Abstract: Arrangement for inserting a spark plug in a V-type engine cylinder head, comprising a separate sleeve surrounding the spark plug and removably insertable in the wall of the combustion chamber by screw threading. The spark plug extends through the cam chain chamber and can be removed without interference with the operation of the endless cam chain.

Abstract: Disclosed is an engine for motorcycles, having first and second engine blocks disposed in a form like V on the frame of the motorcycle. Pistons reciprocatably and slidably received in the engine blocks are connected to first and second crank pins of a crankshaft through respective connecting rods. Representing the included angle between the central axes of first and second cylinders for the first and second piston by .alpha., the rotational phase of the second crank pin is offset from that of the first crank pin by an angle .pi.-2.alpha. in the opposite side of the central axis of the first cylinder to the central axis of the second cylinder. A balancer weight is attached to that portion of the crank shaft positioned opposite to the first and second crank pins and on the bisector line of the angle formed between the first and second crank pins.