This article does NOT cover service or repair of Auto Clutches including a Rekluse, Nor does it cover Slipper Clutches.
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.
How to Know if a Dirt Bike's Clutch Needs Servicing
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.
How to Adjust the Clutch on a Dirt Bike and Ensure Proper Engagement and Disengagement of the Clutch
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:
- Cable Actuation
- Hydraulic Actuation
- "Auto-Clutches" which may have come standard from the factory,
or could have been installed as an aftermarket upgrade.
(Due to the complexity and variations between auto-clutches,
does Not cover these.)
Ideally, if you're going to be working on a dirt bike, it's smart to pick up a factory service manual specific to the motorcycle which you're working on, as this will provide important details and specifications which are critical to the proper operation of the clutch.
Tips for Ensuring the Cable Actuation is Adjusted and Working Properly
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.
How to Ensure a Hydraulic Clutch is Working Properly
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.
As mentioned above, this article doesn't cover auto clutches as there are many variations of these, and diagnosis, repair, tuning or adjustment of an automatic, or semi-automatic clutch should be performed as outlined in an OEM manual specific to the motorcycle being serviced when working with an auto clutch that is standard on a specific motorcycle such as what can be found on the ever popular KTM Minibikes.
If the automatic clutch is an aftermarket addition, it'll be necessary to contact the manufacturer of the clutch for specific details regarding adjustment or service of their specific auto clutch, as there are too many different variations of auto and slipper clutches for this article to cover.
How to Replace a Clutch in a Dirt Bike
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.
Before beginning with replacement of the motorcycle's clutch, it's important to ensure the area around the clutch access cover, or RH engine cover is clean, and before opening up the motor washing the dirt bike
is always a good idea.
- With a clean motorcycle, turn off the gas, then lay the bike over so that the the clutch cover is facing you.
(for those with a quick change cover, you'll find that holding down the rear brake pedal and sticking a screwdriver in the swingarm pivot will provide adequate clearance for getting the cover off and for servicing the clutch, otherwise removal of the rear brake pedal may be necessary.)
- With a screwdriver holding the brake pedal down, or the pedal removed, carefully remove the clutch access cover, or RH engine cover.
- With the clutch cover removed, loosen the pressure plate bolts that will be facing you using a criss-cross and multiple step process, then remove the pressure plate.
- Next, using a pick, remove all the clutch discs from the clutch basket and inner hub.
- With all the clutch discs removed, inspect all the parts as detailed below, replacing parts which show wear, as will be obvious, or will be indicated by wear limits detailed within a factory service manual specific to the motorcycle being serviced.
How to Install New Clutch Plates
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.
How to Inspect the Clutch Components for Wear or Damage
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.
- Clutch Cover
The clutch cover won't generally develop any wear with the exception being circular wear on the inside from pressure plate bolts making contact. If there is any markings from the pressure plate bolts, there are problems which should be obvious.
- Clutch Springs and Hold Down Bolts
The clutch springs that apply pressure to the clutch pack, enabling drive do get sacked out over time and use and if there's any doubts, the best thing to do is to just replace them. The thing is that clutch springs don't usually show visual wear, so if you're wanting to reuse the springs, it's important to measure the free length of the springs and compare the measurement against the specifications in a factory service manual specific to the motorcycle being serviced.
Additionally, be sure to inspect the hold down bolts for any unusual wear, (signs of stretch from over tightening) or thread damage before reassembly and should any damage be noticed, be sure to replace these as having a bolt head circulating loose inside the RH engine cover never turns out
- Pressure Plate
With the clutch springs removed, you'll want to inspect the pressure plate where it makes contact with the last friction disc, as the OEM pressure plate's are notorious for developing a groove here that will be obvious and usually contributes to clutch adjustment havoc. Should you notice a step or groove in the pressure plate, be sure to only replace the pressure plate with a higher quality aftermarket pressure plate.
- Throw Out / Clutch Release Bearing and Clutch Movement
With the pressure plate removed, be sure to inspect the release bearing or "clutch lifter" as they're often referred to as, as well as the release push rod for mushrooming, a steel ball (if used) for any unusual wear, and be sure to check the clutch actuation arm for any wear where the push rod contacts it. Should any of these parts show wear, or if the release bearing seems worn, or any needle bearings are missing, be sure to replace these parts upon reassembly.
Note: If your clutch lifter is of the NON needle bearing type, if you do a little investigation you'll likely find there is an upgrade to this lifter which replaces the lifter with an OEM needle bearing setup that will provide a much better feel and actuation of the clutch.
- Clutch Plates
When inspecting the clutch plates, you'll want to measure each clutch plates thickness against the specifications that can be found in a factory service manual specific to the motorcycle being serviced, as well as you'll want to inspect each friction and drive plate for heat marks, cracking, breakage, or warping by checking the plate against a flat surface. (ie: Kitchen Table or a Pane of Glass)
Steel vs Aluminum Drive PlatesDuring disassembly, if you noticed that some of the drive plates are aluminum, these can be replaced with steel for a greater "flywheel effect"
- Clutch Inner Hub
With all the clutch plates removed, the clutch hub will be visible and can now be inspected. When inspecting the clutch hub, you'll want to look for wear marks or grooves in the female splines of the inner hub, as well as be sure to check for any wear against the towers from contact with the clutch springs.
- Clutch Basket
With the clutch cover alone having been removed, you should be able to visually inspect the clutch basket outer fingers where the tangs of the friction plates make contact for wear or chatter marks. Should wear of the clutch basket be evident, it's not recommended to file these grooves as some may suggest, when the basket shows this type of wear, replacement of the clutch basket should be the only option.
Additionally, while everything's apart, it's important to check the clutch basket for excessive movement on it's cushions by twisting the clutch basket back and forth on the shaft with the primary gear engaged while feeling for any movement. Should any rotational movement between the gear and basket be noticed when doing this, the clutch basket dampers are likely shot, as well as the clutch basket will likely exhibit excessive wear in other places such as the clutch fingers and replacement of the clutch basket should be strongly considered.
- Primary Gear and Associated Hardware
During inspection of the clutch components, be sure to pay attention to any wear that may be developing on the primary drive gear, as well as to remain attentive to any wear on other parts such as thrust plates or washers, collars or hub bearings (between the clutch basket inner hub and transmission input shaft.)