Abstract: A valve-operating mechanism includes cam followers carried on an engine body 1 with their tip ends being in sliding contact with the cam, rocker arms integrally connected to the cam followers and carried on the engine body coaxially with said cam followers with their tip ends being connected to valves, and valve springs for biasing the valves in closing directions. In the valve-operating mechanism, auxiliary springs are connected to the cam followers for biasing and turning the cam followers in the same directions as directions in which the valve springs bias and turn the rocker arms through the valves. Thus, a couple of forces generated over the axis of the cam follower and the rocker arm due to biasing force of the valve spring can be offset in a valve-closing process.

Abstract: In a handheld type four-cycle engine, a valve operation mechanism includes a camshaft rotatably supported in a cylinder head so as to open and close an intake valve and an exhaust valve and a timing transmission placed on one side outside an engine main body and providing association between a crankshaft and the camshaft, and a centrifugal clutch for power output is mounted on the crankshaft on the opposite side outside the engine main body. The timing transmission and the centrifugal clutch being positioned at the two ends of the crankshaft improves the weight balance, the centre of gravity of the engine can be made as close to the central part of the crankshaft as possible, which, together with the reduced weight, can enhance the operability of the engine.

Abstract: In a handheld type four-cycle engine, a valve operation mechanism includes a camshaft rotatably supported in a cylinder head so as to open and close an intake valve and an exhaust valve and a timing transmission placed on one side outside an engine main body and providing association between a crankshaft and the camshaft, and a centrifugal clutch for power output is mounted on the crankshaft on the opposite side outside the engine main body. The timing transmission and the centrifugal clutch being positioned at the two ends of the crankshaft improves the weight balance, the centre of gravity of the engine can be made as close to the central part of the crankshaft as possible, which, together with the reduced weight, can enhance the operability of the engine.

Abstract: An engine head cover structure has a head cover joined to the upper end of a cylinder head so as to define a valve operation chamber therebetween. The head cover includes therein an oil recovery chamber to which oil resided in the valve operation chamber is recovered by suction and a breather chamber that removes blowby gas from the valve operation chamber being provided in the head cover. The breather chamber is defined between a partition plate mounted on an inner wall of the head cover via clips and a surface of the roof of the head cover, and the oil recovery chamber is defined between the partition plate and a partition body welded thereto. It is thus possible to form the oil recovery chamber and the breather chamber without splitting the roof of the head cover, thereby making inspection of the joint for oil tightness unnecessary.

Abstract: In a handheld type four-cycle engine, a valve operation mechanism includes a camshaft rotatably supported in a cylinder head so as to open and close an intake valve and an exhaust valve and a timing transmission placed on one side outside an engine main body and providing association between a crankshaft and the camshaft, and a centrifugal clutch for power output is mounted on the crankshaft on the opposite side outside the engine main body. The timing transmission and the centrifugal clutch being positioned at the two ends of the crankshaft improves the weight balance, the centre of gravity of the engine can be made as close to the central part of the crankshaft as possible, which, together with the reduced weight, can enhance the operability of the engine.

Abstract: In a handheld type four-cycle engine, a valve operation mechanism includes a camshaft rotatably supported in a cylinder head so as to open and close an intake valve and an exhaust valve and a timing transmission placed on one side outside an engine main body and providing association between a crankshaft and the camshaft, and a centrifugal clutch for power output is mounted on the crankshaft on the opposite side outside the engine main body. The timing transmission and the centrifugal clutch being positioned at the two ends of the crankshaft improves the weight balance, the centre of gravity of the engine can be made as close to the central part of the crankshaft as possible, which, together with the reduced weight, can enhance the operability of the engine.

Abstract: A valve-operating mechanism includes cam followers carried on an engine body 1 with their tip ends being in sliding contact with the cam, rocker arms integrally connected to the cam followers and carried on the engine body coaxially with said cam followers with their tip ends being connected to valves, and valve springs for biasing the valves in closing directions. In the valve-operating mechanism, auxiliary springs are connected to the cam followers for biasing and turning the cam followers in the same directions as directions in which the valve springs bias and turn the rocker arms through the valves. Thus, a couple of forces generated over the axis of the cam follower and the rocker arm due to biasing force of the valve spring can be offset in a valve-closing process.

Abstract: In a handheld type four-cycle engine, a valve operation mechanism includes a camshaft rotatably supported in a cylinder head so as to open and close an intake valve and an exhaust valve and a timing transmission placed on one side outside an engine main body and providing association between a crankshaft and the camshaft, and a centrifugal clutch for power output is mounted on the crankshaft on the opposite side outside the engine main body. The timing transmission and the centrifugal clutch being positioned at the two ends of the crankshaft improves the weight balance, the centre of gravity of the engine can be made as close to the central part of the crankshaft as possible, which, together with the reduced weight, can enhance the operability of the engine.

Abstract: An engine head cover structure has a head cover joined to the upper end of a cylinder head so as to define a valve operation chamber therebetween. The head cover includes therein an oil recovery chamber to which oil resided in the valve operation chamber is recovered by suction and a breather chamber that removes blowby gas from the valve operation chamber being provided in the head cover. The breather chamber is defined between a partition plate mounted on an inner wall of the head cover via clips and a surface of the roof of the head cover, and the oil recovery chamber is defined between the partition plate and a partition body welded thereto. It is thus possible to form the oil recovery chamber and the breather chamber without splitting the roof of the head cover, thereby making inspection of the joint for oil tightness unnecessary.

Abstract: An oil reservoir chamber, a crank chamber and a valve-operating chamber are provided in an engine body. The oil reservoir chamber and the crank chamber are in communication with each other through a through-hole, and the crank chamber and the valve-operating chamber are in communication with the each other through a one-way valve which is opened upon rising of the pressure in the crank chamber. The valve-operating chamber and the oil reservoir chamber are in communication with each other through an orifice. By utilizing a pressure pulsation in the crank chamber, an oil mist produced in the oil reservoir chamber is circulated from the oil reservoir chamber to the crank chamber, the valve-operating chamber and the oil reservoir chamber. Thus, in any operational attitude of an engine, the lubricating oil can be circulated without use of special oil pump.

Abstract: In a handheld type four-cycle engine, a valve operation mechanism includes a camshaft rotatably supported in a cylinder head so as to open and close an intake valve and an exhaust valve and a timing transmission placed on one side outside an engine main body and providing association between a crankshaft and the camshaft, and a centrifugal clutch for power output is mounted on the crankshaft on the opposite side outside the engine main body. The timing transmission and the centrifugal clutch being positioned at the two ends of the crankshaft improves the weight balance, the center of gravity of the engine can be made as close to the central part of the crankshaft as possible, which, together with the reduced weight, can enhance the operability of the engine.

Abstract: An oil reservoir chamber, a crank chamber and a valve-operating chamber are provided in an engine body. The oil reservoir chamber and the crank chamber are in communication with each other through a through-hole, and the crank chamber and the valve-operating chamber are in communication with the each other through a one-way valve which is opened upon rising of the pressure in the crank chamber. The valve-operating chamber and the oil reservoir chamber are in communication with each other through an orifice. By utilizing a pressure pulsation in the crank chamber, an oil mist produced in the oil reservoir chamber is circulated from the oil reservoir chamber to the crank chamber, the valve-operating chamber and the oil reservoir chamber. Thus, in any operational attitude of an engine, the lubricating oil can be circulated without use of special oil pump.

Abstract: A crankcase includes first and second case halves which are coupled to each other at a parting plane extending to obliquely intersect the axis of first and second bearing portions. A cylinder barrel and the first bearing portion are formed by molding integrally on the first case half to form an engine block. The second bearing portion is formed by molding integrally on the second case half and a side cover is coupled to an outer side surface of the engine block to define a valve operating chamber for accommodation of a valve operating mechanism. Thus, the distance between the first and second bearing portions for supporting opposite ends of a crankshaft can be reduced without being interfered by the valve operating mechanism, thereby enhancing the durability of the crankshaft. The valve operating mechanism can be assembled after coupling of the first and second case halves forming the crankcase, whereby the assemblability of the valve operating mechanism can be improved.

Abstract: A 4-cycle engine, includes an engine body, having a piston, a crankshaft and a crank chamber, an independent oil reservoir chamber adjacent the crank chamber, the crankshaft extending into the oil reservoir chamber from the crank chamber, an oil mist generator disposed in the independent oil reservoir chamber and being secured to and driven by the crankshaft, and a valve-operating chamber. Further, the engine includes a first passageway connecting the oil reservoir chamber with the crank chamber to provide oil mist communication therebetween, a second passageway connecting the crank chamber with the valve-operating chamber to provide oil mist communication therebetween, and a third passageway connecting the valve-operating chamber with the independent oil reservoir chamber to provide oil communication therebetween, wherein the three chambers and the three passageways form a lubrication oil feed channel to provide one-way circulation of lubrication oil therethrough.

Abstract: A system for lubricating a 4-cycle engine includes a crank chamber having a crank portion of a crankshaft contained therein and storing a lubricating oil therein, a valve operating chamber having a valve-operating device contained therein, wherein the crank chamber and the valve-operating chamber are provided in an engine body. An oil mist producing means is provided in the crank chamber for producing an oil mist from the lubricating oil. The crank chamber and the valve operating chamber are in communication with each other above an oil level of the lubricating oil in the crank chamber through a control valve which is opened upon rising of the pressure in said crank chamber and closed upon reduction of the pressure in said crank chamber. The valve-operating chamber is substantially in communication at its upper portion with the atmosphere, and in communication at its bottom with the crank chamber through an orifice.

Abstract: A 4-cycle engine, includes an engine body having a piston, a crankshaft and a crank chamber, an oil reservoir chamber adjacent the crank chamber and independent therefrom, the oil reservoir chamber having an oil mist generator therein drivably connected to the crankshaft, and a valve-operating chamber. Further, a first passageway connects the oil reservoir chamber with the crank chamber to provide oil mist communication therebetween. A second passageway connects the crank chamber with the valve-operating chamber to provide oil mist communication therebetween. Additionally, a third passageway connects the valve-operating chamber with the independent oil reservoir chamber to provide oil communication therebetween, wherein the three chambers and the three passageways form a lubrication oil feed channel to provide one-way circulation of lubrication oil therethrough.

Abstract: An oil reservoir chamber, a crank chamber and a valve-operating chamber are provided in an engine body. The oil reservoir chamber and the crank chamber are in communication with each other through a through-hole, and the crank chamber and the valve-operating chamber are in communication with the each other through a one-way valve which is opened upon rising of the pressure in the crank chamber. The valve-operating chamber and the oil reservoir chamber are in communication with each other through an orifice. By utilizing a pressure pulsation in the crank chamber, an oil mist produced in the oil reservoir chamber is circulated from the oil reservoir chamber to the crank chamber, the valve-operating chamber and the oil reservoir chamber. Thus, in any operational attitude of an engine, the lubricating oil can be circulated without use of special oil pump.

Abstract: A lubricating and breather system is provided for use with a crankcase and a cylinder block in both a horizontal-type engine and a vertical-type engine, in which the discharge of a blow-by gas and the circulation of oil separated from the blow-by gas into the crankcase can be reliably performed. When the engine is of a vertical-type, it includes a crankcase which is disposed so that a second bearing boss is located above a first bearing boss. The second bearing boss is provided with an annular chamber into which splashed oil produced in the crankcase is passed. A breather chamber is provided in a cylinder block to communicate with the annular chamber, and includes a first return bore provided in a portion thereof which is a lowermost portion when in the horizontal-type engine, and a second return bore in a portion thereof which is a lowermost portion when in the vertical-type engine.

Abstract: An oil reservoir chamber 22 in an engine E is formed into a tubular shape having annular corner portions 22a and 22b at opposite ends, and an oil slinger 25 is secured to a crankshaft 13 and has two splashing blades 25a and 25b with their tip ends being in proximity to the corner portions 22a and 22b, so that a lubricating oil in the oil reservoir chamber 22 is splashed by at least one of the two splashing blades 25a and 25b during rotation of the oil slinger 25 with any operative position of the engine E. Thus, a lubricating oil mist can be produced with any operative position of the engine E by the oil slinger of a simple structure including the two blades.

Abstract: A rotary disc of a speed-regulating centrifugal governor driven by a crank shaft is rotatably fitted to a crank case of an engine. While part of the rotary disc is immersed in lubricating oil stored in the crank case, the rotary disc is disposed adjacent to a timing gear and impeller blades project from the outer peripheral face of the rotary disc so as to form an impeller. Further, guide walls for guiding oil splashed by the rotation of the impeller to the timing gear are integrally formed with the inside wall of the crank case, so that the timing gear of a valve mechanism can be effectively lubricated with the splashed oil.