Prop Kocking Trouble

[LookTube]

I was idling the engine before changing my oil. While in idle everything is fine. When given a little throttle everything is still fine, but when I give it about halfway down on the throttle the lower unit was giving off a constant knock. Loud knock. Over and over again with about two seconds in between knocks. Turn it off and thought maybe it was losing it because it happened so fast. I turned it back on and did it again. It started again around the same rpms. So I jumped out and went to the back of my boat and the prop would spin when it knocked but came to a stop and repeated. So immediately turned it off again and leftist everything alone. Have anyone had this problem and if so what is it and can a light mechanic fix it(meaning myself)?

 

[steelespike]

All the gears are meshed together and spin if the motor is running. There is a clutch dog that is splined to the prop shaft that selects the gears as you shift.
With no resistance at the prop the spinning gears cause the prop shaft to turn faster and faster as you increase the throttle.
Not a good idea.If the boat was in the water the prop shaft would be spinning slowly.
The sound is the clutch dog engaging a gear possibly slightly out of adjustment.
The unusual spinning of the gears is apparently causes currents just enough to move the dog.
As the prop comes up to the same speed they disengage and it repeats.

 

[alldodge]

First you don't want to throttle the engine past 1800 rpm on a hose, not good. You can cause the impeller to suck air and damage it. A 3/4 hose can not supply enough water.

Not knowing what drive you have but in either case, what probably is happening is the gears are just starting to engage. So the knock your hearing is the teeth of the gears just clipping each other.

 

[steelespike]

There is a pinion gear on the drive shaft it is always engaged in the forward and reverse gears which spin freely on the prop shaft
These are always turning if the motor is running.There are dogs on the gears and the Clutch dog which is splined to the prop shaft
when it engages the gear dogs it drives the prop shaft. When idling in neutral being free to spin on the prop shaft ,they will tend to turn the prop shaft
by friction you may note in the water very slow turning of the prop in neutral no thrust just turning.You can imagine how fast the prop might spin if not in the water.

 

[LookTube]

Thank all you guys. All the info is very knowledgable. This is my first boat and I doing my first tune-up so I'm just learning as I go. Now I know not to run the RPMs up like that while out of the water. I hope I didn't do damage to the gears while finding out "what not to do". Like I said before thank you guys. I hope you guys are around because I guarantee I'll be back soon with another post.