Replacement Flex Coupling

[clausont]

I have tried to find where to buy a new flex coupling to replace the damaged one in our Cal 29. I checked PRP and they have one with a three bolt pattern where mine uses a four bolt pattern. I have been unable to find a supplier that has the one to replace mine.
It is behind a single cylinder Farymann diesel, it is about 3" - 4" long with about a 2 3/4" bolt pattern. I may be off some on these measurements.
Any thoughts as to where I may buy one of these couplings?
Thanks

[delmarrey]

Try here for a start.......... shaft couplings, shaft coupling, shaft coupler, coupling

[Steve Pope]

google, google and google again, there are several well known brands that come up on the 1st page (flexible marine couplings). You may even identify your existing one which would make replacement easier.

[pmeyer]

I'm also looking at replacing my coupling. My machinist suggested I look at Lovejoy couplings (Lovejoy).

Woods is another manufacturer of similar gear Welcome -- TB Wood's -- Jaw Couplings).

The basic jaw couplings are pretty cheap, allow a one degree angular misalignment, which another supplier quoted as .065 of an inch, and .015 parallel misalignment. The elastomer might reduce shock loading and vibration. That angular alignment spec reduces the required engine alignment precision considerably. It might even reduce driveline wear and noise.

Has anybody used something like this? Or perhaps someone with some mechanical engineering background has some thoughts.

Paul Meyer
New Brunswick Canada

[Steve Pope]

most engines that are flexibly mounted require a flexible coupling, the aim of any engineer aligning them is to achieve as close to perfect an alignment as possible. The more missalignment the more potential there is for problems down the line. That being said if for some reason the unit becomes missalgned the coupling allows everything to keep working for a considerable time, until it is noticed and fixed or until the coupling eventually fails. Generally this will happen as you are passing through a channel with swirly currents or you are approaching the dock at speed and a million dollar yacht owned by your worst enemy is right in front of you..

[Pblais]

You may want help to get the alignment right. A little off and it eats all the stuffing out of the stuffing box. This needs to be really really close. I've not used the referenced couplings before but you still need a very close alignmnet. Having is as close as can be will only make it sound a lot better at worst.

[MidLandOne]

Originally Posted by pmeyer

That angular alignment spec reduces the required engine alignment precision considerably.

As already said it does not reduce the precision required for the alignment. The coupling should only serve to absorb torsional vibrations and shock loads. Misalignment will result in tears, possibly expensive ones if gearbox life is affected, flexible coupling or not.

My own personal preference is a simple plastic disc coupling such as the Polyflex Disc Couplings one (Global Rubber, among others make them in the USA).

If set up like they show you end up with quite a bit of the outer part of the disc not covered by the flange of the coupling (that is an annular ring of the disc bigger in diameter than the coupling flange results - and can be seen in the Polyflex diagrams).

Any vertical or horizontal misalignment of the two shaft halves distorts the plastic disc and I have found it is very easy and very quick to get an engine accurately aligned just by laying a straight edge over this exposed side of the disc - rotating the shaft and checking the disc with a straight edge, adjusting the engine mounts until the visible outer part of the disc is flat in all rotational positions.

Of course, others mileage in using that method might be different .

[pmeyer]

Thanks to those that responded.

I know more than I would like about accurate engine alignment. When we bought our 1973 Cat27 (Petter AB1W - 6hp and associated Italian tranny) a few years ago I should have been more aware of the plastic tray under the tranny. The tranny leaked oil at a rate of about 1 litre/8 engine hours. Luckily it is easy to top up and check the level while under way - and, it is a sail boat - so we don't motor that much.

The problem was a bad rear tranny seal caused by very bad engine alignment - off by about 3/16 of an inch. You know its bad when you can use a ruler to measure.

Luckily I have a buddy that is a machinist. The center hole in the output connector was oblong and the output bearing and seal was toast. We enlarged the center hole in output connector, bushed it back down to the original size, replaced the seal and bearing (standard off the shelf bearing shop items) and reinstalled the tranny. It worked great all last season. Of course I improved the engine alignment. I could only get it to about .02 inch - way better than 3/16 of an inch - but not really close to my goal of .004 - .006 inch. It even sounds better - and no leaks.

Fast forward to today: Six hp wasn't really sufficient in all conditions. I was able to buy a working takeout 11 hp Universal 5411 engine and associated tranny with coupling, mounts, guage panel, and exhaust. I am in the process of installing it.

I could use the rigid coupling that came with the engine - possibly with a Polyflex type insert. It was my machinist that suggested the Lovejoy type joint. He says it is a standard of machine design and is a bit more forgiving of mild misalignment, and also adds some damping. I'll be looking into that further and will report back. My goal will be to get the alignment as accurate as possible in any event.

MidLandOne - I really like your clever alignment approach with the Polyflex disk. That will be really helpful if I go that route.

Pblais - If a person just has stuffing trouble due to misalignment they are getting off easy. We experienced oil leaks and mechanical damage. We did have quite the leaky stuffing box when we got the boat. I replaced the old stuffing with the WF Gore (virtually) Dripless stuffing. It works great. It even worked well before I improved the alignment. We're down to a drip every few minutes and a cool stuffing box. Two years later I still think the stuff is great.

Steve Pope - It does seem that things fail most often at the worst possible time. We had a jib halyard part as we trying to cross ahead of a ferry. Good think we like adventures.

Thanks for your thoughts. I'll let you know what I learn and what I do.

Paul

[mike d.]

check with defender ind and hamilton marine they carry buck algoquin and others may be able to steer you in right direction. hamilton marine is 800-639-2715 defender is on line don't know #

[S/V Antares]

Vetus has a good flex coupling. The Farryman is a real shhhhhakkkker! Good luck.

[clausont]

Steve - Funny! That is spot on! Been there, done that! In my old 23' Venture of Newport, I was coming into the dock quite nicely with a big twin engine (outdrives of course) power boat docked in front of me. I knew there would not be a problem as the conditions were good. I hit reverse to do the final stop behind the power boat and of course, reverse chose that moment to fail. Needless to say, the boat owner was less than impressed. Happily, no damage to his boat. That was many years ago.

I have googled, I have called, I have talked to PYI (R&D couplers) I had thought "Boy, this is going to get expensive..." Nobody makes the original rubber composite coupling that I can find, and nobody has heard of it.
Looking closely at the coupling, I see where the rubber is in good shape but the flange that was vulcanized to it had rusted between the rubber and the flange su the rubber was not "glued" to the metal anymore. After some calling I found a company in Portland that said they can re-vulcanize the coupling. I will give trhis a try, but I am a little leary of the results in the long run.
The dimensions of the coupler are pretty standard (or should I say "common") - 4" diameter flange, 3 1/4" bolt spacing. Where the problem comes in is the length of the coupler - 3" fore and aft length. Nobody has anything close to that unless I want to start changing flanges and shaft lengths and all. I'd rather try to find a direct replacement for obvious reasons. I also feel that with a coupler that is less than 1/2 the length of the original, the stress induced by the shaking of the engine would be amplified in the shorter coupling. I'm not sure I am expressing my thought quite right, but I think you will understand what I mean anyway. A 3" coupling can compensate for the shaking of the engine better than a 1 1/4" coupling can.
Watching the shaft, coupling, stuffing box and all after I jury rigged the coupler, I don't think the alignment is bad at all. Of course, I have not taken any measurements so I could easily be wrong.

S/V Antares - you know the Farymann! It DOES shake!
Pmeyer - Thanks for that information. I did check it out.
MidlandOne - I will check out the polyflex couplings.
PBlais- I think I will take your advice and have the shop check the alignment after I get the coupler replaced. That is a job I have never attempted. I'm not sure that I wouldn't just make it worse.
Mike D. - I checked with a Buck Algonquin distributor and they carry flanges, but not the coupler.

Thanks all for your help here.

[pmeyer]

Update:
I went to the boat and determined that there is not enough space between the tranny and the stuffing box for my Lovejoy type coupling strategy. In a bigger boat it might have been part of a good solution, but not in my boat. I can add the Polyflex disc at any time and I may yet do that.

I just got back from my machinist buddy's shop. The lathe and dial indicator determined that the shaft is essentially straight - maybe out by 1-2 thousands at the most. We cut a keyway in the shaft for the coupling and drilled a couple of dipples on the shaft for the coupling set screws. We installed the coupling with anti-seize and checked to confirm that the coupling surface is perpindicular to the shaft. It was close. We took off a couple of thousands and made if perfect.

Knowing what we are working with I hope to get the engine aligned very closely. I'm striving for .002 inch. I'll let you know how it goes.
Paul

[GordMay]

Originally Posted by pmeyer

... Knowing what we are working with I hope to get the engine aligned very closely. I'm striving for .002 inch. I'll let you know how it goes.
Paul

EXCELLENT!

ABYC P-6 PROPELLER SHAFTING SYSTEMS
For Shaft Straightness Tolerances, see Tables II and III (pages 4 & 5) at:
https://www.abycinc.org/committees/P-06.pdf

[pmeyer]

Nice to know that I'm in the right ballpark.

[Psyches]

clausont, have you found a solution that worked for your coupling problems?

i just ran into the exact same issue yesterday on our "new", very used, and very first sailboat; the engine is a farymann a30m, sounds like maybe the same 1-cyl engine you have. because it's our very first boat i don't have much experience with this kind of thing - sounds like i'm going to get "experienced" quickly...

we motored for awhile yesterday when the wind died, and stopped the engine after we realized a big black cloud was forming in the cabin (our engine surveyor said we might have an exhaust leak - looks like we do, it's gotten worse); when we shut off then started the engine a few hrs later, we found that the aft end of the coupling "big rubber chunk" had separated from the plate connected to the prop shaft, by about 3/4" or so. i noticed before we shut the engine off that the shaft seemed to be rotating erratically (elliptically) at the engine side, so it's also possible we'll find more problems caused by this - hopefully only the stuffing box needs repacking...

first i'm trying to figure out what to do about the coupling though.