A crankshaft (1) for a crankcase scavenged two stroke piston engine (2) is disclosed. The crankshaft (1) is configured to rotate around a rotation axis (ax) during operation. The crankshaft (1) comprises a crankpin (3) configured to move in a crank plane (cp) during operation, and a first and a second counterweight (5, 7) arranged on either side (S1, S2) of the crank plane (cp). The first counterweight (5) has a first outer radius (r1) measured from the rotation axis (ax) and the second counterweight (7) has a second outer radius (r2) measured from the rotation axis (ax). The first outer radius (r1) is smaller than the second outer radius (r2). The present disclosure further relates to a power unit (10), a crankcase scavenged two stroke piston engine (2), and a hand-held power tool (20).

Balancer shaft 5 and 6 rotatably set through bearings 1114 and an oil pump 2 driven by power from the balancer shaft 5 and 6 are provided in a balancer housing. Oil discharged from an outlet portion 42 of the oil pump 2 is supplied to a main oil gallery 10 through an outlet passage 48. A bearing filter 55 that filters a part of the oil is provided in the outlet passage 48 that extends from the outlet portion 42. A communication passage 50 that branches off from the outlet passage 48 and communicates with the bearings 1114 supplies a part of the oil having been filtered by the bearing filter 55 to the bearings 1114. By filtering the oil that is going to be supplied to the bearing portion, decrease in durability of the bearing portion can be suppressed.

Methods and systems are provided for a stabilizing device of a crankshaft. In one example, a method may comprise randomizing a shape of each fin of a plurality of fins and a space between each fin. Randomizing the fins may decrease noise production as a result of airflow generated by the fins.

Methods and systems are provided for a stabilizing device of a crankshaft. In one example, a method may comprise randomizing a shape of each fin of a plurality of fins and a space between each fin. Randomizing the fins may decrease noise production as a result of airflow generated by the fins.

A balance weight having one or more journals with a reduced mass portion disposed between a pair of journal portions that define circumferentially extending bearing surfaces. The reduced mass portion has a body, which defines a circumferentially extending bearing surface that is concentric with the bearing surfaces on the journal portions, and at least one stiffening structure that is configured to resist flexing of the journal portions relative to one another due to the transmission of bending loads through the balance shaft.

A balance weight having one or more journals with a reduced mass portion disposed between a pair of journal portions that define circumferentially extending bearing surfaces. The reduced mass portion has a body, which defines a circumferentially extending bearing surface that is concentric with the bearing surfaces on the journal portions, and at least one stiffening structure that is configured to resist flexing of the journal portions relative to one another due to the transmission of bending loads through the balance shaft.

A balance weight having one or more journals with a reduced mass portion disposed between a pair of journal portions that define circumferentially extending bearing surfaces. The reduced mass portion has a body, which defines a circumferentially extending bearing surface that is concentric with the bearing surfaces on the journal portions, and at least one stiffening structure that is configured to resist flexing of the journal portions relative to one another due to the transmission of bending loads through the balance shaft.

A balance weight having one or more journals with a reduced mass portion disposed between a pair of journal portions that define circumferentially extending bearing surfaces. The reduced mass portion has a body, which defines a circumferentially extending bearing surface that is concentric with the bearing surfaces on the journal portions, and at least one stiffening structure that is configured to resist flexing of the journal portions relative to one another due to the transmission of bending loads through the balance shaft.

A propeller shaft (1) that is a power transmission shaft has a shaft member (2) as a tubular body made of iron-based metal and a balance weight (3) made of iron-based metal and welded to an outer peripheral surface of this shaft member (2). At least a part of the balance weight (3) of the propeller shaft (1) is covered with a sacrificial metal coating (4) made of sacrificial corrosion prevention material that contains metal whose ionization tendency is higher than that of metal forming the shaft member (2). With this, it is possible to suppress local progression of corrosion at a periphery of the balance weight (3) and improve durability of the propeller shaft (1).

An object of the present invention is to provide a balancer apparatus for an internal combustion engine that can improve design flexibility in the internal combustion engine. The balancer apparatus includes left and right balancer shafts 21L and 21R each including a balancer weight 21a and a rear-side shaft portion 19b and a front-side shaft portion 19a provided on both sides of the weight portion 21a in a rotational axis direction, a rear-side housing 22R including a bearing holding portion 22Rd surrounding an outer periphery of the rear-side shaft portion 19b and rotatably supporting the rear-side shaft portion 19b, and a front-side housing 22F including a bearing holding portion 22Fd rotatably supporting the front-side shaft portion 19a.