72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

[boulevard]

Thanks for reading! I was cuising along full throttle when instantly my engine revved up and the boat stopped. Basically felt like something broke that causes the propeller to spin. My engine began to run really high rpms because there was no longer any load on it.

Can you point me in the right direction. I know absolutely nothing about how outboards work. However I am kind of savvy on motorcycle engines. I just don't know boat lingo and parts. Thank you for your time !!!

 

[boulevard]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

In addition... I can spin the prop by hand signifying to me that it is not locked up. When I put the engine in forward gear it will not engage the propeller.

 

[Wover98]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

Several things come to mind. Could be a sheared drive pin, or a bushing gone bad (rubber bushing inside the prop that is designed to take the brunt of an impact). Does the motor have any push to it at all? Or is it a total freewheel? With motor out of water, in forward does it have any resistance and or any grinding rouch sound/feel to it? Easy to check drive pin, just remove cotter pin and unscrew the nut and pull the prop off. Did you hit anything or feel a thud/bump while running?

 

[boulevard]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

Thanks for you quick response. I have not started the motor out of water to see if it moves at all. I didn't hit anything. I will check to see what it does out of water. Then I will try to discover if this pin you describe is broken. Wow I hope it is that easy.

 

[Wover98]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

I would not run it out of the water(ruin the impeller and over heat real fast), just put it in gear and with plug wires off, turn the prop by hand and check for resistance. Had the motor sat up for some time before you ran it or is it in regular use? The check for the drive pin will take 2-3 minutes, just do it. lol. When the unit quit driving, was it total lack of thrust? or did it have a small amout of thrust at low RPM's? (This would indicate the prop bushing)

 

[outlaw241]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

i agree with wover98,also if that's not the problem could be shift rod clamp could have slipped or broke

 

[boulevard]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

Okay good call on not running it out of water. It was a sudden loss of thrust. When it broke I had no thrust at all. I store the boat outside of the water and use it about every 3 weeks. So it hasn't been sitting long.

 

[14ftgrumman]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

Did you hit something? log, rocks, submerged stump?

Take off prop nut, remove propeller. What condition is your shear (drive) pin in?

 

[boulevard]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

Well I finally got around to tinkering on the motor. The pin is not broken. Everything that I could see around the propeller looked okay. I took the boat out fishing last weekend (using trolling motor) and turned the motor on to see if it worked in reverse and it did not. Any other suggestions??

 

[F_R]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

Start it up (in the water) and look to see if the water pump is working.

If it isn't pumping water, broken drive shaft.

If it is pumping water, it isn't being shifted into gear (shift rod disconnected), OR the lower unit is totally trashed.

Remove the oval plate from the midsection, about half way down, and look in to see if the LOWER shift rod moves up and down when you shift it. Are both screws in the brass shift rod connector?

 

[14ftgrumman]

Re: 72 Johnson 20hp suddenly lost propulsion, prop spins but won't engage

If the shift rod clamp is ok, time to get a manual and open up the LU, if the prop is not to blame.

Take it to a prop shop and have is re-hubbed, then see what happens.

I'm guessing that you checked it? Scribe a line accross the inside of the prop hub, put it on the motor, take it for a short run. Remove the prop and see if the lines are still in line witheach other.

Please tell me you did this?