Shazaam's Tech Library - Chain Adjustment

A useful technical article from guest contributor Larry Kelly of San Diego CA (aka Shazaam!).

As a chain wears it stretches and gets longer, but it doesn’t necessarily stretch the same amount at each and every link. So, in order to adjust the chain freeplay you first need to find the portion of the chain that has worn and stretched the LEAST. You need to rotate the chain and check its slack in at least three different sections.

Every 600 miles or so, put the bike on a paddock stand and find the tightest section of chain (least droop between sprockets) by turning the rear wheel in neutral. Measure the amount it droops from the bottom of the swingarm to the lower edge of the chain. The droop will be largest at a point equidistant between the sprocket centerlines (see swingarm label.)

If this measurement is LESS THAN one inch (25mm) the freeplay should be increased. The concern here is that the chain is adjusted too tight rather than too loose. A too-tight chain will lock-out your rear suspension movement and load the chain in excess of its tensile load rating. Drive chain tensile ratings are matched to the bikes power by the manufacturer, but this tension can easily be exceeded if the chain is installed too tight. Specifically, a number of chain failures can be traced to chains that have been adjusted too tight.

Just as a reminder, before you adjust the chain freeplay, measure and record your rear ride height so you can reset it.

Ducati's specification of ONE INCH MINIMUM is directed at preventing the chain side-loading the transmission output shaft bearings when the swingarm moves upwards during the bike’s acceleration, or after hitting a bump.

The chain is as tight as it can get when the centers of the front sprocket, swingarm pivot, and rear axle are all in a straight line. This only occurs when the bike is dynamically or heavily statically-loaded. The slack adjustment spec on the swingarm plate assumes that the bike is unloaded.

Even at one inch it’ll still be tighter than many other manufacturers' recommendations. Note that Ducati doesn’t specify a maximum distance, so a 1-1/2 inch droop here would not be excessive. Not having enough freeplay is a recipe for chain failure.

This is also the time to clean and inspect your chain for any links that are unusually stiff, which indicates binding from lack of internal lubrication or corrosion caused by link o-ring failure. Also check for any link side-plate damage caused by road debris that may have gotten wedged between the chain and sprocket.

Finally, keep a trending record of any adjustment that was made.

A chain should be replaced when it has stretched excessively. Each link in a new 520 or 525 pitch chain measures 15.875mm (5/8-inch) so 16 links will measure 254mm. When a 16 link section of an o-ring chain has stretched to 257mm (under a 20Kg/44lbs load) it needs to be replaced before it fails. When a Ducati chain snaps, it will often wedge between the drive output sprocket and the engine case, destroying the case and hopefully not locking the rear wheel in the process.

Chain stretch across 16 links can be checked with calipers by first placing the transmission in gear and then rotating the back wheel so as to tension the upper strand of the chain.

info taken from this thread from DSC forums

The eccentric hub should nominally set the axle between the 4 and 5 o'clock position (viewed from the left side). But you can also obtain the proper chain tension when the eccentric is in the wrong position - with the axle set between the 1 and 2 o'clock position. If it is set higher than the 3 o'clock midpoint, there will be inadequate clearance between the lower run of the chain and the swingarm and the rear ride height will be too low. You'll also have inadequate clearance between your rear tire and hugger clearance so it'll rub.

Info taken from this thread from DSC forums

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