250r Clutch Problems [Archive]

El Camexican

05-10-2014, 09:04 PM

There are a few posts on here about which clutch to buy for a replacement, how to adjust them, etc. which have prompted me to write this all down. If you have any clutch questions read on. There are also a few tips for extending the life of a used clutch and such that you may find useful one day.

WHICH TO BUY
Many people seem to think that OEM clutch plates are the best option for a rebuild and rightfully so. The only aftermarket friction plates I’ve ever seen that will outlast a stocker are Kevlar and they aren’t available for all models. While most aftermarket steel plates appear similar to OEM plates, their flatness, which is determined by the quality of the cold rolled steel bands they are stamped from and the tooling used in the process seem to always fall short when you get them hot. I hate to say anything bad about a company like Barnett that in some cases is the only option for replacement parts on some models, but the fact is you will be hard pressed to find a steel clutch plate in a Barnett kit (or most other aftermarket kits) that is within the flatness tolerance specified for any given vehicle by the manufacturer of the vehicle. Even a fair % of OEM clutch plates are out of tolerance when new, but not to worry, a slightly out of tolerance plate is not the end of the world unless you are feeding over 80hp through it. Where most aftermarket clutches really fall short is the friction plates. I broke a few dozen before I gave up and swore to never run aftermarket plates again. Sometimes the tabs would end up in the oil pan of my drag bike after one pass. This is very unlikely to happen on a single cylinder trike, or bike, but it adds credence to the quality of the stock plates that rarely broke.

HOW THEY ARE ASSEMBLED
Typically you have an outer clutch or “basket” which is gear driven by your engines crankshaft. It usually rides on the input shaft of your transmission on special cage bearings. The clutch plates we refer to as friction, or “fibers” fit into this basket and are held in place by tabs, or “ears” on the exterior of the plates that fit inside slots on the interior of the outer clutch basket. Then there is an inner clutch, or “hub” which slides onto the end of your “driven” transmission shaft, also known as your input shaft. The shaft has splines that match the hub and ensures it won’t spin on the shaft. The plates we refer to as the “steels” have a multi-tooth pattern cut into the inner diameter which matches up with a pattern on the outer diameter of the inner clutch hub. These fiber and steel plates are staggered one against the other usually beginning with a steel plate which is often a little thicker than the other steel plates, or held in place with a piece of piano wire to ensure no one ever mistakenly mixes it up with the others. There may even be a spring washer behind it to lessen clutch chatter on some models. Once all these plates are in position the entire assembly, AKA “clutch pack” is capped off with a pressure plate, usually made of aluminum and with a female tooth pattern that matches up with the teeth on the inner hub. The pressure plate is lined up with 4 to 6 posts (some modern bikes have just one now) that extend from the inner clutch hub and is wiggled and jiggled until the teeth I mentioned line up and the pressure plate makes full contact with the other plates. At this point the springs that hold and maintain pressure against entire clutch pack are placed over the mount posts and special length bolts with special washers are threaded into place completing the assembly. There are sometimes spacers that slide over the bolts. If your ride uses these make sure you put them on or you will break your inner clutch hub. Do not over tighten the bolts that hold the springs in place! They typically take 6 to 8 pounds of torque, but all they really need is a snugging as the coil springs act as a spring washer. Don’t ever Loctite them either, you don’t ever want to damage these threads.

HOW IT WORKS
In its natural untouched state your clutch is engaged and ready to transmit power from your engine to your transmission. However, in order to put this power to your rear wheel you must first “engage” the gears of the spinning input shaft of your transmission to the gears on the stationary driven, or “output” shaft which is what ultimately turns your rear wheel via the small sprocket that mounts to the end of it and turns your chain.. To do this you must “disengage” the clutch pack to stop the power of the engine from being transmitted to the input shaft. If you don’t you could damage your transmission, or have your ride lurch out from under you when you move your shifter and engage the two shafts. This as you all know is done by pulling in your clutch lever which pushes or in some cases pulls the pressure plate away from the rest of the clutch pack and allows the friction plates to spin freely against the steel plates which will become stationary while you shift your ride from neutral to 1st gear. That click, or bang you often feel when you haven’t used your ride for a while is caused when the plates come apart under force after having being stuck together for a while. Remember, there is no mechanical separation of the clutch pack when the pressure of the springs on the pressure plate is released like there is on a car or truck, the plates separate only due to the difference in speed and resistance from the immobile output-shaft. If it been a few years since something has run you may have to raise the rear wheels of your ride and ”bang” the shifter in order to engage the “stuck” clutch. Once you get it into gear you can either try revving it up a bit to see if it will release, or pulling the clutch lever in while the wheels are turning and tapping the rear brake. This should free up any clutch plates that haven’t rusted together.

HOW TO ADJUST THE HAND LEVER
Ok, so you have a perfectly good running vehicle but you start to notice that it’s getting hard to find neutral while running. The first thing to look at is the adjustment of the clutch cable. All cable clutches have to have some free play at the lever as the clutch pack will expand with heat and shrink with age and wear. I like to have about ¼” of movement in the lever before I feel resistance from the clutch springs. Anymore and I may not be opening the clutch up fully when I pull the lever in and any less and I might be preventing the clutch springs from exerting their full pressure against the clutch pack. A perfectly adjusted clutch cable is one that moves the pressure plate far enough away from the clutch pack that the friction plates can spin freely while the steel plates remain stationary. It also allows the FULL (this is very important) force of the springs to be exerted on the pressure plate when the lever is released. When all parts are new and fresh there is a fairly wide range of adjustment that your clutch will tolerate, but with time two things change. The fibers start to wear and get thinner and the steel plates start to get heat spots and warp. When this starts to happen and the cable adjustment is incorrect it will be hard to find neutral and shifting may become a little notchy.

CLUTCH PLATES
First of all let’s remember that nothing man made is perfect and that includes clutch plates. There will always be some minimal deviation to the thickness of each plate due to the nature of the cold rolled steel they are stamped from. The stamping process also does no favors to the materials flatness, so in the end there will always be one or more points on the surface of the metal plate that are “rubbed” by the friction plates a little more than others and this is where the problems start. These “high spots” get hot faster than the rest of the plate causing it to warp. The warping effect makes the clutch plate appear thicker and this is where “clutch drag” starts to happen even when the clutch cable is properly adjusted, i.e. a “good” .100” thick plate that warps .010” in two directions becomes .120” in the overall clutch pack width. Consider that there are as many as 8 or 9 steel plates in a clutch pack and we are talking about adding .160 to the overall width of the clutch pack due to warped plates! That’s a lot considering some clutches only open up about .200”. This means that unless the clutch cable is perfectly adjusted to open to the maximum distance there will be more than enough friction between the metal and fiber discs to transmit force to the transmission output shaft making it difficult to shift into neutral. The more times this happens, the more the steel plates heat and warp and the worse the problem gets. Now let’s consider what happens when the friction or fiber plates start to wear. This causes the clutch pack to shrink in its overall width. This in turn allows the springs which push the pressure plate against the clutch pack to “relax” as they extend a longer distance than they would against unworn plates and this in turn equates to less force on the clutch pack when you are trying to put the power to the ground. When you have worn friction plates and warped steel plates it becomes very difficult to adjust your clutch cable to a one setting suits all position. You are forced to tighten the cable (make the housing longer) in order to open up the pressure plate enough that it allows enough slippage at a stop for you to find neutral, but then you risk not having enough “free play” (the amount of movement in the clutch lever that has no effect on the movement of the pressure plate) to ensure that the clutch can engage fully. If you drive it like this for any period of time you will burn the clutch up due to the heat created by the slippage.

CLUTCH SPRINGS
Springs are like octane: too little and you’ll damage parts and too much and you are wasting energy. While it is critical that your clutch springs can exert enough force on the plates to hold them together in the most stressful of situations (which happens to be at top speed, especially if you are going uphill). If you think that putting a set of heavy duty rock crusher springs on your 30hp trike is the answer to all your ills, you’ll soon be at the doctor’s office for a carpal tunnel evaluation when you could have fixed your clutch for a fraction of the money that the operation will cost. I’ll speculate that most stock springs will work fine for at least a 20% increase in HP over stock and that if they are a few thousandths under the factory recommended free length they will still work fine in a stock application. If you have any doubts I suggest you buy some new stockers, or aftermarket stock replacements rather than anything heavy duty unless you have a highly modified engine.

BASKETS & HUBS
Also of great importance to the function of a clutch is the overall condition of the basket “tabs” that hold the friction plates in place and the groves on the inner hub that hold the steel plates in place. Over time both of these surfaces start to get dimples pounded into them from general use and even more so if past riders liked to bang the clutch out hard, or were constantly locking up the rear wheels with the clutch engaged. Once these dimples get deep enough it becomes hard for the clutch plates to move freely back and forth on these surfaces when the clutch lever is moved in and out. When closing the clutch it is harder for the plates to come together and close up which in turn creates more heat. The fix is to either buy a new basket and hub (not cheap) or to file the surfaces flat. While in theory it stands to reason that filing the groves and tabs flat makes them weaker and looser than they were stock, it is a common practice that I’ve never seen cause a failure. The added looseness will cause the surfaces to dimple up again a little sooner than they did the first time, but it’s nothing to lose sleep over. You should alway check the springs in the back of the clutch hub when you have it off the engine. They should either be snug, or almost snug in the plate that holds them in place. If they are loose, or the steel plate is cracked, or damaged you should consider rebuilding it.

LEVERS & CABLES AND HOW TO ADJUST THEM
All cable manipulated clutches have a clutch lever, a cable and an arm, cam or a worm gear that provides a mechanical advantage to move the pressure plate against the springs. If these parts on your ride are stock then proper maintenance and adjustment should be all you need to keep them working correctly. Sometimes, especially if someone has incorrectly routed a clutch cable, the cable housing can be pinched, kinked, or otherwise hampered from smooth operation. If you have any doubts about this you need to disconnect the cable from the point closest to the engine and move the hand lever in and out. There should be no resistance whatsoever in either direction. If there is you either have very dirty cable housing, or you need a new cable. I recommend a new cable anytime there is any unknown cause of resistance or defect in the housing as the internal damage can be worse than the exterior looks. Argue that all you want, but I think anyone who’s ever had a cable fail will agree that it’s cheap insurance. Also keep in mind that if you change any component in the clutch lever/cable assembly you may also be changing the amount of movement that is transmitted to the clutch plates. i.e. a longer distance between the pivot bolt on the clutch lever and the point where the end of the cable seats in the lever will open the clutch assembly more than a shorter distance between the two would, but the force required of the rider to pull the lever will be greater. Similar changes occur if you change the length of the lever closest to the engine that the cable attaches to. If you make it longer the clutch will be easier to pull, but the amount that the clutch pack opens will be reduced. There is often a splined connector on the lever that attaches closest to the engine. For the best possible clutch action it is recommended that you position it in a place that will see it at 90 degrees to the nearest mounting point of the clutch cable housing halfway through its pull. This will provide the least amount of resistance to the user and aside from being easier to pull it will reduce the force exerted on the cable ends that could cause premature failure. You should also try to have all the cable housing adjusters in the most neutral position possible i.e. don’t thread the entire end of the engine side of the cable all the way into the holder and have only two threads of the other end in the clutch perch. This is a sure way to ruin the threads on the hand lever perch and will eliminate the possibility of making a simple adjustment on the trail. It is a lot easier to play with these little details in the shop than it is on a hot muddy engine in the middle of mosquito invested swamp.

MEASURING CLUTCH PLATES
Used friction plates are easy to check. Measure the thickness with a caliper and make sure they aren’t cracked and that there are no chucks of fiber missing from them. If they are a little less than the recommended thickness, but otherwise look good I keep using them. You may see some really shiny friction plates, but usually this happens only after a substantial amount of the plate has worn down, so if you find a thin plate that look “glazed” you may want to throw it out. The used steel plates need to be wiped clean and placed on a perfectly flat surface (granite is best, but a thick flat piece of glass will do as well). With the flat side (not the one with the rounded edges) of the plate facing down and your hand very lightly holding it in place take a .006” feeler gauge and try to get it to pass under the plate in at least 4 to 6 places. If it won’t pass under the plate you MIGHT have a perfect plate (more on that in a moment) if it does pass under the plate you may not want to use it, but keep it around in case you get desperate for a plate one day. If it’s warped more than .008” I toss it in the scrap bin. Now take the “good” plates and start looking at the colors. Completely blue, brown or sliver plates are fine. The consistent color, whichever it is, means the plates were taking the heat from the friction plates in a uniform way, this is good. Plates that have “hot spots” on them are suspect no matter how flat. Small dark brown or blue spots on an otherwise silver plate indicate that the plate is wrapping when in use and is, or could cause slippage under load. When you buy new steel plates you should check them like you did the used ones and anything that is not within .002” of what the supplier says is the tolerance should be sent back. The dealer will get you some good ones if you buy OEM, but aftermarket guys will give you the old “we’ve never had a problem before”. Maybe you can exchange them, don’t know, you'll have to ask.

A FEW TRICKS
If someday you find yourself in a position that you must use a “bad” steel plate, put it in first (against the back of the inner hub) where it will do the least harm. Another scenario you may run into one day is that your friction plates are so thin that your pressure plate is contacting the inner hub before it has transmitted pressure to the clutch pack. If this happens you can add an extra steel plate to the pack to take up the difference, again, I’d add it at the beginning of assembly i.e. put two steel plates against the back of the inner hub. If you do this you must be sure that the female spline in the pressure plate still gets a good grab on the male splines of the inner hub when the assembly is together. i.e. when all the plates are together there should be at least 1 or 2 mm of spline extruding from the clutch pack. There is something else you may want to try, especially if you are drag racing. All steel clutch plates have one face that is smooth and rounded and another that is flat and sharp. Usually the smooth edges are installed outward from the factory and allow the plates to separate easily when the pressure plate is opened. The down side to this is that when the clutch lever is released it is up to the springs in the clutch to close up the pack and force the sharp edges of the plates over the inner hub surface. I prefer to turn the plates around and face the smooth sides inward so that when I dump the clutch the springs will be able to close the pack up with less resistance which translates to less wear and tear on the aluminum surfaces and less heat generated. The only down side is that it may be a touch harder to find neutral at times, but I can tell you from personal experience that setting up the clutch pack like this can extend the life of a steel clutch plate noticeably on a dedicated drag set-up. By the way, those of you who “soak” the friction plates in oil before assembly can skip this ritual if you want. All that is needed is a light amount of oil on the steel plates to let them slip easier the first time the clutch is used, or so they don’t rust if the engine is left for an extended time without oil in the cases.