What causes a worn clutch basket & how to fix it


This "How Do" article below, answers why a clutch would creep, slip, etc. and explains why it does those things and more and most importantly how to fix it yourself without expensive tools! I rate it outstanding and I'm excited how it will educate all the noobie TT members. :ride:

You can at anytime close your eyes for a second and remember the feather light exact feeling you always feel when you almost automatically grips the handlebar and pull in the clutch lever at the local shop on these brand new bikes. Now this brief moment of heaven leaves a sour taste when you open your eyes and see your old bike again. The pain in you left forearm brings you back to reality. You maintain your bike, new cables and a fine clutch lever but the hard, dragging or slipping clutch remains. Heck you might even bought a new set of clutch plates but the clutch just won't function properly. It's an old bike, you think, the clutches weren't that good back then, you try to convince yourself, but you know it was better at one time. Or maybe another bike equal to yours has an excellent clutch. What's wrong? Can it be like new again? It can! We will show you the way to improve your old clutch action to a point you only have dreamt about. And it doesn't have to cost you a dime!

The problem

Your clutch's bad function is probably a combination of several things. The problem we will focus on here is a worn basket. Bikes that have more than a season or so behind them will likely show up these symptoms. The problem and our remedy is applicable on most dirtbikes regardless of brand and year of manufacture. A worn clutch basket will cause any of these problems.

A dragging clutch. No matter how much you pull the clutch lever and certainly way beyond the point if disengagement. Still it won't disengage fully and you can hardly walk the bike in the pits with a gear engaged and just the clutch pulled in.

A slipping clutch. You measure the springs, add washers, lube the cable and adds some slack but it keeps slipping. The ATF oil doesn't fix it. You might even measured the disks thickness and it's just fine but the clutch still slips.

Erratic engagement. Extremely annoying in the trickiest part on the trail. You need the clutch but it won't engage smoothly.

Hard pull. There is nothing more tiring than a rock hard clutch on that trail when you are tired anyway and needs to overtake this tricky part. You think for a moment of undergoing arm pump surgary but you know the problem. It isn't your arm. It's the darn clutch.

A worn basket will have a groove hammered into the contact point between the friction plates on each fin and for each plate


This groove will catch the plate forcing it into the middle of the groove making your attempt to move the clutch disk sideways bound to fail. At the very same time the springs will fail forcing it back and compressing the disk stack with the correct force. You could very well have a clutch that's hard to pull, drags when fully disengaged and still slips under heavy acceleration. Impossible it seems but, no no, it's more then possible, it's even likely. This picture shows a Maico basket. Even these steel baskets wear. Almost all other baskets are made out of aluminum which is softer and therefore they are even worse from this standpoint.

The tools needed are simply a small file and some fine grit paper. I start by filing the area flat. You needs to keep an eye on the surface because you don't want to remove too much material. just enough to barely scratch the bottom of the grooves. The next step is to sand the surface flat. There is no need to achieve a polished surface. A surface that feels flat and slick with a tip of you finger is just fine. There are two reasons to why you shouldn't machine the surface. First you don't want to remove more material then absolutely necessary. If you do the friction plates will shatter back and fourth hammering in another groove before you know it. The less play the better. The second reason is that you want to keep the surface that before was the bottom of each groove. You see this small surface has been plastically deformed and has a kind of forged harder surface that you would want to keep as much as possible of. There are a few reasons to why some bikes are more phrone to get this problem then others. A fairly weak bike with a large clutch diameter is always better. And of course the other way around. An open class engine with a small diameter clutch will develop this problem sooner. The Maico 490 is a example of a very powerful bike with a small clutch diameter. Thanks to being made out of steel it still can function equally well as most bikes. Another common misconception is to believe that the clutch will survive better when not used. Most racers actually don't use their clutches very often on the track. It can very well be just the opposite. The force created when shifting without the clutch and even worse under heavy power will directly transmit into the clutch and really smacking the friction plates against the basket.

The Fix

This fix described is done on a KTM 250GS from 1981. A true evolution bike but it could well be a newer or Japanese bike too. I have successfully carried out this trick on all common bikes.

Here the filing has started:


One can easily see the grooves shrinking. Keep a light hand and take it easy. The aluminum is easy to remove but harder to put there again. Take your time and try to make the surface as flat as possible. One can almost always feel the harder (forged) surface when filing. It's not a hard or difficult job but if you aren't an experienced mechanic you could ruin an expensive clutch basket. When you are done, use the file to carefully remove the sharp edges on both the inside and the outside of the newly fixed surface. You have some filing ahead of you but it's free and your time is entirely spent on something that interest you, so continue working you way around and keep dreaming of that perfect clutch action you eventually will have. Do the sanding in two steps, first use P120 grit to sand it flat and nice. You will then go on to P400 grit to achieve that slick shiny surface that will be the last thing of your thought when falling asleep that night.


This shows the finished surface. A good idea is to take a friction plate and try to move it back and fourth sideways before the filing and sanding. You will feel that it hooks up on everything and cannot move freely in the slots. After you are done you repeat the experiment and you will feel that the plate slides sideways without the slightest obstruction. Now the clutch springs will be able do their job and so is the rest of the clutch disengaging mechanism. As you can see the process leaves quite a bit of aluminum flanges ground off. You need to clean the basket really good since you don't want that inside your running engine. It will not ruin the gearwheels or bearings since it's only aluminum which is pretty soft but it could lead to wear and could mess up one or two sensitive needle bearings or their needle cages. Keep it clean! Mostly this operation is sufficient to achive a world class clutch but, hey.. you can do more.

The clutch hub where the aluminum or steel plates is locked up is likely worn in the same manner.


You can optionally sand these some too. It's not certain that it will improve the clutch any further but it won't make it worse and I suggest that you take an hour of your time to do this too. With a slick even surface on both the basket and the hub you can be confident that your clutch will work as a brand new at it's worst. You are likely to end up with a clutch considerably better than a new stock clutch. The kind of attention we are giving our machine here is that of a high budget factory team. The thing we have that the factory racer won't have though is the satisfaction of having doing it ourselves. Just imagine the faces of your buddys when you ask them to grab your clutch lever and have a feel at the local track. These tricks combined with a fresh cable will give you the clutch action of a hydraulic unit. Sweet stuff!

If you are about to go all the way there is one more route to go. If your friction and steel plates are in good condition and within their wear limit you can keep them but it will always be better to spice up your craftsmanship with a new set of plates. These plates however are stamped and therefore having these sharp edges.


We don't want that. With some care and a gentle hand you should remove the edges with your file.

This will further reduce friction and prevent wear. The picture shows a fairly thick aluminum friction plate. Some plates are made of steel and is much thinner. It's doubtful that you would or could perform this operation on such plates. Use common sense to determine if there is enough supporting flat surface to narrowing it some which is exactly what you will be doing here.

In the end the clutch basket and plates will be ready for assembly. This operation cannot be performed many times on a clutch basket without ending up with too much play. It seems that for each time the grooves come back sooner and sooner. I think that you can do this up to 3-4 times though before the basket is ready for the bin. Carefully done the first time though you can expect the clutch to perform perfectly for a long time depending on how much and how hard you ride. If you are a professional racer you might should consider a tougher billet made basket or a conversion with steel inserts.

Don't forget that this is supposed to be entertaining. Take a cup of coffee and enjoy your achievement.


Good luck with you new hole shot clutch.

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