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Discussion Starter #1
When I had my suspension components rebuilt the rear shock now has an adjustable length shaft and is longer than stock. I would guess about 1-1.5 cm. I believe this means that the little slack setting diagram on the swing arm is now not correct, and I should have more slack in the chain. I am not sure how much. Any thoughts on slack setting is appreciated. I tried to search the forum but all I get is "Your submission could not be processed because you have logged in since the previous page was loaded.", which is not true, and the search fails.
 

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Well, you can always manually check it as you do with bikes without markers.

Rotate your wheel through till you reach the tightest point in the chain. your chain will be tighter or looser depending on the rotation of the sprockets.

Once you reach the rotation which appears to have the chain the tightest, grab a pen and a small piece of carboard (like 8"x8") put it behind the chain (in the middle between sprockets) and mark a line on top of the lower run of the chain. Keep the cardboard in place and push down on the chain, it should be able to be moved down around 1.5" (34-40mm)

Some bikes indicate for different tightnesses, and thus it may need to be less or more slack (check owners manual it may spell it out there), but that's what I usually set mine to.
 

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I have absolutely no idea what cinko is on about but the tightness of a chain is set by the longest distance between the drive & driven sprockets. As the swingarm rotates around a different axis to the drive sprocket this distance changes. If you really want to do it correctly, take off your shock and move the swingarm up & down to find the max distance between the sprockets. At this point you want the chain to be more or less tight, you should be able to move it a few mm. Then reinstall your shock and measure the slack in the chain at the mid point for future reference.
ETA - not teaching you to suck eggs or anything, but trusting you understand this means raising bike, supporting it etc & then do the slack measurement when the bike´s back together & weight back on the rear wheel...
 

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Humm, will try to clarify.
Roll your bike rear tire around clockwise from the chain side. The top portion of the chain stays tight and the bottom has slack. Place a piece something behind the chain with markings, this can be a piece of carboard like I said, or a ruler or tape if you can get it to stay in place.

Push up firmly on the chain (slack side on the bottom) and continue to rotate the tire until you are at the tightest spot. Meaning the chain has the least amount of give/slack. That is the measuring point you are going to use.

Mark that point on the center of the bottom portion of the chain right between both sprockets.
This is the portion you will measure with the bike just sitting and the cardboard/tape behind, force the bottom chain up and down and measure how far it can go down an up, this is the slack. This total travel distance is what you are setting. The reason I use a piece of carboard is I just mark it with my pencil.

Whatever works for you.

This total distance is what I said should be around 1.5” But varies slightly per bike.
If it’s more slack than you want it to be, more the wheel back away from the bike slightly and check again; too tight, pull it back into the bike.

Here's a picture of the bike, and what I mean by the middle bottom of the chain. Sorry I'm at work and that's the clearest photo I had on my phone.

Duc Chain.png

And here's the slack that you should be measuring

cHAIN.png

Hope that's clearer... if not ...feel free to ignore this lol
 

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Discussion Starter #5
Thanks guys, I believe I understand both of your posts. CinKo, my original question was what the measurement, in your description 1.5 inches, should be. That is approximately what Ducati recommends with their sticker on the swingarm. However, since I increased the length of the shock, the resting distance between the sprockets has changed and gotten shorter. I was concerned that if I adjusted the chain to the same slack, then when the wheel was displaced while riding the chain could get too tight and put stress on the bearings.

The method suggested by Neil66 eliminates that possibility by ensuring there is some slack at the longest effective distance between sprocket centers; with the requirement that I disassemble the rear suspension with the bike supported. I was hoping someone would have an answer like "add xyz to Ducati's recommendation and all will be well", so that I didn't have to work :smile2:. If it is useful to anyone else, I support the bike with the suspension removed by putting a piece of rebar through the swingarm pivot and propping it on jack stands.
 

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I support the bike with the suspension removed by putting a piece of rebar through the swingarm pivot and propping it on jack stands.
Nice method. I might use that sometime soon.
 

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Cinko, as I see it you´re outlining how to measure the slack in the chain given no markers on the swing arm for slack... I don´t know any bikes that have an indicator for this, only stickers telling you what you should measure on the chain.

OP is asking, as his ride height has changed, the swing arm angle has changed so do the original Ducati specs for slack still stand?

I explained things from a first principal point of view to give an understanding of why we have a certain amount of slack in a chain. As the rear goes into bump, the rear sprocket moves rearwards & the chain tightens - manufacturers spec is for standard settings and will ensure the chain will not be over tight in bump.

OP - as you have raised the rear, effectively lowering the swingarm so decreasing the sprocket relative distance - your chain slack measurement should be slightly more than duc spec... how much I don´t know but my first post is the best way to make sure although you could do it geometrically if so inclined :D
 
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Neil66, after reading your response I think I through you off with the word "markers" I should have typed "holders"
I wasn't implying there were swingarm somewhere that had measuring tape sticking off of them. I meant having to manually set your chain as opposed to ones that auto held it at the correct slack mark.
 

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Discussion Starter #9 (Edited)
Nice method. I might use that sometime soon.
Remember to hold the front as well. I use a stand with a pin that goes into the bottom triple clamp. If you don't hold the front, the whole thing could collapse. I also bought a long adjustable length rod with heim joints on each end to replace the shock if it is necessary to wheel the bike around.
 

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The other option is to set your chain tension while at the stock ride height. Verify it. Adjust your ride height and now measure your slack again the same way as before. Verify it. This becomes your new slack measurement using the same methodology as before. The physics don't change, just the starting point of the does.
 

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The tightest point of a chain is when the centre of the drive sprocket, the centre of the swingarm pivot and the centre of the rear axle are all in line, as this is when the swingarm is at it's relative longest.
 

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Discussion Starter #14
Looks like a useful tool, provided you know what the slack should be set at, which was my original question.
 

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Lets make this as simple as possible. Get the fattest person you know to sit on the bike. Push the lower run of the chain up and down. As long as it moves you're good. Go ride.
 

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Discussion Starter #16
Now there you go... Science...:laugh: Unfortunately, I may be the fattest person I know. Even more unfortunately I may be heavy enough to make this work out.
 

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The tightest point of a chain is when the centre of the drive sprocket, the centre of the swingarm pivot and the centre of the rear axle are all in line, as this is when the swingarm is at it's relative longest.
That makes sense. It’s hard for me to read and think through what you say though because I keep getting distracted by your ‘tash! :wink2:
 
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The recommended slack doesn’t change just because the swing arm location changed a little. The spec for slack already took into account the range of motion available.
 
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