Drive chain slack adjustment correction

[DavidS]

I think folks may be over thinking this. Adjust the chain so that there is about 1-1.5 inches of slack (after the rear wheel nut is tightened) and go riding......

[howie333]

Well, so far so good.  My free sag is less than 10mm, but preload is @30% of shock travel @ approx. 39mm. Works well. Ii strapped bike down to my weight on seat, and set chain to approx. 1" (25mm) slack. loose when on side or center stand, but runs fine. I figure best to set common chain slack for when in riding position, then record chain slack then on center stand and use as reference for general chain maintenance.   

[peteinpa]

13 minutes ago, howie333 said:

Well, so far so good.  My free sag is less than 10mm, but preload is @30% of shock travel @ approx. 39mm. Works well. Ii strapped bike down to my weight on seat, and set chain to approx. 1" (25mm) slack. loose when on side or center stand, but runs fine. I figure best to set common chain slack for when in riding position, then record chain slack then on center stand and use as reference for general chain maintenance.   

You CAN'T set your slack this way!

It's all great till you hit a bump, the suspension compresses, and the chain gets tighter!

If you want to be anal,   tie down the suspension till pivot, front sprocket, and rear sprocket are perfectly in line. Set about 1/2inch slack at tight spot in chain.

Put bike on centerstand with tiedown removed and measure slack. THIS  your new measurement to aim for.

OR....Just set for 1.5 inch on centerstand.

[howie333]

1 hour ago, peteinpa said:

You CAN'T set your slack this way!

It's all great till you hit a bump, the suspension compresses, and the chain gets tighter!

If you want to be anal,   tie down the suspension till pivot, front sprocket, and rear sprocket are perfectly in line. Set about 1/2inch slack at tight spot in chain.

Put bike on centerstand with tiedown removed and measure slack. THIS  your new measurement to aim for.

OR....Just set for 1.5 inch on centerstand.

Your method is probably right; my weight ends up to pull suspension for the swingarm pivot, front sprocket, and rear sprocket to be very near for that lineup, and only checking @ tight point of chain; still 1/2 slack may be too tight. I have approx. 1.5" or 35mm slack when on centerstand now. If those drive points didn't line up; it may be OK if I rarely or never change bikes load (luggage or passenger).   

[Lone Wolf]

On 2/20/2023 at 5:43 PM, manimal said:

... chain slack varies as you rotate the wheel.  The best theory I've heard regarding this phenomenon is that the rear sprocket is off-center, creating a high spot, and a low spot 180deg opposite (with some variation due to tolerances in the chain bushings/pins). 

It's not the sprocket, it is the 2nd thing you mentioned about the chain.

If you put on any brand new sprocket and chain, it will be consistent throughout and have zero tight spots. So it isn't an off-center sprocket, that would be poor machining, and just doesn't happen.

The cause for tight spots, usually on a well used chain, can be isolated links that are not moving freely and uneven wear for whatever reason (lord knows after 10,000 miles). And it is going to be a small difference, nothing huge - but conventional advice is to "find the tight spot" and adjust for that to be your slack.

Unlike high school, there may not be a tight spot...

[TomTracer]

21 hours ago, DavidS said:

I think folks may be over thinking this. Adjust the chain so that there is about 1-1.5 inches of slack (after the rear wheel nut is tightened) and go riding......

Think about loose vs tight, loose being better than tight. If the chain is so loose you can hear it slapping, its too loose. Too tight wears the rollers, and puts stress on the counter shaft/seals. Don't overthink adjustment, as mentioned earlier. 

[Brentinpdx]

I went and looked at the service manual for my FJ. I wonder if you are reading it right. The diagram shows the measurement to be 5-15 mm of deflection from center. Not from the bottom of the swing arm.  My FZ1 was to measure from the bottom of the swing arm, a buddies Ninja is the same. The FJ is from the chain in a relaxed position with the swing arm in its lowest position on the center stand.

The instructions in the manual say that it should never be more than 25mm.

[howie333]

16 hours ago, Brentinpdx said:

I went and looked at the service manual for my FJ. I wonder if you are reading it right. The diagram shows the measurement to be 5-15 mm of deflection from center. Not from the bottom of the swing arm.  My FZ1 was to measure from the bottom of the swing arm, a buddies Ninja is the same. The FJ is from the chain in a relaxed position with the swing arm in its lowest position on the center stand.

The instructions in the manual say that it should never be more than 25mm.

Manual states Place the vehicle on the centerstand so that the
rear wheel is elevated.
2. Shift the transmission into the neutral position.
3. Check:
• Drive chain slack "a"
Out of specification ~ Adjust. 

If that's so, adjusting chain to 5-15mm w/swingarm down (on centerstand); bringing rear wheel back up in alignment w/ swingarm and sprockets would tighten chain to point of either chain breakage or damage trans bearing or worse. it's too hard to assume by that diagram given if we are seeing that swingarm lined up w/ anything, we have just a description and measurement that could not be correct.

 

Edited February 25, 2023 by howie333

[betoney]

9 hours ago, Brentinpdx said:

The instructions in the manual say that it should never be more than 25mm.

If you do a search, it has been discussed many, many times over the years that the manual is wrong concerning chain tension and some excessive torque specs.

[howie333]

7 hours ago, betoney said:

If you do a search, it has been discussed many, many times over the years that the manual is wrong concerning chain tension and some excessive torque specs.

I know;  and  I guess I'm just going w/ the ~25mm @ drive line alignment, or w/ my weight on seat which is very close; then take  measurements when on center stand for next slack check. I could be off. opinions are always appreciated.

Thank You...   

[KrustyKush]

On my 21 T9GT I’m past 15k miles on the original chain. It still is in great shape. I don’t fuss over the chain much. It has needed a bit of tightening maybe 3 times since I bought the bike new. I set tension as the book sez, 40-45mm slack at midpoint between sprockets, a point specified in the book as a certain distance from the end of the guide on the swingarm. Once the chain is broken in it should hardly ever need any further adjustment before it dies. I check tension once in awhile during chain lube sessions. I push on the chain at the midpoint, bike on center stand, and if it just touches the rubber guide, it is good to go. The fact that I am now closing in on 20k with this chain proves to me that this method is good. 

[howie333]

2 hours ago, KrustyKush said:

On my 21 T9GT I’m past 15k miles on the original chain. It still is in great shape. I don’t fuss over the chain much. It has needed a bit of tightening maybe 3 times since I bought the bike new. I set tension as the book sez, 40-45mm slack at midpoint between sprockets, a point specified in the book as a certain distance from the end of the guide on the swingarm. Once the chain is broken in it should hardly ever need any further adjustment before it dies. I check tension once in awhile during chain lube sessions. I push on the chain at the midpoint, bike on center stand, and if it just touches the rubber guide, it is good to go. The fact that I am now closing in on 20k with this chain proves to me that this method is good. 

I assume 40-45mm slack measured while on centerstand. that's approx. what I measure w/ my 2017 fj-09. 

[nomikem]

1 hour ago, Ziggy105 said:

Excellent choice.

You really didn't want the Beamer.

A long time ago when I first started riding, a mechanic told me that "a loose chain is a happy chain". That has worked for me for 44 years.

[Brentinpdx]

I did a fun ride this weekend and it was full of bumps, twists, and turns.  As I was leaning the bike through some of the twisties I could feel the rear kind of tighten while going over uneven pavement. It felt weird . I got home and checked the chain slack. It was at 25mm with the bike on the center stand and the swing arm hanging. I measured straight up just in front of the rear tire and made sure the upper portion of the chain stayed on the guide. Based on everything I have read here, that is too tight when the swing arm is in full compression. I adjusted it up to 30mm. As I spun the rear wheel it made almost no noise and seemed to spin longer.