TECHNICAL FIELD

[0001] The present subject matter relates generally to an internal combustion engine for a two wheeled vehicle. More particularly, the present subject matter relates to a cylinder block of the internal combustion engine.

BACKGROUND

[0002] An internal combustion (IC) engine comprises a cylinder head, abutting a cylinder block to form a combustion chamber where the burning of air fuel mixture occurs. The forces generated due to combustion of air fuel mixture is transferred to a piston which is capable of reciprocating inside the cylinder block, and this reciprocating motion is transferred to rotary motion of the crankshaft through a connecting rod by the slider crank mechanism. The cylinder head comprises an intake port and an outlet port which allow the entry of air-fuel mixture and exit of burnt gases from the combustion chamber. The entry of air- fuel mixture to the combustion chamber and the exit of burnt gases are controlled by intake and exhaust valves which are configured to open and close based on the running cycle of the IC engine. Generally, this opening and closing is controlled by a valve train mechanism present on the cylinder head and actuated by a camshaft by the transmission of drive from the crankshaft using a cam chain. The crankshaft drives the camshaft and this is achieved by a cam chain which operably meshes between the camshaft and crankshaft. Additionally, lubricating oil is circulated throughout the cylinder head to lubricate the valve train mechanism and the cam chain. Further, as in some IC engines, the lubricating oil also circulates around the combustion chamber to extract heat in an oil cooling system of the IC engine. The cam chain is disposed in a cam chain chamber located on one side of the cylinder head and cylinder block. A chain tensioner is used which exerts a constant pressure on the cam chain throughout its operation. The chain tensioner is accommodated in a tensioner hole on the cylinder block. The lubricating oil lubricating the valve train mechanism in the cylinder head and cooling the combustion chamber is typically drained back to the crankcase through the cam chain chamber. Due to constraints in profile of chain tensioner and the tensioner hole there is a chance that lubricating oil circulating inside the cam chain chamber can penetrate and stagnate around the area between the inner surface of the tensioner hole and the chain tensioner. The resulting oil stagnation can lead to oil leakage, overheating around the area and reduced life of the chain tensioner. This is undesirable, as it affects the overall performance of the IC engine and life of the corresponding components in the long run. Hence, a cylinder block is proposed in the present subject matter in order to alleviate one or more drawbacks highlighted above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to reference like features and components.

[0004] Fig. 1. illustrates the side view of a two wheeled vehicle employing an embodiment of the present subject matter.

[0005] Fig. 2. illustrates the isometric view of an internal combustion engine employing the embodiment of the present subject matter.

[0006] Fig. 3. illustrates the cut sectional side view (X-X) of the internal combustion engine according to the embodiment of the present subject matter.

[0007] Fig. 4a. illustrates the side view of a cylinder block according to the embodiment of the present subject matter.

[0008] Fig. 4b. illustrates the cut sectional top view of the cylinder block according to the embodiment of the present subject matter.

[0009] Fig. 5. illustrates a perspective view of a chain tensioner according to the embodiment of the present subject matter. [00010] Fig. 6. illustrates the cut sectional isometric view of the cylinder block and the chain tensioner assembly according to the embodiment of the present subject matter.

[00011] Fig. 7a. illustrates the cross section view of a typical cylinder block and the chain tensioner indicating a prior art.

[00012] Fig. 7b. illustrates the cross section view of the cylinder block and the chain tensioner according to the embodiment of the present subject matter.

DETAILED DESCRIPTION

[00013] Various features and embodiments of the present subject matter here will be discernible from the following further description thereof, set out hereunder. According to an embodiment, an internal combustion engine (IC) described here operates in four cycles and comprises of a single cylinder with liquid cooling system. Such an IC engine is installed in a straddle type vehicle. It is contemplated that the concepts of the present invention may be applied to other types of vehicles such as two wheeled vehicles with step-through frame employing a mechanical rack type chain tensioner having a similar outer profile within the spirit and scope of the present subject matter. Further "front" and "rear" , and "left" and "right" referred to in the ensuing description of the illustrated embodiment refer to front and rear, and left and right directions as seen from a rear portion of the IC engine and looking forward. Furthermore, a longitudinal axis unless otherwise mentioned, refers to a front to rear axis relative to the engine, while a lateral axis unless otherwise mentioned, refers generally to a side to side, or left to right axis relative to the engine. The detailed explanation of the constitution of parts other than the present subject matter which constitutes an essential part has been omitted at suitable places.

[00014] An internal combustion (IC) engine comprises a cylinder block having a cylinder bore, a piston reciprocating in the cylinder bore, a cylinder head located above the cylinder block and a combustion chamber interposed between the cylinder head and the cylinder block. During operation of the internal combustion (IC) engine, the burning of air fuel mixture occurs in the cylinder block. The forces generated due to combustion of air fuel mixture is transferred to a piston which is capable of reciprocating inside the cylinder block, and this reciprocating motion is transferred to rotary motion of the crankshaft though a connecting rod by the slider crank mechanism. The cylinder head comprises at least one intake valve and at least one outlet valve which control the intake of air fuel mixture inside the combustion chamber, and controls the exit of exhaust gases after combustion respectively. In other embodiments, (such as described for the straddle type two wheeled vehicle as described in the present subject matter) two intake valves and two outlet valves are used. The intake valves and exhaust valves are controlled by a valve train mechanism and are synchronized using a transmission system such as a cam chain to transfer rotary movements of the crankshaft to drive a camshaft. The camshaft is disposed on the cylinder head which in turn actuates the valve train mechanism. The valve train mechanism comprises two rocker arms supported on two rocker shafts respectively. The rocker arms operate the two intake valves and outlet valves to open and close. The two intake valves and the two exhaust valves are capable of reciprocating and the stroke movement of the valves is actuated by the two rocker arms. While a forward stroke is actuated by the rocker arm, the return stroke is actuated by the bias force of an elastic member connected to the valve such as a return spring.

[00015] The main function of the cam chain is to transmit and synchronize the rotation of the crankshaft and the camshaft for optimum control of opening and closing of intake valve and exhaust valve during the particular IC engine cycle. Generally, the cam chain operably meshes between the camshaft and crankshaft and is enveloped inside a cam chain chamber formed together with the cylinder head and cylinder block. A driving gear is mounted on the crankshaft and a driven gear is mounted on the camshaft. The cam chain is mounted in the cam chain chamber and meshed between the driving gear and driven gear. Typically, the driven gear has a number of teeth twice as that of the number of teeth of the driving gear. This ensures that for every two rotation of the crankshaft, the camshaft rotates once. The cam chain is usually supported by plurality of chain guides (like a pivot chain guide) to support and guide the cam chain to maintain tension and prevent chain slippage. The cam chain transmission is a very important aspect in the effective design of the IC engine as it results in reduced noise, and low vibration operation.

[00016] During normal use of the IC engine, the valve train mechanism requires constant lubrication for smooth operation of the various components. Typically, in any IC engine of the two wheeled vehicle, there is an oil path which extends from the crankcase to the cylinder head. The oil path transverses through the cylinder block to reach the cylinder head and once it reaches the valve train mechanism, the lubricating oil is made to circulate around the camshaft, rocker arms, the intake valves, outlet valves and various other components of the valve train mechanism. The lubricating oil needs to be drained back to an oil sump located in the crankcase body after lubrication. This is done by draining the lubricating oil through the cam chain chamber back to the oil sump. Further, in some IC engines employing oil cooling systems, the lubricating oil is circulated along a cooling jacket around the combustion chamber to extract heat. The temperatures around the combustion chamber can exceed 130°centigrade and to employ additional cooling, the lubricating oil can be made to circulate in cooling jackets around the combustion chamber. After circulation, typically the lubricating oil also used for cooling is drained to the oil sump by draining it into the cam chain chamber.

[00017] Commonly in single cylinder IC engines, a mechanical rake type tensioner is used, wherein a pushrod is operated by an elastic member such as a spring exerts a constant pressure of the cam chain. Generally, the cam chain is supported by two chain guides namely, fixed chain guide, and pivot chain guide. The chain tensioner is designed to facilitate the movement of a pushrod with sufficient forward stroke to maintain optimum tension in the cam chain by exerting pressure on the pivot chain guide. When the cam chain shows signs of decreasing tension, the tensioner pushes the cam chain to bring back the tension to the optimum value. The pushrod is designed to only move in one direction, and backward stroke is prevented by a ratchet mechanism in which a ratchet interlocks on serrated teeth provided on an exposed part of the pushrod. The positive bias force on a pushrod by the elastic member pushes on the cam chain guide to maintain optimum tension. There is normally a housing which encloses the pushrod and the elastic member. The pushrod is keyed to the housing so that it cannot rotate along its length. The cylinder block comprises a tensioner hole bored through its body to access the cam chain chamber. The tensioner hole accommodates the chain tensioner.

[00018] In typical IC engines having mechanical rake type tensioner, the pushrod is constantly lubricated on the surface on which it moves to have a smooth operation. This is achieved by utilizing the lubricating oil which splashes around the cam chain chamber in the IC engine. But, due to design of the chain tensioner and the tensioner hole in which it is accommodated, the lubricating oil penetrates the chain tensioner and gets accumulated at the area between the chain tensioner and the inner surface of the tensioner hole, particularly around the junction wherein the tensioner hole has a stepped profile of differing diameter accommodating the chain tensioner. Generally, many cylinder block designs such as one described in the present invention, the tensioner hole comprises a stepped portion of differing diameter. The design of the cylinder block is such that, the length of the longer edge of the cam chain chamber at the cylinder head end is greater than the length of the longer edge at the crankcase portion. This gives a tapering profile which hinders the accommodation of the tensioner if the tensioner hole was bored completely to access the cam chain chamber. The stepped portion provides a means to provide a secure seating for the tensioner. Further, the cylinder head is designed for machining four stud holes for securing the cylinder block, cylinder head to the crankcase. If the stepped portion is not provided, the tensioner hole can foul with the stud hole or disposed close to the stud hole, which can cause stress concentration failures. Also, in many designs the tension of the cam chain is a critical value and in order to set the appropriate tension and adjust the forward movement and backward movement of the plunger, it is desirable to place the tensioner in a desired position. Furthermore, to machine the tensioner hole completely would result in wastage of material. Hence, the suitably stepped portion is retained.

[00019] This problem is specially pronounced in IC engines of vertical type that is, a cylinder axis (the axis on which the piston of the IC engine reciprocates) is almost vertical (at an angle of 70° to 90°) to the central longitudinal axis of the two wheeled vehicle. In such vertical IC engine, wherein due to accessibility the chain tensioner is oriented almost perpendicular disposition to the cam chain chamber, the drained oil from the cylinder head and cooling jacket tends drain below to the crankcase via the inner wall of the cam chain chamber from which the chain tensioner is mounted. Further, the lubricating oil tends to drain through a path taken by the pivot chain guide. Since, the chain tensioner is always in contact with the pivot chain guide, there is increased tendency for the lubricating oil to penetrate inside the chain tensioner. Furthermore, due to vertical disposition of IC engine and design of chain tensioner, during two wheeled vehicle banking during a turn can force the lubricating oil to come in contact with the chain tensioner and increase the chances of penetrating inside.

[00020] The penetration and stagnation of lubricating oil between the chain tensioner and the inner surface of the tensioner hole, will lead to variety of problems such as high probability of oil leaking out of the cylinder block due to excess oil stagnation, it will lead to overheating around the area of oil and may damage the chain tensioner and reduce the life. Since, hot oil is penetrating the chain tensioner, it can damage the internal parts of the chain tensioner causing wear and corrosion. Damage to the chain tensioner can affect the dynamics of functioning which can lead to loose cam chain causing excess noise and vibration and accumulation of lubricating oil may damage the pivot chain guide. Such issues can damage IC engine components and prevent the IC engine to reach its maximum performance. Hence, it is very essential to prevent the accumulation of lubricating oil in the area around the tensioner hole and chain tensioner.

[00021] Hence, to obviate the limitations, the proposed subject matter discloses, a cylinder block for an IC engine wherein the tensioner hole in cylinder block accessible to the cam chain chamber and configured to accommodate the chain tensioner comprises a junction, said junction and the cam chain chamber connected by a groove. This exposes the junction to the cam chain chamber, and thus can freely provide a passage for the lubricating oil to drain back to the cam chain chamber. This results in draining the deposited lubricating oil in the junction and clears the junction of any oil deposits.

[00022] With the above design changes, the following advantages can be obtained such as, smooth performance of the IC engine, longer life of the cam chain, use of a cylinder block wherein the groove is manufactured during the process of casting thus avoiding additional machining operation.

[00023] According to the present subject matter to attain the above objectives, the present subject matter proposes the IC engine for a two wheeled vehicle comprising: a crankcase body, said crankcase body enclosing a crankshaft; a cylinder block extending beyond the crankcase body; a cylinder head disposed above the cylinder block, said cylinder head enclosing a camshaft; a cam chain chamber formed in the IC engine along the cylinder block, and the cylinder head; a cam chain operably connecting the crankshaft and the camshaft, said cam chain disposed within the cam chain chamber; a chain tensioner configured to exert a positive bias force on the cam chain, said chain tensioner comprising a housing having a shoulder; wherein, said cylinder block configured to have a tensioner hole bored on one side of the of the cylinder block to accommodate the chain tensioner, said chain tensioner capable of accessing the cam chain chamber to exert the positive bias force on the cam chain; said tensioner hole includes a first portion and second portion, said first portion disposed proximal to the cam chain chamber and said second portion disposed distal to the cam chain chamber and the second portion having a greater diameter than the first portion to form a stepped profile to accommodate the outer profile of the chain tensioner; said stepped profile encloses the shoulder of the chain tensioner; a groove cut on the first portion of the tensioner hole connecting the axial surface of the stepped profile to the cam chain chamber. [00024] Further, the cylinder block can be manufactured with the groove during manufacturing by casting process that is an D as-cast cylinder blockD . The groove can also be manufactured by machining it after casting process.

[00025] The present subject matter along with all the accompanying embodiments and their other advantages would be described in greater detail in conjunction with the figures in the following paragraphs.

[00026] Fig. 1. illustrates a two wheeled vehicle, having the cylinder block (204) according to the embodiment of the present subject matter. In a preferred embodiment, the IC engine (101) is vertically disposed, that is, the cylinder block (204) is substantially oriented at an angle of 70° to 90° (refer angle C in Fig. 3) with respect to the crankcase. The IC engine (101) is installed in a straddle type motorcycle, and the present invention can be implemented in other two wheeled vehicles having similar mechanical rack type chain tensioner (301) without deviating from the scope of the present subject matter. The two wheeled vehicle comprises, a front wheel (110), a rear wheel (103), a frame structure, a fuel tank (121) and seat (106). The frame structure includes a head pipe (111), a main tube (not shown), a down tube (not shown), and seat rails (not shown). The head pipe (111) supports a steering shaft (not shown) and two telescopic front suspension(s)

(114) (only one shown) is attached to the steering shaft through a lower bracket (107). The two telescopic front suspension(s) (114) supports the front wheel

(110). The upper portion of the front wheel (110) is covered by a front fender

(115) mounted to the lower portion of the telescopic suspension (114) at the end of the steering shaft. A handlebar (108) is fixed to upper bracket (not shown) and can rotate to both sides. A head light (109), visor guard (125) and instrument cluster (not shown) is arranged on an upper portion of the head pipe (111). The down tube is located in front of the IC engine (101) and stretches slantingly downward from head pipe (111). Main tube is located above the IC engine (101) and stretches rearward from head pipe (111). The IC engine (101) is mounted at the front by the down tube and connects the rear of the IC engine (101) at the rear portion of the main tube. A fuel tank (121) is mounted on the horizontal portion of the main tube (112). Seat rails are joined to main tube and stretch rearward to support a seat (106). A rear swing arm (118) is connected to the frame structure to swing vertically, and a rear wheel (103) is connected to rear end of the rear swing arm (118). Generally, the rear swing arms (118) are supported by a mono suspension (117) (as illustrated in the present embodiment) or two suspensions on either side of the two wheeled vehicle. A tail light unit (104) is disposed at the end of the two-wheeled vehicle at the rear of the seat (106). A grab rail (105) is also provided on the rear of the seat rails (126). The rear wheel (103) arranged below seat (106) rotates by the driving force of the IC engine (101) transmitted through a chain drive (116) from the IC engine (101). A rear fender (127) is disposed above the rear wheel (103). There is front brake (119) and back brake (122) arranged on the front wheel (110) and back wheel (103) respectively.

[00027] Fig. 2a. illustrates a perspective view of the IC engine (101) employing the embodiment of the present subject matter. The IC engine (101) is made up of a cylinder head assembly (203), cylinder block (204), a cylinder head cover (202) and crankcase (205). The crankcase (205) is made up of left-hand crankcase (205d) and right-hand crankcase (205b). The IC engine (101) also has a sprocket (205e) disposed outside (on the other side) of the LH crankcase (205d) and is linked to the rear wheel (103) with the chain drive (116). In the present embodiment, the IC engine (101) is an oil cooled engine utilizing lubricating oil for cooling the combustion chamber. The oil is circulated around cooling jackets disposed around the combustion chamber to extract heat and consequently cool the surroundings around the combustion chamber and cylinder block (204). As a consequence, the IC engine (101) comprises a heat exchanger (240) which functions to cool the hot oil flow coming from the input (241). The heat exchanger (240) is exposed to the natural flow of atmospheric air which cools the oil before it circulates back into the IC engine (101) through the output (242). The cylinder block (204) comprises a tensioner hole (610) having a flange portion (610d) to receive and secure the chain tensioner (301) inside it. In the present embodiment, referring to Fig. 2 the tensioner hole (610) is facing the rearward direction of the IC engine (101), as viewed from the two wheeled vehicle rear. [00028] Fig. 2b. illustrates a cut section of the IC engine (101) along line X-X showing the main components of the cam chain transmission system according to the embodiment of the present subject matter. The IC engine (101) comprises a piston (not shown) reciprocating in the cylinder block (204) due to force imparted to it by the combustion of air fuel mixture. This reciprocating motion is converted and transferred to a rotary motion of a crankshaft (304) through a connecting rod (not shown). A driving gear (209) is connected to the crankshaft (304) and rotates integrally with it. The cylinder head (203) comprises of a valve train arrangement to control the intake of air fuel mixture and outlet of exhaust gases. The camshaft (208a) controls the movement of the valve train arrangement and comprises of at least one inlet cam lobe (not shown) and at least one outlet cam lobe (not shown) which actuates the valve train when required. A cam chain (201) operably connects the crankshaft (304) and camshaft (208a) to drive the camshaft (208a) in the cylinder head (203). A driven gear (208) is integrally attached to the camshaft (208a) and the cam chain (201) is configured to be meshed between the driving gear (209) and driven gear (208) to transfer rotary motion of the crankshaft (304) to the camshaft (208a). In the present embodiment, the ratio of the driven gear (209) is twice that of driving gear (208) such that for every two revolutions of crankshaft (304) the camshaft (208a) should rotate one revolution. Since transmission by the cam chain (201) is a positive drive, the transmission losses are minimal, provided parameters such as tension on the chain is maintained to the best optimum value. Further, two chain guides, namely pivot chain guide (302) and fixed chain guide (303) is disposed to support and guide the cam chain (201) during its operation. The chain guides serve two important functions, to support and guide the cam chain (201) within the cam chain chamber (501) to prevent wobbling and whipping action, and to maintain a constant pressure on the cam chain (201) by transferring the pressure exerted by the chain tensioner (301) to the cam chain (201). The latter functionality described is a very important function of the pivot chain guide (302). The pivot chain guide is mounted on one side of the cam chain chamber (501) and comprising a contact portion (302a) which is configured to come in contact with the flat surface of the pushrod (502) of the chain tensioner (301).

[00029] Fig. 4a. illustrates the front view of the cylinder block (204) according to the embodiment of the present subject matter. In the present embodiment, a tensioner hole (610) is bored through the cylinder block (204) to access the cam chain chamber (501) within the cylinder block (204). The tensioner hole (610) is having its inner circumferential profile matching with that of the chain tensioner (301) and is capable of receiving the chain tensioner (301). The chain tensioner (301) is mounted such that it is oriented angularly with respect to the horizontal axis. Further, an longitudinal axis of the chain tensioner (Z-Z) is approximately perpendicular to the imaginary line (Y-Y) joining the centre of the driving gear (209) and driven gear (208).

[00030] Fig. 4b. illustrates the cross sectional view of the cylinder block (204) when viewed from the top according to the embodiment of the present subject matter. The Fig. 4b. illustrates the importance of having a stepped portion (610c) of the inner surface of the tensioner hole, as without the stepped portion it would foul with a stud hole (620) and may lead to catastrophic failures.

[00031] Fig. 5. illustrates the perspective view of the chain tensioner (301) according to the embodiment of the present subject matter. The chain tensioner (301) comprises a housing (504), the pushrod (502), said pushrod (502) having a contact portion (502a), and a mounting flange (505). The housing (504) encloses an elastic member (not shown) which applies positive bias force on the pushrod (502) to cause a forward stroke movement. Further, the housing (504) comprises of a locking mechanism (not shown) to prevent the backward stroke of the pushrod (502) due to the constant forces the pushrod is subjected to by the cam chain (201). The housing (504) is accommodating the elastic member and the locking member and hence, designed to be considerably large as compared to the pushrod (502). Further, the chain tensioner (301) has the housing (504) having a diameter considerably larger than the pushrod (502) and the chain tensioner (301) is suitably designed to have the desired shape. Hence, due to this profile the chain tensioner (301) has a sudden change in diameter (see portion of chain tensioner having reference numerical 503) from the housing (504) to the pushrod (502) at a junction (703). The chain tensioner (301) comprises the mounting flange (505) which matches with the outer contours of the tensioner hole (610d) and designed to receive the mounting flange (505) when the chain tensioner (301) is assembled inside the tensioner hole (610). The mounting flange (505) and the outer contours of the tensioner hole (610d) have bored opening (403a) to insert fasteners and secure the chain tensioner (301) after assembly. As illustrated in Fig. 4a. the outer contours of the tensioner hole (610d) is shaped to receive the mounting flange (505) of the chain tensioner (301) and comprises another set of bored openings (403a) to match with the bored opening on the mounting flange (505).

[00032] Fig. 6. illustrates cut sectional isometric view of the cylinder block (204) and the chain tensioner (301) according to the embodiment of the present subject matter. It is observed that the inner surface of the tensioner hole (610) in the cylinder block (204) matches the outer profile of the chain tensioner (301). To facilitate accommodating the chain tensioner (301), the inner surface of the tensioner hole (610) comprises similar stepped profile having differing diameter. The tensioner hole (610) includes a first portion (610b) and second portion (610a), said first portion (610b) disposed proximal to the cam chain chamber (501) and accommodating the pushrod (502) of chain tensioner (301). The second portion (610a) is disposed distal to the cam chain chamber (501) and accommodating the housing (504). The second portion (610a) is having a greater diameter than the first portion (610b) to form a stepped profile (610c) to accommodate the outer profile of the chain tensioner (301).

[00033] Further referring to Fig. 6, when the chain tensioner (301) is assembled inside the tensioner hole (610), the stepped portion of the chain tensioner (301) matches with the stepped portion of the inner surface of the tensioner hole (610) forming a junction (703). Typically, in IC engines the cylinder head components are cooled by the lubricating oil circulating within the crankcase. In the present embodiment in addition to cooling of cylinder head components, the IC engine (101) being a oil cooled engine, a oil gallery surrounds the combustion chamber which extracts heat from the combustion chamber and cools the combustion chamber. The lubricating oil also after circulating around the cylinder head drains into the cam chain chamber (501). This lubricating oil after circulation around the cylinder head components is made to drain to the cam chain chamber (501) to drain it back to the oil sump in crankcase. This lubricating oil which drains into cam chain chamber (501) has a probability of entering the chain tensioner (301) and gets deposited in the junction (703). Further, in IC engine (101) wherein the cylinder block (204) and cylinder head are oriented substantially vertically (in the present embodiment, the cylinder head and cylinder block (204) are oriented about an cylinder axis, said cylinder axis oriented at an angle of 70° to 90°) the lubricating oil while draining into the crankcase body through the cam chain chamber (501), there is an increased tendency for the lubricating oil to take a path along the pivot chain guide (302) and deposit around the zone of the pushrod and enter the chain tensioner (301). Due to the location of the chain tensioner (301) and the pushrod (502) located perpendicular of the IC engine (101), there may arise a possibility of a layer of oil present in the cam chain chamber (501) and getting stagnated in junction (see Fig. 7a, oil collection zone 702 in prior art) and not being capable of flowing back inside to the crankcase. In such situations, there is chance that the lubricating oil may leak or otherwise, affect the functioning and performance of the chain tensioner (301). The lubricating oil may have elevated temperatures due to cooling of the combustion chamber and this heated oil may damage the chain tensioner (301) and corrode the surfaces causing contamination and leak. Hence, a groove (601) is introduced connecting the stepped portion (610c) of the tensioner hole to the cam chain chamber (501). The groove (601) exposes the junction (703) of oil accumulation to the cam chain chamber (501) to enable drainage of lubricating oil. This ensures that even if lubricating oil is deposited in the junction, the lubricating oil will not leak and interfere in the functioning of the chain tensioner (301). The groove (601) in one embodiment is located towards the bottom base of the tensioner hole (610) to enable effective drain of lubricating oil. [00034] Fig. 7a. illustrates the cross section view of a typical cylinder block (204) and the chain tensioner (301) indicating a prior art. It is observed that, during drain of lubricating oil after circulation, there is a probability of entering inside the tensioner hole (610) through the gap between the pushrod and the inner surface of the tensioner hole (610). Once, the lubricating oil enters the tensioner hole (610), it gets accumulated in the junction (see 702) and results in oil leakage and affects the performance of the chain tensioner (301). Fig. 7b. illustrates the cross section view of the cylinder block (204) and the chain tensioner (301) according to the embodiment of the present subject matter. It is observed that the accumulated oil is drained out through the groove (601) back to the cam chain chamber (501) where its drains back to the oil sump below the crankcase.

[00035] It will be appreciated that the present subject matter and its equivalent thereof offers many advantages, including those which have been described forthwith. Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of the present subject matter, the present disclosure may be practiced other than as specifically described.