Deciding on Gear Accurately 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 carefully with these gearboxes you will actually be damaging the gear box.

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

If you do, something needs to vary or one day your lower unit will not have any drive and it will always bounce out of gear.

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

They’ve an input shaft that is driven from the engine or ‘power head’. (This input 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 fixed 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 is 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 inside spline that is in fixed mesh with the propeller shaft.

Picture the Clutch Dog having a front and a back. At every end it has massive, square teeth. When you select gear on the motor you move the Clutch Canine forwards and backwards alongside the propeller shaft.

When the Clutch Dog is moved to select gear it engages with the identical sized square teeth on the particular gear that is being engaged.

Keep in mind that both of the output gears (forward and reverse) are rotating as they are in constant mesh with the pinion gear (input gear).

If you select gear slowly, the Clutch Canine will slowly move into mesh with the gear. This sluggish movement causes the enamel of the gear to ‘skip’ over the tooth on the Clutch Dog. This steady skipping wears away the great sharp edges of the tooth and will eventually cause the motor to jump out of gear.

Find out how to Select Gear

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

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

· Do not shift into reverse if you end up moving forwards quickly. It creates an enormous quantity of pointless force on the gearbox (and engine). Sluggish the boat down of the plane, come back to an idle and pause in impartial to let the boat gradual proper down. Reverse is purely a reverse, not a break…

Engine Idle Speed Too High

· Another cause for damage being completed to the Clutch Canine is your idle speed is likely to be too high. For those who motor is idling higher than round 900rpm in neutral you will be doing damage each time you’re selecting gear.


· Make sure your idle speed is set to what the Producer recommends!

· Positively select gear

· Pause in impartial between gear changes.

· Let the boat sluggish down earlier than turning into reverse

· Have the gear oil changed each one hundred hours or yearly, which ever comes first.

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