Engine Vibration Diagnostic?

Don12364 · Mar 11, 2012

The usual recommendation for shaft overhang is one to one and a half shaft diameters absolute maximum. Yours looks to be about four shaft diameters.
Consider the prop is pushing the boat so the shaft is under compression lengthways. Any out of balance in prop weight or blading pitch will initiate a small wobble and the shaft compression could well amplify this - not to mention any side effects from your somewhat dodgy shimmming procedure!

Benny17441 · Mar 11, 2012

Go ahead and do the things that you know need to be done. For starters tune up the engine so that it can run through its RPM range. Repair or replace the old prop. Replace the engine mounts and properly realign. I would suggest that you eliminate from the list of possible causes those things that would need to be done anyways. Broken or damaged engine mounts as well as faulty alingment are major causes for unwanted vibrations.

kloudie1 · Mar 11, 2012

was the shaft perfectly straight at installation?
Try moving the zinc to the other side of the strut.. If that makes a noticeable difference in vibes (less), then ya should shorten the shaft to the same length as the old one. That can be done in the water by removing the coupling and cutting a couple of inches of shaft off with a Sawzall or a jig saw with a metal cutting blade. The cut should be close to square but doesn't have to be perfect.. I am assuming that you have a long enough keyway to do that.. Not an easy job, but if you have enough access, not too bad.. Good luck !

AtlanticAl · Mar 11, 2012

You say running in reverse dosent cause any problems, I am no expert, and have only ever seen one of those folding propellers once, but, i was told they are not good in revese, firstly, due to the shape of them, they are designed to fold up neatly, and designed for forward thrust, when you reverse, their is nothing but centrifugal force to hold the blades out, this force is opposed by the weight of the boat, that the propellor is trying to pull in reverse, so the propellor, never gets to its full doployement in reverse, bit like sticking an outboard in reverse, it flies out of the water, the extra couple of inch on the new shaft, could be the problem, but i shouldnt think it is, i tend to think if it was the shaft, you would be able to see a bend in it just now, what i would do, is dive under the boat, tie some wire round the prop to kee it from opening, then run the engine in both forward and reverse, if it smoth both ways, its not the shaft, its the prop.

AtlanticAl · Mar 11, 2012

Oh one other problem, those props, can move more than just to the center when they wear they can move further, so what i said about tying them with wire to stop it moving, i may move slightly to one side, you better take the prop off and see if it vibrates without it, because if you grab the prop when its folded, you will find their is still some movement in it, from one side to the other.

Granfalloon · Mar 12, 2012

Prop Suggestion

AtlanticAl said:
Oh one other problem, those props, can move more than just to the center when they wear they can move further, so what i said about tying them with wire to stop it moving, i may move slightly to one side, you better take the prop off and see if it vibrates without it, because if you grab the prop when its folded, you will find their is still some movement in it, from one side to the other.

After you have done the previous recommendations - consider a CDI Performance Prop. The have props that work well on your type engine.

bigpapaporsche · Mar 12, 2012

Another item to check

Coast Awhile said:
After you have done the previous recommendations - consider a CDI Performance Prop. The have props that work well on your type engine.

I have considerable experience with diesel engines as well as trouble shooting various vibrating problems. Although I am not familiar with your exact engine, I would suggest that you inspect the front damper/pulley on the crankshaft. Many damper/pulley use rubber to sandwich the two pieces together to absorb vibration. A simple inspection of the damper should be done. Just inspect the rubber between the inner/outer parts (if so equipped) to see if it is soft or other wise deteriorated. Many time there are indexing marks stamped on the inner and outer parts to show that they are still in alignment.

moehorenfeldt · Mar 12, 2012

Firstly, your zinc must be before the strut. It has two purposes, one is as a protection for the metals exposed to any stray electical issues, especially in salt water, and the other is to prevent the shaft from moving out of the boat, for example, such as would happen if the shaft coupling failed. The extra weight near the prop exacerbates the vibration likely induced by the prop, since as you say, there is no vibration in neutral. The atomic 4 really has no reverse gear, it's a clutch-cone affair, which is much less powerful than a gear driven reverse, however, as someone else pointed out, the foldin props have defitiancies, and do require refurbishing, often. My own preference, unless your are a racer, is for Performance Props from CDI, I believe, which make a big difference in how the boat performs with an A bomb.

JeffM · Mar 12, 2012

Wow, lots of variables here that can all interact. Did you do the shaft alignment with the boat in the water? It should be in the water and allowed some time to settle into its floating shape before doing any alignment.

Folding and feathering props are notorious shakers when they get old, so that needs to be checked. Not knowing the exactly how that prop assembles, are you certain that the everything was properly reinstalled? I assume you checked that the cutlass bearing in the strut didn't have play in it.

I agree with the other comments that the extra shaft length and zinc location can be a problem, or add to any problem.

Good luck ... that shake is hard on things.

carlpaez · Mar 12, 2012

Cool Beans said:
-Engine is an Atomic 4, original mounts. . .
-Prop is an old Martec folder, soon to be pulled and sent in for rebuild. . .
-Shaft is new (1" dia.), BUT. . .I was going through some pictures and it is longer than what came out by about 3 inches. . .
-New cutless bearing.
-Alignment isn't perfect, but better than when I started. I used paper shims between the flange faces (an old school way I found in one of my design books). I had to shim the front of the engine up slightly, done in the water.

I honestly can't recall how bad if any vibration existed before any of this work was done. I also couldn't get past an idle due to a clogged carb that I put off cleaning for awhile, lol. . .

No noticeable vibration in neutral. In reverse, there is no vibration or it is minimal (hard to tell). In forward, there is what I would consider substantial vibration, it gets worse as you throttle up. You can "hear" the boat shake (or at least that's what it sounds like to me). the rattling grill is the worst. Both blades are freely operating, so I'm assuming they are opening correctly. . .

First thought was alignment, which i checked and corrected as well as possible. Next I plan to have the prop removed and rebuilt. It is worn out according to what I have read (and probably hasn't been serviced in 37 years). I would think this is the most likely culprit.

Would vibration like this be an issue by itself with the extra shaft sticking out? You can see before and after pictures. . .I didn't even notice when I reinstalled it that it was longer If a balanced and true prop were installed, would the extra shaft matter much?

I'm trying not to pull the boat again until fall (hope not to anyways). While it is in the water, what else can I check for that could be causing vibrations? Would running the motor in gear with the prop removed prove anything?

I'm just worried the vibrations might break the strut off, causing the prop to swing up and chop a hole in my hull. . .an sinking me in Little Creek

I appreciate any and all 2 cent contributions, which will be added to my boat fund

P.S. How much if any vibration can be considered normal?

Dear boat owner,
I think you have several things to correct:
1. A much too long shaft makes for a whirlwind flutter in airplanes (the Electra by Lockheed), a bad vibration in sailboats.
2. the weight of the zinc in the cantilever side only compounds the unbalance dynamic condition of a too long shaft.
3. If the engine/shaft are not properly aligned, the system will vibrate in forward
4. Folding propellers are good to reduce drag when sailing, but must be serviced at least every few years, your looks like it needs it. If the blades do not deploy symmetrically they too can contribute to the dynamic unbalance situation you seem have.
Sometimes you have to pay the piper, so get the boat out of the water and do things right,

-0)

Carl Paez

RobertLangdirect · Mar 12, 2012

My Folding Prop

See the pics, please. I think I have the same prop, a martek.

But look at the position of my prop vis a vis the shaft length aand your prop. Also -- look at the zinc placement -- -- -- OH! THere was NO ZINC. Well, I put my inboard of the catlass bearing. Why stick the weight out at the end?

As I was fixing GOOD TRADE, after she was on the hard for more than a few years, I ran the motor (tanked in water) and put her in drive. The noise from the prop flying about was enough to make me bang my head going for the key and jump off the ladder thinking that I tore open the hull. So -- I offer -- DO NOT AIR RUN THE PROP! I certainly will not do that again.

I have no basis to form an opinion regarding shaft length, but I would think that close is close enough. Worse come to worse, take off the prop and give it a try. Noise still then, it's the shaft.

Then, borrow a normal three blade prop and give it a try. Noisy then and the same noise, I'd say look at the transmission coupling.

tommays · Mar 12, 2012

The shaft is WAY to long

On Zzzooom which has the same prop you pretty much have to do a bit of reverse to be sure the prop fully opes as if you do not it will shake if one blade hangs a bit

NYSail · Mar 12, 2012

Have you watched the engine while this is happening? I have seen broken mounts that look fine when engine is not running under load. As soon as there's a load (in gear) the engine bounces all over... until something else breaks.

Like others have said shaft is too long and zinc should be on other side of strut. Did a prop shop sell that to you all trued and sized?

Maine Sail · Mar 12, 2012

Cool Beans said:
-Engine is an Atomic 4, original mounts. . .
-Prop is an old Martec folder, soon to be pulled and sent in for rebuild. . .
-Shaft is new (1" dia.), BUT. . .I was going through some pictures and it is longer than what came out by about 3 inches. . .
-New cutless bearing.
-Alignment isn't perfect, but better than when I started. I used paper shims between the flange faces (an old school way I found in one of my design books). I had to shim the front of the engine up slightly, done in the water.

I honestly can't recall how bad if any vibration existed before any of this work was done. I also couldn't get past an idle due to a clogged carb that I put off cleaning for awhile, lol. . .

No noticeable vibration in neutral. In reverse, there is no vibration or it is minimal (hard to tell). In forward, there is what I would consider substantial vibration, it gets worse as you throttle up. You can "hear" the boat shake (or at least that's what it sounds like to me). the rattling grill is the worst. Both blades are freely operating, so I'm assuming they are opening correctly. . .

First thought was alignment, which i checked and corrected as well as possible. Next I plan to have the prop removed and rebuilt. It is worn out according to what I have read (and probably hasn't been serviced in 37 years). I would think this is the most likely culprit.

Would vibration like this be an issue by itself with the extra shaft sticking out? You can see before and after pictures. . .I didn't even notice when I reinstalled it that it was longer If a balanced and true prop were installed, would the extra shaft matter much?

I'm trying not to pull the boat again until fall (hope not to anyways). While it is in the water, what else can I check for that could be causing vibrations? Would running the motor in gear with the prop removed prove anything?

I'm just worried the vibrations might break the strut off, causing the prop to swing up and chop a hole in my hull. . .an sinking me in Little Creek

I appreciate any and all 2 cent contributions, which will be added to my boat fund

P.S. How much if any vibration can be considered normal?

Yes that shaft over hand matters a HUGE amount especially with a folding prop, which moves the blades even further from the bearing. This creates "shaft whip" and it can get really nasty..

This statement is part of ABYC P-06 for a reason....

"6.5.5.4 The distance between the forward end of the propeller hub and the aft end of the last strut bearing shall be limited to one shaft diameter."

This means for a 1" shaft the max allowable spacing is 1" between the prop and the strut. For a 3/4" Shaft you have 3/4"....

Yours appears to be about 4" and then you have a folder to compound the issue. A folder moves the blade centers aft even further away from the bearing... Your blade center is probably 9" from the strut bearing on a 1" or smaller shaft, creating whip... I'd start there.....

RichH · Mar 12, 2012

Most A4 installations have solid mounts, alignment is done by the insertion of 'shims' between the engine and the solid mount. A4s are so 'smooth running' they dont need flexible/rubber mounts.

Yes indeed there are many factors that will produce untowards vibrations.

I make the following suggestion to rapidly isolate if this is a prop problem or a shaft/engine alignment problem:
Go overboard that tie the blades of the prop closed, run the engine in gear at full rpm. If no vibration its the prop. If vibration then its the shaft/engine alignment or the shaft has lost its 'true' and needs to be straightened ... even brand new shafts should be checked for 'true' before installation.

Capt JimF · Mar 13, 2012

Re: Prop Suggestion

Hi, had the same problem: I had two boats with vibrations in the two (2) blade props. A 1980 Hunter 33' that noted a vibration on the delivery ticket when new and was still there 16 years later when I bought it and a Hunter 40' I just bought a month ago. I had the cutlass bearing replaced on both when I did the bottom job and heres the key: I purchased a: 'Campbell three (3) blade prop from North by West for about $675.00' they had the pattern in stock, about 10 days delivery . The workmanship and customer service was phenomenal. In both cases the vibration was gone in all rpm ranges, especially on the higher end and it literally felt like I had a new or bigger engine in both cases, with minimum prop drag! Compared to cost of a folding prop you can't beat it! Fair Winds....

McQueen Smith · Mar 13, 2012

Where I believe the prop shaft length to be a major factor, as stated above, there is something else to ALSO consider. Lap Fitting the old prop to the new shaft could be at least a partial source of the vibration. At the below link, it is said that even if both the prop and shaft were made of the same dimensions, the tools or machines to do that forming may not be precise. In shorter terms, the "bevel" of each part may be off enough, to allow the prop to wobble on the shaft?
http://www.pbase.com/mainecruising/fitting_a_prop

Engine Vibration Diagnostic?

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