| 摘要 |
<p>Disclosed herein is a four-stroke engine comprising a block having an intermediate portion defining a cylindrical bore having an axis, a head end, and a crankcase end, a head end portion extending from the head end of the intermediate portion in integral one-piece relation thereto and including a planar valve seat surface extending at an acute angle to the axis of the cylindrical bore and having a valve seat with a center and a perimeter defined by a radius extending from the center, and a crankcase end portion extending from the crankcase end of the intermediate portion in integral one-piece relation thereto and including a partially cylindrical portion coaxially aligned with the cylindrical bore, and a recessed portion extending from the partially cylindrical portion and having a peripheral wall spaced at a distance greater than the radius from a line extending perpendicularly to the valve seat surface and from said valve seat center.</p> |
