A valve assembly for an engine includes a gas exchange valve, a valve guide, and a seal. The gas exchange valve includes a valve stem. The valve guide includes an outer surface having a stem seal retention surface disposed at a seal end thereof. The valve stem extends through the valve guide such that the valve is reciprocally movable over a range of travel along the longitudinal axis with respect thereto. The seal is mounted to the stem seal retention surface of the valve guide such that the seal is in running, sealing engagement with the valve stem. The stem seal retention surface includes a shoulder surface to help retain the seal.

A method of determining a condition of a component (e.g., valves) of an engine having a manifold air pressure sensor during a cold test includes providing pressurized air to an intake of the engine. The method includes rotating a crankshaft of the engine. The method includes measuring pressures with the manifold air pressure sensor as a function of crankshaft rotational position. The method includes comparing the pressures with a predetermined baseline. The method includes indicating a condition of the component based on the comparison of the pressures with the baseline.

The present invention concerns an air motor comprising a piston and a housing, the piston being received in the housing and dividing the housing into two primary chambers of variable volume. Said motor comprises a first direct supply valve for supplying a first primary chamber of the two primary chambers and a second direct supply valve for supplying the other primary chamber, said two valves each being movable relative to at least one respective seat. The first valve and the second valve are mounted on a same stem movable relative to the housing in a direction parallel to the direction of movement of the piston, and the stem is configured to be moved between a first position and a second position by moving means activated by the piston.

A two-stroke, opposed-piston engine includes a cylinder with an inlet piston controlled inlet port and an exhaust piston controlled exhaust port, the cylinder defining a combustion chamber with the inlet piston and the exhaust piston, a charge air channel in flow communication with the inlet port, a conduit extending directly from the combustion chamber to the charge air channel, and a valve arranged to selectively open and close flow communication through the conduit.

A valve assembly for an engine includes a gas exchange valve, a valve guide, and a seal. The gas exchange valve includes a valve stem. The valve guide includes an outer surface having a stem seal retention surface disposed at a seal end thereof. The valve stem extends through the valve guide such that the valve is reciprocally movable over a range of travel along the longitudinal axis with respect thereto. The seal is mounted to the stem seal retention surface of the valve guide such that the seal is in running, sealing engagement with the valve stem. The stem seal retention surface includes a shoulder surface to help retain the seal.

An internal combustion engine may include at least one cylinder and at least one hollow-heat valve. The at least one hollow-head valve may include a valve shaft and a valve head, and may be guided in a valve shaft guide. The engine may also include at least one valve seat ring on which the valve head sealingly lies when the at least one hollow-head valve is closed. The engine may additionally include a valve shaft seal with at least two seal lips and oil disposed between the valve shaft and the valve shaft guide. The at least one valve seat ring may be composed of a sintered metal including infiltrated copper. The valve shaft may include one of a chromium-containing coating and a boron carbide-containing coating.

An enhanced piston for improving the efficiency of an internal combustion engine has a cylinder with a combustion chamber and a lower cylinder portion. A cylinder head is disposed on the cylinder. An enhanced piston is moveably disposed within the cylinder and is connected to a piston rod. The enhanced piston has a piston cavity. There is an upper piston valve connected to an upper piston valve rod. The upper piston valve is disposed within the piston cavity wherein the upper piston valve selectively seals said piston cavity from the combustion chamber. A piston cavity port is disposed on a bottom portion of the piston cavity and is selectively opened and closed with a lower piston valve. The lower piston valve seals the piston cavity port from the lower cylinder portion. This way the gases are selectively sealed in the piston cavity under pressure until released in the combustion chamber.

An enhanced piston for improving the efficiency of an internal combustion engine has a cylinder with a combustion chamber and a lower cylinder portion. A cylinder head is disposed on the cylinder. An enhanced piston is moveably disposed within the cylinder and is connected to a piston rod. The enhanced piston has a piston cavity. There is an upper piston valve connected to an upper piston valve rod. The upper piston valve is disposed within the piston cavity wherein the upper piston valve selectively seals said piston cavity from the combustion chamber. A piston cavity port is disposed on a bottom portion of the piston cavity and is selectively opened and closed with a lower piston valve. The lower piston valve seals the piston cavity port from the lower cylinder portion. This way the gases are selectively sealed in the piston cavity under pressure until released in the combustion chamber.

An engine is provided with: a crank case that has a first crank shaft insertion hole and a second crank shaft insertion hole along the vertical direction; a crank shaft that is inserted into the first and second shaft insertion holes; and a cylinder unit that extends in the front-rear direction from the crank case. The cylinder unit is provided with a cylinder base that is positioned inside the crank case, and a cylinder block that is positioned outside the crank case. The cylinder unit is detachably attached to the crank case.

An internal combustion engine may include at least one cylinder and at least one hollow-heat valve. The at least one hollow-head valve may include a valve shaft and a valve head, and may be guided in a valve shaft guide. The engine may also include at least one valve seat ring on which the valve head sealingly lies when the at least one hollow-head valve is closed. The engine may additionally include a valve shaft seal with at least two seal lips and oil disposed between the valve shaft and the valve shaft guide. The at least one valve seat ring may be composed of a sintered metal including infiltrated copper. The valve shaft may include one of a chromium-containing coating and a boron carbide-containing coating.