Workshop - Ignition

Details for this section are for the Lambretta 175 Li Series 1 and 2 however there are many similarities between these models and other models of Lambretta threewheelers/Lambros. This information and the pictures included are provided from the 'Instructions for Repair Shops' for these models published in 1963. It is intended for informational purposes and we would recommend seeking professional advice before undertaking anything described in the Workshop section. This section refers ONLY to kickstart models.

 

DESCRIPTION AND GENERAL DETAILS

Ignition is obtained through the flywheel magneto, H. T. Coil and sparking plug.

The flywheel magneto consists of a stator plate carrying two coils, the contact points, the condenser and the flywheel rotor which acts as the engine flywheel. The stator plate is fixed to the flywheel support flange by three screws, and as the screw holes are elongated it is possible to vary the position of the stator plate according to timing adjustment requirements.

The changing of the coil on the stator plate is quite normal providing the same type and make of coil is used.

The rotor consists of a rotating mass in which are located 4 magnets. In the centre it carries a conical hub for the keying on to the crankshaft. The hub's outer surface is appropriately profiled to act a cam for the contact breaker arm. The lubrication between contact breaker and hub is through an oiled felt pad which rubs on the cam through the action of a spring strip fixed to the stator plate.

The H. T. Coil, consisting of a double winding highly insulated on a ferrous magnetic nucleus, is fitted with two terminals for connection to the low tension circuit, and a central connection with knurled ring for the spark plug lead.

In view of the variations introduced to the electrical circuits, the flywheel and H. T. Coil are not interchangeable between 1st and 2nd series machines, as the circuit on the 1st series is a 6V type, and the circuit on the 2nd series machines is a 12V type. 4 pole flywheels for first series; 4 or 6 pole flywheels for second series.

The spark plug, 225 Bosch thermal degree type (or 2400 for heavy work), is of the long reach type (18 mm). Extreme care must be taken by the user not to fit the short reach type plug (14 mm) as this will cause extremely bad engine running and damage to the cylinder head.

 

TIMING OF THE FLYWHEEL MAGNETO.
The timing of the flywheel consists of adjusting the ignition spark in relation to the established position of the piston at Top Dead Centre (TDC)

If the timing is too advanced, starting difficulties and black timing will occur, knocking, and bad slow running; while if the timing is retarded, overheating, bad acceleration and high consumption will occur. It is absolutely important that the gap of the contact breaker be kept consistently within the limits prescribed in the following notes, and checked periodically. The timing operations for the flywheel are as follows:

64	Remove cylinder head as per operations 1, 7, 9 up to removal of cowl, 28. Remove flywheel cowl ring and dust cap as per operations 24 and 25. Fit tool 57988 in place of the cylinder head.

65	Apply a timing gauge to the tool (See Fig. 24).
66	Check the gap fully opened and condition of points. Their surface must be clean and flat, if not touch up with a very fine file. The gap should be between 0.35 mm and 0.45 rum (0.014" to 0.0157") which can be easily checked with the feeler gauge 48054 through the window cut in the flywheel rotor pack. If the gap does not come within these limits, the necessary adjustment can be made through the adjuster screws.
67	Detach the Green wire feeding the L. T. Coil from the rectifier box on 2nd series vehicles or from the junction box placed under the seat support beam on the 1st series vehicles. Connect to one of the terminals on the Tester Tool No. 05017 the green wire from the flywheel and one terminal to earth.

68	Find the Top Dead Centre, put Gauge clock to zero at this point.
69	The Tester will light up at TDC, and turn flywheel slowly in the opposite direction to the engine rotation, in other words, in the opposite direction to that indicated by the arrow on the flywheel.
70	When the Tester light goes out, i.e. the contact points close, read the dial gauge, which should record a reading of 2.5 to 3.0 mm, corresponding to an angle of rotation of 23° +/- 1° or 32/33 mm. measured on the flywheel external diameter. Should the points close outside of the above figures, remove flywheel, and after having loosened the three screws fixing the stator plate, move this in the opposite direction to the engine rotation, to retard, or in the same direction to advance, until the points open within the prescribed position.