A clutch damper is included in the drive train in-between the primary drive chain and the clutch. It is located under the right hand engine cover. It is designed to buffer rotation between the crankshaft and clutch/gearbox.
Special tools needed:
Alternator rotor removal tool (a long 16mm fine thread bolt)
Clutch damper spring compression tool (can make one from aluminium section)
Signs of clutch damper issues include roughness and knocking from the clutch area, particularly at low idle and during start.
Drain the oil and remove the alternator, rotor, kick start and right hand engine cover. You will see the primary chain and the clutch/damper assembly held by a bearing on a large bracket. Remove the 4 hex head bolts and slide off the bracket and bearing assembly. The clutch damper retaining circlip is now visible:
Remove the circlip and slide out the clutch damper, leaving the primary chain and sprocket behind. Once the clutch damper is out, the primary chain and sprocket can be removed. Be sure to note the number and positions of any shims and washers. In this case a 0.5mm shim was fitted between the sprocket and clutch
The damper fitted to early bikes (up to XS750-2D) (left picture, upper) has the primary chain sprocket held in place by a large circlip. There is a projection on the sprocket, which faces away from the clutch (right picture, left). Later types (XS750E onwards) have no circlip, instead the sprocket is held in place by a ridge on the damper (left picture, lower). The sprocket does not have the projection and is symmetrical (right picture, right).
A service bulletin warns against fitting the early damper to later engines, as the higher speeds may cause problems with the circlip (see technical service section).
Damper Inspection and Disassembly
The damper takes the drive from the primary chain on the outside of the unit (via the sprocket) and transmits it to the clutch via the three projections in the left picture below, which engage with the clutch basket slots shown in the right picture.
With a new damper, the hub with the three projections has no free play compared to the damper body. There should be significant resistance to rotation, as the spring comes into play. This unit has excessive free play (would move 30+ degrees with no resistance) and signs of damage to the teeth where it engages with the clutch basket. The clutch basket shows matching damage. Finally there is damage to the clutch basket fingers, but this may be unrelated to damper issues.
If the free play in the damper is excessive, your only option is to replace the damper with a less worn one. However, if the free play is slight, you can dismantle it further and do a repair that will extend the life a little.
You need to compress the spring so that you can remove the circlip. A tool is made from 20mm x 20mm aluminium section with 2 x M8 40mm bolts positioned so the threads are 78.5mm apart at the centres. The tool is best used in a large vice, but a large G clamp will also work. The threads push on the silver collar and allow the circlip to be removed. Then undo the vice and the spring assembly will come out.
Note the position of springs and shims again. The collar comes out after the circlip, followed by 4 spring washers. Finally a bearing comes out with a thick and thin shim. Note they are all shown upside down.
The thin shim on the left goes away from the clutch (next to the damper body). The 4 bevelled washers go together like this to create the spring. Tie the entire assembly together in the right order before leaving it!
Now you can inspect the damping mechanism through the six holes in the outer ring of the unit.
The spring pulls the inner hub away from the unit (to the right in the picture above), and the pins shown slide to the middle of the banana-shaped slots. Turning the inner hub forces the pins to slide up or down in the slots. The shape of the slots forces the hub to the left, against the spring. This is the origin of the damping effect.
In this case the pins and slots are badly worn. This allows the pins to move sideways in the slots, with no or little left to right movement (and hence no damping).
The inner hub is held on the unit by the pins, which have been drifted in. They are held in place by 3mm hardened locating dowels, which have no access from the rear.
Hence drill a 2mm hole in the outer hub opposite to each dowel (you can do this by eye, as it doesn’t have to be too accurate). After a mm or so, you will break out into the dowel drilling and can see the end of the dowel:
Now you can get a 2mm drift behind the dowels and tap them out. It should not take too much force.
The pins can be accessed from the 5mm holes opposite:
Place a 5mm drift or rod through the hole onto the back of the pin. Some good whacks with a 4lb hammer should force the pin out. It is important to keep everything in line to avoid bending the drift (vice just used for photo – actual drifting done on some wood on the floor):
If necessary you can enlarge the access hole to accept a larger drift. Once the pins are out you can remove the inner hub and see the dowel holes clearly:
This is how the inner hub engages with the clutch outer basket. It slides in and out with the damping motion.
The pins and slots are badly worn (see below). As the pin was slightly lower than the edge of the slots, most of the wear took place just below the edge, leaving a lip. The wear is only on one side of the pins, so they could be rotated 180 degrees and reused. However, there is no way to address the wear in the slots. The hub was never listed as a separate part by Yamaha and was only available as part of a complete damper assembly (#1 in the parts diagram).
Reassembly is the reverse of the dismantling procedure. However, a service bulletin and kit gives instructions how to take up play between the primary drive sprocket and the clutch basket. Assemble the sprocket onto the damper without the primary chain and fit to the clutch hub. Fit the circlip. Measure the gap between the sprocket and the clutch. Now dissemble and fit a shim from the service kit that best fills the gap. The kit comes with 0.4mm, 0.6mm and 0.8mm shims. In this case the gap measures 0.95mm and the original 0.5mm and 0.4mm shim were fitted. The kit also contains a revised primary chain, damper collar and some other parts.
This bracket already has the oil guide and oil retainer fitted: