly that working against clutch spring tension, releases the clamping action on the clutch plates when the clutch lever is engaged.

Drive (friction) Plate – Consumable, fiber coated, ring-shaped friction surface that interfaces between the clutch basket tangs and pressure plate. Has tabs sticking out that match the cutouts between the clutch hub tangs and is coated with a friction material that vaguely resembles brake pad compound.

Driven (metal) Plate - Steel or aluminum ring-shaped disks that interface between the clutch hub and the friction plates. Steel plates are most often found in enduro/trail machines and provide longer wear and greater flywheel effect. Aluminum driven plates, near universally found in motocross type machines, are lighter, less durable and provide less flywheel effect. Additionally, aluminum driven plates wear out nearly as quickly as the friction plates themselves, in the process fouling transmission oil at an accelerated pace.

Clutch Springs – Short coil springs that continuously hold the drive and driven plates together through spring tension. Their duty is preventing slippage except when the clutch lever is engaged. Most often, five or more clutch springs are used per motorcycle clutch assembly. Firmer rated springs or more springs are typical of performance engines. Softer rate or fewer springs requires less clutch lever pulling effort.

Clutch Basket – A bowl-shaped gear-driven housing bolted onto the end of the clutch shaft that holds the entire clutch assembly.

Clutch Engaged/Disengaged – On most motorcycles, the clutch is operated by the clutch lever, located on the left handlebar. No pressure on the lever means that the clutch plates are engaged (driving), while pulling the lever back towards the rider will disengage the clutch plates, allowing the rider to shift gears. Some cars and mopeds have a centrifugal clutch, using centrifugal forces to engage the clutch above certain rpm, see Saxomat. Racing motorcycles often use slipper clutches to eliminate the effects of engine braking.


Clutch Basket Servicing Procedure

Begin by either draining the motor’s transmission oil, or lay a small bike over on its side, ISDE style (clutch side up). With the bike on its side, the oil doesn’t need to be drained as it pools below the level of the clutch side cover. Next, remove clutch cover (on bikes so equipped) or the entire clutch side engine cover in order to expose the clutch basket. If the entire side cover must be removed, the kick starter, shifter and/or brake pedal might have to be removed first, depending upon the bike make and model (get a manual). Some models might even require the draining of engine coolant and/or disconnection of power valve linkage. Pray that your scoot has a clutch cover. With the clutch basket exposed, loosen the five or six fasteners on the face of the pressure plate that compress the clutch springs. In most cases M6-sized fasteners are used, most commonly shod with 10mm hex heads. On occasion you’ll find an 8mm hex head or socket head (KTM) fastener. No matter which, back these bolts out evenly, a little at a time, alternating fasteners back and forth across the clutch basket. If the entire assembly has the tendency spin, drop the bike into gear to prevent this. With all of these fasteners completely loosened, lift out each bolt, washer and clutch spring and set them aside some place where they’ll stay clean. Measure the free length of the clutch springs and compare that to the specification for minimum free length listed in your service manual. If the clutch springs have sagged, (insufficient minimum free length), they’ll need to be replaced. With pressure plate retaining fasteners removed, the pressure, friction and driven plates may now be lifted out of the clutch basket. Remove the pressure plate first and set it aside with the clutch springs, someplace where it won’t get dirty. When removing the pressure plate, be careful with the clutch actuation rod. Oftentimes there is a flat needle bearing, spacer, or even a simple ball bearing, that can drop out and become lost. Be sure to pay attention to the order in which these parts go back together. Be advised that for a basic clutch plate replacement, removal of the clutch actuation rod probably isn’t necessary. However, while you’ve got things apart it’s not a bad idea to check the rod for wear or bending, especially if clutch action has been faulty. Just be sure not to lose any of these small parts or forget how they came apart. Now it’s time to lift out the friction and driven plates. Friction plates sometimes have the tendency to stick together, or even stick to the clutch basket face. A screwdriver or other prying tool can be carefully used to break the slight stiction holding them together. Be careful not to score clutch basket or clutch plate faces and stop immediately if they don’t come readily apart—something must be wrong if that’s the case, and you’ll need to seek higher guidance. With all clutch plates removed, inspect the clutch basket, looking for grooves worn into the basket fingers or scoring on the face. Grooving adversely impacts clutch actuation effort and smoothness. If the clutch basket fingers are grooved more than, say, 1/32nd of an inch or so, they’ll need attention. In extreme cases, the only option is replacing the clutch basket. However, if the grooving is less serious, they can be smoothed out using a hand file. Bear in mind though, this creates more slop in the clutch actuation, so that next time the grooving is likely to be considerably worse. Essentially, it’s a temporary fix that buys you some additional riding time. Note that the clutch basket rides on one or two thin needle bearings. If you’re forced to replace the clutch basket, it’s prudent to change this needle bearing as well. With all that out of the way, we can begin to reassemble things. If you’re just replacing the friction plates, separate out the old friction plates from the driven plates. To replace the clutch, restack the new plates inside the clutch basket alternating friction plate/driven plate. A friction plate always goes in first, and as such all clutch assemblies always have one more fiber plate than metal plate. Be sure that a fiber plate is the last plate that goes in on the top of the stack as well. Do not stack the plate’s together dry—coat all of them with transmission oil before you stack them together, or you’ll burn the clutch up the first time you ride the bike. If your bike is equipped with aluminum driven plates, it’s highly recommended that they be replaced, or at least checked during the replacement process. Again, your service manual will have a thickness specification for both friction and driven plates. If you’re using your scoot for off-road racing or trail riding, we’d highly recommend you consider replacing aluminum driven plates with aftermarket steel ones. This switch offers three potential benefits to the typical off-road set: Better driven plate longevity (read: forever), less fouling of transmission oil, and greater flywheel effect. Continue the reassembly process by dropping in the pressure plate. Check your service manual, since some bikes require marks on the pressure plate and clutch basket to be lined up on reassembly. Begin to tighten it down by replacing the clutch springs and their fasteners. Be sure to start these bolts by hand to avoid cross threading them and hosing the clutch hub. Tighten them down evenly, alternating bolts in a cross wise manner. These bolts don’t get torqued very much, so be sure not to manhandle or over-tighten them. There’s a torque spec in your owners manual—use it. Complete the task by replacing the clutch cover or side cover with fresh gaskets. If you drained your oil, be sure to replace it with the proper amount of fresh transmission lubricant. We use Golden Spectro SAE 80w motorcycle gear lubricant in our two stroke gear boxes. In a four-stroke engine, remember to use a 10w40 or better motor oil rather than gear lubricant.