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How to Adjust Drive Chain Slack
Gen2 Hayabusa
Gen2 Hayabusa
The drive chain will need to be tightened periodically, especially when the chain is new. It also will need to be adjusted when replacing the drive chain or switching to different sized sprockets.
The movement of the rear suspension requires that the drive chain have a certain amount of looseness for both to operate properly. The looseness in the chain allows the suspension to operate without stretching or breaking the drive chain or stressing the bearings that the chain wheels turn on. The looseness of the drive chain is called chain slack. When weight is placed on the bike, the suspension compresses which pulls the chain tighter, reducing the chain slack. The reaction of the rear shock and the swing arm to road irregularities reduces chain slack during operation even further.
The ideal chain slack is that which would allow complete compression of the rear suspension while not attaining 0 slack until that point. The manufacturer has determined the proper amount of chain slack to be a minimum of 1.3 inches as measured with the rear suspension compressed by weight of the bike only. In practice, this amount of slack should allow for a complete bottom-out of the rear suspension without stressing the chain or other parts of the final drive.
Adjust looser, not tighter. A chain that is too loose will be obvious upon inspection before it ever becomes loose enough to fall off the sprockets or cause severe damage. A chain that is too tight could snap. For this reason, I always give preference to adjusting the drive chain looser rather than tighter. If the chain comes off, it will either wrap around the engine sprocket and gouge the bottom of the motor out or wrap around the swing arm causing a rear wheel lockup. A chain that has come off does not usually fly out harmlessly. Proper chain slack is important but it is also simple enough to be one of the maintenance procedures that the manufacturer expects owners to be able to do themselves.
Do not run the engine when measuring or adjusting chain slackor performing any other drive chain procedures. Amputations. Need I say more?? It has happened many times and you will find pics online if you search! Just DON’T do it!
Measure chain slack on the top and bottom chain runs, then add those two for a final figure. This procedure is described in detail below. It is not how the manufacturer recommends measuring chain slack. They recommend measuring the chain slack on one run but if you have not already discovered, that is impossible because of the swingarm is in the way. You can only measure part of the chain slack on both runs.
Make small adjustments. As amazing as it may seem, turning the adjuster screws one sixth of a turn is often enough to tighten the chain properly. There are adjustment reference marks on the swing arm. You will never need to adjust the blocks one entire mark tighter in a single adjustment or even half a mark tighter. That would be much too tight.
Tools:
rear spool stand
15” steel ruler
Sharpie marker
36mm impact socket
24” breaker bar
10mm open end wrench
12mm open end wrench
rubber mallet
torque wrench
Measuring Drive Chain Slack
1. It is best to find the point of greatest tension in the drive chain before measuring the slack. Put the bike on a rear spool stand. Rotate the wheel slowly to find the point of greatest tension. Please be very careful not to roll fingers into the sprockets. Feel the chain from outside of the run and roll the wheel the direction that will not pull fingers into the sprocket.
After the point of greatest tension is found the drive chain slack may be properly measured midway between the front and rear sprockets. I find the chain slack on a rear stand to be a bit looser than it is with the bike on the side stand. I usually put the bike on the side stand to measure the chain slack after finding the point of greatest tension in the chain. Then I put the bike back up on the rear stand to perform the adjustment.
2. Slide a 15” steel rulerinside of the swing arm on the left side. The ruler edge should touch the left front inside of the swing arm. To hold the ruler steady, the top of the ruler will rest perfectly against the top tube of the swingarm.
3. Pull the bottom run of the chain down using approximately 2 lbs of force. Measure the distance of travel in the bottom run. Now measure the top run of the chain in the same way, pulling it upward with approximately 2 pounds of force. Add the measurements together for the total chain slack. Combined measurement should be be 1 and a third to 1 and one half inches. If it is out of spec, it needs to be adjusted.
Drive chain slack: 1.3 inch ~ 1.5 inches.
Pull the top chain run up and measure the travel. Pull the bottom chain run down and measure the travel. Add both measurements for total chain slack.
Adjust Drive Chain Slack
4. Note the position of the adjuster blocks in relationship to the marks above and below of the axle slot. Movement of the adjuster block will be almost imperceptible after typical chain adjustments. Where larger adjustments (such as replacing the chain) are required it is helpful to know where the block was before the adjustment. Although this is matter of much conjecture, the blocks should always be positioned identically in relationship to the marks on both the left and right to maintain proper axle alignment.
There are all kinds of tools and techniques that supposedly do a better job than the axle adjuster marks but I have never tried any of them. They may have some merit. I have only relied on the axle adjuster marks and my rear sprocket always seems to wear more on the inside than the outside.
When visually checking adjuster block position, I square up my line of sight by looking straight down the hollow center of the axle.
5. Use a Sharpie markerto mark both the LH and RH axle adjuster screws. On each, place a mark on the flat that is facing outward. These will be used as reference points for how much each adjuster bolt was turned. It is not normally necessary to mark more than one flat because the adjuster bolt is usually not turned more than 1 flat to adequately adjust the chain.
6. Use a 36mm impact socketand a 24” breaker barto loosen the axle nut. Make the nut loose enough that the washer behind it is free.
7. Use a 10mm open end wrenchto hold the LH adjuster screw steady. Use a 12mm open end wrenchto loosen the LH adjuster screw locknut. Do not move the adjuster screw yet.
Repeat the locknut loosening procedure on the RH adjuster.
8. Use the 10mm open end wrench to turn the LH adjuster bolt only a very small amount at a time, counterclockwise (out) to tighten the chain or clockwise (in) to loosen the chain. One sixth of a turn, (one hex flat) will make approximately a 1/8 inch adjustment in chain slack.
Turn the RH adjuster bolt the same amount as the left was turned.
Use the Sharpie marks to check that both sides have been turned the same amount.
9. Bump the rear tire forward tight against the adjuster bolts with a blow of your fist or use arubber mallet.
Measure the chain slack as directed in steps 2 and 3 above. Adjust both sides equally if necessary.
With the axle nut loose, the swing arm forks are not compressed. Expect the chain slack to be approximately 1/8 inch tighter after the axle nut is tightened and the wheel is pulled back accordingly. Also expect the chain slack to tighten up another 1/8” after being taken off the rear stand and placed on the ground.
10. When the proper chain slack is achieved, (remember that it will be 1/4” less after you tighten the axle nut and put the rear wheel on the ground) hold the adjuster bolt with a 10mm open end wrench and tighten the adjuster bolt locknut against the front of the adjuster block slot with a 12mm open end wrench.
Repeat this process for the adjuster on the other side.
11. Use a36mm impact socket and torque wrenchto tighten the axle nut. Inspect the adjuster block marks on the swing arm. The adjuster block and marks should look the same on both sides when the rear wheel is properly aligned.
Torque, Axle Nut: 72.5 ft lbs.
12. Take a final chain slack measurement with the bike on its side stand. Repeat steps 6 through 12 to readjust the chain slack if it is not in spec range of 1.3 inch ~ 1.5 inch.
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