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).
The function, fitting, and timing of Ignition Coils TA and Ignition Distributors VA 4B and VA 6B.
| Identifier | ExFiles\Box 61b\4\ scan0162 | |
| Date | 4th January 1928 | |
| (Document Metadata from left margin of Page 2) Edition VII Edition V I 4. I. 26 II 8. 6. 27 III15.12.27 [V25.10] Edition Stuttgart, 4th January 1928 Chr. Schock. (Page 2 Text) IGNITION COILS TA FUNCTION: They transform the low tension current from the battery into high tension current which is fed from the Ignition Distributor to the sparking plugs. SAFETY RESISTANCE: The primary winding of the ignition coil has a resistance 157 inserted in front of it. This enables it to take a comparatively powerful current without getting overheated or burning out when, on the engine stopping, the contact breaker contacts happen to be left closed for some time owing to the battery ignition not being switched off through forgetfulness. This SAFETY Resistance is fixed on the cover plate 156 of the ignition coil so that it can rapidly cool down if the Ignition Coil is properly mounted. The Resistance for a 12 volt Ignition Coil has different dimensions from the 6 volt Ignition Coil. It is protected by a cap 157 c. TERMINALS: Terminal 1 must be connected to Terminal 1 (the insulated contact breaker contact) of the Ignition Distributor. (Cables of 1,5 sq. mm. copper section, WKA 505/1 X.) Terminal 15 must be connected to terminal 15 in the switch-box; the end of the resistance is joined to it. (Cable WKA 505/1 X.) Terminal 4 must be connected to Terminal 4 on the Ignition Distributor. (High Tension cable WKA 3/1 X.) FITTING: The ignition coil must be fitted either on the engine or on the engine side of the dashboard in the immediate vicinity of the ignition distributor, so as to make the primary cables as short as possible. Care must be taken that the ignition coil is not heated by the steadying resistance; it is therefore best fixed upright as shown in fig. 2. If horizontal fitting is inevitable, the two fixing screws 160 must lie one above the other, as shown in fig. 1. The screws (160) are supplied either with 18 mm (NSR 1484/50 X) or with 32 mm (NSR 1484/76 X) length of shank, as may be required. If the coil is not fitted on the engine but on the dashboard, one of the two fixing screws must be connected by a cable with the engine frame or the chassis (fig. 2), earth lead 31, cable WKA 505/1 X. FIXING THE CABLES: The method of fixing the low tension cables will be evident from Figs. 7, 8 and 9. — 2 — (Page 3 Text) IGNITION DISTRIBUTORS VA 4B AND VA 6B. FUNCTION: The Ignition Distributor contains the contact breaker which interrupts the battery current flowing through the primary winding of the Ignition Coil. The high tension current generated in the secondary winding of the Coil is fed from the Distributor to the sparking plugs where it jumps the gaps as a spark. MOUNTING: Fig. 4 gives an example of how the Bosch Ignition Coil may be mounted. Its longitudinal axis is perpendicular and must in no case be inclined more than 45°. Direct coupling to the horizontal camshaft is not permissible. To prevent the Ignition Distributor from shifting in the direction of its axis and to keep it firmly on its seat on the engine housing, a locking device 121 is provided. In the groove of the bearing neck of the Ignition Distributor there is a segment shaped pressure piece 121c in the hole of which the conical end of a spring bolt 121b screwed into the engine housing engages. The centre of the spring bolt is 0,8 mm. lower than the centre of the segment boring so that the spring bolt pulls the Ignition Distributor down on its seat. In motorcars with fairly considerable vibration it is advisable to fix a second spring bolt and segment which must however be placed at an angle of about 120° to it, so that the bearing neck shall be pressed against one side of the engine housing. The pressure exerted by the spring is 5,5 kilos. DRIVE: It must be driven at the speed of the cam-shaft by claw-coupling (dog-clutch). — 3 — (Page 4 Text) Worm or bevel gear is permissible, but no lateral pressure must be exerted on the shaft of the Ignition Distributor. Play at "a" (Fig. 4) must not exceed 0,2 mm; the collar "b" must not be more than a fraction smaller than 26,5 mm. TIMING THE IGNITION DISTRIBUTOR TO THE ENGINE: The piston of cylinder 1 must be put at top dead centre at the compression stroke. The shaft of the ignition distributor must be turned in the direction in which it revolves when the engine is running until the distributor finger points to the distributor segment marked 1 (Fig. 5)*). In this relative position of engine piston and ignition distributor, the shaft of the ignition distributor must be coupled to the engine shaft driving it. 20° automatic timing of the ignition distributor correspond to 40° timing measured on the crank-shaft since the former is driven at the speed of the cam-shaft. The above adjustment therefore gives 40° advance ignition. If this advance ignition is too much, the piston of cylinder 1 must not, as given above, be put at top dead centre but at as many degrees beyond top dead centre as less advance ignition is required. Example: 10° beyond top dead centre, if only 30° advance ignition are required. If, on the other hand, 40° advance ignition are not enough for maximum efficiency of the engine, the piston of cylinder 1 must be put as many degrees before top dead centre as more advance ignition is required. Example: 10° before top dead centre, if 50° advance ignition are required. In order to prevent any back-firing on starting up with the last mentioned adjustment, it is advisable in this case to mount an ignition distributor with automatic and hand-timing, as this makes it possible, with the additional hand-timing, to set the retard ignition required on starting up at top dead centre or beyond top dead centre. The additional hand-timing further enables the motorist to regulate the time of ignition independently of the momentary speed of the engine. Terminal 1 of the distributor disc must, when the timing has been set, be connected by a cable to the sparking plug of cylinder 1 which was used for the timing. The remaining sparking plug cables must be connected to the distributor disc so as to correspond to the direction of rotation of the distributor shaft, and to the engine so as to correspond to the order of sparking. DIRECTION OF ROTATION: clockwise (looking on top of distributor disc.). TIMING LEVER: The timing arm 109 for hand timing is cast on to the housing. To limit the timing range a stop pin 103e can, if desired, be fitted on the housing. This stop pin may also be used to protect the housing against any twisting when the hand-timing is not made use of. CABLE TERMINALS: Terminal 1 must be connected to terminal 1 on the Ignition Coil. Cable 1,5 sq. mm. copper section: WKA 505/1 X. Terminal 4 must be connected to terminal 4 on the Ignition Coil. High tension cable of 1,5 sq. mm. copper section WKA 3/1 X. Terminals 1—4 (1—6) of the distributor disc must be connected to the sparking plugs (H.{Arthur M. Hanbury - Head Complaints} T. cable 1,5 sq. mm. WKA 3/1 X). Screw 103 f must be earthed to the engine frame by a cable of 1,5 sq. mm. WKA 505/1 X. LUBRICATION: A filling-bracket 109 d is cast on the timing lever arm. It is filled with thick grease (melting point 100°). The opening of the bracket is closed by a screw 109 e.{Mr Elliott - Chief Engineer} For lubricating the distributor shaft this screw must be tightened up one turn from time to time (after about every 2000 km). When the screw cannot be tightened any further, the grease is used up and must be renewed. To do this, remove the screw 109 e, fill the bracket with grease and then replace screw to the extent of a few threads, but not entirely. FIXING THE CABLES: See page 5. *) This position is marked on front of the distributor housing (can be noticed when removing the distributor disc) by means of a sign. — 4 — | ||