Abstract:
A cylinder block construction for an overhead cam shaft type V-engine having a timing chain passage formed to allow the cylinder block to be used for diametrically opposite cylinders. Timing chain guides are positioned in the timing chain passage with one of the timing chain guides providing chain tension control. Tension control is achieved by pivotably mounting one of the chain guides and biasing the chain guide against the timing chain with a chain tension means mounted in an opening in the cylinder block. Symmetrical openings are formed on either side of the timing chained passage to receive the chain tension means. The unused opening is capped.

Description:
This application is a continuation of application Ser. No. 236,612, filed Feb. 20, 1981, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an improved cylinder block for an overhead cam shaft type V-engine. 
     BACKGROUND OF THE INVENTION 
     In a V-type engine, in which an overhead cam shaft is driven by means of a timing chain, the cylinder block has to be formed with a chain passage through which the timing chain is allowed to pass. At the tensile and slack sides of the chain, arranged in a sliding manner, are two chain guides. The chain guide at the slack side is elastically urged toward the chain by a chain tensioner in order to apply a predetermined tension to the chain. Therefore, the chain passage has to be formed with a larger space outside of the slack side than the space outside of the tensile side of the chain. On the other hand, there is a case in which the timing chain is arranged at that side of one of the V-shaped cylinders, which is different from the side of the other cylinder, such that it is directed at a right angle with respect to a crankshaft. In the so-called &#34;tandem V-engine&#34; having its respective cylinders inclined in the longitudinal direction, for example, timing chains are sometimes arranged at the righthand side of one cylinder and at the lefthand side of the other cylinder, respectively. In the so-called &#34;transverse V-engine&#34; having its respective cylinders inclined in the transverse direction, on the contrary, timing chains are sometimes arranged at the front side of one cylinder and at the rear side of the other cylinder, respectively. 
     In such engines, if the slack side of the timing chain of one cylinder is positioned in the V-shaped space of two cylinders, the slack side of the timing chain of the other cylinder is positioned at the outer side which is opposite to the side facing that space. In other words, the tensile side of one cylinder and the slack side of the other cylinder are positioned at the sides facing that space. As a result, the conventional cylinder block, in which the larger space is formed only outside of the slack side of each timing chain, has to be formed into a different shape for each cylinder so that a completely different mold has to be prepared because of a slight difference in the shapes. Moreover, the number of different parts is so increased that their management becomes troublesome. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention has been conceived in view of the background thus far described and contemplates to provide a cylinder block for an overhead cam shaft type V-engine, in which the cylinder blocks of the respective cylinders forming a shape of letter &#34;V&#34; are made common so that the number of parts can be reduced. 
     In order to attain that comtemplation, according to the present invention, the chain passage, through which a timing chain is allowed to pass, is formed with substantially the same spaces at both the tensile and slack sides of the aforementioned timing chain. The above and other features of the present invention will be more fully understood from the following detailed description and with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     FIG. 1 is a side elevation in partial section showing an overhead cam shaft type V-engine for a motorcycle according to the present invention; 
     FIGS. 2 and 3 are sectional views taken along lines II--II and III--III of FIG. 1 respectively; 
     FIG. 4 is a sectional view showing a cylinder block taken along line IV--IV of FIG. 1; and 
     FIG. 5 is a sectional view taken along line V--V of FIG. 4. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIGS. 1 to 4, reference numerals 1 and 2 indicate a front cylinder and a rear cylinder, respectively, both of which are symmetrically mounted on crankcase 3. In FIG. 1, more specifically, the respective cylinders have cylinder heads 4a and 4b formed in adjacent sides with intake ports 5a and 5b, respectively, and in opposite sides with exhaust ports 6a and 6b, respectively. In the embodiment being described, cylinder blocks 20a and 20b described hereinafter and cylinder heads 4a and 4b are common between the front and rear cylinders 1 and 2. 
     Numeral 10 indicates a crankshaft, while numerals 11 and 12 indicate main and auxiliary shafts which form a part of a reduction gear mechanism. The rotation of the crankshaft 10 is transmitted to main shaft 11 through gear 13, keyed to crankshaft 10, and a clutch 14 mounted on main shaft 11. The rotation of main shaft 11 transmitted is further transmitted through reduction gear train 15 to auxiliary shaft 12, the rotation of which are further transmitted through damper 17 to damper shaft 16. The rotations of the damper shaft 16 are further transmitted through bevel gear 18 to output shaft 19. The output shaft 19 protrudes backwardly from the crankcase so that its rotations are transmitted to a rear wheel through a not-shown propeller shaft (not shown) connected to the protruding end thereof. 
     Numerals 20a and 20b indicates identical cylinder blocks of front and rear cylinders 1 and 2, respectively. Numerals 21a and 21b indicate pistons which are made reciprocally movable up and down within cylinder blocks 20a and 20b, respectively. Numerals 22a and 22b indicate connecting rods connecting pistons 21a and 21b and the aforementioned crankshaft 10. Incidentally, numerals 23a and 23b indicate ignition plugs. 
     Numerals 25a and 25b indicate overhead cam shafts positioned in cylinder heads 4a and 4b, respectively, so that intake and exhaust valves openings are controlled by rotation of cam shafts 25a and 25b. Cam shaft 25a of front cylinder 1 has sprocket 26a fixed thereto at the righthand side, as viewed forward (i.e., at the lefthand side of FIG. 1) of the engine, whereas cam shaft 25b of rear cylinder 2 has sprocket 26b fixed thereto at the lefthand side, as viewed forward of the engine. 
     Drive gear 27a for driving cam shaft 25a of the front cylinder 1 is secured in the vicinity of the righthand end portion of crankshaft 10, whereas drive gear 27b for driving cam shaft 25b of rear cylinder 2 is secured in the vicinity of the lefthand end portion. A dynamotor 30 is attached to the lefthand end portion of crankshaft 10. 
     Numerals 30a and 31a indicate outer gear and inner sprocket respectively, integrally made, which are made integral and rotatably born on intermediate shaft 32a arranged on a line joining crankshaft 10 and cam shaft 25a of front cylinder 1. Intermediate shaft 32a is eccentric at the portion, on which gear 30a and sprocket 31a are born, and has adjusting plate 33a attached to the axial end. Gear 30a is held in meshing engagement with gear 27a, made integral with crankshaft 10, so that the spacing between gear 30a and gear 27a is changed if intermediate shaft 32a is rotated. As a result, adjusting plate 33a is used to determine the rotational position of intermediate shaft 32a, and for this purpose bolt 34a engages an arcuate slot formed in adjusting plate 33a. More specifically, adjusting plate 33a and intermediate shaft 32a are made rotatable by loosening bolt 34a or are fixed by fastening bolt 34a. For the rear cylinder 2, gear 30b, sprocket 31b, intermediate shaft 32b, adjusting plate 33b and bolt 34b are identical in construction to corresponding parts of front cylinder 1. 
     Numerals 40a and 40b indicate chain passages, of which chain passage 40a is formed at the righthand side of front cylinder 1 whereas chain passage 40b is formed at the lefthand side of rear cylinder 2. Timing chain 41a runs on gears 26a and 31a through chain passage 40a, whereas timing chain 41b runs on gears 26b and 31b through chain passage 40b. Specifically, respective timing chains 41a and 41b are arranged at the right and left different sides of respective cylinders 1 and 2 such that they are directed at right angles with respect to the crankshaft 10. 
     Numeral 42b indicates a chain guide which is in sliding contact with the tensile side of timing chain 41b, as shown in FIG. 1, and which has its lower and upper ends retained in crankcase 3 and cylinder head 4b, respectively. On the other hand, numeral 43b indicates a chain guide in sliding contact with the slack side of timing chain 41b and which has its lower end portion rockably held by holding member 44b which in turn is fixedly inserted in crankcase 3. Chain guide 43b is elastically urged toward chain 41b by the action of chain tensioner 45b attached to cylinder block 20b. For the front cylinder 1, chain guide and the holding member are identical in construction to corresponding parts of rear cylinder 1. 
     Chain passages 40a and 40b formed in cylinder blocks 20a and 20b are formed with substantially the same sufficient spacings at the longitudinally front and rear sides of timing chains 42a and 42b, and 43a and 43b. The front and rear walls of chain passages 40a and 40b are symmetrically formed with openings 46a and 46b, and 47a and 47b, respectively. Chain tensioner 45b of rear cylinder 2, shown in FIG. 1, is fixed in righthand opening 46b of cylinder block 20b shown in FIG. 5, whereas cap 48b covers the other opening 47b. In front cylinder 1, on the other hand, chain tensioner 45a is fixed in the lefthand opening 47a of FIG. 5, whereas a cap (not shown) covers the other opening 46a. 
     Although, in the embodiment thus far described, the respective cylinders are arranged in the longitudinal direction, the present invention can naturally be applied to an engine of the type having the respective cylinders arranged in the transverse direction. 
     According to the embodiment described, moreover, since not only the cylinder blocks 20a and 20b but also the cylinder heads 4a and 4b are made common, the production efficiency of the engine can be greater than that obtainable when only the cylinder blocks are made common. 
     As has been described hereinbefore, according to the present invention, since the chain passage is simultaneously formed with the same spaces outside of both the tensile and slack sides of the timing chain, it can accommodate the chain guides and the chain tensioner even when the timing chain positions are reversed. As a result, it becomes possible to use the same cylinder blocks for the respective cylinders. If the cylinder blocks are to be cast, both production efficiency, supply and management are improved as only one mold is needed. 
     The invention is not to be limited to the embodiment shown in the drawings and described in the description, which is given by way of example and not of limitation but only in accordance with the scope of the appended claims.