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Quick Tech: Dirt Bike Clutch Troubleshooting

Image courtesy of motocrosshideout.com

Image courtesy of motocrosshideout.com

A motorcycle’s clutch has a huge impact on a bike’s handling and power. Without a smooth-operating clutch, a bike’s rear wheel is more likely to break loose which can lead to losing races, or worse, crashes.

Dirt bike clutches tend to require regular maintenance and rebuilds.

Are you hearing grinding noises? Is your clutch slipping?

Let’s take a look at some common clutch problems and how to fix them.

Troubleshooting Grinding Noises

If you’re hearing grinding noises, warm up your engine and put the transmission in neutral.

Turn the throttle to get the engine to run steadily, just over idle. Now, pull in the clutch lever.

See if you can detect a significant reduction in vibration and that grinding noise.

If the noise is reduced, that’s good news.

It most likely means that the needle bearing and bushing that fit between your clutch basket and main transmission shaft are worn.

There’s no easy way to measure the needle bearing. But check your manual for a list of dimensions for the bushing diameter. It’s recommended that you always replace the needle bearing and bushing together as a set.

What if the grinding noise doesn’t lessen when you pull in the clutch lever? That may indicate a more serious issue.

You should check the bolt that retains the primary gear to the crankshaft and the nut retaining your clutch hub. If both of those are tight, then your crankshaft main bearings are likely worn out. 

Troubleshooting Problems with Lurching or Dragging

Both lurching and dragging are typically caused by deep notch marks that form in your clutch basket and inner hub. Those notch marks form because of clutch plates’ tangs. When it goes on too long, the plates will stop engaging or disengaging. They simply stick in place.

Notches less than 0.02 inches can be draw-filed (filed in only one direction) down. But it’s a delicate process. If you file too much material from the clutch basket or your inner hub, your clutch will be more prone to dragging. That can result in your bike creeping when you put it in gear.

Before you draw-file notches from your clutch basket, you need to check the basket for fractures at the base of each finger. If you find any cracks—even hairline fractures, you need to replace the basket. If the fingers break off with the bike running, you’ll experience catastrophic engine damage. And if you draw-file a basket with fractures, you increase the likelihood of failure.

Installing aftermarket clutch kits require that you remove your original primary gear, your kick-start gear and the rubber bushings in the clutch basket.

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2 Comments

  1. Dave Hoelcher says:

    Something not mentioned here is the clutch stack thickness. Each fiber plate has a minimum & maximum thickness spec. You should measure & record each plate, then compare it to specs. You can add up the number of plates then multiply times minimum, then maximum thickness. If your plate stack thickness is larger than that spec, you may have a dragging clutch. If your stack is less than spec, time to replace, springs too. Always soak new plates in your gearbox oil. My Honda district service rep had me frying tires with front wheel against the wall to remove excess fiber plate thickness on a new CB750SC back in the day…MrH

  2. My cluch barley needs to be pulled in order to shift….i wrecked my bike …the purch is fine same as cable ….did I knock something lose in the case ????

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