Visit our Popular Forums

Dave-Fethiye · 10-06-2007, 09:25

Hello all,
I recently bought a 12m motor yacht which has tons of work to do. It has been on dry land for about 8 months and the previous owner was having it looked at by a marine company. That company was no doubt going to take the prev owner to cleaners and so prev owner sold out to me.

Good results so far is that even though company said that engine needed total rebuild, we got it running last week with a replacement starter motor.

The only problem (well not the only one, but one of many

) is that the company disconected the engine from the prop shaft.

It looks to me like it needs a new coupling of some kind and to re-connect it. I have a photo below.

Any idea what type of coupling to use and how do I connect it the engine to ensure that the alienment is correct ?

Any advice would be very helpful as I am new to this.

CSY Man · 10-06-2007, 09:37

Hmm, looks like you have heavy corrosion going on there.
I would take those pieces out and have them sandblasted/painted
or just replace.
Looks like the coupling is missing. You can buy them at West Marine.

Also, where is the salt water coming from that causes the rust?
Stuffing box leaking excessively?

senormechanico · 10-06-2007, 09:46

I think the photo IS of the flexible coupling, but I agree with CSY Man.
Get the source of all that corrosion before you launch, and replace those bolts. The stuffing box is the #1 suspect.

If you can afford it, replace the stuffing box with a dripless seal, they're great. Zero water leakage, one time adjustment, and no shaft wear.

The coupling is probably OK if it is plastic, but if those end plates are spongy, chuck it.

The engine alignment is done with the motor mounts. They can slide sideways and the studs have threads which allow each corner of the engine to be adjusted vertically as well. The goal is to make sure the engine is aligned both vertically and laterally with the shaft (which needs to be held in the center of the stern tube while checking all this).
The mating surfaces of the flanges should line up evenly when brought together. Something like .010 runout is acceptable as I remember.

Get it in the ballpark when the boat's out of the water, then after launch you can motor safely until you can let it set for a few days, then do the final.

Steve B.

AnchorageGuy · 10-06-2007, 10:43

Dave, Try to remove both the coupling and the coupler on the back of the transmission and take both of them to an engine shop. They will be able to match them up (they must match) and order you new ones. If this were me I would not even consider reusing this one. The corrosion will most probably come from the stuffing box so deal with that, remove ALL of the old packing and repack with the appropriate size. You will not be able to check this until it goes back in the water. At the same time check the cutlass bearing. If you don't know how to do an engine alignment then DON'T. Get a qualified mechanic and have them show you what they are doing for your future education. Misalignment can and will cause you much grief down the road not to mention expense. BTW we accept no less than .003 to .005 tolerance in alignments. In addition, if that is indeed a flexible coupler then the alignment should be done with a spacer machined to the size of the flexible coupler and put in its place for alignment. Proper alignment really can't, or shouldn't be done with the flexible coupler in place.

Dave-Fethiye · 10-06-2007, 11:44

Thanks for the advice.

I expect to take off the coupling tomorrow.

( I will try and get some better pictures as well )

As I said before - I am a newbie to boats...

... But the term "flexible coupler" seems to indicate flexibily - i.e. tolerance.

If a flexble coupler is used, does the alignment have to be so spot on ?

I hope this isn't a silly question !

Kuapa'a · 10-06-2007, 12:02

Aloha Dave,

Yes, your alignment needs to be spot on. The flexible coupler is not there to compensate for sloppy alignment.

Pick up a copy of Nigel Calder's book "Marine Diesel Engines". It's a terrific piece of work - you'll learn a lot and the book will pay for itself many times over.

Have fun, enjoy working on your 'new' boat... I really wish you all the best.

John K.

AnchorageGuy · 10-06-2007, 17:43

This is not a "flexible coupler" but a "drive saver" and is designed to save the engine from being ripped off the mounts if something causes the shaft to seize. The saver pulls apart and keeps much more damage from being done. As john says the alignment needs to be correct. Of course you can just get it close and pay dearly later.

Dave-Fethiye · 12-06-2007, 11:28

I have been over to the boat today and took some more photos.

I also undidi some of the bolts but I hadn't taken a crowbar with me to lever the coupling off.

Maybe these pics show more detail.