This invention relates to reciprocating engines, ^" an more particularly to small single cylinder, two-stroke petrol engines. Ever-present aims in the design of such small, low-powered engines are compactness and economy in production. These aims apply, of course, whether or not th engine is_ designed as a limited-life discardable unit or as a relatively durable and readily maintainable unit. Attainment of the above two aims is more difficult in the instance of the latter type unit and it is principally to the improvement of this type unit that this invention relates.

BACKGROUND ART Several instances are known of two-stroke engines^ which incorporate a cantilevered crankshaft, i.e. one possessing two journals on one end portion and terminating at its other end in a crank. The crankcase is preferably open on one face confronting the crank for access thereto for various reasons, one of which may be for rope-pull starter engagement. A crank pin for attachment of the big end bearing of the connecting rod of the piston is either formed integrally with, or pressed into, the outer face of the crank. Some two-stroke engines have been available with their cylinder barrel and crankcase composed of an integral casting and such a construction greatly simplifies production processes and maintenance. However, efforts to incorporate this integral casting on engines employing cantilvered crankshafts have encountered difficulties in assembly of the connecting rod to the crank pin. If a split bearing is used on the connecting rod, provision for access of assembly tools must be made and this detracts from the compactness and unitary form of construction. On the other hand if a roller, or other annular, bearing is used, as is desirable in good quality, durable type engines, insufficient lateral displacement of the connecting rod is available to enable its big end to be lifted over the crank

pin for positioning thereon.

INDUSTRIAL APPLICABILITY It is the main object of the invention to provide a single cylinder engine which incorporates a cantilevered crankshaft housed within a unitary casting composed of cylinder barrel and crankcase, and which can be readily assembled and disassembled both in production and during maintenance.

DISCLOSURE OF THE INVENTION To this end according to one general form of the invention there is provided a single-cylinder, reciprocating engine block assembly comprising a metal casting which includes a cylinder barrel and an open-face crankcase for an engine, a crankshaft including a drive shaft journalled in said crankcase and a crank near one end thereof and terminating short of the open face of said crankcase, a piston reciprocable within said barrel, a connecting rod on said piston and having its big end attached to said cran by an annular bearing, said assembly being characterised in that the attachment of said big end to said crank is by means of a crank pin securable to said crank via access provided through said open face of the crankcase and through said annular bearing on the big end of said connecting rod. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to a preferred embodiment shown in the accompanying drawing of an exploded view thereof.

BEST MODE OF CARRYING OUT THE INVENTION As shown a single cylinder, two-stroke engine includes a cylinder block assembly 1 composed of an aluminium alloy, or iron, unitary casting which provides a cylinder barrel 2 and open-faced crankcase 3 for the engine. The opening 4 in the face of the crankcase 3 is to one side and a pair of spaced bearings (not shown) which at the other side rotatably support journals 5 and 6 on a drive shaft extension 7 of the crankshaft 8. At the opposite end thereof the crankshaft 8 terminates in a crank 9 confronting the open face 4 of the crankcase 3. Thus the crankshaft 8

is cantilevered from the integral drive shaft 7. An inspection plate with gasket (not shown) is attached to the open face 4 of the crankcase 3 to close the same. A removable cylinder head (not shown) preferably of aluminium alloy, closes the outer end 10 of the barrel 2.

A piston 11 is slidably mounted in the barrel 2 and pivotally carries the small end and bearing 12 of a connecting rod 13 on- a gudgeon pin 14 transverely fixed within the piston 11. The other, big, end 15 of the connecting rod 13 is bored and accommodates an annular bearing 16, such as a roller bearing, for rotational mounting upon a crank pin 17 carried by the crankshaft 8. By this invention the crank pin 17 is screwed into a threaded hole 18 on the face 19 of the crank 9 and consists of a metal pin threaded at one end 20, having a capturing flange 21 near the other end, and an intermediate cylindrical journal 22 of larger diameter than the threaded end 20 but smaller than the flange .21.

In assembly of the piston 11 and connecting rod 13 to the crankshaft 8, they are firstly inserted, with the connecting rod 13 foremost, through the open end 10 of the barrel 2 until the big end 15 of the connecting rod 13 lies adjacent the crank 9 on the crankshaft 8 and surrounds the threaded hole 18 therein. The crank pin 17 is then introduced through the open face 4 of the crankcase 3 through the centre of the annular bearing 16 and screwed into the threaded hole 18 in the crank 9. When fully tightened the intermediate journal 22 on the crank pin 17 provides a snug seating for the annular bearing 16 while the capturing flange 21 abuts both the bearing 16 and the big end 15 of the connecting rod 13 to retain it in position against the crankshaft 8. It will be noted that the assembly is. simple and effective and readily capable of disassembly for maintenance purposes. The face of the flange 21 may be provided with peripheral tool slots 23 to facilitate tightening and untightening of the crank pin 17 upon the crankshaft 8.

Preferably an axial integral post 24 extends out

from the flange 21 to serve as an abutment for pawls, or dogs, (not shown) on a rope-pull starter.

A preferred embodiment has been described above and it will be obvious that other forms, or modifications, of this embodiment are possible within the scope of the invention. For example, instead of a crank pin 17 being threadably engageable with the crankshaft 8, it may be a pressfit therein, or otherwise affixed. The crank pin may have a threaded hole for screwing onto a threaded post fixe upon the face 19 of the crank 9.