Vire 7 - Construction of the Engine

General Data

The Vire 7 engine is designed and built for marine use. The engine is supplied with a reversing gearbox and with its hand lever it is possible to select forward, neutral and reverse positions. The reduction ratio is 2:1 in forward, or 2.5:1 in reverse. When in forward gear the propellor rotates in the opposite direction to the engine. A flywheel magneto supplies current for ignition and a 6 volt 16 watt AC current for lighting, if required. The engine is fitted with a 12 volt starter generator; the power output of which, as a generator, is 90 watts.

The carburettor is of membrane type, which guarantees the feeding of fuel irrespective of engine angle when the boat is under way.

A vane type pump provides cooling water circulation. There is no thermostat in the cooling water system.


The engine is a single-cylinder, water cooled 2-stroke (2-cycle). The cylinder and cylinder head are cast in one piece.

In order to achieve even running of the engine, an exhaust gas collector with a water jacket is fitted. This collector is beneficial in a 2-stroke engine, where the length, diameter and shape of the actual exhaust pipe and silencer can vary from boat to boat. In order to reduce weight, the collector has been made of light alloy. Because of this, the collector is water-cooled. This also reduces thermal radiation to the engine space and cools the exhaust.


An impellor type water pump is fitted to the rear of the gearbox. It is driven through the gearbox by an extension of the idler gear shaft. The sea water suction line is connected directly to this pump, which pumps water through the exhaust collector water jacket and thence into the cylinder block. Because of this system, the cooling water thereby maintains the engine water temperature at an acceptable level under all running conditions. Webmaster's Note: It is important to pay attention to the seals between the water pump and the gearbox. If these fail, water will get into the gearbox, with potentially damaging results.

Hot water from the pump can either be: -

  1. discharged directly overboard, or
  2. injected into the exhaust system at a point above the water line and used to cool the exhaust system, thus enabling rubber petrol-proof exhaust hose to be used for this water cooled section. (See Mounting the Engine in the Boat - Exhaust and Cooling Systems).

Threaded plugs are fitted to the cylinder and the exhaust gas collector for the purpose of draining the system.


A diaphragm pump operated by pressure fluctuations in the crankcase is incorporated in the carburettor. The advantage of this type of carburettor is that it will function under all angles of heel.

Fuel is drawn through a strainer into the pump chamber and is then transferred to the carburettor chamber where it is metered and controlled by a needle valve and the idling and main jets. A choke is fitted in the carburettor venturi to assist cold starting .


Ignition is supplied by a flywheel magneto, which also incoporates a 6 volt AC lighting supply, if required. (See AC Lighting Wiring Diagram) The total power absorbed must not exceed 16 watts at 6 volts.

Starter Generator

The starter generator is driven from the crankshaft by a V-belt. When starting the engine it acts as a starter motor, drawing current from the 12 volt battery. The recommended capacity of the battery is 30-38 Ah (Maximum 45 Ah). When the engine is running the unit operates as a generator and produces current for battery charging and lighting if connected. (See Starter Generator Circuit Diagram)

The cross section of the cables indicated by the thinner lines in the diagram should be 2.5 (0.0039 The cross section of the cables indicated by the thicker lines is 16 (0.025 The electrical system comprises the following parts: -

Reversing Gear

The reversing gearbox is coupled directly to the rear of the engine. The propellor thrust is taken up within the gearbox. Forward and reverse action is provided by two cone clutches on a splined shaft.

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