How to Set the Shift Cam Assy on an Outboard Boat

How to Set the Shift Cam Assy on an Outboard Boat

The shift cam assy is a very important part of your boat’s outboard engine. It shifts the inlet camshaft to bring one of two possible cam profiles into contact with the inlet valves, altering not only the timing and the cam lobe height but also the lift (how wide the valve is opened). The low-rpm cam profile has less timing advance and duration, which reduces overlap (the period during which the inlet valves open before the exhaust valves close), improving efficiency and reducing emissions.

It is important to correctly set the shift cam assy so that it is firmly and properly held in neutral position when the shift lever is manipulated. However, there are many factors that can cause the shift cam assy to become incorrectly set. The most common problem is when the splined hole in the shift cam becomes misaligned.

In order to resolve this issue, you will need to drain the gear oil and remove the shift cam bushing/seal assembly. Using a drill and a special long shift shaft screw, you can then see down the splined hole in the cam. Once you can see that the splined hole is centered, the shift cam assy should easily slide back into place.

Another common problem is when the shift cam assy is shifted out of its neutral position. Normally, when the shift lever is manipulated the push rod 19 is pushed by a spring 23 against the shift cam 18A. The end of the push rod 19 engages one of the recesses 22 of the shift cam 18. Then, when the shift lever is manipulated again, the end of the push rod is urged against the shift cam 18A in a different direction to engage an other one of the three recesses 22, which selects a new position of the shift cam assy.

Generally speaking, the shift cam assy is a link mechanism that is located inside the engine room covered by an engine cover. Depending on the type of shift cam, it may be difficult to provide sufficient space for this link mechanism within an outboard engine.

Therefore, a different design of the shift cam supporting structure must be prepared for each type of the rotational or vertically-movable shift cam. As a result, manufacturers are required to prepare and administer two types of gear cases, which is troublesome for the administration in production.

The present invention provides a solution for these problems. As shown in FIGS. 2 and 3, the shift mechanism 14B of the first embodiment has major components such as a shift rod 15, a shift cam 18B, an assist device 17, a push rod 19 and a shift dog 20. The shift cam 18B has a rear face which includes a can profile having three consecutive recesses 22. The end of the push rod is always urged by a spring against the shift cam, so that it rests in one of the three recesses 22, which sets the shift cam assy in one of three shift positions.

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