Chain slack or Chain tension

oioioi

oioioi

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Can I get some guidance or confirmation on proper chain slack, or the proper way to measure the slack.
My service manual calls for 20mm-30mm of slack. It says to do it while the bike is on the side stand and NOT centre stand. Fine I got that.

I understand the slack needs to be measured at the centre point of the swing arm. This happens to be roughly at the point where the chain guard ends on the bottom side of the swing arm.

Should the lowest point of the slack be measured when the chain is in its natural position or should I be pressing it down as far as possible and consider this to be the lowest position.
As for the highest position, I am pushing the chain up to is furthest position.

1758939247705.png

The picture above has an an arrow indicating the slack of 20-30mm. I am understanding it as the dotted lines being the slowest and highest points that the chain can reach. Both being above and below is natural place.

I have watched a few videos and read some threads and they all seem to be unclear on this. The difference is probably minimal, therefore it may not matter but I want to be sure I am doing it right.

For the record, I am using a Motion Pro Slack Setter Tool.

So far I have applied the tool to the chain/swingarm, pushed the chain all the way up. Note the measurement off of the scale. Then press the chain all the way down, note the measurement and subtract the two to get the difference as my slack.
 
Wingboy said:
Measure it at a few different points. Chains don't wear evenly in their entire length.
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This. If there’s a frozen link or two it can end up super tight in one position and super loose in another.
 
Keep it simple. Bike in neutral, on side stand. Place a 1’ ruler vertically on the floor at the midway point of the chain. Press down the bottom run of the chain with your baby finger, mark the ruler. Press up on the same part of the chain, mark the ruler. The space between the marks should fall in your 20-30mm range.

Take a mental note of how much slack 25mm (1”) is. In the future you can use the length of your thumb between the last nuckle and the tip (it’s not a precise spec, close is good enough).
 
oioioi said:
For the record, I am using a Motion Pro Slack Setter Tool.
So far I have applied the tool to the chain/swingarm, pushed the chain all the way up. Note the measurement off of the scale. Then press the chain all the way down, note the measurement and subtract the two to get the difference as my slack.
Click to expand...

FYI, the Slack Setter tool has two scales so you don't have to subtract the two measurements. Loosen the hex screw at the bottom of the graduated tube and spin it so that the "Slack Measurement" scale is facing outwards. The outer tube will then measure your up-and-down motion as the relative slack.

I do press both up and down when taking my measurement, not just up. Like your diagram implies, the downward deflection is considerably less than the upward deflection, so it's probably not a significant difference most of the time. I also mark my swingarm so that I know I'm taking the measurement from the same place between the sprockets each time.
 
Ash said:
FYI, the Slack Setter tool has two scales so you don't have to subtract the two measurements. Loosen the hex screw at the bottom of the graduated tube and spin it so that the "Slack Measurement" scale is facing outwards. The outer tube will then measure your up-and-down motion as the relative slack.

I do press both up and down when taking my measurement, not just up. Like your diagram implies, the downward deflection is considerably less than the upward deflection, so it's probably not a significant difference most of the time. I also mark my swingarm so that I know I'm taking the measurement from the same place between the sprockets each time.
Click to expand...
Wow, that tool is a new one for me!

Setting chain slack is a ballpark thing, getting +/- 20% on an inch should be easy for most people without tools (or with a simple school kids ruler).

Remember to set your rear sprocket true (parallel) to the front sprocket after setting slack.
 
Mad Mike said:
Wow, that tool is a new one for me!

Setting chain slack is a ballpark thing, getting +/- 20% on an inch should be easy for most people without tools (or with a simple school kids ruler).

Remember to set your rear sprocket true (parallel) to the front sprocket after setting slack.
Click to expand...
It looks like it could be ripped off quite easily with a 3d printer.

EDIT:
People already have models available for free.
 
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Mad Mike said:
Wow, that tool is a new one for me!

Setting chain slack is a ballpark thing, getting +/- 20% on an inch should be easy for most people without tools (or with a simple school kids ruler).

Remember to set your rear sprocket true (parallel) to the front sprocket after setting slack.
Click to expand...
The slack setter tool is a luxury, for sure. It's nice because you don't need to get your eye down at chain level to get an accurate measurement like with a ruler (parallax). Just zip the slide thingy up and down and the friction of the outer tube keeps the measurement on the graduated tube, and you can then bring the whole tool up to your face to read it.

The Motion Pro chain alignment tool is another luxury, and way more precise than the swingarm marks. There are even laser-pointer alignment tools if you want to go completely overboard.
 
Ash said:
The slack setter tool is a luxury, for sure. It's nice because you don't need to get your eye down at chain level to get an accurate measurement like with a ruler (parallax). Just zip the slide thingy up and down and the friction of the outer tube keeps the measurement on the graduated tube, and you can then bring the whole tool up to your face to read it.

The Motion Pro chain alignment tool is another luxury, and way more precise than the swingarm marks. There are even laser-pointer alignment tools if you want to go completely overboard.
Click to expand...
Makes me think of my collection of useless tools. I’d file it with this tool.

IMG_2071.jpeg.
 
For what it's worth, the tech inspectors at track days around here like to see 40 or 50mm of slack on my bike, which is about double what the factory recommends. It's generally better to be too loose (within reason) than too tight.

At the other extreme, my XSR900 owner's manual calls for 5 to 15mm (.20 to .60 inch) of slack, which is crazy tight and very hard to eyeball. I'm not sure that I believe them, but it even has in bold text that more than 25mm of slack can damage the frame and swingarm.
 
Mad Mike said:
Makes me think of my collection of useless tools. I’d file it with this tool.

View attachment 76089.
Click to expand...
I'm a sucker for tools. Some are really useless and some are really helpful.

I rechecked my slack tonight in different spots and they all seem to be reading within the range.
Maybe my chain was a little looser before my tire change as it seems a little on the tighter side. I will recheck tomorrow when I get back from a ride.



Thank you for the input. I was doing it correctly or at least very close to correct.
 
Ash said:
At the other extreme, my XSR900 owner's manual calls for 5 to 15mm (.20 to .60 inch) of slack, which is crazy tight and very hard to eyeball. I'm not sure that I believe them, but it even has in bold text that more than 25mm of slack can damage the frame and swingarm.
Click to expand...
For small amounts of slack, you can get your eye level with chain and then push chain up (or down), lock your eyes onto the bottom (or top of chain and then reverse the pressure. It will be easy to see if slack is 1/2 link height, whole link height or much more than a link height.
 
Ash said:
For what it's worth, the tech inspectors at track days around here like to see 40 or 50mm of slack on my bike, which is about double what the factory recommends. It's generally better to be too loose (within reason) than too tight.

At the other extreme, my XSR900 owner's manual calls for 5 to 15mm (.20 to .60 inch) of slack, which is crazy tight and very hard to eyeball. I'm not sure that I believe them, but it even has in bold text that more than 25mm of slack can damage the frame and swingarm.
Click to expand...
That’s possible, chains can operate with a lot of slop, you can probably go 2” without risk of spitting the chain. ATVs go about that much.

The limiting factor is clearance. I have couple of 45 year old Yammies that have 1/2” slack - any more and the chain can contact the chain case. In your case, deceleration probably causes clearance issues as the slack transfers to the top side of the chain.
 
Ash said:
For what it's worth, the tech inspectors at track days around here like to see 40 or 50mm of slack on my bike, which is about double what the factory recommends. It's generally better to be too loose (within reason) than too tight.

At the other extreme, my XSR900 owner's manual calls for 5 to 15mm (.20 to .60 inch) of slack, which is crazy tight and very hard to eyeball. I'm not sure that I believe them, but it even has in bold text that more than 25mm of slack can damage the frame and swingarm.
Click to expand...
With those guys I set it loose, and then readjust it to where it should be after tech.
 
oioioi said:
Can I get some guidance or confirmation on proper chain slack, or the proper way to measure the slack.
My service manual calls for 20mm-30mm of slack. It says to do it while the bike is on the side stand and NOT centre stand. Fine I got that.

I understand the slack needs to be measured at the centre point of the swing arm. This happens to be roughly at the point where the chain guard ends on the bottom side of the swing arm.

Should the lowest point of the slack be measured when the chain is in its natural position or should I be pressing it down as far as possible and consider this to be the lowest position.
As for the highest position, I am pushing the chain up to is furthest position.

View attachment 76067

The picture above has an an arrow indicating the slack of 20-30mm. I am understanding it as the dotted lines being the slowest and highest points that the chain can reach. Both being above and below is natural place.

I have watched a few videos and read some threads and they all seem to be unclear on this. The difference is probably minimal, therefore it may not matter but I want to be sure I am doing it right.

For the record, I am using a Motion Pro Slack Setter Tool.
So far I have applied the tool to the chain/swingarm, pushed the chain all the way up. Note the measurement off of the scale. Then press the chain all the way down, note the measurement and subtract the two to get the difference as my slack.
Click to expand...
When it comes to V-Stroms - I used to always default to the Godfather's advice.
I use my eyeballs only, since I don't have a ruler or fancy tool.

1759066032424.png
 
shanekingsley said:
When it comes to V-Stroms - I used to always default to the Godfather's advice.
I use my eyeballs only, since I don't have a ruler or fancy tool.

View attachment 76093
Click to expand...
Hmmm. I’m going to respectfully disagree with the godfather on one point - CENTER stand. It matters.

The geometry of most swingarms is such that without load on the rear wheel (on CENTER stand) the rear axle drops which will lengthen the distance between sprockets, this takes slack out of the chain. If you set the chain to spec on the CENTER stand, it will be too loose once you drop the rear wheel to the ground.

Always check chain slack on the side stand.
 
Belts run under tension.

Chains require slack. If the chain is tight at any point in the suspension travel, then it is not slack enough. Tension shouldn't even be in the chain vocabulary.

Unless you a have a fancy offroad bike that has the drive sprocket on the same axle as the swingarm, the chain slack will change as the suspension moves up and down. It usually gets tighter as the suspension is in jounce and slacker as the suspension rebounds.

Step one is to make it possible to align all 3 of these in a straight line:

1. Front sprocket rotational centre
2. Swingarm pivot dead centre
3. Rear axle rotational center

When everything is in a straight line, then the chain is at its point of minimum slack. This is where you follow the diagram on the box the chain came in and set the slack to that ¼" or whatever it says.

The bike I ride is notorious for looking like the chain is about to fall off, but when the suspension is compressed enough to line up the 3 axes, the slack disappears. If I set the chain with not enough slack, the suspension will bind up before the spring and shock can do its job. It's literally using the output shaft and the chain as a travel limiting strap.

If you don't have enough slack, you can damage countershaft seals, bearings, the output shaft splines. This damage takes a long time to cause a problem somost people don't make the connection.

Some bike designs might make it impossible to line up all three... I don't know. That's how it's been for all the bikes I've owned and worked on.
 
sburns said:
Whoa that belongs in the Tool tag thread, no idea what that's for. Sprialgraph?
Click to expand...
Good guess, but your not even close.
 
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