Probable dumb question - Chain tension?

[ftl900]

I've been a street geek for awhile now, and many moons ago when I last rode dirt, I don't recall the chain being so slack.

Lately it seems like dirt bikes have 3 or 4 inches of slack- like the chain is just riding up the top of the swingarm.

Whassup with that?? I have always had at most an inch to an inch and a half of slack in my street bike chain, and I like it fairly taut.

Am I wrong, or is it everybody else???

Thanks!!! [/i]

[crazyaboutriding]

when on a stand (back tire off the ground like when taking off the back tire) there should be just about 1 and a half inches. one inch is about too tight.

[kdxquebec]

Because of mud and big swingarm travel I think...The chain becomes tight with sand and mud.

This is a beginning eh? others will continue the list

[m0rie]

All I have to say is if it looks like a KTM chain its way to damn loose!

[motorhed220]

sit on the bike dude, and you will see the chain tighten right up, this is cuz the whole bike is underload, you should be able to fit three fingers high along the chain until just before the rubber guard on the swingarm...thats what i have and it works like a charmp, cracking weelies and hookin up like mad, and i have never once lost the chain on this setting

[ftl900]

Thanks a bunch... I'll readjust it just a tad looser then.

Is this the part where I am supposed to ask which is the best motor oil to use???

[Colorado Mike]

Keep an eye on your chain slider too, they are a wear item, and you don't want to start sawing through the swingarm.

[skipro3]

Why dirtbike chains are adjusted loose:

The radius of the swingarm travel is from the swingarm pivot bolt. But the chain's arc is from a more forward position: the front sprocket. As the swingarm travels through it's range of motion, the distance from the rear axle to the front sprocket gets further apart, and causes the chain to tighten up. On a street bike, the travel of the rear suspension is only 5 inches or so. An inch or two of slack in the chain is plenty. But on a dirtbike, the rear suspension travel can be over 12 inches. As that swingarm moves upward, the distance between sprockets gets larger and the chain gets tight. It therefore needs more slack at rest than a streetbike. To test this, place your bike on a stand and disconnect the bottom shock mount. Then lift the rear tire up as if the bike was compressing it's suspension from a big hit. You can see that the chain gets snug. In fact, if the chain isn't set with enough slack, the chain will prevent the bike from utilizing it's full travel length. This will cause the chain to streach as well. There are 2 main problems with a loose chain set up to provide enough length for full suspension travel; it can ride across the top of the swingarm and wear it out, and it could become derailed from the sprocket easy. To overcome these drawbacks, a chain guide is installed to the swingarm to keep the chain on the sprocket and a hard rubber chain slide is installed on the swingarm so the chain won't saw through the metal. Also, there's a set of chain rollers that keep the chain from setting up an ocillation at higher speeds.

Hope this helps.

[Colorado Mike]

I remember a long time ago, back when the rocks were still warm and works bikes were first getting outrageously long travel suspensions...(like 5" or so). One outfit got the idea to put bearing on the swingarm, and mount two side-by-side sprockets on it. one of these was connected to the CS sprocket via a short chain, and the other drove the rear sprocket with another chain. This exercise in engineering won them a constant chain tension at the expense of more frictional losses, added complexity, and weight.

Sliders good.

[skipro3]

If the chain could be kept parallel to the swingarm, then the chain tension would not change (as much) during swingarm articulation. A device called an A arm used to be a pretty common aftermarket add-on. It required a longer chain though. That was about mid 1980's.

[ftl900]

Dang, SKIPRO3... thanks for the primer!! Now I understand perfectly!

[skipro3]

If the swingarm bolt was through the countershaft sprocket, you could run the chain pretty snug, allowing only for temperature changes in the metal.

But it isn't so don't.

[Matt-itude]

someone has a chain tension fettish.

[Rhodester]

.....adding to the point that 'ski' said....if you look at the chain tension when the countershaft, the swing arm pivot, and the rear axle are perfectly lined up (compress the suspension to do this), you'll have the chain at it's tightest point in the suspension travel. Every other position in the suspension travel will be a shorter overall distance from the countershaft to the rear axle and therefore will have looser chain slack. You can always compress the suspension to this tightest point to set your chain slack if you want to. Sometimes I'll do this just to double check and make sure the chain is not too tight at that point so that no binding and parts breaking happens. I've seen some real stupidity out on the trail over this issue (sprockets with half the teeth broken off, etc.).

[canyncarvr]

There are rules...and there are damn rules...

One of the 'rules' is, believe nothing of what you hear and half of what you see. An addendum for the fairly literate amongst us (are there any??)...believe not a whole lot of what you READ, neither.

1. I spent the afternoon trying to adjust the chain slack on MY streetbike. I never found the dang thing!! And...no....there's no RUBBER BAND attached to the rear wheel, neither.

For starters...according the jenuwine service Manuel (that's the guy's name that works on my bike. Heck...no AMERICAN will do the job!!!):

Put your bike on the side stand. If your suspension is adjusted correctly, that means your shock will be topped out..all of your free sag will be gone.

Measure the distance from the swingarm to the bottom of the extended (hold it up!) chain at the end of the chain slipper. Spec is 55-65mm. In the real world that means 2.165-2.559".

Free sag being gone, you will have the same situation with the bike on a center stand, rear wheel off the ground. **edit** Unless your unitrack kuckle (rear suspension) is trashed.

If you're running 1 1/2"...it is too tight!!

Now then...for the best oil.....

[m0rie]

All this talk of chains and we'll be lucky if Jaybird doesn't appear here to enlighten us all with the proper methods for all things chain related...

[skipro3]

Jaybird is a complete prick.

[KDXer]

Carn Jerry, tell us what you really think...

[skipro3]

Inda would have to step in and strike most of it. Probably ban me too.

[Indawoods]

I learned to stop responding to threads he was responding too. Probably added a few years to my life.