The Clutch and Final Drive

My clutch push rod seemed to be welded to the pressure plate and the clutch plates were either distorted (metal) or worn down (cork). So, off to Stucchi went the emails and a month later 5 new bronze disks and 5 steel plates arrive.

The pictures above showing the various steps to assemble the clutch are self explanatory. The primary drive gear has two dogs in the front that engage with corresponding slots in the flywheel hub boss. These should be a tight fit with no movement. The slot key that sits in the crankshaft and retains the primary gear should sit in its slot with no play (lightly forced into the slot).

The helical spring on the crankshaft should be 31-32mm long unloaded and should take a load of 65-70kg to compress it 19.5mm. If you can compress it 19.5mm with a load of less than 55kg replace the spring.

The 5 bronze plates are 1mm thick and must be replaced when they become less than 0.8mm thick. The 5 steel disks are 1mm thick and usually do not wear. The 2 clutch lining plates are 3mm thick and must be replaced when less than 2.4mm thick.

The ID of surface for the 25 clutch rollers on the larger helical gear must be 54.7mm +0+0.019mm while the corresponding OD of the surface on the fixed clutch hub should be 42.7mm -0.025mm-0.050mm. After coating the groove on the hub that is the race for the rollers with grease I laid the 25 rollers on and slid the large helical gear over them.

After mounting the bronze and steel disks in the order shown in the photo/parts diagram I screwed in the clutch push rod from the other end into the final pressure plate till one thread protruded from the disk.

Moving to the RH side, I checked that the clutch push rod was straight and the threads in good condition. There is a small radial bearing (Table 7, #32) that needs to be in good condition. A tempered cap (Table 7, #31) sits on this bearing. The bearings will wear a groove in the outer periphery of this cap. The manual says the maximum depth of the groove relative to the center of the cap cannot exceed 0.8mm.




There are three springs on the RH side: the innermost thin wire spring acts on the kick starter idle gear. New and unloaded, it should have a length of 20-21mm and 1kg should compress it by 10mm to a length of 10-11mm. This rests on a disk that should be free of any grooves from the spring digging into the surface. The frontal ramps on the kick starter idle gear (#40) should be vertical and square and should mate cleanly with the corresponding ramps on the kick starter ratchet gear.

The two larger outer springs provide the pressure for the clutch. Both of them should measure 45mm when new and unloaded and need 155kg to shorten it by 20mm to a compressed length of 25mm. If the pressure required to do this is less than 140kg replace the springs. Tighten the knurled disk till the length of the compressed springs is 27.5mm. You should be able to rotate the whole assembly with your hand making sure the springs are centered. With the spring at this length and about one thread protruding from the last pressure plate on the LH side of the engine, I was ready to finish the final clutch adjustment on the RH side.

After assembling in the order shown in the photo, I mounted the aluminum cover plate with the vertical clutch lever. The max allowed difference in diameter between the pivot boss on the lever and the pivot itself cannot exceed 0.20mm.

I connected the vertical clutch lever with the clutch cable to the clutch lever on the handle bar. When the handle bar lever is fully pulled in (clutch disengaged) the outer disk should not get pushed beyond the four jaws of the fixed clutch hub or protrude beyond the face of the helical gear. The various adjusters for the clutch cable can be loosened or tightened. The vertical clutch lever acts on the clutch pressure rod via a rounded , tempered tip of the screw that goes through the lever. When new, the tip of this tempered hemisphere should extend 3.5mm beyond the plane of the lever. I tightened this screw till it put pressure on the cap but yet I could rotate the cap with my fingers (the manual recommends a clearance of 0.20mm between the tip of the adjuster screw and the cap that sits on the radial bearing).

After racking up some miles, oil collects in the clutch case and the clutch starts to slip. The oil needs to be drained and the plates flushed clean. See the section under the Oil Pump for more detail.

I carefully closed the LH side primary side cover by pressing in the cover against the pressure of the spring behind the smaller primary drive helical gear and tightening all 6 screws equally to prevent the spring pressure from distorting the aluminum cover.

The kick starter was missing on this bike and so a new one came from Stucchi. You need to make sure that the initial point of contact on the kick starter quadrant is square to the kickstarter ratchet gear. The kickstarter shaft extends through the engine terminating in a nut and washer that is a loose sliding fit against the engine case. There seems to be a strange hole at the LH end of the kickstarter shaft but its purpose is not clear.



I used for the final drive chain a Regina 520 non-O ring chain from Stucchi. I had an O ring chain but it was too wide to clear the space between the output sprocket and the crankcase. The chain was adjusted for about 25mm movement when the rear axle, swingarm pivot are in a straight line - max of the arc of travel of the swingarm. The manual also gives a max movement of 40mm at the center of the chain when the bike is on its center stand. Either way, with a normal complement of riders on the bike the chain should not be too tight.

The manual specifies the following method of determining the max length of the chain before replacement. Grip the chain in a vice and stretch it so that the rollers pull against each other. Measure the pitch of the chain (distance from the center of a roller to the center of the adjoining roller). This cannot exceed 16.04mm. This should be 15.88mm for a new chain. Obviously, you must measure at various links, a pretty laborious method! Maybe just easier to see if the max adjustment at the chain adjusters has been used up and the chain is still too loose at the midpoint of the swingarm travel.

The gear ratios are as follows:

Engine gear (50 helical teeth) to clutch gear (72 teeth) of 1.44:1
Gearbox output sprocket (15 teeth) to rear wheel sprocket (48 teeth) of 3.2:1
Gearbox internal ratios:
1st gear: 1:5.07 (final drive ratio is 1.44:1)
2nd gear: 1:2.84 (final drive ratio is 13.06:1 a huge drop which is offset by really blipping the throttle before pushing into second)
3rd gear: 1: 1.52 (final drive ratio is 6.99:1, another large drop requiring more blipping!)
4th gear: 1:1 (final drive ratio of 4.6:1)