Are you damaging your gearbox when changing gears?
clutch gearboxes
Outboard motors and most stern drive gearboxes (such as Mercruiser’s Alpha transmissions) use a dog clutch setup to select and change gears.
If you select gear slowly and carefully with these gearboxes, you will actually be damaging the gearbox.
Do you hear a grinding or grinding noise when you select forward or reverse?
If it does, something needs to be changed or one day your lower unit will have no transmission at all and will constantly jump out of gear.
First, I’ll explain how the gearbox/lower unit works.
They have an input shaft that is driven from the motor or “powerhead”. (This input shaft is called the drive shaft. The drive shaft has a gear connected to the bottom called the pinion gear. The pinion gear is always in constant contact with the forward and reverse gears. Whenever the motor is In operation, the pinion gear is turning the forward and reverse gears.Between the forward and reverse gear is the mechanism that selects the gear.This is called the Clutch Dog.
The Clutch Dog sits on the propeller shaft sticking out the back of the gearbox and drives the propeller. The Clutch Dog has an internal spline that is in constant contact with the propeller shaft.
Imagine that the Clutch Dog has a front and a back. At each end it has large, square teeth. When you select a gear on the engine, you move the clutch back and forth along the propeller shaft.
When the clutch moves to select a gear, it engages square teeth of the same size in the particular gear being engaged.
Remember that both output gears (forward and reverse) are turning as they are constantly in mesh with the pinion (input gear).
If you select the gear slowly, the dog clutch will move slowly to engage the gear. This slow motion causes the gear teeth to “jump” over the clutch teeth. This continual jumping wears down the nice sharp edges of the teeth and will eventually cause the engine to jump out of gear.
How to select equipment
The way to avoid damaging your gearbox is to positively select the gear. This literally means cranking the engine so you hear clean gearbox engagement, not chatter.
· You should also pause in neutral when shifting from forward to reverse or vice versa. This gives the propeller time to stop spinning.
· Do not shift into reverse when driving fast. It creates a lot of unnecessary force on the gearbox (and engine). Slow down the plane’s boat, go idle again, and pause in neutral to let the boat slow down. The reverse is purely a reverse, not a break…
Engine idle speed too high
Another cause of the damage being done to the Clutch Dog is that its idle speed might be too high. If your engine is idling at more than around 900 rpm in neutral, you’ll be doing damage every time you select a gear.
So…
· Make sure your idle speed is set to the manufacturer’s recommendations!
Positively Selected Team
· Pause in neutral between gear changes.
Let the boat slow down before shifting into reverse.
Have the gear oil changed every 100 hours or yearly, whichever comes first.