Vibrating shaft at slightly high revs.

[delmarrey]

Originally Posted by Hoohaa

Good point about the shaft movement.
The old man sugested some sort of vynl or non metal bearing?? Does anyone know about them?

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Putting in a pythondrive would help but it sure didn't cure mine. The problem with a synthetic/plastic bearings is heat, even with lubrication. In the old dazes, rose wood was used, but underwater.

Q: Does your shaft vibrate in reverse? If not, then the shaft is whipping due to the stress on the shaft. Pulling on the shaft keeps it straight.

[Hoohaa]

Oddly the shaft wobbles in forward and reverse when put into gear. At low rpm and high rpm.


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[delmarrey]

With that! First, I'd start with the coupler on the back of the tranny, make sure it's tight and running true.
Then the coupler on the shaft, make sure it's tight and running true.
Then dial them in together, providing the shaft is straight.

Next I'd go for the prop. Make sure it's not damaged and in good shape. If these are not the problem, then it has to be the shaft diameter vs length.

FYI, if you take a 1" shaft 7' long and hang it horizontal from its ends, that it would actually sag in the middle slightly from its own weight.

How old is the shaft?
SS, after being bent or worked, can crack or work-harden over time especially at the coupler or prop areas. If you take a small piece of SS and bend it back and forth fast, you'll notice that it'll stop bending in the same location. That's because the bend starts to work-harden from the stress and heat. Much like chain plates.

[Cheechako]

Originally Posted by senormechanico

Listen to delmarray. He really knows his stuff.

Steve

Well... maybe don't listen to his math.... 380mm is 15.2" not 6.7 feet!

[delmarrey]

The drawing above, post 189, shows an OAL of 6.7'. With only a packing gland in the middle seems pretty flimsy. Try putting 1" diameter at 6' long shaft in a lathe between centers and spin it up to 600 RPMs. If it wasn't perfectly straight it would start whipping.

[Hoohaa]

Just a clarification. The shaft is 1 1/8'' diam and about 2 years old now.. Sorry about that.
I think we can rule out the prop and a bent shaft.
I will have another go at aligning it.

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[delmarrey]

Well then, I would blame it on your couplers and/or alignment.

[Cheechako]

Well, I had to go back and review this thread just to refresh.
-It is a pretty long shaft, supported by 2 cutlass bearings and a packing gland.
-So it has some support at regular intervals.
-Reviewing the video again, I'll just repeat that I'm not convinced the motion you have is that unusual. Cant really say some of my boats looked any different.
-As I said earlier the "hull effect" causes unbalanced pressure on the prop and thus the shaft due to the prop blade turning near the hull.
-Add to that, that cutlass bearings aren't a tight fit and have loose clearance to the shaft.... why wouldn't there be a bit of movement?
-In the video, the engine end is stable and not moving. Why you got into the motor mounts when that is the case ....isn't that a wild goose chase?
-Is there an actual issue you are trying to solve? Cutlass bearing wearing out quickly? or something?


Is the whole arrangement optimum? No. Is it a problem? Not sure...

[Hoohaa]

Well Its been a year and allot has happened.
I am sorry to all the contributors on this post for leaving things a bit high and dry.
Last December we had a very strong wind go through my mooring and it dragged my boat onto 2 other boats causing some significant damage to all involved.
Long story short. Insurance claims and repairs saw me back to square one about 3 months ago.
The only plus side was.. Sorry there was no pluss side.
I got the boat slipped, repaired antifouled ect. While she was up I bought a feathering prop for her and got the mechanics in to tackle my alignment problem.
In the end they raised the motor more the 20mm or almost an inch.
When you looked at it on the slip you could see the prop shaft was resting on the bottom of the stern tube. But I can't explain why the prop shaft didn't spring up every time it was uncoupled from the motor?
Today, she still wobbles but not enough to make the knocking sound that it used to when she was pushed hard. So I am living with it and so far the new prop is doing great.
My next problem is that the engine has developed a horrible pop. But I will save that for my next post.

[GILow]

So, did you try replacing the soft coupling?

[Hoohaa]

No.
Pretty shore it was not the problem. It may have had a miner effect?
It was alignment. But I can't figure out why the shaft didn't pop up when everything was disconnected.
One of the things that I am thinking about is a miss alignment i n the stern tube. But you would hope that the guys that did the realignment would have checked it out properly.
Its always been hard for me to get hands on while the boats been on the slipp. Its either work commitments or it's just not practical to expect a business to have you hanging around while they get on with doing the job.
In the end I have had to put my trust in them and hope they do a Profesional job.
The other constraint here has been the huge costs of slipping and time on the slipp to carry out jobs. This is Sydney and its horrendously expensive to get work done here.
That's why I post here in the hope that I can do it myself and learn something in the process.
Sorry about the rant.

[GILow]

Well, for the low cost of the coupling and the benefit of having a spare I would have replaced it right at the start. The thing sure looks buggered to me. Just compare it with a photo of a new one.

Bloody glad I can do my own work, when I read these sorts of posts.

Sorry for the trouble it is giving you, you'll get it right in the end.

Now that my engine systems are all going nicely I sometime don the earmuffs, pull the engine access panels and just watch the whole lot running as I chug along. I have a mate who used to work in the engine room of a big ship and he describes a similar feeling of mechanical contentment.

[Three Sisters]

Were the motor mounts replaced ? Hopefully the mechanics gave instructions on how they proceeded to adjust the motor mounts. From the photos they appeared to be over-complicated.

Well then, you are at an acceptable level. This is good news.

Your boat is...she's beautiful. You should be proud.

Now for the popping sound from the engine ...stuck valve ???

[Hoohaa]

Thanks for the input guys
Gilow, Your probably right about the coupling but there not that cheap. And if you new what things cost me this year you would understand why I didn't replace it. Normally I don't hold back replacing parts.

Sisters. The mounts were not replaced. Instead we raised it them with spaces. I know its not ideal but the adjustment was allot higher than we expected so we had to make do with the time we had.
Here is a pic.

[Topfin]

It can be trust induced misalignment, caused by worn, isolators, posting them too high on the studs. this is common on deeper reduction transmissions. Many OEM supplied isolators don't factor in thrust demands