Prop Shaft Problems & OEM Ground Wire Flix

[Geoffreykwright]

Hi - I was motoring yesterday and my prop stopped turning.  The engine was running and I had the transmission in FORWARD but the prop & shaft were not turning.  I had thought maybe the shaft became uncoupled from the engine.  I spoke to a mechanic I know and he suggested 3 things:  (1) maybe the transmission cable came disconnected, (2) transmission fluid low/out, (3) prop shaft uncoupled.

I checked today - the tranny cable is fine and functioning correctly.  Fluid was a bit low, but the colour was fine.  The coupling was visually ok...now here is where I am confused.  I can turn the shaft by hand right in front (forward) of the stuffing box and it turns fine.  If I turn it at the coupler the couple turns by itself but not the shaft.  I am guessing this is not supposed to happen?  All of the bolts on the coupler seem tight and nothing looks out of place.

Can someone help?

Thanks in advance.

[Stu Jackson]

If I turn it at the coupler the couple turns by itself but not the shaft. 

The shaft is loose in the aft coupling.

[KWKloeber]

Hi - I was motoring yesterday and my prop stopped turning.  The engine was running and I had the transmission in FORWARD but the prop & shaft were not turning.  I had thought maybe the shaft became uncoupled from the engine.  I spoke to a mechanic I know and he suggested 3 things:  (1) maybe the transmission cable came disconnected, (2) transmission fluid low/out, (3) prop shaft uncoupled.

I checked today - the tranny cable is fine and functioning correctly.  Fluid was a bit low, but the colour was fine.  The coupling was visually ok...now here is where I am confused.  I can turn the shaft by hand right in front (forward) of the stuffing box and it turns fine.  If I turn it at the coupler the couple turns by itself but not the shaft.  I am guessing this is not supposed to happen?  All of the bolts on the coupler seem tight and nothing looks out of place.

Can someone help?

Thanks in advance.\

A pic of your stuffing box and coupling might help.

If you are saying that the coupling turns independent of the shaft (prop side or transmission side turns freely??) then obviously the coupling is loose on the shaft.  Sounds like set screws on the coupling are loose or sheared off and key is sheared (if there was one.)

KK

[Geoffreykwright]

Here is a photo...

to be clear, if I turn the shaft itself by hand the shaft and the coupling both turn.  if I turn the shaft by grabbing the coupling only the coupling turns - not the shaft.  I did not see anything sheared off.

[KWKloeber]

Here is a photo...

to be clear, if I turn the shaft itself by hand the shaft and the coupling both turn.  if I turn the shaft by grabbing the coupling only the coupling turns - not the shaft.  I did not see anything sheared off.

and if you hold the coupling, and turn the shaft, the coupling will stay and the shaft turn?
Regardless, the back half of the coupling is loose on the shaft.  You can't see inside to see what's loose.   See if you can turn the set screw on the back half.

Pic is alittle fuzzy, but the pright spot looks like the spinning coupling has "polished" the shaft.   Best to pull the shaft out of the coupling to see what's going on.  You can do this by loosening the bolts, inserting a socket between the halves, and using the bolts to force the shaft and coupling apart.  You'll need to take small bites at a time.

kk

[Geoffreykwright]

Well - turning the shaft itself turns the coupling.  turning the coupling does not turn the shaft - only the coupling turns.  I did not try turning the shaft and holding the coupling, but I agree with your assessment that the shaft seems loose in the coupling.

I am a bit new to diesels...I will first see if I can turn the set screw on the back half.  if that does not fix it is there anything to worry about removing the coupling and either putting it back on or replacing it?

[Geoffreykwright]

If I remove the coupling, will the shaft pull through the hull?  Do I need to secure the shaft prior to removing the coupling?  If yes - how to secure it?  Put an extra anode on it?  Would a simple hose clamp with some para-cord attached on the shaft do the trick?  Just don't want to open a can of worms.

thanks in advance.

[Ron Hill]

Geoff : What you've got inside the coupling is a keyway with a key that also fits in a keyway inside the shaft.  That insures that the shaft will turn when the coupling (attached to the Xmission) turns.

Then there are two square headed dimple nuts that keep the shaft in place when it's shifted from FWD to REV.  These dimple nut are tied together with lacing wire.

A few thoughts

[KWKloeber]

If I remove the coupling, will the shaft pull through the hull?  Do I need to secure the shaft prior to removing the coupling?  If yes - how to secure it?  Put an extra anode on it?  Would a simple hose clamp with some para-cord attached on the shaft do the trick?  Just don't want to open a can of worms.

thanks in advance.

Working on a boat -- on anything on a boat -- there's NO such thing as NOT opening a can of worms.  However, your shaft won't fall out of the shaft log as soon as you disconnect the shaft.  You have friction working on the log and cutlass, and PSS.   Though a little fail safe isn't a bad thing.  A hose clamp in front of the PSS would work, no para necessary.

You must have hit something with the prop, and sheared off the key inside the coupling.  Hopefully it sheared and didn't damage the tranny.

Ken

[Stu Jackson]

Ken's description is very good.  Just take a look.  

When we bought our boat, I poked around back there a LOT at first, so I would understand how it worked.  The MANUAL has a great description of the stuffing box, and a drawing of what's there.

So, I'm pokin' around, and there's somethin' missin'.  

The blinkin' KEY itself!!!

I went to a local machine shop, armed with the knowledge of how big the key had to be from reading the Mainsheet tech notes.

Here's my record:

Transmission: shaft key   4-July-98   Alameda Prop      $3.25    Installed 1/4/98, 1/4" stock  (backup in nav station)

I also put a plastic wire tie around it, still there.  

This was also the day after we bought Aquavite.   

Good luck, sounds simple.

There may be NO reason to disconnect the shaft & the coupling.  Leave it alone if you can.  If you take it out, ya got other issues to deal with, like mating the old shaft with the old coupling - not a good idea.  Maine Sail has a great writeup of matching and split couplings on his website.

[Geoffreykwright]

Stu (and everyone) - thanks - good advice.  It may well be the key - but don't I need to open the coupling to access the key?

[Ken Juul]

Yes that is correct.  But since the shaft/coupling connection is loose, should be very easy to get apart.

[Stu Jackson]

but don't I need to open the coupling to access the key?

Mine slid in from aft, there's a slit in the shaft, no coupling disassembly required.  That's where the cable tie is holding the key in place even though I banged it in with a mallet.  

It's definitely aft of the coupling.

[Geoffreykwright]

All - thanks for all your kind advice. 

Just a quick update to close this thread...I opened the coupling and the shaft has broken right where the set screws are :-(  There is some evidence of corrosion (some green) in there so it looks like it was fatiguing slowly over time (its a 15 year boat with 820 hours on the engine).

Going to need a new shaft...a mechanic friend of mine is going to help me with this.  It is (or sadly was) a brass shaft.  Going with stainless steel this time around.

Anyway - thanks again.

[Ron Hill]

Guys : The only way the key will slide in is from the back side!! (tapered grove!!)

BTW, you can get a replacement brass key from a local ACE hardware store !!

A thought