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If you or your rider is on a 2 stroke, you're likely aware that the clutch is often intentionally slipped and abused to get the bike into the power "Right Now", as well as most know that constant slipping of the clutch is a popular & well used technique for getting through power robbing sections, it's important to know this places a lot of heat and wear on the clutch plates so occasional clutch replacement is to be expected.
Additionally, If you ride regularly, or compete, it's wise to have a backup set of plates and springs for a quick change while at a track or a riding area.
If you're wondering what's up with not being able to get the bike to hook up, the condition of a clutch can be easily determined with a quick test ride, or a memory recall.
Presuming that the chain and sprockets are in good shape, and you have a rear tire that looks good, If you roll on the gas in any gear with the clutch out and the motor build revs, but the bike really isn't pulling like it should, or the bike creeps when the clutch should be disengaged (the lever pulled to the bars), the clutch may be out of adjustment, it could be smoked, or there could be other issues which we're covering below.
First, it's important to ensure that the clutch is engaging and disengaging properly, and there aren't external problems causing excessive, or inadequate free play at the lever, clutch fade, clutch slippage or other problems that brought you here.
Dirt bikes use 3 common & popular methods of controlling clutch engagement and disengagement and these which we're going to go over separately are:
On a cable actuated clutch, ensuring proper adjustment of the clutch cable is essential to the proper operation of the clutch. An improperly adjusted, damaged, improperly routed or binding cable can cause a clutch to slip, or not perform as it's intended, so it's critical that the clutch actuation is smooth, and there's an article you may want to review with more info on ensuring the clutch cable is lubricated and working smoothly.
Presuming that the cable actuation is smooth... Ensuring there's a proper amount of free play at the lever so as to permit full engagement and disengagement of the clutch is the first thing to cover.
With a properly adjusted clutch, there should be a minimum of 1/8" to a maximum of 3/8" free play between the end of the lever and the perch, with the lever at a released state. If the clutch lever is tight against the perch without any noticeable play within the cable's pull from a released position, the cable needs adjusted to allow slack in the cable which will allow the clutch full engagement. A clutch cable that's too tight could easily cause a clutch to slip since the cable will not allow the clutch to fully engage, and this should be addressed before continuing.
If there IS any slack at all in the cable, and the clutch is slipping, more slack is NOT going to make things better, there IS something amiss under the cover.
If it seems there's slop between the clutch lever and perch where the lever pivots, be sure to get a high quality clutch perch and lever to tighten this up. If there's more than 3/8" of movement before tension of the clutch is felt, you may be able to take this up with the adjuster on the handlebars, or through an inline cable adjuster but if the movement seems excessive, their may be deeper problems which we'll get into below.
A hydraulic clutch is generally regarded as adjustment free, but the hydraulic system consists of many parts which do occasionally present problems with not creating adequate pressure at the lever to fully disengage the clutch, and this is often the result of air being introduced to the hydraulic system by opening of the system, as the result of a failed seal, or even neglected maintenance.
If the clutch lost pressure after removing the hydraulic line even for a moment or carefully, you're going to need to bleed the clutch thoroughly and the best way of doing this is to allow the system to bleed via gravity alone. Simply open the bleeder on the slave cylinder and continue to pour the specified hydraulic oil (or brake fluid if that's what the manufacturer recommends) into the reservoir while it drains from the bleeder on the slave cylinder until all the air is removed.
Occasionally hydraulic clutches do have problems with proper engagement of the clutch, but this is not common and is usually related to a piston becoming frozen in the bore of the master or slave cylinder, and is usually evident by a slave cylinder that sticks, or doesn't fully release. Another telltale sign of possible hydraulic system problems is by looking for signs of leakage from under the outer dust boot of either the master or slave cylinder, as well as a contaminated fluid reservoir any of which should be addressed.
If it's determined that the clutch is smoked and replacement is certain, you should have no worries, as this is pretty simple, and can probably be wrapped up in 30 minutes or so barring any damage, or wear of other parts.
Most modern motocross bikes have what's known as a "Quick Change Cover" for accessing the clutch, and most clutch repairs, short of replacing the clutch basket can be performed through this access cover, although older dirt bikes frequently require removal of the RH engine side case.
While things are apart be sure to keep everything clean and organized and inspect all the clutch components as detailed below, then upon reassembly, be sure to consult a service manual specific to the motorcycle being serviced for torque specifications, and always use a new gasket or o-ring when reinstalling the cover.
After all the clutch components have been inspected, (providing everything looks good), new clutch plates & springs can be installed and the clutch reassembled and adjusted.
Installation of the new clutch plates is simple, but there are a few steps you want to do to ensure a trouble free clutch.
During reassembly of the clutch, you'll need to soak the friction plates in a bath of clean oil and this is best accomplished (with the least amount of mess) by using a 1 gallon freezer ziploc bag and a sufficient quantity of new oil to cover the clutch discs.
Also, upon reassembly of the clutch, be absolutely certain that you begin, and end with a friction plate, then reassemble everything exactly as it was removed, or as outlined in a factory service manual specific to this motorcycle.
Lastly, If there are aluminium drive plates within the clutches, be sure to take into consideration the additional flywheel effect that can be gained by replacing these aluminium plates with steel.
With the clutch reassembled, be sure to adjust the clutch (if necessary), then check out all our other dirt bike maintenance resources & articles to keep your ride race ready.
Just replacing parts by throwing new clutch plates and springs in occasionally without much attention given to why the clutch was slipping, or how parts are wearing isn't recommended, as there are many other parts at work in the clutches operation, and we'll go over each of these below in order that you should see them as you disassemble the dirt bike's clutch.