From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical description of the Frazer Nash-B.M.W. 2-litre Chassis, including details on the engine, clutch, and gearbox.
| Identifier | ExFiles\Box 126\3\ scan0142 | |
| Date | 1st October 1936 guessed | |
| 3 The Frazer Nash-B.M.W. 2-litre Chassis—contd. the flywheel is attached by setscrews. The starter gear ring is a separate member shrunk on to the flywheel, though on some models the teeth are cut direct into the flywheel rim. The timing gear is enclosed by a light pressed-steel cover, a duplex roller chain being employed for driving the camshaft. The sprocket is attached by Woodruff key and nut to a parallel spigot on the end of the camshaft. Four plain bearings support the camshaft, which is on the lefthand side of the crank case. Near the centre a skew gear drives a shaft slightly inclined from the vertical, on the upper end of which the distributor is mounted ; while the lower end drives a rotary-gear-type oil pump arranged in the sump below the oil level. On the 2-litre models only, a special edge-type external filter is fitted on the near side of the engine, requiring an occasional partial turn of an external handle. Oil is pressure fed to all the main bearings, including, as previously mentioned, the small ends of the connecting rods, the overhead-valve gear, along the rocker shaft to the bushes, etc. An interesting design point in connection with the overhead-valve mechanism is the bearing taken by the lower ends of the tubular push rods in the tappets. The tappet is of thimble form, and a similarly shaped, but much smaller, thimble is permanently fixed to the lower end of the push rod, which is loosely inserted in the tappet. At the upper ends each push rod is fitted with a cap containing a semi-spherical depression for the adjustable ball-ended stud in the rocker. Two concentric springs are fitted to each valve. The rocker shaft is held in four pedestal bearing brackets, springs being arranged between adjacent rockers, enabling them to be moved sideways from the normal position for valve grinding, etc. The whole of the rocker gear is enclosed in a light pressed-steel cover. This is retained by tightening down two knurled nuts screwed on to studs which project through the top of the cover, while in the centre of the cover is conveniently arranged the oil filler. Two horizontal Solex carburettors are fitted, of the type embodying the patented automatic quick-starting device. The air inlets are provided with copper gauze filters and the hand throttle control is fitted on the dashboard. Regarding the electrical equipment, the coil and distributor are of Bosch manufacture, the distributor having automatic timing control and also a hand control on the dashboard. A Bosch dynamo of the constant-voltage type is fitted and is driven by the fan belt. The starter, also of Bosch manufacture, is of the sliding-armature type. The power unit has a patented cushion mounting. At the front end two flat rubber pads are fitted between the engine supports and two sheet-metal brackets welded on to the tubular frame side-members, which here are close together. The rear support is beneath the back end of the gear box, which rests on a built-up sheet-metal bracket welded to the central cross-member, a rubber block being again interposed. [Diagram of clutch mechanism] Arrangement of clutch. Clutch. A single dry-plate clutch is fitted. The presser plate is held against the friction material by nine coil springs, each held in a steel thimble, while the withdrawal mechanism consists of three fingers pivoted in the usual manner and each being fitted with an intricately bent hairpin spring. The construction of these withdrawal fingers is a typical example of economic construction which yet cannot be criticised on the score of weakness or inefficiency. Each finger is stamped out of a piece of flat steel plate, the sides slightly flanged over and the two ends bent to form abutments on the presser plate and withdrawal ring respectively, while a second strip of steel bent at right angles projects through a slot in the first piece, while the radius of the angle forms a fulcrum on the clutch outer member. A commendable feature is the fact that the withdrawal ball race is automatically self lubricating. Referring to the driven plate, the thin steel central disc is of unusual form, the periphery being cut away, leaving twelve narrow star-like projections, each of which is drilled for a single rivet. The two bonded asbestos friction facings are attached to these, there being six rivets in each facing, so that the rivets are alternatively attached to each face. A cushion drive is provided in the centre of the driven disc, there being a series of six compression springs arranged in a circle in six slots machined on the flange of the central sleeve, and these springs are, of course, compressed in taking up the drive. Gear box. A four-speed gear box is employed, having synchromesh engagement for the two top ratios. The clutch shaft is formed integrally with the constant-mesh pinion. This gear has a set of internal teeth which engage with splines on the outside of a sleeve. This sleeve may perhaps be regarded as the main member of the box, as it carries an engaging member of two cone synchronising clutches and two gears. Externally, it is splined throughout its length, and internal splines are arranged at the front end, which slide on the splined end of the third motion shaft. For actuation purposes this sleeve has a ring mounted on it, which is slid over the splines and locked by two circlips. This ring is partly encircled by a yoke member, which in turn is pivoted near the centre of a large horseshoe-shaped member, as shown in the cross-section of the gear box. The upper part of this member may be picked up by the depending finger on the change-gear lever, while the lower ends are pivoted to the ends of two set pins screwed in the base of the gear box casing. The sleeve may therefore be slid in and out of engagement with the dog clutch in the front constant-mesh pinion, but before engagement takes place the inner element of a cone loosely mounted on the sleeve comes in contact with a cone member mounted by a spigot on the rear end of the constant-mesh [Diagram of gearbox cross-section] Four-speed synchromesh gear box. | ||