An engine is described having a crankcase, a liner and a head assembly. The crankcase is split along a plane defining a two part crankcase, where fluid passages are passing through only one of the crankcase portions, so as to not require crossing the split line. A connecting rod also includes a tapered end, and the piston has a complementary carrier receiving the connecting rod.

The overhead camshaft engine (10) includes a cylinder block (11), a crankcase (12) attached to a lower part of the cylinder block to define a crankcase chamber (32), a bearing retaining member (60) attached to a part of the cylinder block, a crankshaft (20) rotatably supported by a pair of bearings (21, 22) supported by the cylinder block and the bearing retaining member, respectively, and a crankshaft pulley (53) attached to a part of the end of the crankshaft projecting outward from the bearing supported by the bearing retaining member.

A small air-cooled internal combustion engine includes an aluminum cylinder block at least partially defining an aluminum cylinder bore, an aluminum cylinder head attached to the aluminum cylinder block, and an aluminum push rod tube separate from and press fit between the aluminum cylinder block and the aluminum cylinder head. The aluminum push rod tube includes a cylinder block end portion, a cylinder head end portion, and a main body extending between the cylinder block end portion and the cylinder head end portion.

A small air-cooled internal combustion engine includes an aluminum engine block including a cylinder extending along a longitudinal cylinder axis and a block mounting surface, a piston configured to reciprocate within the cylinder, a crankshaft coupled to the piston and configured to rotate about a crankshaft axis in response to reciprocation of the piston, and an aluminum crankcase cover including a cover mounting surface. The block mounting surface contacts the cover mounting surface. The block mounting surface and the cover mounting surface are both positioned at an angle to the crankshaft axis and the angle is not 90 degrees.

A machine having a reciprocating slider crank mechanism, wherein an axis of a crankshaft, an axis of a first balancer shaft and an axis of a second balancer shaft are not arranged on the same plane, wherein vibration is highly controlled. The machine includes the reciprocating slider crank mechanism configured so as to satisfy setting formulae below:
U.sub.Cr=U.sub.P0.5
.sub.Cr=180
U.sub.B(Fr)={U1.sub.B(Fr).sup.++U2.sub.B(Fr).sup.2}.sup.1/2
U1.sub.B(Fr)=U.sub.P0.5{Lx.sub.B(Rr)/(Lx.sub.B(Rr)Lx.sub.B(Fr))}
U2.sub.B(Fr)=U.sub.P0.5{Ly.sub.B/(Lx.sub.B(Rr)Lx.sub.B(Fr))}
.sub.B(Fr)=180arctan(U2.sub.B(Fr)/U1.sub.B(Fr))
U.sub.B(Rr)={U1.sub.B(Rr).sup.2+U2.sub.B(Rr).sup.2}.sup.1/2
U1.sub.B(Rr)=U.sub.P0.5{Lx.sub.B(Fr)/(Lx.sub.B(Fr)Lx.sub.B(Rr))}
U2.sub.B(Rr)=U2.sub.B(Fr)
.sub.B(Rr)=180arctan(U2.sub.B(Rr)/U1.sub.B(Rr)).

A machine having a reciprocating slider crank mechanism, wherein an axis of a crankshaft, an axis of a first balancer shaft and an axis of a second balancer shaft are not arranged on the same plane, wherein vibration is highly controlled. The machine includes the reciprocating slider crank mechanism configured so as to satisfy setting formulae below:

U.sub.Cr=U.sub.P0.5

.sub.Cr=180

U.sub.B(Fr)={U1B(Fr).sup.++U2B(Fr).sup.2}.sup.1/2

U1.sub.B(Fr)=U.sub.P0. 5{Lx.sub.B(Rr)/(Lx.sub.B(Rr)Lx.sub.B(Fr))}

U2.sub.B(Fr)=U.sub.P0.5{Ly.sub.B/(Lx.sub.B(Rr)Lx.sub.B(Fr))}

.sub.B(Fr)=180arctan(U2.sub.B(Fr)/U1.sub.B(Fr))

U.sub.B(Rr)={U1.sub.B(Rr).sup.2+U2.sub.B(Rr).sup.2}.sup.1/2

U1.sub.B(Rr)=U.sub.P0.5{Lx.sub.B(Fr)/(Lx.sub.B(Fr)Lx.sub.B(Rr))}

U2.sub.B(Rr)=U2.sub.B(Fr)

.sub.B(Rr)=180arctan(U2.sub.B(Rr)/U1.sub.B(Rr)).

The certainty of supplying air to a scavenging channel through a piston groove is improved. In a cylinder wall 2, a gas venting port 10 is formed below and adjacent to a scavenging port 6a. The gas venting port 10 is independent from the scavenging port 6a, and is opened/closed by a piston as each of an air port 4a and the scavenging port 6a is. Upon a piston groove 8 being brought into communication with the gas venting port 10 as a result of the piston moving up (FIG. 1(II)), blown-back gas in a piston groove 8 can move to a crankcase through the gas venting port 10. Along with this, air can enter the piston groove 8 from the air port 4a.

In a single cylinder internal combustion engine in which a plug hole is provided striding between a cylinder head and a head cover, and an intake side camshaft and an exhaust side camshaft are disposed at positions sandwiching the plug hole therebetween, a long hole portion formed long in a direction orthogonal to axes of the camshafts is formed as a part of the plug hole. A part of a plurality of cam holder attaching bolts used for fastening the cam holder to the cylinder head are disposed within the long hole portion. A breather chamber disposed around the long hole portion is formed between the head cover and a breather plate attached thereto.

A small air-cooled internal combustion engine includes an aluminum cylinder block, an aluminum cylinder head welded to the aluminum cylinder block, and a weld securing the aluminum cylinder block to the aluminum cylinder head, wherein a joint having a first length is formed between the aluminum cylinder block and the aluminum cylinder head and wherein the weld extends for a second length that is at least 25% of the first length.

A secondary-air supply structure for a saddle-ride type vehicle includes a cylinder block and a cylinder head which extend upward from a crankcase, and right and left secondary-air supply pipes which are connected to the right and left of an exhaust outlet portion of the cylinder head and through which secondary air is supplied to an exhaust port. The right and left secondary-air supply pipes extend from the front surface of the cylinder head to the right and left of the cylinder head, respectively, and include bent-back pipe sections extending along the right and left surfaces of the cylinder head and bent back toward the front side.