Motorcycle chain tension vs suspension deflection

[bob prohaska]

I'm getting puzzled about setting chain tension on an '01 SV650S.

The manual says 20-30mm slack _on_the_side_stand_ but that setting
causes a cyclic growl at low speeds, say 35 MPH. Higher speeds
seem to quiet down.

To me, the sound suggests a tight chain, but it's unclear to me if
the chain gets tighter or looser as the rear suspension compresses.
The suspension is stock, I weigh less than 150 lbs.

At one point I dismounted the rear shock, raised the swingarm to
maximum sprocket spacing and set the slack to zero. On the center
stand the slack measured about 40 mm, which seemed quieter.

After a bit of riding I started to hear noises I didn't like. When
I checked the slack on the sidestand it seemed greater than 40 mm
and the chain could touch the centerstand mount, obviously not good.

So, I'm back to 25-35 mm slack on the sidestand and wondering
what's correct. I don't like the sound, but if it's normal
I'll quit worrying about it.

Thanks for reading,

bob prohaska

[Mark Olson]

Post by bob prohaska
I'm getting puzzled about setting chain tension on an '01 SV650S.
The manual says 20-30mm slack _on_the_side_stand_ but that setting
causes a cyclic growl at low speeds, say 35 MPH. Higher speeds
seem to quiet down.
To me, the sound suggests a tight chain, but it's unclear to me if
the chain gets tighter or looser as the rear suspension compresses.
The suspension is stock, I weigh less than 150 lbs.
At one point I dismounted the rear shock, raised the swingarm to
maximum sprocket spacing and set the slack to zero. On the center
stand the slack measured about 40 mm, which seemed quieter.
After a bit of riding I started to hear noises I didn't like. When
I checked the slack on the sidestand it seemed greater than 40 mm
and the chain could touch the centerstand mount, obviously not good.
So, I'm back to 25-35 mm slack on the sidestand and wondering
what's correct. I don't like the sound, but if it's normal
I'll quit worrying about it.

My position has always been that you always want to maintain a non-zero
amount of slack at whatever swingarm position results in the rear
axle being the furthest away from the countershaft, with the chain
in its tightest position. Since chains wear unevenly, this can mean
that at its loosest point, a worn chain may result in too much slack
when the swingarm is at a low point.

My guess is that your chain is unevenly worn. I tend to replace chains
when they are still technically servicable but vibrate from uneven
wear. I'm also a big believer in replacing chain and sprockets as
a set.

[chrisnd @ukrm]

Post by Mark Olson
My guess is that your chain is unevenly worn. I tend to replace chains
when they are still technically servicable but vibrate from uneven
wear. I'm also a big believer in replacing chain and sprockets as
a set.

+1

Chris

[bob prohaska]

Post by Mark Olson
My position has always been that you always want to maintain a non-zero
amount of slack at whatever swingarm position results in the rear
axle being the furthest away from the countershaft, with the chain
in its tightest position.

Agreed entirely. I thought that's what I was doing by setting the
slack (tight but not too tight) with the swingarm raised to what
seemed like the tightest elevation.

Post by Mark Olson
Since chains wear unevenly, this can mean
that at its loosest point, a worn chain may result in too much slack
when the swingarm is at a low point.
My guess is that your chain is unevenly worn.

This is a novel proposition to me. There's a definite variation is
chain slack as the wheel rotates, but I always attributed it to
eccentricity of the sprocket, not the state of the chain.

Post by Mark Olson
I tend to replace chains
when they are still technically servicable but vibrate from uneven
wear. I'm also a big believer in replacing chain and sprockets as
a set.

Agreed on the replacement as a set policy. The present chain is original,
with less than 30k very easygoing miles on it. By "lift off the sprocket"
testing the chain is essentially unworn, revealing no more than a tenth
of a tooth on the rear sprocket.

Being an o-ring chain it hasn't been lubricated very systematically.
Perhaps I should start there, then check whether the chain slack cycles
with wheel rotation or chain rotation.

Thanks for writing!

bob prohaska

[Mark Olson]

Post by bob prohaska
Being an o-ring chain it hasn't been lubricated very systematically.
Perhaps I should start there, then check whether the chain slack cycles
with wheel rotation or chain rotation.

You could knock me over with a feather if it turns out to be the
sprocket being out of round. It's been my experience on every chain
driven bike I've owned, that the chain wears unevenly, and the more
it wears, the more uneven it gets.

I used to have a Scottoiler on my '01 SV650S. It was brilliant. If I
get another one[1], I'd definitely fit it with the touring reservoir.
Multiple benefits- chain & sprockets last longer, longer intervals
between adjustments, and the tiny bit of oil mist that makes it to
the inside of the rear rim makes cleaning a snap.

[1] My KLR650 has a Loobman manual oiler. Crude in comparison to the
Scottoiler but still much better than no oiler.

[bob prohaska]

Post by Mark Olson
You could knock me over with a feather if it turns out to be the
sprocket being out of round. It's been my experience on every chain
driven bike I've owned, that the chain wears unevenly, and the more
it wears, the more uneven it gets.

Please consider yourself standing securely 8-)

Lubing the chain very lightly (ATF diluted with kerosene)
markely improved the chain and the noise.

Unfortunately, in the course of looking around I discovered
the rear brake pads are down to metal on rotor. No real damage,
but the bike's idle until it gets new pads. Very surprised I
didn't hear it.

Thanks for writing!

bob prohaska