C-27 Prop-shaft

[deisher6]

During docking this afternoon the engine quit while at idle and in reverse.  When we finished tying up I restarted the engine.  The engine ran fine but did not seem to move the boat when put in gear.  A quick look revealed that the transmission was turning but the prop-shaft was not.  I was able to insert my thumb nail between the shaft and the coupler on the transmission.  The set screws on the coupler are safety wired and seemed snug.  I could not rotate the shaft by hand.  The  stuffing box was cool to the touch.  We had been motoring for about 15-20 minutes. 

Apparently the shaft has backed out of the transmission coupler.  There is a hose clamp on the shaft that kept the shaft from going on through the stuffing box.

My plan is to remove the coupler from the transmission and attach it to the prop shaft.  I noticed that there is a keyway on the prop-shaft.I hope that there is not a half moon key involved in the coupler but will soon find out.  Then will loosen up the stuffing box and try to slide the shaft forward enough to mount the coupler back onto the transmission.  If necessary I might try pushing on the prop to get the shaft forward.

I welcome any suggestions!

I am thinking that the engine and prop-shaft are not in good alignment.  The vibration might have been enough to work the shaft out of the coupler.

I welcome any opinions.

Thanks.

regards charlie

[deisher6]

I am thinking that I must be on the right track.  Backed out the prop shaft another 1/8 of an inch so that I could remove the flange on back of the transmission.  Looks like in the short run I will replace the brass or bronze key.  Later this summer when I pull the boat I will replace the shaft or have a new keyway machined in the old shaft. 



The key way on the shaft looked pretty well worn on the fwd side.

Any suggestions or ideas?

regards charlie

[deisher6]

The collar slipped back onto the prop shaft very easily, a little to easily.  I tightened up the set screws. The prop shaft then slid forward to match up with the transmission.  I replaced the four bolts that hold the collar  to the transmission with new ones.  It looked like the collar aligned up with the transmission pretty well although I did not use feeler gauges to check.  I had to re adjust the stuffing box.  I put about 4 hours on the engine.  All seems to be working well.  Checking with a nearby machine shop, there should be no problem machining a new keyway in the shaft the next time that I pull the boat.  I have wanted to replace the cutlass bearing and check out the shaft log.

This was a free repair a marine junk yard gave me the new key.  It took a couple of hours wrapped up around the shaft in the cockpit lockers.  I wish that I was 5ft 2in with 80 inch arms. 

I will now occasionally check the shaft to see if it is backing out.

Two starboard engine mounts were loose or worn.  I tightened them up while I was in the area.

regards charlie

[moonlight]

I'm amazed at the picture of the coupler, old key.
It looks filthy, when in fact it should fit tight enough that there's no room for filth.
So I'd expect to see a more polished appearance.
Supported by the statement that "...it slipped on the shaft easily, maybe a little too easily..." my $0.02 says your coupler is either the wrong size, or has been over worked at some point allowing too much slip.
If you do a haulout, best to take coupler and shaft to the machine shop.  Have them put it together.  They may be able to wrap the shaft with a thin bushing (think a square of feeler gauge type material wrapped around but leaving the keyway clear, and fit the proper size key), or you buy a new key, coupler, and shaft.  It's clearly been very sloppy, allowing for that wear that should be almost impossible.  Or if the shaft is true, maybe you'll just have to replace the coupler.  Should only be enough room in the fit for a fine film of oil or anti-sieze, and it should push most of that out.  Easy slip fit is a sloppy fit and causes the failure you've experienced.  It should be a SOLID mechanical connection on all faces and flanges, but I'm getting long winded and belaboring the point!

[deisher6]

Hey Moonlight:
Thanks for your insight. 

I agree with you completely.  I just thought that I would start this topic to alert any other older C-27 owners about possible problems.  The keyway in the collar and the shaft are not the same width.  However the repair should hold until I pull the boat later this summer.

Several local commentators suggested dimpling the shaft at the set screws.

Again thanks for your comments.

regards charlie