This invention relates to an internal combustion engine and, in particular, to an automobile engine.

Engine designers always view engine compactness as an important consideration. Compactness for any engine is a design consideration. It is undesirable for an engine to be bulkier or heavier and more space consuming than required to perform its particular duty in operating a motor vehicle whether a motor car a three wheeler. If bulk, space occupied and weight are excessive, a number of capital and operating cost consequences result. First, an engine must be contained within a protective compartment in the case of a motorcar. Obviously to keep manufacturing and sales costs as low as possible, it is undesirable for the protective compartment to be too large.

Space constraints for engine packaging apply to various vehicle types whether 2 wheeler, 3 wheeler or 4 wheeler as follows. Generally, any engine used in 3-wheeler, 4 wheeler or larger vehicles comprises a cylinder head, cylinder block, crank shaft, crankcase structure and transmission and differential components. Typically, the crank case structure comprises some key engine elements for example crankshaft and transmission elements like input shaft, output shaft and so on. Generally, car engines have separate housing arrangements of crankcase, transmission system and differential. Alternatively, the crankcase structure comprises two split portions (commonly known as crankcase halves) which are assembled together once the transmission and engine elements are fitted in a desired position inside the crankcase structure. Further there are additional housing structures for accommodating the differential and other engine components which are mounted separately on the above mentioned crankcase structure. Such separate housing structures occupy space and add to engine weight.

It has always been a challenge for engine designers to make the crankcase structure and engine compact whilst still giving required engine performance, compactness being considered with respect to length, width and height of the engine.

Packaging of an engine within a three or four wheel vehicle presents challenges at desired position or location, for example where the engine is to be rear mounted. A convenient location for mounting the engine may be beneath a rear bench seat of the vehicle. Current engines, with appropriate performance x characteristics, are not easy to accommodate in this location because of the significant height constraint bearing in mind the need to accommodate cylinder block, cylinder head, transmission system and differential. In addition, as rear wall location of vehicles imposes a significant constraint, a horizontal orientation of the kind involved in the Honda engine (Honda's Japanese Patent Publication No. JP2007232079 which has crankshaft, input shaft, drive shaft and differential axes generally laid out, almost "in line", in a horizontal orientation is likely to be unacceptable. Yet such rear engine location would be highly desirable to reduce vehicle length.

Height constraints have been addressed using horizontal engine orientations in which cylinder head, cylinder block, transmission system and differential are laid out horizontally as in the Honda specification. Engines are also known in which the transmission system is located adjacent the cylinder block and cylinder head.

A significant challenge in small engine development is to reduce space required by the transmission system and differential arrangement within the engine. In US 4798254, a transmission system for an automobile, multi-cylinder engine is • located in a volume bounded by planes respectively passing through differential and crankshaft axes. The differential and transmission are located side by side with the crankshaft. This arrangement addresses engine dimensional constraints of height and length but does not address constraints with respect to width of the engine, being a multi-cylinder engine which has a cylinder block taking up width. Also, this engine being multi-cylinder, does not require a balancer which further demands increases in engine length or height. Further in said US Patent 4798254, clutch, alternator and fly wheel and starting systems arrangements are employed outside the crankcase structure which occupy considerable amount of space outside the crankcase structure. Such space consumption is a serious constraint on engine compactness.

Further, in US 4798254, the crank case structure accommodating the transmission and differential elements has multiple compartments or splits (as shown by numerals 6b and 12) which pose many design, assembly and serviceability constraints. For example the differential axis, cylinder head and cylinder block must lie in same plane. Assembly of transmission components within the crankcase structure is difficult. Also, cylinder block replacement undesirably requires the crankcase structure to be replaced as the cylinder block is integrated with crankcase.

So, engine designers have considered extending engine dimensions in the longitudinal direction of the vehicle where there is a relatively less important constraint. An example of this approach to engine design is described in Honda's Japanese Patent Publication No. JP2007232079 which has crankshaft, input shaft, drive shaft and differential axes generally laid out, almost "in line", in a horizontal orientation. This design achieves two key objectives in current engine design. First, the height of the engine is reduced as far as possible. Second, the transverse dimensions of the engine are also within acceptable limits.

However, since the Honda engine has allowed for increase in length to reduce height, concerns arise as to the possibility of "oil starvation" and lack of sufficient lubrication as a vehicle driven by the engine negotiates upwards or downwards slopes. In such cases, a major proportion of lubricating oil may be confined to clutch/oil sump or cylinder head/valve train portions of the engine. This prevents effective engine lubrication.

It is the object of the present invention to provide an internal combustion engine that is more compact in sideways, vertical and horizontal dimensions than conventional engine designs.

With this object in view the present invention comprises an internal combustion engine comprising a cylinder head; a cylinder block accommodating an engine cylinder having a cylinder axis; a crankshaft having an axis; and an crankcase having integral structure for accommodating crankshaft, alternator, clutch, transmission system and differential and said crankcase having two split portions (commonly known as halves) connected in a plane parallel to said cylinder axis; wherein said crankcase structure of said engine comprises two sections substantially defined by a vertical plane containing said crankshaft axis, intersects said crankcase structure; wherein a first section of the crankcase structure includes said cylinder block and differential, said first section also including said crankcase housing portion for accommodating the differential located proximate said cylinder block and cylinder head; and said second section of the crankcase structure accommodates the transmission system and a balancer for driving at least one engine component accommodated in said crankcase structure Crankshaft and transmission system components such as input and output shafts are advantageously positioned in a plane perpendicular to the cylinder axis passing transversely through the centre of the crankshaft. It follows that the x crankshaft axis is oriented perpendicular to the cylinder axis. The crankcase structure has two split portions connected in the plane parallel to the cylinder axis. The crankshaft is journal led in the two portions with a suitable bearing arrangement, such as a journal / bush or roller bearing arrangement.

The engine is advantageously a single cylinder engine, the single engine cylinder being selected to accommodate a sideways or width dimension constraint for a vehicle using the engine. The cylinder has a cylinder axis which is inclined to a horizontal plane passing through the crankshaft axis at as small an acute angle as possible, for example in the range 10 to 20 degrees to the horizontal plane, and ideally approaching as close to horizontal as engine operability considerations will allow, since this angle of inclination is a measure of engine compactness, the object of the present invention. That is, as the angle of inclination of cylinder to defining plane increases, the height of the engine also increases and compactness is lost. Subject to engine operability constraints, notably sufficient cylinder inclination on gradients for proper lubrication, the cylinder axis would extend parallel to the horizontal plane as this would minimize the height of the engine. However, such alignment of cylinder axis and horizontal plane is not practically possible and there will be a minimum angle of inclination below which effective lubrication cannot be achieved. The optimal angle of inclination will depend on criteria which usefully include required grade ability, engine capacity and gear ratios. This angle of inclination ensures efficient lubrication at the intended grade ability performance and well accommodates the height constraint required in mounting the engine in vehicle.

The differential is located proximate the cylinder head and engine block. That does not require that the crankcase housing portion, housing the differential, contacts the cylinder head.

Crankshaft drive is transmitted to a vehicle drive shaft through the transmission system which includes input shaft and output shaft and differential, input shaft and output shaft being mounted with gears corresponding with transmission ratios for the engine. Typically, between 3 and 5 transmission ratios would be provided. A 5 transmission ratio engine is particularly advantageous and can be achieved within the compact engine objective of the present invention.

The transmission system may include a drum shift type gear shift arrangement with a plurality of forward gears (located within the crankcase) and a reverse gear, this gear being located outside the drum length. Had it been necessary A to locate the reverse gear within the span of drum length, a larger drum length would be required which would necessitate larger crankcase volume this reducing engine compactness. The gear shift mechanism is a drum shifter in which forks for reverse gear are formed integral with, rather than separate from, a shifter rail to save space and increase gear shift efficiency, by up to 30%. Movement of shifter rail enables movement of the fork and gear change in a drum shift gearbox. The integral fork mechanism may be employed suitably to any of the forward gear.

Conveniently, a centre point of the crankshaft and input shaft are located substantially in the above mentioned plane and the input shaft axis is -substantially vertically below the crankshaft axis.

The engine conveniently includes water and/or oil pumps respectively provided for supplying water for water cooling of the cylinder head and block; and lubricating oil for lubricating crankshaft, block, head, balancer, transmission and differential. Such pumps are driven from the crankshaft through a balancer linking engine crankshaft and drive shaft for water and oil pumps. Conveniently, such balancer, as well as water and/or oil pump(s), are located on the cylinder axis in the second section of the integral crankcase.

In such case, water and oil pump shafts are also located in the second or opposite section of the crankcase. Water and oil pumps may be driven by one common drive shaft linked with the engine crankshaft through the balancer assisting the objective of engine compactness. Such common drive shaft is located in the second section of the engine crankcase.

The above engine configuration provides flexibility in location of key engine and transmission components and provides optimum and balanced positioning of transmission and engine components, particularly in a single cylinder engine which would otherwise be subject to significant vibration. In addition, the cylinder head and cylinder block are not formed integral with the crankcase but are rather connected to it at a mating surface. This makes engine serviceability easier.

Further, the differential housing is positioned substantially in the centre of the engine and does not exceed the engine width. Additionally, the differential, when located in a vehicle is positioned substantially at the centre of the wheel track of the vehicle. This arrangement allows use of drive shafts of identical and equal length. This reduces inventory cost as well wear and tear pattern is equal for both shafts.

An important object is an efficient engine lubrication system for the valve train components, crankshaft, transmission and differential which does not interfere with engine operation. Further it is important to have a appropriate oil return path which avoids accumulation of oil in sealing area, unnecessary loading of clutch by return oil getting accumulated in the clutch chamber etc. To that end, in case the cylinder head and cylinder block, due to the compact engine design, do not have sufficient inclination to enable oil return to an oil sump by gravity, especially during the situation while the vehicle is passing through gradients, further the present compact design of engine poses clutch position which comes in the way of oil return path To eliminate oil accumulating in sealing area and return oil entering into clutch of its chamber, an oil drainage pathway is provided in a manner that does not load the seals at cylinder and cylinder head or load the clutch thereby increasing friction. Oil coming from valve train components, such as due to rotation of timing or cam chain, is also separated and diverted, by a plate, behind the crankcase wall to prevent loading of the clutch.

As mentioned above, the lubrication system is provided with oil return path comprising separators, passages/pockets and opening at appropriate locations. Towards this, an oil pocket provided offset to the cylinder head sealing towards the cam shaft bearing wall surface This position of pocket avoids oil going beyond the sealing area The said pocket is connected to an the oil drainage pathway which passes along an inclined surface of the cylinder head and cylinder block, said surface being separated from engine cylinder(s) by a wall in the crankcase about clutch area and towards the differential thus leading returned path towards the oil sump.

The said inclined surface is defined by a downward sloping bottom wall of the cylinder block and cylinder head. The slope being of acceptable grade ability to ensure effective lubrication. The said bottom wall is offset towards downside from sealing area so that oil will not accumulate in the sealing area and gets drained easily.

Conveniently, the oil drainage pathway also includes an oil separation arrangement including a separator located adjacent to clutch for directing oil (flowing due to rotation of timing chain cavity) away from the clutch to an oil sump while minimizing loading of the clutch area with oil. This would increase friction and reduce clutch operating efficiency. Therefore, oil flowing from the timing cavity is x diverted, away through an opening in a wall of the crankcase and the separator directs oil away from the clutch towards the oil sump.

An another separator may include means, such as ribs or plates located in at least one of the clutch cover and crankcase to keep oil of the sump away from the clutch. This arrangement prevents the oil loading the clutch area or pocket with undesirable increased friction. Any oil that resides in the clutch pocket is dynamically thrown out from the clutch once the engine (clutch) starts rotating and thereafter there is no significant drag as oil is diverted away from the interface. Once the oil is thrown out of the clutch pocket, the drainage pathway through this separator permits return of oil to oil sump.

The engine, even when mounted substantially parallel to ground, does not present challenges of oil starvation when a vehicle using the engine as prime mover negotiates upward and downward slopes (direction and location of engine mounting) when such oil drainage pathway is provided as mentioned above. In addition, the engine - employing an integral crankcase - permits use of common oil for engine, transmission and differential. This is cost efficient and also enables quicker oil warm-up.

References to vertical plane (B-B) and horizontal plane (A-A) in the description and figures do not require that the engine is physically split at these planes. The references to planes are used solely to aid visualization of the engine.

The engine is suitable for a number of applications in three and four wheel vehicles. In this regard, the engine can be seen to have a compact configuration in all key dimensions, vertical, transverse and longitudinal. In other words, the engine has the smallest possible bounded volume within these dimensions. The engine configuration allows ready mounting within a vehicle or beneath the seat, for example the rear seat, of a three or four wheel vehicle.

The internal combustion engine of the present invention may be more fully understood from the following description of a preferred embodiment made with reference to the following drawings in which:

Fig. 1 is a first left side schematic view of an internal combustion engine in accordance with one embodiment of the present invention.

Fig. 2 is a right side schematic view of the internal combustion engine of Fig. 1.

Fig. 3 is a top schematic view of the internal combustion engine of Figs. 1 and. Fig. 4 is a second left side schematic view of the internal combustion engine of Figs. 1 to 3.

Fig. 5 is a third left side schematic view of the internal combustion engine of Figs. 1 to 4 showing an oil drainage pathway and oil separation arrangement.

Fig. 6 is a rear side schematic view of the internal combustion engine of Figs. 1 to 5 showing an oil return pathway.

Fig. 7 is a schematic view of the gear shift mechanism for the internal combustion engine of Figs. 1 to 6.

Fig 8 is a rear schematic view of the internal combustion engine of Figs. 1 to 5 showing differential and drive shaft.

Fig. 9 is a first left side schematic view of an internal combustion engine in accordance with another embodiment of the present invention.

Fig. 10 is a schematic rear view showing differential positioned relative to wheel track in a vehicle comprising an internal combustion engine as illustrated in Figs. 1 to 9.

Figs. 1 to 6 show an internal combustion engine 100 of four stroke type to be mounted in a vehicle which could be a three or four wheel vehicle. There are constraints on the vertical, transverse and longitudinal dimensions of the engine which may require to be located under a rear seat of a vehicle as described in the Applicant's co-pending Indian Patent Application No. 0019/CHE/2012, the contents of which are hereby incorporated herein by reference.

Engine 100 includes a cylinder head 119 and a cylinder block 117 accommodating a single cylinder 116 having a cylinder axis 200 and a crankcase 101. Crankcase 101 has two portions or halves 210 and 211 connected in a plane C-C parallel to cylinder axis 200 indicating the connecting or joining surfaces of the crankcase 101 portions in Fig. 3 & 8.

Crankshaft 120 is journal led between the two crankcase halves 210 and 211, which may be termed crankcase LHS and crankcase RHS, through a roller bearing arrangement.

Crankcase 101 has a mating surface 101A with cylinder block 117 and connection of the crankcase 101 and cylinder block 117 is at this mating surface 101A. Crankcase 101 and cylinder block 117 are not formed integral but are rather x connected together. This assists engine servicing and cylinder block 117 replace ability, if required. The cylinder block 117 and cylinder head 119 are both inclined at a same noticeably small acute angle, indeed substantially horizontal, to a transverse horizontal plane A-A intersecting crankcase 101 and an axis 122 of crankshaft 120. This small acute angle of inclination of cylinder block 117 and cylinder head 119, and cylinder axis 200, to horizontal plane A-A accords with the objective of achieving engine compactness. The angle of inclination is 12.5 degrees to the horizontal plane and compares with a grade ability of 11.8 degrees. The 12.5 degree angle was selected taking engine capacity and gear ratios into account.

Engine 100 is a carburetted engine and fuel and air are mixed in carburetor (not shown). Fuel is combusted in combustion chamber 110 of pent roof configuration and, during engine 100 operation, piston 115 is driven to reciprocate in cylinder 116 to cause rotation of crankshaft 120. As crankshaft 120 rotates it defines a volume of revolution 123. Crankshaft 120 includes a counter-balance 124, which reduces vibration. Crankshaft 120 is also integrated with an alternator 170.

Crankshaft 120 drive is transmitted to a drive shaft of the engine 100 through a transmission system 141 and differential 146 housed within housing portion 140 of crankcase 101. Exhaust gases from combustion are exhausted through exhaust valve 112 and exhaust passage 112A.

Cylinder head 119 is provided with an overhead valve train comprising intake and exhaust valves. Intake valve 111 and exhaust valve 112, two of which may be provided in a four valve single overhead cam engine, have timing controlled by a valve timing system comprising cams, operation of which is controlled by cam or timing chain 410 driven within a timing cavity 412 by sprocket 415. All these valve train components are lubricated with lubricating oil supplied through the engine lubrication system.

Crankshaft 120, alternator 170, transmission system 141 and differential 146 and clutch 172 are all housed within the LHS and RHS portions of crankcase 101, differential 146 - as described above - being housed within a differential housing portion 140 of crankcase 101. Crankcase 101 is therefore an integral crankcase as that term is understood in the engine arts, such crankcase 101 allowing use of common oil for engine 100, transmission system 141 and differential 146.

The crank case structure has two halves 210 and 211 connectable in plane parallel to cylinder axis, the connecting or joining face marked as C-C.

The integral crankcase 101 is divided into two sections 104 and 105 by a vertical plane B-B intersecting the crankcase 101 containing the crankshaft axis 122. The two sections 104 and 105 include extensions 104a and 105a, having circular outer surfaces which form crankcase housing portion 140 housing the differential 146.

First section 104 includes the cylinder block 117, cylinder head 119 and differential 146, this being considered the cylinder section. The differential output shaft 147 is located in this cylinder section. Section 105, on the other side of plane B-B to section 104, is termed the opposite or second section 105 and it accommodates key components of transmission system 141.

The differential 146 is located proximate the engine block 117 and cylinder head 119. The described engine arrangement makes the engine 100 compact in design in contrast to conventional designs where the differential 146 is distal from the cylinder block 117 and cylinder head 119 requiring greater engine height.

Transmission system 141 is of drum shifter type, , and includes output shaft 143, input shaft 142 and gear shifting drum 144. Crankshaft 120 and transmission system components such as input and output shafts 142 and 143 are substantially positioned in a plane perpendicular to the cylinder axis 200 which passes transversely through the centre of the crankshaft 120. The crankshaft 120 and transmission system components such as input and output shafts 142 and 143 are substantially positioned in a line perpendicular to the cylinder axis 200 which passes through the centre of the crankshaft 120. It follows that the crankshaft axis 122 is oriented perpendicular to the cylinder axis 200.

Each of input shaft and output shaft 142 and 143 are mounted with gears corresponding with transmission ratios for the engine. A 5 transmission ratio transmission system 141 with five forward gears is used in engine 100. A reverse idler gear 165 is also included within the transmission system 141. A centre point of crankshaft 120 and input shaft 142 is located substantially in the same plane, as vertical plane B-B, this facilitating engine 100 operability. Drive to the transmission system 141 is provided from crankshaft 120 through clutch 172.

Referring now to Fig. 7, the fork arrangement 610 of the drum shift 144 is such that shifting rail 615 will move with gear shifting fork 617. That is, fork 617 is made integral with shifting rail 615.

Fork 617 and fork 619 are fixed on the shifting rail 615. Gear shifting drum 144 rotates about axis X-X during a gear shift. Due to provision of helical grooves 620 in the gear shifting drum 144 , fork 617 moves along the axis Y-Y and so shifting rail 615 and fork 619 also moves on the axis Y-Y. Sleeve 625, which is engaged with fork 619, also moves along axis Z-Z which results in the gear shifting of reverse gear 165. This avoids increase in length of the gear shifting drum 144 to accommodate reverse idler gear 165, thus making the gear shift arrangement compact and not demanding increase in the size of crankcase 101. The gear shift arrangement also achieves a 30 % improvement in gear shifting effort without any requirement to increase the length of gear shifting drum 144. This aids compactness, since forks 617 and 619 and shifting rail 615 are made integral and gear shifting efficiency.

Engine 100 includes a balancer 160 on the cylinder axis 200, the balancer being driven by crankshaft 120. Balancer 160 is located adjacent a crankcase 101 wall opposite to the cylinder block mating surface 101A at which integral crankcase 101 is connected to cylinder block 117, that is, in section 105. The balancer 160 has design to reduce centre distance and to avoid interference, such as through clashing, with crankshaft 120 and counter balance 124.

Engine 100 is water cooled and includes water and oil pumps 180 as shown in Fig. 2. Such pumps are driven from the crankshaft 120 through the balancer 160 linking crankshaft 120 and drive shaft for water and oil pumps. Water and oil pumps 180 may be driven by one common drive shaft linked with engine crankshaft 120 through balancer 160. Such common drive shaft is located in section 105 of crankcase 101 opposite to the cylinder section 104. This further helps in achieving engine compactness.

Crankcase 101 may conveniently be used as a mounting member for mounting a range of engine components including starter motor 130 though the drive shaft of starter motor 130 is housed by an extension 102 of crankcase 101.

Crankcase housing portion 140 housing the differential 146 forms a mounting member, for mounting components of the exhaust system.

With reference to Figure 8, the differential 146 accommodated in housing portion 140 is positioned substantially in centre position of engine 100, thus accommodating the differential within width of the engine 100 making the engine compact and symmetric in design. The center of the differential 146 substantially matches with the wheel track center for a rear pair of wheels 550, as shown in Fig.

10, this arrangement allowing employment of identical and equal length of drive shaft (551,552) which reduces inventory cost as well wear and tear pattern is equal for both the drive shafts 551, 552.

Efficient lubrication of engine 100 is an important object and is simplified by use of a common oil to lubricate crankshaft 122, transmission system 141, differential 146 and timing chain 410 and valve train. Efficient lubrication requires that oil be filtered and returned to the oil sump to prevent oil starvation.

Lubricating oil for engine 100 is filtered by oil filter 185, of conventional kind and circulated through engine 100, first being supplied to lubricate timing chain 410 and valve train components, such as the valve guides and cams of the valve timing system. Oil then flows through a drainage pathway of the engine lubricating system, as shown by arrow 'A' in Figs. 5 and 6, in downward direction passing through passage/pocket 131 along an inclined surface defined by a downward sloping bottom wall 116 of the cylinder block 117 and cylinder head 119 towards the differential 146 through an opening 190 provided in the crank case wall 132. The slope is of acceptable grade ability (here 12.5 degrees to horizontal) to ensure effective lubrication. The said pocket131 is offset down side of cylinder head sealing area 119a towards camshaft bearing wall 133 so as to prevent oil flowing beyond the sealing area 119a. The said bottom wall 116 is offset or lowered towards downside of sealing area 119a so that oil will not accumulate in the seal area and gets drained easily.

Oil coming from valve train components, such as timing or cam chain, is diverted by a separator plate 192 to be collected through an opening 191 in the crankcase wall behind clutch 172 and taken away from the clutch 172 towards oil sump as shown by arrows 'B'.

Separator ribs 173 located in crankcase 101 and clutch cover 134 restricts oil entering into the clutch 172 from the oil sump 175. Oil is recalculated through the oil drainage pathway by the oil pump 180.

The advantage of keeping oil away from clutch 172, and keeping a reduced dynamic oil level in this part of engine 100 by above mentioned arrangements, is reduced friction.

Oil coming from the cylinder head 119 is also collected through pocket 131 and inclined passage at bottom wall116 of head and block below head cover seal 119a level and diverted towards differential 146 shown by arrows 'A' through opening 190 in crankcase 101 wall. Such an oil drainage pathway avoids loading of the head cover seal 119a.The seal could be T seal or any other suitable sealing arrangement.

Inclusion of the oil drainage pathway within the engine design to recover oil to an oil sump 175, where it can be recalculated through engine 100 by oil pump 180, substantially avoids challenges of oil starvation when a vehicle using the engine 100 as the prime mover negotiates upward and downward slopes. In addition, the engine 100, employing an integral crankcase structure 101, permits faster warm up of the common oil for engine, transmission and differential. Still further, the engine design avoids integration of crankcase 101 and cylinder block 117. Such design enables easier engine servicing and replace ability of either crankcase or cylinder block 117, if required.

Modifications and variations to the internal combustion engine of the present disclosure may be apparent to skilled readers of this disclosure. Such modifications and variations are deemed within the scope of the present invention.

WE CLAIM:

1. An internal combustion engine comprising a cylinder head; a cylinder block accommodating an engine cylinder having a cylinder axis; a crankshaft having an axis; and a crankcase having integral structure for accommodating crankshaft, alternator, clutch, transmission system and differential and said crankcase having two split portions connected in a plane parallel to said cylinder axis; wherein said crankcase structure of said engine comprises two sections substantially defined by a vertical plane containing said crankshaft axis, intersects said crankcase structure; wherein a first section of the crankcase structure includes said cylinder block and differential, said first section also including said crankcase housing portion for accommodating the differential located proximate said cylinder block and cylinder head; and said second section of the crankcase structure accommodates the transmission system and a balancer for driving at least one engine component accommodated in said crankcase structure.

2. An engine as claimed in claim 1 wherein said crankshaft and input and output shafts of said transmission system are positioned in said vertical plane.

3. An engine as claimed in claim 2 wherein said vertical plane is perpendicular to a cylinder axis and passing through the crankshaft axis.

4. An engine as claimed in any one of claims 1 to 3 being a single engine cylinder having a cylinder axis passing through said crankshaft axis is inclined to a horizontal plane at a small acute angle.

5. An engine as claimed in claim 4 wherein said small acute angle is in the range 10 to 20 degrees to the horizontal plane.

6. An engine as claimed in any one of the preceding claims wherein said transmission system includes a drum shift type gear shift arrangement with a plurality of forward gears (located within the crankcase) and a reverse gear, this gear being located outside the drum length.

7. An engine as claimed in claim 6 , the said transmission and gear shifting mechanism comprising forks and shifter rail arrangement wherein forks of one of the transmission gears are formed integral with said shifter rail.

8. An engine as claimed in claim 7 wherein forks of reverse transmission gear are formed integral with said shifter rail.

9. An engine as claimed in any one of claims 3 to 6 wherein a centre point of said crankshaft and input shaft are located substantially in said vertical plane.

10. An engine as claimed in any one of the preceding claims wherein said engine components include at least one of water and oil pumps; said pumps being driven from the crankshaft through said balancer linking said engine crankshaft and drive shafts for said pumps.

11. An engine as claimed in claim 10 wherein said balancer is located on the cylinder axis in the second section of the said integral crankcase.

12. An engine as claimed in claim 10 including water and oil pumps driven by one common drive shaft linked with said crankshaft through said balancer, said common drive shaft being located in said second section of said integral crankcase.

13. An engine as claimed in any one of the preceding claims wherein said cylinder head and cylinder block are not formed integral with the crankcase but are connected to said crankcase at a mating surface.

14. An engine as claimed in any one of the preceding claims wherein said crankcase portion housing the differential is positioned substantially in the centre of the engine so as not to exceed the engine width.

15. An engine as claimed in claim 14 wherein, when located in a vehicle, said differential comprising a pair of drive shaft is positioned substantially at the centre of a wheel track for said vehicle.

16. An engine as claimed in claim 15 wherein drive shafts for a pair of wheels of said vehicle are of identical and equal length.

17. An engine as claimed in any one of the preceding claims wherein said cylinder head is provided with an overhead valve train and a valve timing system lubricated with lubricating oil by an engine lubrication system wherein said engine lubrication system comprises an oil drainage pathway extending between said overhead valve train and an oil sump wherein said oil drainage pathway includes pockets, openings , oil separators for draining, separating and diverting oil away from the crankcase to the oil sump.

18. An engine as claimed in claim 17 wherein said oil drainage pathway passes through a pocket and along an inclined surface of the cylinder head and cylinder block, said surface being separated from said cylinder by a crankcase wall, about clutch and towards the oil sump.

19. An engine claimed in claim 18 wherein said pocket of drainage pathway is offset to the cylinder head sealing area towards the cam shaft bearing wall surface.

20. An engine claimed in claim 17 wherein said inclined surface is defined by a downward sloping bottom wall of the cylinder block and cylinder head; said bottom wall is offset or lowered towards downside of sealing area.

21. An engine as claimed in claim 17 wherein one of said oil separator is located adjacent a clutch and oil sump for directing oil away from the clutch to the oil sump.

22. An engine as claimed in claim 17 and 21 wherein lubricating oil flowing from an engine timing cavity is directed by said oil separator away from clutch portion towards the oil sump through an opening in a wall of the crankcase.

23. A vehicle comprising the engine of any one of claims 1 to 22.

24. A vehicle as claimed in claim 23 wherein said engine is mounted beneath a rear seat of a three or four wheel vehicle.