Vibrating shaft at slightly high revs.

[Hoohaa]

I spent today trying a few different things.

1. Removed the flexible coupling and loosened the metal coupling and slid it up so that the two flanges could come together.
I put a couple of bolts in it and checked the gaps with feeler gauges. Made some adjustments and then idled the motor in gear. Wobble was still there.

2. Then I set up a ruler to check the wobble while I turned it by hand. The wobble was virtually none existent.

3. I removed the bolts and rechecked my gaps made some minor adjustments I managed to get the alignment pretty good. I then moved the metal coupling back and reinstalled the flexible coupling.
Turned it by hand again and presto, the wobble was virtually none existent, so I idled the motor in gear and the wobble is back…

Even though there is no obvious shaking or excessive movement of the Engine I am starting to think this is an Engine mount problem? What do you think?

[senormechanico]

Imho, bent prop blade.
The main difference from turning it by hand is loading of the prop blades to the water.
Uneven loading would cause slight bending of shaft under load.

[Three Sisters]

I think you are getting there. Testing the many pieces of the puzzle.


As an extra test, once your alignment is where you want it, before bolting the couplings together, mark a spot on the coupling, turn the shaft maybe 1/4 turn and recheck that spot that you marked on the coupling with, of course, the same feeler gauge, turn another 1/4 turn and so on. All good ? Try another mark if so inclined.

At this point you are eliminating one culprit at a time as to the source of the wobble.

If you are able to locate replacement motor mounts, the description in the sales brochure may reveal the adjustment procedure for raising the engine. Emails around the world are free.

Through all of these adjustments, the shaft needs to remain centered in the stern tube, as others have previously written.

[Cheechako]

Originally Posted by Three Sisters

I think you are getting there. Testing the many pieces of the puzzle.


As an extra test, once your alignment is where you want it, before bolting the couplings together, mark a spot on the coupling, turn the shaft maybe 1/4 turn and recheck that spot that you marked on the coupling with, of course, the same feeler gauge, turn another 1/4 turn and so on. All good ? Try another mark if so inclined.

At this point you are eliminating one culprit at a time as to the source of the wobble.

If you are able to locate replacement motor mounts, the description in the sales brochure may reveal the adjustment procedure for raising the engine. Emails around the world are free.

Through all of these adjustments, the shaft needs to remain centered in the stern tube, as others have previously written.

I almost mentioned this earlier. It's something I haven't thought much about previous to this thread. But seems to me it's certainly possible for an unsupported prop shaft to not be centered in the cutlass/shaft tube. Those thick rubber hoses used to attached the packing gland could very well be attached to the tube on a bit of an angle, and they are stiff enough to pressure the shaft one way or another when it's unsupported. Then the shaft could contact the cutlass on one side more, and so would contact the other side at the other end of the cutlass. What effect this would have I have no idea. Another reason to do shaft, packing, alignment work when hauled I suppose. But if you do the whole alignment thing with this unknown you may be wasting your time.

[Hoohaa]

Originally Posted by Cheechako

I almost mentioned this earlier. It's something I haven't thought much about previous to this thread. But seems to me it's certainly possible for an unsupported prop shaft to not be centered in the cutlass/shaft tube. Those thick rubber hoses used to attached the packing gland could very well be attached to the tube on a bit of an angle, and they are stiff enough to pressure the shaft one way or another when it's unsupported. Then the shaft could contact the cutlass on one side more, and so would contact the other side at the other end of the cutlass. What effect this would have I have no idea. Another reason to do shaft, packing, alignment work when hauled I suppose. But if you do the whole alignment thing with this unknown you may be wasting your time.

Yes it's possible. As you said. It's not easy to check until she is out of the water.


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[Hoohaa]

Originally Posted by Three Sisters

I think you are getting there. Testing the many pieces of the puzzle.


As an extra test, once your alignment is where you want it, before bolting the couplings together, mark a spot on the coupling, turn the shaft maybe 1/4 turn and recheck that spot that you marked on the coupling with, of course, the same feeler gauge, turn another 1/4 turn and so on. All good ? Try another mark if so inclined.

At this point you are eliminating one culprit at a time as to the source of the wobble.

If you are able to locate replacement motor mounts, the description in the sales brochure may reveal the adjustment procedure for raising the engine. Emails around the world are free.
.

TS. I have been able to find the engine mount dealers but I am still getting info on them. I did find out that they will cost about $180 each.
I will be back on board Friday and will your 1/4 turn idea..


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[Hoohaa]

Originally Posted by senormechanico

Imho, bent prop blade.
The main difference from turning it by hand is loading of the prop blades to the water.
Uneven loading would cause slight bending of shaft under load.

I am almost certain we can eliminate the prop. Because its the same no matter how fast the shaft is turning. Even when turning ver slow.
If it was the prop you would expect it to get progressively worse the higher the rpm.. and have virtually no effect while idling in gear.

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[Three Sisters]

Originally Posted by Hoohaa

TS. I have been able to find the engine mount dealers but I am still getting info on them. I did find out that they will cost about $180 each.
I will be back on board Friday and will your 1/4 turn idea..


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From your photo the engine mounts look like threaded rod, three nuts, washers, and a polyurethane bushing. Excluding the brackets. Threaded rod, in that size, 1 inch diameter ??, hardened ??, gets pricey fast.

[Hoohaa]

This is the beast.
http://www.polyflex.com.au/mounting-...8ctf-gen-mount


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[Three Sisters]

It's an all-in-one type deal. No user serviceable parts. Had to chuckle at the convex/concave washer, remarkably similar to an automobile shock absorber kit of yesteryear. And the adjustment sequence ? Is it obvious ?

[OceanSeaSpray]

Have a look here: http://www.cruisersforum.com/forums/...ml#post1327930


Chances are that your flex coupling could be causing the problem. I have seen many shafts run much more quietly when hard coupled. Read the details and see whether it applies to your installation.


Eric

[jimbunyard]

Man, this thread is all over the place...

For starters, I'm with those who're thinking unbalanced/untrue/bent prop.

The orange coupling is a Drivesaver, manufactured by Globe Rubber Works, and is primarily intended to avoid damage to the marine gear in case of impacts. It has a secondary function in isolating the shaft and prop from stray electrical currents; some would say for proper bonding a shaft brush or jumper strap should be used... It is not what is traditionally known as a 'flexible coupling', which are designed to absorb slight misalignments and vibration.

Originally Posted by Hoohaa

I originally said that the wobble occurred at higher revs but i had a better look at it and its always wobbling at the stuffing box.
Summarizing.
The system has always wobbled ( not vibrated) at the stuffing box since I bought the boat.
1 year ago on advice from a shipwright, Surveyor. I replaced the cutlass bearing and rebuilt the skeg. New coupling and new shaft.
The problem is still there.
Its possible that before I purchased the boat that the prop hit something, sustained some damage thats not readily visible and bent the shaft in the process.
I think all things considered its either shaft alignment or the prop?

As previously noted, could be either.

Originally Posted by Hoohaa

Also. I was thinking of loosening the Allen key bolts on the coupling and sliding it towards the gearbox wich would allow me to use feeler gauges directly between the flanges.
Can you see any issues if i do this?

Originally Posted by Hoohaa

Have justtaken the F Coupling out again. Here are some pics of it so you can judge for yourselfs.note the rough edges are outside everything that makes contact.
Also. Its very hard material so i don't think it does allot of flexing.
I will loosen the coupling and bring the plates together so i can check them properly with a feeler gauge. Also added a pic of the spaces I will be using on the mounts.

The generally accepted 'correct' way is to mount the coupling on the shaft, then check face runout of the assembly on a lathe or similar apparatus, in case the coupling is not completely true. Obviously, moving the coupling after this is done could alter the relationship of coupling and shaft. In practice, it is done frequently, it may or may not make any difference.

Engine alignment requires precise movements at all four corners of the engine to get the faces of the output flange on the gear and companion flange on the shaft as perfectly square to each other as possible. This often requires adjustments of 1/8 - 1/4 turn on a fine thread stud to accomplish. One would have to be very lucky indeed to find 'washers' or 'packing' of the correct thicknesses to align an engine, especially a small one.

Originally Posted by Hoohaa

Ok. I have moved the motor sideways. To Port. 2.5 mm. The flanges look pretty well aligned horizontally. The flanges are measuring within 0.1mm or just over 3 thousandth but i am still not 100% confident with the measurements. I tested it at very low rpm and it's still wobbling but I can't gauge if there has been a reduction.
I want to make a vertical adjustment using the engine mounts but suspect that they need to be packed rather than screwed up or down. I will attach a pic of the mount and hopefully someone will recognize it and confirm which is the correct way to adjust the height.

The mounts you have may be perfectly ok; if the yellow material is the flexible element, they may well be polyurethane, which has a much longer life span than rubber. If there is a problem with the threads, a die can probably had for 20.00-30.00 or so to clean them up, you will not be able to align the engine without the fine adjustment provided by the adjusting nuts. If the nut on the bottom of the stack of washers somehow holds the mount together, buy another one and install and use it in its' proper place.
This is one place you need liberal amounts of never-seize.

Alignment, while simple enough in theory, can be a little tricky in practice. Remember that the fixed point of where the shaft goes through the cutlass bearing is what you have to align the engine to, i.e. the axis of the crankshaft and the prop shaft have to match, and since the shaft is held at the cutlass end, the engine has to be moved to accommodate it.

As for the actual aligning, flange to flange is by far the preferred method. Even with a high quality spacer as illustrated above, measurement errors are compounded by additional hardware and difficulty in ensuring repeatability. Far better to remove the anode, put the prop coupling in its final operating position and align from there.

Water should be warming up down there, an easy test would be to pull the prop and see how the shaft runs without it...

[GILow]

Originally Posted by jimbunyard

The orange coupling is a Drivesaver, manufactured by Globe Rubber Works, and is primarily intended to avoid damage to the marine gear in case of impacts. It has a secondary function in isolating the shaft and prop from stray electrical currents; some would say for proper bonding a shaft brush or jumper strap should be used... It is not what is traditionally known as a 'flexible coupling', which are designed to absorb slight misalignments and vibration.

Interesting assertion. I wonder how you can be so confident of this?

The OP's pictures look a LOT more like a polyflex coupling than what you have pictured here, and given the engine is mounted on polyflex engine mounts, (according to the OP) it seems probable both were from the same manufacturer. Finally, the OP is in Australia, and polyflex is very, very commonly found on boats in Aus. A quick Google failed to find a distributer of the Globe Rubber Works Drive Saver in Australia, but I concede it could be imported.

Either way, the device you have pictured, and the original polyflex coupling both lack the apparent damage on the outer rim, and neither have the captive nuts even remotely as close to the edge of the polymer as that pictured by the OP.

Anyway, this thread is an interesting read, and I am learning there are many ways to skin this particular cat. (With apologies to the cat lovers out there. )

Matt

[OceanSeaSpray]

It is exactly the type of "must have, essential, wonderful and magic" coupling that promotes shaft whirling issues. If the shaft is floating at the seal and supported at the cutless bearing only, it shouldn't be there.


If something is bent, then it shouldn't be hard to find it.


Another tell-tale is whether it vibrates in forward gear, but not (or a lot less) in reverse. If it is bent or something is out of balance, it should be bad both ways.

[Hoohaa]

Originally Posted by OceanSeaSpray

It is exactly the type of "must have, essential, wonderful and magic" coupling that promotes shaft whirling issues. If the shaft is floating at the seal and supported at the cutless bearing only, it shouldn't be there.


If something is bent, then it shouldn't be hard to find it.


Another tell-tale is whether it vibrates in forward gear, but not (or a lot less) in reverse. If it is bent or something is out of balance, it should be bad both ways.

Its the same in reverse. I take your point that the only reason the coupling should be there in this case is to protect the system from shocks. Or maybe very slight misalignment. Its a very hard material.
Allot of people still think that there is something bent or something with the prop. All is less than 2 years old except the prop.
Am I wrong in assuming no damage on the prop because the wobble is present and looks the same at speed and while idling. I would think that damaged prop wobble would increase exponentially as the rpm increases.

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