Deciding on Gear Appropriately on an Outboard Motor

Are You Damaging Your Gearbox when Altering Gear?

Clutch Dog Gearboxes

Outboard motors and most stern drive gearboxes (like Mercruiser’s Alpha drives) use a Dog Clutch set up for selecting and shifting gear.

If you choose gear slowly and careabsolutely with these gearboxes you will actually be damaging the gear box.

Do you hear a grinding or chattering noise when choosing either forward or reverse gear?

In the event you do, something needs to change or at some point your decrease unit will not have any drive and it will always bounce out of gear.

Firstly I will clarify how the decrease unit/gearbox works.

They’ve an input shaft that is pushed from the engine or ‘energy head’. (This enter shaft is called the driveshaft. The driveshaft has a gear connected to the bottom of it called the Pinion gear. The pinion gear is always in constant mesh with the forward and reverse gears. When ever the motor is running, the pinion gear is rotating the forward and reverse gears. Between the forward and reverse gear there’s the mechanism that selects gear. This is called the Clutch Dog.

The Clutch Canine sits on the propeller shaft that protrudes out the back of the gearbox and drives the propeller. The Clutch Canine has an inner spline that’s in fixed mesh with the propeller shaft.

Image the Clutch Canine having a entrance and a back. At each finish it has large, square teeth. When you choose gear on the motor you move the Clutch Dog forwards and backwards along the propeller shaft.

When the Clutch Canine is moved to select gear it engages with the same sized square tooth on the particular gear that is being engaged.

Remember that each of the output gears (forward and reverse) are rotating as they’re in fixed mesh with the pinion gear (input gear).

If you choose gear slowly, the Clutch Dog will slowly move into mesh with the gear. This slow movement causes the teeth of the gear to ‘skip’ over the enamel on the Clutch Dog. This continuous skipping wears away the good sharp edges of the tooth and will eventually cause the motor to leap out of gear.

Easy methods to Select Gear

· The way to avoid doing damage to your gearbox is to positively choose gear. This means to literally bang the engine into gear so that you hear one clean engagement of the gearbox, not chatter.

· You should also pause in impartial when shifting from forwards to reverse or vice versa. This allows the propeller time to stop spinning.

· Do not shift into reverse when you are moving forwards quickly. It creates a huge quantity of unnecessary force on the gearbox (and engine). Sluggish the boat down of the plane, come back to an idle and pause in neutral to let the boat slow right down. Reverse is only a reverse, not a break…

Engine Idle Speed Too High

· Another cause for damage being executed to the Clutch Canine is your idle speed may be too high. If you happen to motor is idling higher than around 900rpm in neutral you will be doing damage every time you are selecting gear.


· Make positive your idle speed is set to what the Manufacturer recommends!

· Positively choose gear

· Pause in impartial between gear changes.

· Let the boat gradual down before becoming reverse

· Have the gear oil modified every a hundred hours or yearly, which ever comes first.

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