Chain drives, too tight, too loose???

Make sure you have the counter shaft, swing arm pivot and axle in a straight line.

Ever since the ATVs inception,  the chain drive (adapted from motorcycles) was and still is the most affordable, lightweight, most efficient and easily engineered type of final drive system.  Sure they get a bad rap for being maintenance hogs compared to other types of drive systems, but seriously how much time does it take to spray some lubricant on that chain every ride or so?  Well this article deal specifically about proper tension or tightness of the chain on your chain driven ATV.

Many people replace their chains prematurely because they have never had their chain in proper adjustment.  More often than not the chain is too tight causing undo stress on the chain, sprocket teeth, axle bearings and the counter shaft bearing and seal.  With proper adjustment you can extract the maximum life from all these components.

You can look in your owners or service manual for the proper amount of play, but real problem is where do you get that measurement and under what circumstances?  The manuals usually state that you take the measurement at the center of the chain up or down, but are generally ambiguous about if the ATV is on a stand or the ground under its own weight.  What follows is the procedure to find the proper measurement for YOUR specific machine, regardless what the manual says.

Notice on a 24" shaft to shaft bike the proper tension is .24" up or down from the centerline of a taught chain.

How the stated measurement in the manual is ascertained is the engineer measures the chains free play when the position of the swing arm, swing arm pivot and counter shaft make a straight line.  The chain will always be the tightest at this point in the arc that the axle moves.  The actual figure will always be between 1%-3% of the total length between the counter shaft and the center of the axle.

The following procedure will outline how to arrive at a measurement that you can use when the bike is on the ground under its own weight.

1. You must remove the shock to properly ascertain the proper adjustment stated above.  So while your at it now would be a good time to grease up those shock and suspension bearings and bushings.

2. With your machine on a stand or jack so the swing arm can be moved freely up and down.  Place another jack or blocks of wood under the swing arm until the axle, swing arm pivot and counter shaft line up in a straight line.

3. Measure the distance between the counter shaft and axle best you can.  Now if you were not asleep or wearing a dunce cap in math class, some simple math will be needed.  Take your measurement and multiply it by .02 (that is 2% in decimal form in case you slept through that too).  In the example above, 2% of 24″ (the distance between the two shafts) is .48″.  Dividing by 2 gives you the distance of the chain slack up or down, in our example .24″.

4. Adjust your chain adjuster on the axle (an eccentric on some machines) while having a straight edge on the chain long enough to span from the counter shaft sprocket to the rear sprocket.  Adjust until you have the measurement you came up with in step 3 in the center of the chain.  Tighten the axle nut or adjusters and recheck as things tend to move a bit when you tighten them up.

5.  Now that you have the proper tension set at the most taught spot in the suspension arc.  Replace the shock and put the machine on the ground.  Now your chain will be tensioned properly.  BUT WAIT!!! your not done!

6. To keep from having to remove the shock each time you want to check or adjust the chain, build yourself a GO/NO GO gage out of a block of wood.  Mark a position on the top of the swing arm where you will always take your measurement.  A good place is just at the end of the chain slider.

7. Measure the distance from the top of the swing arm to the underside of a link on the chain while holding the chain taught(up).

8.  Take a block of wood and make an “L” shaped notch that is the exact dimension you measured in step 7.

There you have it!  An easy way to check to see if you chain is out of adjustment without having to remove your shock every time.  And now you can rest assured that your chain and sprockets will last as long as possible.

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