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Chain Slack

39K views 59 replies 26 participants last post by  dandywarhol 
#1 ·
I just wanted to confirm with others that the chain slack range is 5mm - 15mm, as per Owner Manual. This seems like a very tight range to me. Obviously, if this is what Yamaha is saying is the range, then its the right range, but I'm wondering if the procedure for measuring the slack is "standard" or specific to this bike. I have always measure the chain slack by pressing up and down and measuring the distance between the high and low point at the top of the link. Is this how others are doing it as well.
 
#48 ·
waiting patiently for the member who sets his chain tension wrong to come back and say, "DO NOT SET YOUR CHAIN TENSION THIS WAY... "

Seriously though, setting chain slack is on par with checking tire pressure. Pull the chain up and down in the middle of the length between the two sprockets. Measure how far it moves... boom there's your chain slack. Don't worry about if the top of the chain moves or not, just make sure you're not putting uber force on the chain. Don't worry about whether the bikes on the side stand or upright, or if you're sitting on it... That will only make a difference of a couple mm. Remember it's always specified as a range for a reason. You don't want it too tight that the chain runs out of travel throughout the suspension travek and too loose that you risk the chain coming off the sprockets or slapping into your swingarm. If it's really that hard Motion Pro makes a tool for measuring chain slack and if that's still too complicated for you just take your bike to the dealer and tell them to check your chain tension for you.
 
#50 ·
But, astcyr, YOU didn't actually say, "What is the correct slack". But you gave a "general" concern that we all have. Don't mean to beat you my friend, but the whole idea of the post is WHAT IS THE CORRECT SLACK? My whole idea of sitting on the bike would give you a more precise slack measurement, during operation, with your weight on the bike. Even the guy on youtube(forget his name) that takes a screwdriver, and lifts the bottom chain till the top chain starts to move, and he says, "Thats your slack". To pull the chain down, with the chain weight already pulling the chain low and then pulling the chain back up and saying, there your slack, might be 100% correct. And the guy in the youtube video is a motorcycle track instructor. AND, he does it without sitting on the bike. Now this is MY BIKE only; When I take a measurement sitting on the bike(upright), and take a measurement just on the stand(without sitting on the bike), I have a 1/4" more slack measuring on the stand. I have to think that sitting on the bike, with my weight pulling the tire backwards, is a more realistic measurement.
Isn't what your trying to accomplish, is to see what the correct measurement(slack) is during operation, with your weight on the bike? Maybe both of our ways accomplish the same thing. From what I've read(manual), the 10-15mm; Most people have said that is too tight, and 20-25mm is the correct slack. I can't help but think, that out of ALL the racers/bikers that someone would post the CORRECT slack for such a simple setting. My brother says 3/4", and with his "decades" of racing/cruising (etc), I have to go with him.
 
#49 ·
A little too much slack is better than not enough, as far as I’m concerned. Here’s MotoAmerica Superbike racer David Anthony, setting a new lap record in Vegas. Quite a bit of chain slack there, and it doesn’t seem to be hurting anything... ?

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#54 ·
Chain tension depends on the relative centrelines of the gearbox sprocket, rear sprocket and swingarm pivot point. If the pivot point and gearbox sprocket were concentric then there would be no need for chain slack at all. The larger the distance from the gearbox sprocket to s/arm pivot means more slack is required as they are moving in dissimilar arcs. The 09/XSR swingarm pivot is very close to the gearbox sprocket therefore requires little slack.

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#56 ·
I've read all the posts (and many others on the topic) and here's THE facts from a scientific point of view which makes the manufacturer's figures right.
The handbook recommended 5 -15mm slack on the sidestand is correct by design, although personally, I'd err towards the 10/15 end.
I changed my rear suspension unit and moved the rear wheel more than through the arc the wheel makes on the bike and the difference was only a few mm.
The swingarm pivot/gearbox and rear sprocket are all in line when the rider sits on the bike (around 85kg) which means the chain CANNOT get any tighter than all in a straight line. If the slack is set to more than that you risk damage to components (as stated in the handbook) and sloppy gearchanges.
Part of the confusion over chain slack is which Yamaha manual you read. Earlier handbooks states to measure from the chain guard to the chain as a DIMENSION, whereas the later manuals state SLACK of the chain itself.
It's the same end result but people read it as SLACK which is wrong.
Here's the 2 handbook info versions. Both versions if followed to the letter give the same amount of chain slack.
Hope this clarifies things and those who still go down the "It was always an inch and a half in my day" really need to accept that frame geometry has changed for the better and chains require less slack.

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#57 ·
I can't believe I'm actually contributing to this thread. lol. This horse should have been beaten to death by now. But I have three points that I actually don't think have been mentioned.

Setting your chain to the too tight specs in the manual will result in two side effects, HEAT and NOISE. (Not to mention increased chain, sprockets and output shaft bearing wear but that's pretty obvious.)

Here's something you guys can do that will help show you the effects in actual solid test result numbers...

With your bike "cold" from sitting overnight, set your chain slack to the manual specs of 5-15mm. Heck to make the test more obvious set it to 6mm, that's within Yamaha specs. Now ride your bike on a set course, for a set length of time and try to maintain a set amount of throttle "aggressiveness". This is easy to do if you use your bike for commuting to work. As you're riding, notice the amount of noise coming from your drivetrain. Now here's the important part... as soon as you finish your route, use a temp gun to see what the chain and rear sprocket temps read.

Now set your chain to 30-40mm or so, let the bike again sit overnight, and repeat the test. If the test conditions are kept as close to the same as possible, I can just about guarantee you that the stock specs of 5-15mm will be louder and the driveline temps will be higher.

Here's the last tip I don't think has been mentioned. This chain slack tool makes checking your chain brainless and super easy...

BPA chain slack tool
 
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