This invention relates to engine blocks, and more particularly to integral castings for single cylinder, **•» two-stroke engines.

5 BACKGROUND ART

A viable small petrol engine must be inexpensive, compact and durable. Attempts to achieve these requirement have produced engine blocks of both aluminium alloy and cas iron, but the choice of material very often is a compromise 10 between all three requirements. When a further requirement is included such as ease of maintenance many prior attempts have fallen far short of requirements.

It is a principal object of this invention to provide a single cylinder, air cooled, two-stroke engine 15 block which is an acceptable compromise in respect of all o the abovenoted requirements.

DISCLOSURE OF INVENTION In accordance with one general form of this invention there is provided an engine block assembly 20 comprising a casting forming an open-ended cylinder barrel, crankcase with single open side, and cooling-air cowl; a cylinder head attached to one open end of said barrel and composed of aluminium alloy; a cantilevered crankshaft journalled in bearings at a side of said crankcase opposite 25 said open side; a piston slidable in said barrel and connected by a connecting rod to said crankshaft; and an air impeller on said crankshaft housed within said cowl;. said cowl being open on one side to accept said impeller and being adapted to be closed by a mounting plate for said 30 engine when assembled thereon. BRIEF DESCRIPTION OF DRAWINGS

A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: 35 Fig. 1 is a perspective of an engine block casting according to the invention; and

Fig. 2 is a similar but partly sectioned and fragmented view of the engine block upon a mounting plate

and depicting the pattern of cooling air flow.

BEST MODE OF CARRYING OUT THE INVENTION The engine block assembly illustrated consists of a casting 3 to provide a cylinder barrel 5 with external

5. cooling fins 4, a crankcase 6 with an open side 7, and a cooling air conducting cowl 8. It is a known characteristi that, although the use of cast iron in the construction of engine blocks tends to generate excessive weight, a cheaper machining process is involved and economy in cost of

10 material is achieved. As an alternative material aluminium alloys have frequently been used but invariably incorporate a cast iron liner within the cylinder barrel. On the other hand, however, due to the fact that little wear occurs in cylinder heads aluminium alloy is preferred due to its

15 light-weight characteristic.

Nevertheless, the design of the instant engine block is such that a suitable tolerance on weight factor is achieved. In the unitary casting 3, the cylinder barrel 5 has an open outer end 9 and as shown in Fig. 2 is arranged 0 to be closed by a cylinder head 10 of aluminium alloy.

Cooling fins 11 on the head 10- are swept by a cooling air draught 12 directed by a passage -13 in the cylinder head 10. The open-side 7 of the crankcase 6 provides access to the crank on the crankshaft (not shown) as well as the big 5 end of the connecting rod from a piston (not shown) slidable within the bore 14 of the barrel 5. This open side 7 of the crankcase 6 may be closed by a sealing inspection plate (not shown) .

The cowl 8 consists of an annular housing 15 0 integrally connected with the crankcase 6 by spaced inclined buttresses, or webs, 16 which form an open cage 17 between the cowl 8 and the crankcase 6. The side 18 of the crankcase 6 opposite the open side 7 provides a pair of spaced bearings (not shown) for the crankshaft journals (not 5 shown) . The cage 17 surrounds the side 18 of the crankcase 6 and one side of the housing 15 is open to communicate with the passage 13 and the cooling fins 4 of the barrel 5. Preferably the crankshaft (not shown) is of cantilevered

form and its drive shaft extension extends from the crankcase 6 on the axis of the cowl 8. The outer side 19 o the cowl 8 is open to permit the mounting of an air impelle 20 upon the protruding drive shaft. Preferably, the impeller 20 is composed of upright radial blades 21 on the inner face of a circular-disc flywheel 22. When the engine block assembly is mounted upon its mounting plate 23, which may be a baseplate of a lawnmower, the open side 19 of the cowl 8 is closed to complete an air ducting system. Thus it can be seen that air drawn into the cowl 8 through the cage 17 by the impeller blades 21 will be force around the annular housing 15 of the cowl 8 and over the cooling fins 4 of the cylinder barrel 5 and through the passage 13 to pass over the fins 11 of the cylinder head 10. A filtering screen (not shown) may be provided at the air entry to the open cage 17.

INDUSTRIAL APPLICABILITY It will be appreciated that the engine block assembly is extremely compact, leading to a reduction in the amount of material utilised in the casting 3, and with the use of an aluminium alloy cylinder head 10, an overall light weight construction is achieved. As the engine block assembly includes an integral casting 3 with a single opening 7 in the crankcase 6 which can be sealed quite readily, problems in obtaining good sealing for crankcase compression do not arise, thus alleviating the need for seal testing during production. Furthermore, an engine constructed according to the above principle, is readily maintainable. Whereas a preferred embodiment has been described in the foregoing passages it should be understood that other forms are also possible within the scope of this invention.