This invention relates to a cam shaft drive arrangement for a four-cycle engine and more particularly to such a drive arrangement for a four-cycle engine of an outboard motor.
In many four-cycle engines, the cam shaft is driven from the crankshaft by means of a flexible transmitter in the form of a toothed belt. When belt drive cam shaft timing arrangements are employed, the belt is positioned outside of the actual engine body. That is, unlike gear or chain timing mechanisms, the belt should be protected from the engine lubricant and preferably positioned externally of the main engine body. This presents some particular potential difficulties.
That is, because the timing drive belt is positioned externally of the engine, this means that the drive for the cam shaft is spaced from the outermost bearing that supports both the crankshaft and the cam shaft. Thus, bending loads are placed on the cam shaft that can cause high wear to either the bearing and/or the shaft which is borne.
It is, therefore, a principal object of this invention to provide an improved timing belt arrangement for four-cycle internal combustion engines.
It is a still further object of this invention to provide an improved bearing and belt drive arrangement for the cam drive of a four-cycle engine.
The aforenoted problems are particularly acute in conjunction with outboard motors. As is well known, such outboard motors are quite compact in nature. Because of the premium for space, the positioning of the cam shaft drive on the end of the engine, as is necessitated by the use of a drive belt, tends to increase the overall length of the engine. This is particularly undesirable with applications where space is at a premium, such as with an outboard motor application.
These problems are further aggravated when other accessories are driven off of the engine. That is, these further accessory drives can add considerably to the length of the engine.
It is, therefore, a still further object of this invention to provide an improved cam shaft drive arrangement employing a drive belt for use in outboard motors.