Introduction: DIY - Motorcycle Chain Tension Adjustment & Rear Wheel Alignment

About: Just a guy who doesn't know when to quit, and is constantly in search of a solution to a problem that doesn't exist yet.

Next to tire pressure and chain lubrication, chain tension (slack) and rear wheel alignment are among the most ignored simple maintenance tasks. This despite it being a major factor for both the longevity of the chain and tire, the motorcycles handling, as well as basic safety. To see what happens when a motorcycle chain falls off due to neglecting it, click here to see a short video. The saddest part is that it could have been totally avoidable with less than an hour of time and a few tools.

Here we're going to go over how to check the chain slack and adjust chain tension, as well as align the rear tire on a 2017 Kawasaki Ninja 650 ABS. It would also be exactly the same process on the 2017- Kawasaki Z650. On most modern bikes, the process is extremely similar, so regardless of what bike you ride, you should find some value in this tutorial. Also, this guide might get updated over time. To see the latest version, click here.

Let's begin!

Difficulty: Easy
Tool Requirements: Basic-intermediate
Time: 1 Hour
Cost: 0$


Working on any vehicle can be risky to both yourself and the vehicle. No warranties or guaranties, explicit or implicit, are made or implied regarding the compatibility, suitability or effect on any current warranties. All modifications should be made within the reader's capability and under their own exclusive responsibility.

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Step 1: How Often

Per Kawasaki's enginerds, the chain slack should be checked (and adjusted if necessary), every 600 miles. The rear tire alignment should be checked simultaneously, and adjusted if necessary.

There are those that would recommend you check it before every ride (at least visually), but that's way too much for most people to be practical in real life. The good news, however, is that while you really should be checking it about every 600 miles or once a month, you will rarely have to adjust it. And to check it it only takes about fifteen minutes, so don't procrastinate. Remember, the alternative is this.

Also worth mentioning is that the most important time to check the chain tension and rear tire alignment is during the first 500-1000 miles of the bike, which is when the chain will suffer it's initial (and most significant) stretch as well as general part mating and settling. This is one of the important things the glorified 'first service' should take care of (which I totally recommend you save the coin and do yourself).

Moral of the story is check it often, adjust it sporadically, and don't forget about it.

Step 2: What You'll Need

  • Motion Pro Chain Slack Setter or a Ruler - With all routine maintenance tasks, doing the work yourself (in lieu of a mechanic) saves you enough money that it's worthwhile, both time-wise and economically, to get any tool that makes your more likely to not put off or delegate the job. This is one of those tools. It makes checking chain slack much, much quicker and easier than using a ruler, and it gives you much more consistent results. For the price it's a no brainer for any motorcycle owner. However, in a pinch a regular foot long ruler can work just as well.
  • Motion Pro Chain Alignment Tool - There are many ways to check chain alignment, however the best, quickest, and easiest method I've found so far is this tool. Other options are simply to use the hash marks on the frame, string, or tape measure, but for doing it on a regular basis, nothing beats the precision and speed of this thing.
  • 27mm Socket - For the axle nut. Be aware that this size is typically not included in normal ratchet kits.
  • Pliers - To remove the cotter pin on the rear axle nut.
  • Cotter Pin - 4.0x35mm - To secure the rear axle nut. It isn't ideal to reuse the original cotter pin, but in an emergency it can be done. The correct size per Kawasaki is 4.0x35mm (Part 550AA4035, 2.95$), but any similarly sized cotter pin can be used. Typically it's cheaper and more worthwhile to just buy the kit and use the size you need, keeping the rest as spares.

*Note - If you're preforming this DIY on a 2012-2017 Kawasaki Ninja 300, the 22mm and 27mm sockets are not needed. The Ninja 300 uses 17mm and 24mm sockets, respectively.

Step 3: Put the Bike Up on a Rear Stand

For this job, we're going to use a rear stand.

If you don't have rear spool sliders already, then now would be a great time to get them. Luckily they're cheap and can be installed in seconds. Plus, in theory they also work as frame sliders. The bolt size is 8mm, and I personally recommend the models that have a spacer to slightly extend it from the swingarm, since it reduces the risk of scratching the swingarm or bike when putting the bike on, or taking off, the stand. The model I went with was this one, but if not you can take a look here for other models you might like more.

Regarding the rear stand, I used a Speedmetal Rear Race Stand, which I like because it's a single piece (sturdy) as well as aluminum (rust free and lightweight). A cheaper unit like the Venom rear stand that a lot of people have would work just as well, of course.

Pro Tip: On the 2017 Kawasaki Ninja 650 there isn't any differently colored master link on the chain. I really recommend you mark the chain with a permanent oil pen so you know where you started and where to end when lubricating the chain.

Note: There is controversy on whether the chain slack should be checked on the sidestand or a rear stand. In either case the swingarm is loaded, so both I and a majority of motorcycle owners check and adjust the chain tension while on a rear stand. Mostly for convenience and speed.

Step 4: Measure the Initial Chain Slack

The first step is to measure the initial chain slack. Remember, the correct chain slack (for this bike) is 20-30mm when measured roughly at the middle of it's length. In this case we measured 35mm which is out of spec and way too loose.

Keep in mind that if you measure a value between 20-30mm, the chain slack is correct and you don't have to do anything. When the manual says "check every 600 miles", you should really do so because most of the times it's only checking. In practice you probably won't have to adjust your chain more than every 2-3k miles. So if you get a value that's well within spec, skip to step 13.

I personally used a Chain Slack Tool because it's a lot easier than fiddling with a ruler. Anything that makes you more likely to keep on doing a routine maintenance task is worth it, and this is one of them. Simply hold the top of the tool against the bottom of the swingarm, put the yoke around the chain, and move the arm up and down. Remove the tool and read the value.

If you're using a ruler, remember that you have to measure at the same point of the chain link (either top, center or bottom. Choose one and stick with it). This means that you want to measure from the top of the link (for example) when pushing the chain up, and at the top of the link when pushing the chain down. It's tempting to measure at the top when it's up and at the bottom when it's down, but this would be the wrong way to measure it. Take a look at the diagram above if this is unclear.

Step 5: Remove the Chain and Nut Cover

Now that we know we have to adjust the chain tension, let's begin the prep.

Please, don't skip this. Take a moment and remove the rear chain cover to make your life easier as well as reduce the risk of scratching it when removing the cotter pin (guess how I know). All it takes is two easily visible and accessible allen bolts.

Also, remove the rubber cover on the axle nut.

Step 6: Remove the Cotter Pin

Now we have to remove the Cotter Pin. The OEM pin is very strong and stiff so be careful to not let your pliers slip when pulling it out and bang something delicate. The trick is to bend it as straight as possible, until it can easily be pulled out. Or you can just cut it with some cutting pliers.

Step 7: Loosen the Rear Axle Nut

We have to loosen (but not remove!) the rear axle nut. We will need a 27mm socket for the nut side, and a 22mm socket for the bolt head side. Be aware that these are not typical sizes and are probably not included in your standard socket set.

You are going to want to keep the bolt head secured in place with one hand, and loosen the nut side. Don't do the opposite, namely try to remove the bolt side with the nut held still. This is because then you're rotating the entire axle, which is simply unnecessary.

Though this can be done with wrenches and small ratchets, 6 point sockets (opposed to 12 or more) and a long breaker bar make the job much easier with much less risk of damaging either the bike or yourself.

You only want to loosen the nut enough to be able to rotate it freely by hand. Don't remove it completely.

Step 8: Adjust Chain Slack

To adjust the chain slack we need a pair of 12 and 14mm spanners. While holding the big nut steady with the 14mm spanner, loosen the 12mm nut. Once the 14mm nut is free to move, tighten it clockwise in one-quarter to one-half rotations measuring the chain slack constantly until it tightens up to around 25mm of chain tension. This taking for granted the chain was too loose.

Once the chain tension has been properly set, hold the 14mm nut steady and rotate back the 12mm nut until they are both locked together. No threadlocker is needed given how both nuts secure each other, but it can be applied if desired.

Typically, during routine maintenance I find that the chain tension is too loose rather than the other way around, but sometimes you may find it as so. If that's your case, loosen up both nuts and give the rear tire a push forward (while holding the bike and rear stand steady). This will loosen the chain (increase chain slack). Then simply proceed as above for loose chains.

Step 9: Adjust Rear Tire Alignment

Whenever the rear axle nut is loosened, you should check and readjust the rear tire alignment. This means that any time you adjust the chain tension you will have to adjust the rear tire alignment (and vice-versa).

There are many ways to adjust alignment, with the easiest being simply using the hash marks on the swingarm. However forums abound with comments about how the swingarm's marks aren't precise, so I like using a specific tool. For quick and painless checking on a routine basis, I use a Chain Alignment Tool. I'm sure a nice gadget like a Laser Chain and Belt Alignment Tool would be even better, but for the price few people can justify it. One benefit this tool has over strings or measuring tape is that you can quickly look at it at any moment when adjusting the alignment, rather than having to stop to take measurements all over again.

To use the tool, simply clamp it on the rear sprocket and look at how the rod aligns with the chain. It will be readily apparent if the rear tire is aligned with the chain or not. And though the rod looks shortish, you can easily align it visually in such a way that it projects against the whole length of the chain. Just make sure you only look at the rod with only one eye open to avoid parallax errors.

Similar to how we just adjusted the chain tension, play with the nuts on the right side of the swingarm end to adjust the rear tire alignment. Constantly check the alignment to make sure you haven't gone too far. Once you're satisfied with the alignment, measure the chain tension again just to make sure you haven't messed up it's value. Then get ready to torque up the rear axle nut. It isn't necessary to remove the sprocket alignment tool just yet, though.

Step 10: Torque Up the Axle Nut

The correct torque for the rear axle nut is 108 N·m (11.0 kgf·m, 80 ft·lb). You really should be using a torque wrench for this, honestly. But if not, it translates into pretty darn tight. It's rougly the same torque that is typically applied to a car's lug nut. As before, we want to hold the bolt head steady while tightening the axle nut.

Once we have brought up the axle nut to the right torque, we have to tighten it a bit more until the hole in the axle aligns with one of the grooves in the nut.

Step 11: Recheck Chain Tension and Wheel Alignment

Sometimes during tightening things can go a bit whack. You always want to double check chain tension and tire alignment one last time after tightening the rear axle. Just in case.

Step 12: Install the Cotter Pin and Covers

Now that we're sure that everything went well, install a new cotter pinand put it's cover back on.

The final step is to apply some threadlocker to the two allen bolts we removed previously and bolt the chain guard on again.

Step 13: All Done!

That's it! Job's finished. Wasn't that hard, was it? With this you'll save plenty of time and money in the future, so it's certainly a maintenance item worth taking care of yourself. Now, the only thing left is to clean and lube the chain. If you'd be interested in a few tips & tricks, you might want to check it out.

By the way, if you just bought you're Ninja 650 and you're still looking around for upgrades, check out my 2017 Kawasaki Ninja 650's mods list. It's a list of all the upgrades I currently have on the N650 pictured here. You might find something that you like. After all, what's the point of a motorcycle if you don't farkle it to death?

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