The Bullet: Mysteries
& Myths -
Don't just love but get to know your bullet more
- by B. R. Gurunandan
Primary Chain Adjustment
Also called Clutch-chain, Double (duplex) Chain, etc.
This chain, running in an oil-bath, leads a charmed life compared to the rigours of dust, misalignments, and iffy lubrication the Final Drive Chain (FDC) has to brave. All the same, it wears out too, and needs a periodic check, and once-in-a-while, an adjustment. The adjustment of the Primary chain slack is by means of a slipper or pad which has a screw & locknut to set the position.
The primary chain drives the Clutch-sprocket from the crank-sprocket or engine-sprocket. Both these axes are fixed with respect to each-other, so the adjustment is straight-forward compared to the FDC. It is possible to misalign the FDC or adjust it in a wrong position of swing-arm or run-out, whereas the Primary Chain needs only the run-out to be taken care of. So, in principle, the Primary chain is just a special case of the FDC adjustment.
Here is how to go about adjusting the Primary Chain :
First, a test to see if it is really necessary. Because
a) it rarely is,
b) you have to open the oil-filled clutch-case to do this adjustment.
Open the oil-filling bolt or screw, and feel the tension in the chain.
If there is any slack, repeat test at different positions to see if it has been intentionally set loose ( at some positions ) to compensate for run-out. Of course, all this is done with engine stationary !
Remember also to decompress the engine while turning it for this test, or you may find some " tight spots " in the top-run while the bottom run is slack.
Assuming there is distinct slack felt in all positions in above test, the next step is to drain oil from and open the Clutch-case ( also called Primary-case or Chain-case ) Usually, the foot-rest has to be removed first, and sometimes even the brake pedal needs slackening ( I am describing the RHS gear-shift model )
The Clutch-case is fixed by a single bolt, and when you open that, almost
half a litre of oil will spill out from all along the length. So be sure to have
something big to catch the oil and try to slant the bike so that the exit point
The actual adjusting and locking is simple enough for anyone who has ventured so far, but sometimes there are questions...
* How much slack should there be in the chain ?
As in the case of the FDC, you should aim at zero-slack as long as you get no tension in the chain at any position with the engine off... which means, take care of run-out !
* What happens if the chain is left slack ?
There is a bit of clatter from the chain-case, and gear-shifting becomes more & more inconsistent.
* How do I tell when the chain is too slack ?
Mainly by feel, but loose chains vibrate or clatter on revving.
* What happens if the chain is too tight ?
There is fairly rapid wear in the system, and the danger of breakage.
* How do I tell when the chain is too tight ?
Mainly by feel, but tight chains often hum or whine on revving.
* When the chain is pressed, the clutch moves towards crank ?!!
Something is loose ! Check the tightness of hub-nut, but it is more likely that the clutch or gearbox-bearing is near the end of it's life. No, it won't explode or crumble, but do schedule a closer inspection and repairs soon.
* There is run-out in the Primary. What now ?
Adjust it in it's tightest position. If the runout was huge and objectionable clatter persists, determine if the run-out is from the crank-sprocket or clutch-sprocket. Usually, it is from the Clutch-sprocket. Unfortunate, because that is much costlier than the crank-sprocket. And it lasts an eternity, so you don't want to throw it away now.
* OK, can we run thru the whole process ?
We assume there was no run-out, or that the slack is far more than needed to compensate for run-out :
If there is runout, find the right spot for adjustment (described in FDC chapter) Unlock the adjuster lock-nut, and turn adjuster till excess slack is taken up.
Theoritically, you should do this with a hot engine. Because between the two axes is Aluminium, which expands more than the steel of the chain, and hence tightens the chain when hot. In practice, the effect of this factor is almost insignificant, but it is a good habit anyway.
Observe how far out the adjuster is. If it is out more than 5mm you need to check some things...
Check if the adjuster-pad is grooved.
Check if the chain and sprocket is worn out.
Replace what needs to be. Or shim the adjuster with a tyre-piece etc, so it's well & truely in. Tighten the locknut. Check for slack ( lack of ) in several places.
Ensure the O-ring is seated in it's groove all thru and fit the cover. ( If you have checked the Rotor-Stator gap already ) Check the cover-fitting bolt & washer are surgically clean or it will leak.
Fill in SAE-20 or any thin cheap oil till it overflows from level-plug.
Note : Hi-Quality, Hi-Additive oils are NOT called for in motorcycle clutch applications. They will actually reduce the efficiency & life of the clutch by inducing slipage. Here, we only want to lube the chain, not to make the clutch slippery.
By B. R. Gurunandan
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