Prop shaft wobble

[sinnerman]

[QUOTE=wholybee;3917722]

The wobble can be caused by a bent shaft, poor alignment, a shaft coupling that isn't flat/square, or an engine of poor tune.....

Exactly.

All of the above.

Since the mounts wee replaced, start with the engine (V-Drive) to shaft alignment.

Do the algnment with the boat in the water.

Alignment is an art, and requires someone who is methodical and with a lot of patience to get it right.

There is a good chance that the guy who last performed the alignment did not know what he is doing...

I would also imagine that an alignment is more difficult with a V-drive..

My two cents

cheers.

[MicHughV]

Your cutlass bearing is shot....plain and simple..and your engine alignment is probably questionable.
Your shaft needs to fit tightly in there.

However, here's the thing, if the shaft is misaligned, it will initially fit tight, but will soon wear the cutlass bearing, and a sloppy cutlass will soon wear a stainless steel shaft.

Trust me, happened to me. Couldn't believe how much the shaft had worn and I had to replace it.

#1 thing to do is to ensure the shaft is perfectly aligned. Only way to do this, is out of water.

What I do, is cut about a 1/8" wide sliver off the cutlass bearing. This I position on the inside end of the shaft tube.
Then I insert the shaft, and once thru', will attach the coupling and shove the whole thing up to the engine coupler.

You will able to see at a glance is your shaft alignment is correct. If not, the engine mounts needs to be loosed so that the engine can be moved so that it mates with the prop flange. You will need a feeler gauge to slide between the flanges to fine tune the connection. You're looking for 0.005", no more.

Once you've got all this dialed in, you can remove the shaft coupler, the sliver of cutlass bearing and replace the stuffing box gland, whatever make it might be, re-insert the shaft, etc, etc.

Once the boat is splashed, separate the coupler again, and repeat the feeler gauge check.

It's a long process, but you gotta do it right. Besides wearing out the cutlass bearing you can also cause damage to engine transmission.

[Toccata]

QUOTE: Your cutlass bearing is shot....plain and simple..and your engine alignment is probably questionable.
Your shaft needs to fit tightly in there.

However, here's the thing, if the shaft is misaligned, it will initially fit tight, but will soon wear the cutlass bearing, and a sloppy cutlass will soon wear a stainless steel shaft.

Trust me, happened to me. Couldn't believe how much the shaft had worn and I had to replace it.

#1 thing to do is to ensure the shaft is perfectly aligned. Only way to do this, is out of water.

What I do, is cut about a 1/8" wide sliver off the cutlass bearing. This I position on the inside end of the shaft tube.
Then I insert the shaft, and once thru', will attach the coupling and shove the whole thing up to the engine coupler.

You will able to see at a glance is your shaft alignment is correct. If not, the engine mounts needs to be loosed so that the engine can be moved so that it mates with the prop flange. You will need a feeler gauge to slide between the flanges to fine tune the connection. You're looking for 0.005", no more.

Once you've got all this dialed in, you can remove the shaft coupler, the sliver of cutlass bearing and replace the stuffing box gland, whatever make it might be, re-insert the shaft, etc, etc.

Once the boat is splashed, separate the coupler again, and repeat the feeler gauge check.

It's a long process, but you gotta do it right. Besides wearing out the cutlass bearing you can also cause damage to engine transmission.

Reply:
The only part I have trouble with in your comment is the following:
You haven't described a relationship between the cutlass bearing and your temporary bearing at the inner end of the stern tube.
FWIW. I did the same thing BUT I didn't finally fit/glue the cutlass bearing into the strut housing until the shaft was turning in its happy spot (with your described arrangement) This took several trys to get the OD of the cutlass bearing right allowing the shaft to spin freely.
THEN I glued/secured the cutlass bearing in place in the strut.
Note; the shaft doesn't have to be in the centre of the stern tube (if there is no inner bearing) but I reckon it looks better and chances are, that was how it was setup originally. ie; engine bearers and inner shaft seal were probably based on the shaft being centred in the tube.
The trick then is to correctly support the shaft if you remove the inner temporary bearing while doing the alignment. That introduces a whole raft of tricks/techniques. Weigh the shaft and halve that number, add the shaft coupling weight and support with a scale OR chock the shaft in place before removing the temporary inner bearing making sure the shaft still spins freely in the cutlass bearing before commencing the in water alignment.

MicHughV, I think between us we have given the OP enough info to now understand this is complex but not unachievable. Just think about each part and the role it plays. Optimise that bit and move to the next stage.
My first thought is check and correct your shaft and coupling for straight and true (ie square to the shaft)

I too had a bent shaft. I suspect that at some stage a travel lift picked the boat up with the aft sling under the shaft. It (the bent shaft) caused real grief until it was sorted out

[skipperpete]

MicHughV I’m not sure I agree with “ the cutless bearing is shot” but your advice about alignments is excellent, the stern tube is the datum point and the method you describe to centre the shaft in the tube is pretty smart ( provided the stern tube is the same i.d both ends). The P bracket or A frame is also a slave to the stern tube and its not unusual to re bed a P bracket (or bend it) to achieve concentricity. A prop shaft that isn’t straight down the middle of the tube can damage itself and the tube, not to mention the possibility of an annoying rumble or knocking sound. On the inboard end, not too many shaft seals enjoy being forced to align with the external diameter of the stern tube first and then a shaft that’s not in the centre of that stern tube. Sure, the rubber extension allows it to run outta line but its not good and the dripless seals can suffer a lot from this same off centre problem.
I’m currently struggling with doing a P bracket straightening job on my own boat….. in the water…. With the shaft out, not because I enjoy the work, I’m just too far from an available and affordable haulout to tow her so I’m going to get the P bracket close to where it needs to be, put in the old but straightened shaft and new propeller and gently idle for a day or two to the closest humane haulout and put in a new propshaft through a properly aligned P bracket.

[Toccata]

I think we have comprehensively answered this question.
Maybe "Cashew" (OP) will come back with either more questions or an observation about usefulness of our answers....
Being pedantic
Regarding centering in the stern tube. I used a piece of cutlass bearing (OD sized to match the tube) cut it in half longitudinally, slipped the halves under the shaft at both the inner and outer ends of the tube. This then created a datum to check the P bracket position/alignment, but I still had to slightly under size the cutlass bearing OD as I just could not bend the P bracket for perfect alignment. The glued in cutlass bearing did that trick. (I am talking fractions of a mm).
I guess I could have released the P bracket from the hull and realigned it while rebolting it. But in my boat it's set into a recess in the grp, big job to release it.
Then Prop Shaft connected at the inner end (to gearbox).
Then the half bearing shells can be slipped out, also confirming that you haven't inadvertently applied downward pressure on the half shells. Recheck alignment in the water.

[SailingHarmonie]

Originally Posted by clakiep

Engine shaft alignemend has to be done with the boat floating. On the hard only a pre-alignement !

Capt. Claus São Paulo/BRASIL

That really depends on the boat. Some boats are very flexible and it matters.

Others are built to a higher standard and it matters little.

[skipperpete]

Originally Posted by Toccata

I think we have comprehensively answered this question.
Maybe "Cashew" (OP) will come back with either more questions or an observation about usefulness of our answers....
Being pedantic
Regarding centering in the stern tube. I used a piece of cutlass bearing (OD sized to match the tube) cut it in half longitudinally, slipped the halves under the shaft at both the inner and outer ends of the tube. This then created a datum to check the P bracket position/alignment, but I still had to slightly under size the cutlass bearing OD as I just could not bend the P bracket for perfect alignment. The glued in cutlass bearing did that trick. (I am talking fractions of a mm).
I guess I could have released the P bracket from the hull and realigned it while rebolting it. But in my boat it's set into a recess in the grp, big job to release it.
Then Prop Shaft connected at the inner end (to gearbox).
Then the half bearing shells can be slipped out, also confirming that you haven't inadvertently applied downward pressure on the half shells. Recheck alignment in the water.

That’s another good way to achieve concentricity. I hope the OP does post about how he eventually resolves his propshaft problem.

[MicHughV]

Some good ideas posted here.
I realize that every boat is different, but the key is having the shaft centered inside the stern tube.
Only then can the two flanges be mated up.

On my first boat I was surprised to see how misaligned the two flanges were, after noting a serious shaft wobble, off by a good 1/2". Cost me a new prop shaft.

Another point I'd like to make. The inside diameter of the cutlass bearing must match exactly the shaft diameter. Confusion often happens, when, for instance, by mistaking a metric 25mm shaft for a 1" shaft. They are not the same, close, but not close enuff.

[Cashew]

Thank you all for your input, it is much appreciated. In the meantime, we have diagnosed the root cause and it is due to bad workmanship.

Here is what happened: The contractor who replaced our motor mounts was instructed to replace the shaft seal with a dripless one, but was not able to find one that fits and instead decided to refit our old stuffing box. We accepted this as conventional stuffing boxes also have advantages.
As said before, I noticed the wobble but was not sure about the cause.

We had a bit of water ingress from the hose clamps over the last months, which I retightened multiple times and thought it was caused by temperature differences, as the mechanic had worked in low winter temperatures. I also adjusted the stuffing box but it did not hold for long.

A few days ago I found about half a gallon of seawater in the bilge, I found it dripping from the inner part of the stuffing box. I found one of the two hose clamps holding it was corroded. I then installed two new hose clamps and tightened them again. When we left the marina the morning after, I felt the temperature of the stuffing box and it was running hot. We returned to the marina, I tried to adjust the packing but it did not help. While adjusting, I removed the nut completely from the thread and noticed that almost no water entered through the metal which was a sign that something must be wrong.

So we decided we have to haul out and pulled the shaft.

Here is the diagnose:
The mechanic used a rubber hose which did not match with the end piece of the stuffing box where the packing gland sits. He decided to fill the gap of multiple mm with self amalgamating tape. That setup was not straight, so when the engine was running, the stuffing box wobbled - not the shaft. With the wobble of the box and the vibration of the engine, it looked like the shaft was vibrating too but in fact it is not.
The whole setup was also not tight, because the tape, wrapped around multiple layers, remains soft. The metal part wiggled out every now due to the wobble and then and the tape deformed.

Every time I tightened the hose clamps, the increase in compression decreased the room for the tape and pushed it into the rubber hose, creating a rubber clump at the aft end of the metal, inside the hose.

Eventually, when I installed the new hose clamps, I must have tightened them even more than the ones before and that clump inside the hose got so big that it created a seal that wrapped around the shaft and prevented seawater from reaching the packing gland, and that was when it started to run hot.

I am just glad that we did not have a dangerous failure with this setup.

Pictures are attached that should help to follow what happened inside the hose.

We are now waiting for parts and decided to install a Manecraft Dripless shaft seal. It has the feature that it can be closed by a hand operated hose clamp in case of failure, which we like.
It is also the only one available in a reasonable time.

[skipperpete]

That’s absolutely unforgiveable. You could easily have lost your boat had that separated at sea and gone un noticed till the water level got high in the bilges.

[Toccata]

what a "contobilae"!!
Note contobilae is a made up mess of a word (by a local marine engineer here in Paynesville) to describe an absolute balls up. Appropriate word for your situation.
Just emphasises the need for keeping an eye on spinning things in the driveline.
Hope the seal arrives soon and solves your problem.