In basic concept the drive did not change from the first production T150 to the last T160. The connection between crankshaft and clutch input shaft was by chain, where a shock absorber was always used. The chain tension was always adjustable with a form of slipper tensioner. However the detail variations are legion. I intend to look at three areas in detail, giving a resume of the changes involved, and some “hints and tips”
Firstly, Chain Tensioner Arrangements. The very earliest Triples used a twin blade system, adjusted from the front of the chaincase. The tensioner rod was allowed to float around the front split spindle. As the lower run of the chain is always travelling “backwards” it was obviously thought that this tensioner mechanism would lie quietly in the bottom of the chaincase. This version of the mechanism was soon modified, and an eye-bolt was added, with a modified rod, to tie down the rear of the mechanism to the outer chaincase. It is easy to spot a very early outer cover, if it has not been modified, as there is no nut (1/4 UNF thread, 7/16AF spanner size) underneath it. To locate this fitment, look underneath the outer chaincase at about 7o'clock, sighting the centre of the shock absorber unit. Early cases can be modified by milling a small internal platform for the head of the pillar bolt, and spot facing a seating for a washer under the nut. There was no change to the casting of the outer chaincase in production, just this machining change.
On a different tack for the moment, the very earliest outer chaincases also used a clutch adjustment cover that used a different screw hole arrangement. The screws were in a “square” pattern, rather than the trapezoidal shape that we are more used to. There was no provision for the screws to be in the later position, although later outer chaincases and inspection covers that have had material added to the castings have not had the now excess original material deleted. Not deleting redundant material was common practice, as it allowed a blank casting to be machined to any previous configuration, and I have often be grateful as this allows me to do certain modification to parts to allow a greater interchangability that would have otherwise been possible. While inspecting chaincases you may note a small boss at the lower front of the inner cover. This was going to be used as the sealing area for an oil level plug, and some early literature shows this plug. I have never seen an engine so built. It must have been realised that the lower edge of the drive side main bearing would act as an automatic level.
The tied down tensioner continued in use until 1973, when the arrangement was totally changed. A much more robust tensioner blade was fitted, pivoting around a now solid front spindle and positioned by a vertical adjuster bolt. The bolt screws through a new boss added to the chaincase, and the system cannot be “retrofitted” to earlier chaincases without difficulty. I have seen late castings machined for the earlier arrangement, another example of the multi use discussed above. Any outers like this could of course be modified to the latest arrangement because the boss material is in place. The eye bolt of the earlier system was of course deleted, but the internal machining operation continued. The oval flat seen on the chain side of the inner chaincase, which was necessary for the twin blade system also continued to be machined on all chaincases, although the clearance given by this operation was no longer required.
The T160 also used a variation of the vertical adjuster. The slipper was a different shape, and the adjuster bolt was longer, with machined flats for adjustment rather than a screwdriver slot. The extra length was required to allow adjustment of the slack fitting T160 type chain, which was not ideally suitable for the fixed distance between the crankshaft and gearbox mainshaft.
Secondly, Oil Seal Arrangements. The primary drive assembly has always been sealed in the same manner. A lip seal is used at the rear of the shock absorber, and another is used around the pull-rod in the shock absorber retaining nut. As the primary cases are used as a buffer chamber for the engine breathing system no seal is used at the engine sprocket. Two types of shock absorber centre, also known as the “spider” were used in the T150, and some of the later types have now found their way into R3's. Early engines were fitted with the “short” nose spider, and later engines were fitted with a “long” nose version. Short nose versions require a spacer, 572479 to be used on the clutch input shaft. It is important that these pieces are fitted correctly if oil leaks are to be avoided.
When fitting oil seals there is a general convention that the seal is fitted “spring to the oil”. If the seal is fitted in an area where there is a pressure differential across the seal then the convention is “spring to the pressure”. Although ideal this convention breaks down when dealing with the clutch/shock absorber seal in early engines. It would be ideal if the seal could always be fitted with the spring towards the needle roller bearing but on occasion this arrangement is unsuccessful. To find out why we have to look at the spacer, spider length, fitting methods and component positioning.
The whole shock absorber and clutch assembly is positioned to the outer primary case by the pull rod.. When the pull-rod is adjusted to the minimal end clearance required for successful clutch operation this is also the amount of end float on the whole assembly. This governs where, axially, the clutch oil seal at the rear of the primary sits on the spider or spacer. In the early arrangement the seal normally sits close to the shock absorber end of the spacer. This end of the spacer also has a small chamfer to assist in spreading the seal during assembly. If the seal is fitted “spring to the oil” then on occasion the seal lip can be trying to seal on the chamfer instead of on the diameter, and this is unsuccessful. As the lip of the seal is not centrally positioned, but is closer to the spring end of the seal fitting the seal the other way round will move the lip and result in it having a better position. It also should be remembered that the spacer should be “glued” to the clutch input shaft with a little loctite, and the rear face of the short spider that abuts this spacer should have a thin smear of jointing compound on it.
Correct assembly is also very important to stop the seal being trapped and torn during assembly. The spacer needs to be fitted to the clutch before the clutch is put into the bellhousing. I normally fit the spacer and then dummy fit a spider and nut to ensure it is fully home as the loctite cures. When the clutch is fitted in the bellhousing it must be pushed fully in, so that when the inner primary is fitted the seal and spacer are not in contact. Then, when the shock absorber is to be fitted the clutch must carefully be pulled outwards into position, locating the spacer within the seal. It is during this operation that the chamfer on the spacer will be used to spread the seal. Passing the shock absorber over the pull-rod it can be engaged with the clutch splines and slid down them. The clutch can be held stationary and engaged with the seal by holding onto the pull-rod. If the clutch is allowed to fall back into the bellhousing the seal can be nipped between the spider and spacer. If the splines are tight then the shock absorber nut and its spacer must be dummy fitted and the shock absorber wound down into position by tightening the nut with an open ended spanner, all while still holding the clutch in position. It is important that the clutch has been built up centrally, either by eye or using the building jig, or the splined shaft will not be entering the primary case through the middle of the needle bearing, and assembly will be that much more difficult.
Thirdly, Gasket Arrangements. Part numbers for the primary side gaskets have changed a number of times, but fortunately the latest gasket arrangements suit nearly all models. The T150 and RIII use the same clutch inspection gasket. I believe no “early” gasket for the square shaped screw position cover exists, but a later gasket can be used with care. The T160 clutch inspection gasket is of course specific to this model. The outer primary gasket is usable for all models, and the T160 inner primary gasket is also usable for all models. There is a small piece of this gasket “missing”, where the gearchange cross shaft exits this case, but this is in the void area and of no concern. I still have one outer primary gasket that has extra material and a central hole around the “lump” that hangs off the rear bottom corner of early chaincases. This boss was an early design for a left foot gearchange. I have also seen a RIII inner gearbox with extra material in it for the entry of this mechanism. I believe there was an scare in the late '60s that the USA would introduce compulsory left foot gearchanging earlier than they eventually did, and that a system was designed for the Triples that was never fitted.
When dealing with T150 and RIII models it is important to fit the small finger shaped gasket in the centre of the chaincases. (I use the late part number 71-2793 for this item). It is retained under the chain oiler pipe clip. If it is not fitted the outer chaincase will be bowed (albeit a very small amount). Also the screws fitted here will have a unsealed helical passage along one side of the thread. As the threaded bosses in the inner chaincase often break through into the clutch housing there is a chance of an oil leak along the screws. If the chain oiler is not fitted it is very important that the gasket is fitted, and held in place by a bolt and washer. I have seen a number of engines where, even if the gasket has been stuck in place the oiler pipe clip boss has been left unfilled, and as it also breaks through to the clutch housing a major oil leak has been apparent. If I have the opportunity while working on any primary I will now seal by welding any screw threads that have broken through to the clutch area.
Finally, a couple of tips. It is vitally important to fill the primary chaincase after draining the oil for service or repairs. The “lore” that the chaincase will fill itself is incorrect. If the case is run dry for any length of time the needle bearings that support the shock absorber, and the radial thrust needle race especially will fail. a failure will cause extensive damage to the shock absorber spider and the cases themselves. These bearings are lubricated by oil that is thrown of the drive and drains down the inner and outer covers, being collected by small holes above the bearing housings. A Twin, has a variable crankcase volume does “pump” a fair amount of oil laden mist into the chaincase, but as a Triple's crankcase volume does not effectively alter there is no pumping action. It is not necessary to be very accurate with the amount of oil put into the case as the lower edge of the main bearing is the level, and any excess will drain into the crankcase.
Due to demand I have developed a repair technique to reclaim outer primary cases that have damage to the shock absorber support bearing housing and thrust face, and I can repair cases that are quite extensively damaged in this area. The seating and clamp arrangement for the radial thrust race outer washer is occasionally damaged independently, and the repair method recovers this area too.
It is acceptable to drill a small hole at the bottom of the clutch adjustment housing to drain the area back into the main chaincase. This hole was standard on later models, and saves a quantity of oil being trapped in this area. If nothing else the owner can save a messy floor when taking the adjustment cover off!
Some bikes throw oil out of the clutch cable abutment. A simple and elegant fix is to push a length of thin wall tube into the abutment from underneath. When re-fitted this tube will enter the clutch adjustment mechanism area through the cable hole, and very effectively seal the cable from the oil of the chaincase. An oil feed stub from all pre late T160 models (part number 706574) is ideal for this purpose. It may then be necessary to reduce to size of the bottom nipple of the clutch cable to pass through the tube, remembering to carry out the same operation to the spare cable!
Copyright © 2000 Philip Pick
Version 0.1 Date December 2000