Motorcycle chain slack is a fundamental piece of maintenance, right up there with checking your oil and tire pressures. Very basic, pretty easy, and also really important.
Why does chain slack matter? Well, if your chain gets too loose, it could jump off the sprocket, jam up, and chuck you on the ground. A loose chain is also going to slap around and make a bunch of noise and create a lot of driveline lash.
A too-tight chain, while less common, is also bad. If your chain is too tight it’s going to wear out the sprockets and chain faster, plus it can inhibit suspension action.
How much chain slack you need varies based on the bike, so check your owner’s manual or the sticker on your swingarm for the spec. For streetbikes, the figure is usually between 30 and 40mm. Your owner’s manual will also tell you whether to measure the slack with the bike on the sidestand, or with it held vertical on a rearstand.
Armed with a slack figure, it’s time to take a measurement. Using a ruler or tape measure placed against the underside of the swingarm midway between the sprockets, pull the chain down and note the measurement, and then push it up and check the number. Now calculate the total deflection by subtracting the smaller number from the larger number.
If your chain needs to be adjusted, the first thing you need to do is crack the axle nut loose. Don’t spin it off, just loosen it enough to allow the wheel to move in the swingarm. There are several different styles of axle adjusters out there, but most will have a lock nut that you need to crack free. Then turn the adjuster ¼ turn at a time to shift the axle position and change the chain slack. Make sure you’re moving the left and right side the same amount, and check the reference marks on the adjuster to verify that the wheel is straight in the swingarm.
Once you’ve made an adjustment, recheck the tension. It might take some trial and error.
Once you think you’ve got the slack set, stick a rag or a screwdriver under the chain and rotate the wheel to pull the axle forward against the adjusters, then tighten down your rear-axle nut to the proper torque. Then pull the rag out and tighten the locknuts on the adjusters. Finally, recheck the slack one more time. With that done, you might as well wipe your chain down with some cleaner and give it a shot of lube.
And that’s it! One of the most basic maintenance procedures there is, so you don’t have any excuse not to do it! I hope you enjoyed this vid. If you have questions or video topics, leave ‘em in the comments section. Until next time, ride safe.