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Propeller Shaft Spinning
#17442
09/04/17 03:26 PM
09/04/17 03:26 PM
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Joined: Mar 2017
Posts: 27 Annapolis
JPM
OP
Senior Member
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OP
Senior Member
Joined: Mar 2017
Posts: 27
Annapolis
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So, I replaced an engine a week or so ago. The new (used but new to the boat) engine runs just fine. I need to make a few tweaks to idle speed, etc but I was able to motor out to the race course this weekend. However, on the way back in I experienced a vibration that was similar to a prop that wouldn't open. I had the main up so I had the crew go head to wind and I went over the back on the swim ladder and found that the prop would open easily. When I checked the shaft at the coupler, I noticed that the shaft would spin freely within the coupler and there were small metal filings on the sole of the boat beneath the coupling.
I am new to owning a boat with an inboard engine (previous boat was a J24) so I'm a bit out of my comfort zone. It would seem to me that the key or the set screws would be a likely source of failure but I know nothing about how to inspect this. Is this something I can do with the boat in the water or do I need to haul the boat?
Also, is it possible that the engine and the shaft weren't aligned when I did the engine swap? I dropped the new engine on the old motor mounts and it seems like things lined up OK....but again, I'm new to this...
Any help would be appreciated...
Last edited by JPM; 09/04/17 03:49 PM.
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Re: Propeller Shaft Spinning
[Re: JPM]
#17443
09/04/17 05:20 PM
09/04/17 05:20 PM
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Joined: Sep 2000
Posts: 393 Rockwood, MI, USA
Russ Atkinson
Senior Member
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Senior Member
Joined: Sep 2000
Posts: 393
Rockwood, MI, USA
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At the rear of the transmission is a "hat coupler" mounted to the stub shaft of the transmission. Attached to that is another coupler that holds the propeller shaft. That shaft coupler is attached to the transmission coupler with 4 bolts. The shaft coupler is attached to the propeller shaft with two square head machine screws and a keyway. The square headed screws are locked to the shaft coupler with two nuts.(FYI, none of the parts screws or nuts related to the shaft coupler are stainless - get some lubricating oil and bandaids for the skinned knuckles you will most likely have) Finally, there should be a stainless wire running thru the square nuts that further prevents them from backing off the shaft.
If the shaft is turning in the coupler then one of three things probably happend The shaft has moved aft enough that the key has fallen out. Or, somehow you have sheared off the key, or during assembly of the new engine the key was never put back in when the engine was changed
If the shaft is turning free in its coupler then it can fall out. Usually the only thing keeping it in the boat is a sacrificial zinc mounted on the shaft behind the strut. (Gambler a J/30 out of Sandusky, Ohio had this happen and nearly sunk. The shaft came out of the boat). Big hole in boat where shaft comes thru lets in a lot of water
Metal shavings could be from the shaft spinning against the bottom of the square head bolts. Could be from the shaft spinning in the coupling and wearing either the shaft or the coupling or from a sheared key
Fixes, 1st, remove the coupler from the shaft, see if there is damage to the shaft or coupling (if the screws have cut a groove in the shaft, it won't hurt anything). 2nd, get a key and put it back together 3rd, align the engine. Use feeler gage to measure distance between shaft coupler and transmission coupler (.003 max runout). Loosen the front engine mounts only. Adjust left to right and up and down
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Re: Propeller Shaft Spinning
[Re: JPM]
#17444
09/05/17 11:58 AM
09/05/17 11:58 AM
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Joined: Sep 2000
Posts: 393 Rockwood, MI, USA
Russ Atkinson
Senior Member
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Senior Member
Joined: Sep 2000
Posts: 393
Rockwood, MI, USA
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Additional info. You can do all the work described earlier with the boat in the water. You won't have a lot of room 2-3" max to move the shaft aft to remove the shaft coupler from the shaft. Also, all nuts and bolts are metric. Don't know the size of the keyway- again, probably metric. There is one thing that may keep you from doing the work with the boat in the water. If there is a sacrificial zinc mounted in front of the strut it may prohibit you from moving the shaft far enough aft to remove the coupler.
Worse case, if you can not slide the shaft back to get the coupler off the shaft, Perhaps you can get a short key into the coupler/shaft. Then tighten the two square head screws, lock them with the nuts, Wire the two square nuts, align the engine to the shaft and deal with it at the end of the season or in the spring.
Next spring, think about re stuffing the stuffing box and checking the cutlass bearing
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Re: Propeller Shaft Spinning
[Re: JPM]
#17445
09/05/17 05:07 PM
09/05/17 05:07 PM
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Joined: Apr 2007
Posts: 493 Chicago, Il. USA
D. Bartley
Governor at Large
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Governor at Large
Joined: Apr 2007
Posts: 493
Chicago, Il. USA
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On my 1980 boat, I believe the key is 3/16 brass. NOT steel. The key is a fusable link... it's supposed to break if something keeps the prop from turning while in gear... like a line wrapped around the prop. As Russ said, another way for it to fail is if the two bolts holding the shaft came loose. You might find the key on the floor below the prop.
Dennis Bartley Planxty, s/n 23994 hull 205
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