Overhead camshaft - An overhead camshaft was chosen to both facilitate the design of the die-cast cylinder block and give the engine greater RPM range of operation. Generally speaking, it provides a fair compromise between emission control requirements and high speed operations thanks to the substantial valve accelerations allowed.

Figure 8

As shown in Figures 8 and 9. this cylinder head is very compact, which is important on a V-type engine. Its height ensures a great rigidity. It must be pointed out that the non-machined combustion chamber shape gives greater freedom to optimum dimensioning of valves and the use of rocker-arms without offset. The left and right cylinder heads are designed so that they can be machined in the same transfer machine.

Figure 9

Lubrication - The oil pump speed and size have been chosen to obtain an in-use output over 14 liters per 1000 engine RPM as soon as 600 crankshaft RPM is reached.

The pressure regulation takes place at about 0.45 MPa (4.5 bars) by a piston discharge valve with return to the suction side of the pump.

The full-flow oil filter is a throw-away type cartridge consisting of a paper filtering element.

There is a by-pass relief valve in the engine block oil circuit to avoid deterioration of the filtering element when oil viscosity increases (cold weather).

The cartridge installed in production at Douvrin (Franco-Swedish Engine Company (Pas-de-Calais, France) provides a filtering threshold of 5 to 8 x 10-3 mm. to efficiently protect the engine during the break-in period, while those supplied as spare parts have a threshold of 10 to 15 x - 10-3 mm. Regarding lubrication of joints, a special feature of this engine is the location of the oil passage holes in the crankshaft, in order to continuously lubricate the connecting rod joint; this arrangement derives from the absence of oil grooves in the bearing cap inserts.

Elimination of this groove enables reinforcement of the oil film at each instance when gas pressure becomes greater than the inertia forces of the piston/connecting rod assembly.

This reinforcement of the oil film contributes to the elimination of noise under load.

Cooling - The single outlet water pump has a stationary seal; it is belt-driven at 1.10 times the speed of the crankshaft. Its pressure-output characteristics, measured with a water temperature of 185° F. (85° C.) for various engine speeds, are shown in Figure 10 with approximate indications of the pressure losses due to the flow circuits. The output of the single- outlet pump is divided and feeds the two cylinder banks through a double manifold directly attached by bolts to the cylinder block

Figure 10

Coolant flow regulation is obtained with a three-way type thermostat operated by an expanding wax temperature sensor. The coolant flow to each of the 6 cylinders is controlled by calibrated water passage holes tn the two cylinder head gaskets.

The center-to-center distance of the cylinder liners of each bank is l08 mm.; the thickness of the water room is 5.8 mm. at the upper flange and 9.5 mm. along the liners.

Ignition -

Conventional ignition - The top view of the engine (Figure 11) shown without the air filter shows the location of the ignition distributor.

Figure 11

It is driven by the right band side camshaft, and its rigid mounting on the cylinder head insures a particularly low vibration level.

In the conventional ignition system, there are two breakers and a double high voltage rotor, in order to work with a separate coil for each cylinder bank. In order to adjust the correct timing for the two banks, the following procedure is used:

Timing is adjusted with a stroboscopic light at the timing mark of the left bank only by rotation of the distributor body. Timing of the right bank can then be set by adjusting the corresponding breaker from the outside of the distributor. The dwell angle check on the right bank breaker shows if the components are correct and compatible.

For some applications, two alternative ignition systems have been developed:

- A breakerless transistorized ignition system which allows both reducing maintenance costs and obtaining a stable, durable spark timing as required by emission regulations, with a minimum risk of misfiring due to ignition system failure.

The ignition curve is, however, conventionally controlled by a mechanical centrifugal advance, and a retard/advance vacuum control.

- A fully electronic ignition system such that this spark is triggered by a sensor indicating the position of the left camshaft. There are no longer mechanical parts subject to wear, therefore timing does not deviate from its original setting. Advance in relation to RPM is obtained electronically by signals from the sensor; correction in relation to load is obtained through a diaphragm actuating a potentiometer.

Continue on the next page >>>