If you have a small boat that you take out fishing, or even a larger boat that is designed to carry multiple passengers, you will likely have an outboard motor in the back. These are very common in smaller boats, the propulsion system that drives them, consisting of an engine, propeller, and a gearbox.
They are unique in that they provide not only the propulsion that you need to go through the water, but also steering control. They are designed to be used on the back of the boat, pivoting on mountings that allow you to control the direction of the thrust of the motor. This article will address the gearbox of an outboard motor, and what you can do to inspect and maintain this very important aspect of an outboard motor that you may personally own.
What Is An Outboard Motor?
As mentioned before, these motors are on the back of small watercraft, and are controlled by someone manually operating it, typically sitting at the back of the boat where the motor is located. These are probably the most common types of motors that will be found on boats, and despite how simple they appear to be, they are actually very sophisticated devices.
They are divided up into multiple components including the powerhead which is the engine, the midsection which is where the exhaust housing is located, and at the very bottom is called the gearbox. The motor also contains a tiller, a mounting bracket, and an anti-ventilation plate adjacent to the water intake, propeller and the skeg. Let’s now look at what a gearbox does, and how you can begin to determine whether or not it needs maintenance.
What Is An Outboard Motor Gearbox?
Also referred to as the gear case, this is where the thrust of the outboard motor actually originates. First of all, there is a crankshaft which descends from the engine, directly into the gearbox itself. This is connected to the pinion, something that comes through the driveshaft, and this is where the rotational power of the motor occurs. There are two separate gears adjacent to the pinion which will rotate in an opposing direction.
Both the gears and the pinion are turning the moment that the engine is powered up, and by adjusting a lever on the outside of the motor, the clutch that is located in between the two gears, can be moved, allowing you to choose a direction. The clutch itself is actually fitted with the gear, mounted directly on the propeller shaft. This rotates the propeller, and as a result of it spinning in the water, is what will ultimately create your thrust. Essentially, the outboard motor gearbox is what allows propulsion to occur, transmuting the power of the engine into its physical equivalent, allowing the boat to move.
Outboard Motor Gearbox Inspection Tips
If you have recently purchased a new outboard motor, then you will likely never have to worry about the functionality within the gearbox itself. Most motors last for many years before they need any type of maintenance at all, but if yours is older, there are a few things that you might want to consider doing. Those that do not have any type of mechanical skills will likely take this to a boating shop where it can be maintenance to buy a professional. However, if you would like to attempt to improve the functionality of your motor, then these outboard motor gearbox inspection tips will help you do just that.
Crankshaft And Driveshaft Inspections
If you are not getting as much thrust as you once did from your outboard motor, there could be a problem with the connection of the driveshaft in the crankshaft. The crankshaft is what the piston rod will turn, taking this back-and-forth motion, also called reciprocating motion, converting it into a Rotary spin. The crankshaft is what will turn the driveshaft, which is what descends down the spine of the motor into the gearbox itself. If there has been some type of disconnect between the crankshaft and driveshaft, the place where vertical spinning changes to horizontal spinning, which is what causes the propeller to spin, then you are not going to have proper thrust.
Checking The Cavitation Plate
This particular section sits above the propeller, the place where air bubbles are created and exhaust exits the motor. The bubbles that you see are caused by the spinning propeller. If you have ever looked down into the water, and have seen bubbles coming up, right above this is the anti-ventilation or cavitation plate. The purpose of this particular plate is to reduce the amount of bubbles that are produced which can actually affect the spinning of the propeller.
Although floating debris will still be a problem, this plate makes it possible for the water flow around the propeller blades to be much more consistent, allowing your boat to be propelled at higher speeds. If this plate has been damaged, or is removed, not only will it affect the efficiency of the motor, but the propeller surface can actually wear away much more quickly, necessitating its replacement. This is located adjacent to the gearbox, something that you should take a look at, since you will be making adjustments in this area.
Gears Inside The Gearbox
In most standard motors, there are five separate gears, each responsible for a particular purpose. A right hand propeller will have a clutch that will be engaged with gears 1 and 2, and sent through gear 5 to the output shaft. A left hand propeller, when engaged with the clutch, will connect with gear 3 and 4, and will also connect with the output shaft through gear 5. If any of these gears are worn down, it can affect the ability of the propeller to spin. You can either order the parts to fix this yourself, or if you are simply noticing that the output speed from the propeller is not as fast, or if the clutch is not working, it will definitely be time to open up the gearbox and make replacements or adjustments.
By using these easy outboard motor gearbox inspection tips, you should be able to determine if there is a problem in the gearbox which needs to be resolved. The most obvious indication that something is wrong on this part of your outboard motor is that the clutch will not engage, or the speed of your motor has diminished significantly. You can try to fix this on your own, which is possible for people that have worked on outboard motors before, or you can take this to a local shop to have it repaired. At the very least, you will be able to recognize what may be happening with your outboard motor which may need to be repaired to improve its performance levels, or may simply need to be replaced.