Prop is making thumping / clicking noises when hand rotated (video)

ryno1234

ryno1234

Petty Officer 2nd Class
Joined
Dec 8, 2014
Messages
150
When rotating my prop by hand, I hear a thump / click noise (Alpha 1 Gen II). This happens in both directions but is considerable quieter in one versus the other. I tried using various shift engagement on the shift control to see how that might affect the noise thinking maybe I'm somehow slightly in gear, but I couldn't seem to find the sweet spot where the noise would go away, it was always there.

I did just replace my hub because my last one had the castlenut teeth slightly bent out. We took a hard wave at heavy throttle and I think the prop nut twisted. I'm just speculating, but we couldn't get on plane after that very easily and there was a definite vibration. Replaced the hub and vibration is gone and I can get on plane, but now I have this clicking / thumping

You can see a video of it here:

Any ideas?
 
T

TMW123

Seaman Apprentice
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Jun 27, 2017
Messages
47
That definitely sounds like the dog clutch is dragging a little to me. If you start it in neutral does the noise continue? I think a cable adjustment might be needed.
 
Texasmark

Texasmark

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Dec 20, 2005
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14,834
From the rear trying to turn the prop CCW results in resistance and the prop doesn't want to turn.....that is for F gear. Slowly turning the. prop CW and watching the prop in relation to the LU casting and listening, you will notice the prop moving away from the gear case slightly and then returning abruptly....like the teeth on a saw. As TMW stated, that is the overrun clutch functioning.

The purpose of the clutch is to disconnect the prop from the powerhead any time the prop is turning faster than the engine.....like when ypu are coming off plane. If you were on plane and chopped the throttle without the clutch function you'd have to dig your teeth out of your windshield.....if you had one.....figure of speech.
 
ryno1234

ryno1234

Petty Officer 2nd Class
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Yo
Texasmark said:
...the purpose of the clutch is to disconnect the prop from the powerhead any time the prop is turning faster than the engine.....
Click to expand...
You mentioned Powerhead. Just being clear, this is an I/O Alpha I Gen II. Perhaps the comment is just as applicable, just wanted to be clear :)

I appreciate your help as always.
 
S

StewartL

Seaman
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Jul 23, 2025
Messages
56
That click is not normal and indicates an internal issue.

Since the noise started after your hub replacement and hard impact, the problem is likely inside the lower unit. The most probable cause is a damaged forward clutch dog or gear. The impact that bent the prop nut likely also jarred the gears.

You need to have a mechanic inspect the lower unit. Running it could cause further damage.
 
Texasmark

Texasmark

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ryno1234 said:
Yo

You mentioned Powerhead. Just being clear, this is an I/O Alpha I Gen II. Perhaps the comment is just as applicable, just wanted to be clear :)

I appreciate your help as always.
Click to expand...
Ok how about engine and the remainder of the drive train since they are all linked together.
 
Texasmark

Texasmark

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StewartL said:
That click is not normal and indicates an internal issue.

Since the noise started after your hub replacement and hard impact, the problem is likely inside the lower unit. The most probable cause is a damaged forward clutch dog or gear. The impact that bent the prop nut likely also jarred the gears.

You need to have a mechanic inspect the lower unit. Running it could cause further damage.
Click to expand...
If you knew about the action of the clutch dog previously, and now you are realizing a different noise, after an altercation, then by all means check it out.
 
ryno1234

ryno1234

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So, does it sounds plausible then that being heavy on the throttle while hitting a wave that largely stopped the boat's forward movement would put enough excess strain on the outdrive to actually cause damage? If so, I can promise I will consider that in the future when plowing through waves.
 
ryno1234

ryno1234

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Dec 8, 2014
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150
racerone said:
Waves have nothing to do with it.----Adjust the shift cable to get rid of the clicking.
Click to expand...
Sounds like a reasonable idea, however I already did that. I've adjusted through the entire length of the cable from forward to reverse. The click exists throughout meaning it has nothing to do with the cable.

Also, to be clear - I'm not just talking about a "wave" as might be normal during boating. I'm talking about turning 3,500 rpm then hitting a high 3-4 foot wake from a large / heavy boat that nearly stopped us in our tracks.

Thinking from a mechanical perspective you have a prop turning to support that 3,500 RPM engine speed and then a sudden stop with the engine still attempting to turn at 3,500. Seems to me like something that *could* create damage.
 
R

racerone

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38,967
Not much different that a boat stopped and then hitting the throttle.----Done all the time.
 
kd4pbs

kd4pbs

Petty Officer 1st Class
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Mar 5, 2012
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249
The prop didn’t stop. The boat did. Big difference. Has nothing to do with waves. Walls and other hard underwater obstacles are different story. If anything that would’ve affected your outdrive like that had happened, your prop would be mangled.
 
Texasmark

Texasmark

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ryno1234 said:
So, does it sounds plausible then that being heavy on the throttle while hitting a wave that largely stopped the boat's forward movement would put enough excess strain on the outdrive to actually cause damage? If so, I can promise I will consider that in the future when plowing through waves.
Click to expand...
No!
 
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