Walk around at any motorcycle gathering and count the bikes with limp, sagging chains. Often, the worst examples also are bone dry with rust and/or crud built up on them. Since you’re a MO reader and regularly clean/lube your chain, you’re ahead of the game. However, you still need to make sure that the chain’s slack is within specifications. If you lube your chain regularly, you will probably not need to adjust it every time you return from a ride, but as a chain nears the end of its usable life, you will need to adjust the slack more and more frequently.

How To Tell If Your Chain Needs Replacing

Ten Steps To A New Chain And Sprockets

How To Clean Your Chain

Although a rear stand is not required to adjust your chain, it will make the process much easier. When your chain is cold, measure the slack halfway between the sprockets by moving the chain up and down. Press down on the chain slightly to make sure it is at its lowest point. To get an accurate reading, hold a tape measure in front of the chain and look across the top of the links. Adjust your line of sight until the tops of both sides of the chain line up, which assures your eyes are perpendicular to the chain and parallel with the top of the links.

Next, move the tape measure so that one of the inch markings aligns with the top of the chain. Now, press the chain up until it is tight, and, bringing your vision up to align the top of the chain again, note the measurement. A little math will tell you if you if the slack is within your bike’s recommended specifications. Since chains don’t always wear evenly, check the slack measurement in a couple of places. If you need to adjust the chain, set the chain tension to accommodate the tightest point. Also, if the chain is dramatically tighter in one place, consider replacing it.

Check the chain’s slack at the midpoint between the sprockets. Measure in several places to find the chain’s tightest section.

Check the chain’s slack at the midpoint between the sprockets. Measure in several places to find the chain’s tightest section.

Before you get down to the nitty-gritty of adjusting the chain, take a look at the chain and sprockets. We’ve covered this previously in our articles: How To Tell If Your Chain Needs Replacing and Ten Steps To A New Chain And Sprockets. If your chain is due for a replacement, then there’s little reason to adjust the old one. Just go to your local shop and get the parts you need and then settle into a pleasant hour or two of wrenching.

Once you’ve adjusted your chain a few times, you’ll get the feel for when it is loose, but the only way to be certain is to use a tape measure.

Once you’ve adjusted your chain a few times, you’ll get the feel for when it is loose, but the only way to be certain is to use a tape measure.

For bikes with lock nuts on their chain adjusters, use a wrench to hold the adjuster in place with a wrench while loosening the lock nut. Loosen the axle nut just enough to enable the chain adjusters to move it. If the axle nut is loosened too much, you can accidentally knock the rear wheel out of alignment, adding extra work to the task. For now, assume that your wheel is properly aligned and make the same adjustments to both chain adjusters.

Remember to turn the adjusters the same amounts on both sides of the bike to keep the wheel in alignment.

Remember to turn the adjusters the same amounts on both sides of the bike to keep the wheel in alignment.

With the exception of eccentric adjusters, you can only move the axle away from the countershaft sprocket via the adjusters. So, don’t get carried away or you’ll have to start all over from scratch. Small adjustments of a quarter turn (or less if your chain is only slightly loose) are the safest bet. Measure the slack after every change. When the chain is within factory specifications (usually around 1.2–1.5 inches), tighten the axle nut to keep it from slipping. If you go too far and the chain becomes too tight, loosen the chain adjusters two full turns and use a rubber mallet or dead-blow hammer to knock the rear wheel forward against the adjusters and begin again.

Though less common than the screw-type adjusters, eccentric adjusters are found on many bikes, though most frequently on those with single-sided swingarms.

Though less common than the screw-type adjusters, eccentric adjusters are found on many bikes, though most frequently on those with single-sided swingarms.

When the chain has the proper amount of slack, torque the axle nut. Next, tighten each adjuster about one eighth of a turn against the axle. Hold the adjuster in position and set the lock nuts.

If you tighten the chain too much, back the adjusters off two full turns and bang the wheel forward until the axle mates with the adjusters, then start over.

If you tighten the chain too much, back the adjusters off two full turns and bang the wheel forward until the axle mates with the adjusters, then start over.

The last step in any chain adjustment is making sure the rear wheel is properly aligned. Don’t trust the stamped marks on your bike’s swingarm, unless you’ve verified they are correct by checking the rear wheel alignment several times. A variety of methods of checking the wheel’s alignment are available through the aftermarket, but the least expensive is the “string method.”

Using a string to check wheel alignment may seem like a lot of work, but a crooked rear wheel will trash an expensive chain and sprockets and could affect the bike’s handling.

Using a string to check wheel alignment may seem like a lot of work, but a crooked rear wheel will trash an expensive chain and sprockets and could affect the bike’s handling.

Take a piece of string a little more than twice the length of the bike, find the center and wrap it once around the forward edge of the front tire just below the front discs. Take each end of the string down opposite sides of the bike. Lie down on your stomach, pulling the strings taut so that they both lightly touch the leading edge of the rear tire. Since the rear wheel is wider than the front, the strings will leave a slight gap as it passes the rear edge of the front tire. Your assistant should make sure that the front wheel is straight by checking the gap on both sides.

Now, keeping your hands steady with the string only lightly touching the rear tire, compare the gaps between the strings and the rear edge of the rear tire. If they are not equivalent, the adjuster on the side that has the smaller gap will need to be tightened slightly.

Finally, measure the chain slack one last time. You’d be surprised how often something tightens up. Don’t forget to put a new cotter pin through the axle nut.

If you don’t have an assistant, a simpler but less precise method for checking rear wheel alignment is to spin the rear wheel a few times and watch that the sprocket stays aligned in the center of the chain. If it rubs against one side or the other, the wheel is out of alignment. In that case, find someone to help you perform the “String Method.”


[This article was adapted from Evans Brasfield’s book 101 Sportbike Performance Projects. Learn more about it here. Read the MO review here.]

  • Old MOron

    I’ve seen the string test described as fixing the string to the rear wheel and checking at the front. Oh well, I’m sure both methods work, even if I’m generally too lazy to bother. And now that I don’t have a center stand anymore, well, I really hope the chain looks centered on the sprocket.

    I like these articles, Evans. Keep ’em coming. I also like to tease people, so please insert a gratuitous mustache joke here, as I can’t seem to think of one just now.

  • Kingsix87

    Thanks for the article. I’m sure many will find it useful. Perhaps it will be good to clarify that checking chain slack should be done with the rear tyre on the ground and the bike weighting on it, without a rider. The rear stand in the photos also does that, but if the rider uses a centre stand, that lifts the rear wheel off the ground, then he or she should check slack before putting the bike on stand.

    • Ian Parkes

      Why wouldn’t you do it with the rider on the bike? Surely that’s the position chain will adopt most of the time it’s in use.

      • Johnny Blue

        I doubt that the manufacturers would complicate maintenance by suggesting to have a rider on the bike to properly set chain slack.
        Also, if the swingarm pivots on the same axis as the sprocket, then the position of the wheel won’t make a difference. BMW had a bike like that I think.

        • therr850

          I’ve often read the slack should be checked with the countershaft, swing arm pivot and axle in line so the slack will be correct when the chain is at its tightest position. Now I am confused. Thorough article though. Thank you.

          • Johnny Blue

            No. The recommended slack is usually with the bike on its wheels. Then the slack will be correct when the sprocket and swingarm pivot are in line with the swingarm.
            If your bike has a recommended 45mm slack (seems to be usual on a sportbike at least) and you set that with the swingarm aligned the way you said, then when the bike is on its wheels the slack might be too big and the chain can come off the sprockets.

    • Evans Brasfield

      Good point!

  • TheManInBlak

    I appreciate these posts as a novice wrench, but more detailed pictures with arrows and descriptions about what sections you’re talking about or which areas to measure would be a god-send.

    • therr850

      OMG! That takes me back to Arlo Guthery and 8X10 Glossys with circles and arrows and a paragraph of description on the back. Way coool. Thanks.

  • Born to Ride

    All that string test and alignment adjustment woes are the reason a single sided swing arm is a huge selling point for me on bikes with chains. The last 4 bikes I have purchased all have eccentric type adjusters and I would have bought a ninja 1000 specifically for that feature over its competitors had the insurance company not told me that my premium would be astronomical for that bike. Instead I bought another bike with an SSSA.

  • Flubbly

    The Profi-Laser or Motion Pro sprocket alignment tools are good alternatives to the string method – affordable, accurate, and much less fudging. Or you can use the straight edge of a stiff metal ruler held against the sprocket.

  • di0genes

    The first sentence of this article should say “read the owners manual”. Motorcycles with long travel suspensions have chains that will appear to be too slack when they are adjusted correctly. A too tight chain will do far more damage to chains, sprockets, and transmission bearings than a chain that is too loose.