output shaft coupling

Assuming the shaft and prop turn freely with no obstructions, what, other than alignment issues could cause the output shaft flange on a Twin Disc transmission to fail?
The engine and transmission combination have been in the boat +/- 25 years. Same prop.
The engine was recently "realigned" after service to the Variable Pitch Propeller shaft.

Thanks K1W1,

In my life ashore I've installed a number of smaller engines and am familiar with the mechanics of alignment, using feeler gauges, dial indicators etc. I admit to having been frustrated on occasion with the process but have always managed more than acceptable results.

In this case we had to remove twenty five feet of five inch Hundestad shaft and replace a pillow block. A lot of other work was done on the assembly and then it was reinserted. The new pillow block is exactly the same spec as the original and after being cleaned up, all the components went back into their original places.

When it came time to reconnect the mechanics on this job insisted that the 671 needed to be raised. I protested but relented as they are qualified and I did not have the equipment, strength or resolve to trade places with them.

I mentioned that the uncoupled shaft turns freely just to block a bunch of well intentioned contributors from suggesting having ingested a rope or log in the aperture, binding on the rudder etc.

To me this is a direct result of misalignment but I want to be aware of all other possibilities before sitting down with the accounting people to discuss who is paying for what is going on today...

Missing shims are a possibility but I don't think so since the re-assembled shaft was apparently too high, necessitating raising of the engine. (which I've questioned all along)

Just a few inches aft of the transmission is a large thrust bearing. This was removed and put back into the same spot. It is without shims. The bearing that was replaced is intermediate and was speced from the original Hundestad drawings.

Fortunately Twin Disc has come through with all the parts for the twenty-five year old box with little difficulty. Unfortunately, getting them to Puerto Rico overnight is an all together different matter.

K1W1,

It is obvious from your many posts that you are an industry knowlegdeable but pulling the designer from this limited input makes me wonder if your sitting somewhere watching the saga unfold...If so come on over, introduce yourself and I'll us a drink

The vessel in question is in fact an 84' Don Brooke designed, ketch rigged motorsailer named Wireless, ex ACE and maybe Lollipop.

Good call

At present we have freed the engine and tranny from the mounts and have it hanging from the overhead. The damaged coupling is out and we are freeing up the seals and carrier. In addition to these parts I have new sump strainer elements, a new breather assembly and temp and pressure gauge assemblies "on the way"

Just completed a five hour seatrial yesterday and had good results. Interestingly, when we realigned the engine this time it ended up almost exactly where it had been for the previous thirty years instead of where the mechanic insisted (against my repeated objections) that it sit after the recent powertrain servicing.

The coupling was suffering from advanced corrosion but I think we all know that the alignment was the final straw.

On another note the packing on the inboard end of the stern tube was made up so tight that after about three hours it started smoking so bad I thought for a while that we were on fire!

This has been a long winter,
Peter

So, we are up and running again.

After replacing the output coupling and the associated bearings, seals etc we realigned the engine and ran sea-trials.

The alignment, dropped back roughly to where it was was before the "experts" decided the engine had to be elevated, seems perfect. No vibration.

Our first crack at sea-trials were a bit disappointing. Less rpm that before and after three hours of running the packing box started smoking!

After things cooled a bit I released the packing. After several hours a small drip of water finally migrated through the tube.

Yesterday I repeated my sea-trials. No smoking but the stuffing box registered as high as 225 F on my handheld IR thermometer.

My question, on a five inch shaft running at cruising revs for an extended time, what would be a typical, or allowable, stuffing box temperature?

Thanks K1W1. I hoped you would continue to weigh in on this one.

Here is some of the missing info...
Hundestad instructs that the +/- 10' stern tube be packed with water soluble grease. This slurry depletes via the aft end of the tube (bronze to bronze, no cutlass or packing) and is replaced by pumping more grease into either end of the tube via a canister and pump in the ER.

I can not locate a supplier of WS grease and have Hundestad recommendations on water resistant grease. We packed the shaft and tube with the recommended grease during reassembly.

With the packing completely removed, water does not readily migrate through the grease and is almost imperceptible at the inboard end.

There is a pillow block bearing (new) about three feet forward of the stern gland. Its temperature was about 95F.

I'm headed to the dark side now to loosen the packing again but my enthusiasm for hanging upside down in the deep bilge is waning...

Hola,

To my surprise, there are no hoses of tubes to introduce cooling water. Nor are their any of the protuberances on the cutlass that I am used to seeing on our traditional workboat installations.

underway there is no geometry that I can see that would promote the flow of water into the tube.

$60k and counting. Not including the rum that I've been forced to use for stress management most evenings.

Hi K1W1,

Here lies the problem with this particular (antiquated) instalation. There are no water feeds to the stern tube. The lubrication of the packing is provided by contact with a water emulsifying grease that is no longer available.
Modern greases are highly water resistant and therefore are preventing water from reaching the packing as it had previously been able to do.