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Old 04-10-2009, 07:44   #1
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Video Link - Still Trying to Diagnose Squeal in Forward

Hi Folks, Started a new thread to summarize.

- 1982 Yanmar 2GM, Km2a transmission (cone type)
- Has loud squeal in from about 1200 rpm, increasing in loudness, up to about 2900 - 3000 rpms, where its seems to phase out (of course, engine is louder at higher rpms)
- It is NOT the belts, water pump or alternator (have had belts off while running - still does it)
- It does NOT have any squeal noise in neutral or reverse

On old thread some knowledgeable members have suggested:

- stuffing box - could be, but still does it even when nut is loosened, and lots of water is flowing

- Cutlass bearing / alignment - could be, cutlass is new 2 years ago, but have had engine out for cleaning. No noticeable vibration in prop shaft, engine, etc at any rpm range.

- Transmission / forward gear - My mechanic brother helped me take the transmission apart 2 years ago, as its wasn't shifting well. We lapped the drive cones to the gears and it has shifted perfectly since then. He did not notice any badly worn parts at that time. Engine is old, but has reasonably low hours, I believe.
Is it possbile that the thrust washer, or another part, only engaged while in forward, could cause this?


I did have a local mechanic look at it a couple of months ago. He thought the engine, trannie sounded / worked fine. He checked the trannie oil, and said it was fine (no burnt smell, as if a bearing was going, etc) He said the engine was good for many more years.
However, we were tied to the dock, when he checked it. Could not rev up very high there (docks not too robust), so he only heard a slight squeal. It gets much louder as rpms increase.

Here is a link to a video of the problem. Please have a look / listen, and let me know what you think!!

The engine is revving near max at beginning of video - squeal is much more noticeable near end, when we drop, then slightly increase rpms.

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Old 04-10-2009, 08:35   #2
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- - Nice video - squeal is just as the rpm's decrease near the end of the video?
- - Couple of ideas - some are long shots - As the rpm's hit that range you may have insufficient ocean water entering the shaft log cutlass bearing setting up the squeal. Power boat typically have an air bleed off line in the shaft log/stuffing box to allow sea water to transit the cutlass bearing and exit through the vent hose keeping cool seawater flowing through the cutlass bearing.
- - Another - did you check the "dampener plate" when you had the transmission off? It is the vibration plate mounted on the engine fly-wheel and accepts the splinned shaft from the transmission. The "dampener plate" has springs holding two plates together, one plate bolted to the engine and the other accepting the tranny shaft. It is typical on older boat engines for water to rust the area between the plates or the springs and then you get noise.
- - Another long shot is bearing squeal in alternator and/or other pumps/motors mounted on the motor and even engine mounts. A doctor's stethoscope can help find the culprit.
- - Also look at the propeller shaft right where the stuffing box packing rides, a glazed area on the shaft could set up a squeal. You really cannot totally remove the stuffing box when in the water so there will still be some contact between the shaft and the stuffing box - which could also be a little out of line with the prop shaft causing a rubbing somewhere other than where the "stuffing material" is located. Marks, scoring, glazed areas will reveal if there is a posible problem there.
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Old 04-10-2009, 18:21   #3
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Are you sure it is coming from the transmission?

If you are not positive figure out exacty where the squeal is coming from. A stethescope earpiece and tubing mated to a long steel rod (threaded, welding rod, solid, whatever. Use the rod as a probe to touch all the different parts. Narrow it down to the front, rear or center of the tranny.
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Old 04-10-2009, 19:55   #4
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Thanks for the replies!

Osirissail - No, it is squealing during most of the video, but it is more pronounced near the end of the video, when I drop the rpms. The higher rpms / engine noise make it hard to distinguish between the different noises, and it seems to go away somewhat at 3000+ rpms, or so.

I do agree with you that it could be the prop shaft rubbing on the stuffing box, or even the cutlass bearing, creating a bit of a wear point, etc. It is funny that it doesn't do it in reverse, but prehaps that could be explained by the fact that the engine woukd be applying torque in the opposite direction, and therefore may not be rubbing / wearing on the same point.

Re: the pumps, etc - As I had both the raw water pump, and alternator belt off, it is definitely not coming from them, or their belts. The engine mounts are new, and tight, so I am not leaning towards them. It does seem to come more from the back of the engine (ie trannie / stuffing box)


Therapy - No, I do not know where the sound is coming from for sure. The menchanic that looked at it tried the screwdriver in the ear thing, touching it to various engine parts, but wasn't sure where it was coming from either. He thought it was just general engine noise. In his defense, as mentioned, we were tied to the cosk, and didn't rev it too high in gear. He did not get to hear the pronouced squealing that you hear near the end of the video.

I will try to get a stethescope and do as you described. The engine has worked fine all year, and sicne we don't motor that much, I had put the sound on the back burner. Now, as the boat will be hauled for winter in a few weeks, I am feeling the need to do some more testing, while still in the water. Of course, after it is hauled ,I can check the shaft, cutlass, etc for wear, but will be unable to test under load, as I can now.

The sound seems t obe coming from the back of the engine / trannie, but could also be from the stuffing box, or even cutlass. You can hear it somewhat outside, in the hull. However, I am not sure if that tells us anything, as the engine, trannie, shaft, etc all have contact with the hull, one way or another, and could reverberate the sound throughout??
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Old 04-10-2009, 22:25   #5
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- - The stethescope is the answer or you can make one with a length of 5/16" plastic vinyl tubing and a piece of rigid plastic pipe/tube. You will just be listening from one ear. Be sure to plug the other ear with an ear plug to lessen extraneous noise.
- - Normally these things are something stupidly simple that we just cannot center on them. One might be a foreign object, (piece of marine life, etc.) that got sucked up into the custlass bearing through the "rifling" in the rubber.
- - How good is the alignment of the prop shaft to the transmission flange? If it is out of alignment that would cause a stuffing box squeal that would be apparent in - say - forward gear versus reverse gear. But, acutally with the transmission in neutral you should be able to increase the rpm's to the mid or cruising range - and if the squeal is there, it is not in the area from the aft end of the tranny to the prop. It is somewhere in the engine/front end of the tranny. You should be able to hold the prop shaft from rotating when in neutral.
- - Engines move forward in their mounts when the boat is in forward gear. And likewise the whole engine moves aft when put into reverse. Only if you have a hull mounted thrust bearing does the engine not move. The older the mounts the more the engine moves. This movement will change the angle of the prop shaft as it enters the stuffing box and cutlass bearing. With strong stiff engine mounts this fore/aft movement is minor, but with soft or old mounts it can be significant enough to cause some unrelated part to start rubbing on part of the engine making the squeal.
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Old 05-10-2009, 06:24   #6
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If you disconnect the propshaft coupling from the transmission and separate them, you can then run the engine and transmission and determine if the noise comes from the transmission or the prop.
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Old 05-10-2009, 13:36   #7
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Osirisail - Thanks for the great info. It does not do it in neutral, even when reving the engine up to any rpms.
Will try to check with stethescope, or tubing, next weekend.

I thought that the trannie to shaft alignment seemed OK, as there is no vibration, etc. However, it may be entering the stuffing box / and even cutlass at a slight angle, even though there is no vibration.
I have written about this engine aligment before - I don't know if all boats are like this, but in mine:
- the prop shaft is supported (lined up) by the cutlass bearing, which is a couple of feet away. As there is not bearing in the stuffing box, and it is not a bearing itlself (ie does not keep shaft perfectly centered before bolting coupler to engine) there is enough play in the shaft, as I am bolting it up, that it bolts up tight, and I cannot use feeler guages to check clearances. What i mean is that, if it was a bit out of alignment, the coupler just seems t omate up flat, as the shaft coupler side is presented to it. As there is no close bearing holding the shaft firmly in the center of the stern tube, for example, the shaft is free to move slightly, so that the coupler mates up tight.



Stanley - The only reason I hadn't tried it, with the coupling disconnected, is that I felt that this may be a false test, as the load would also be removed from the trannie. So, if it doesn't squeal anymore, with the shaft disconnected, I am not so sure that I could then say that the problem is in the shaft/stuffing/cutlass, as maybe the lack of load on the trannis is hiding the issue - only surfaces with the load on.
Thoughts??
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Old 05-10-2009, 15:26   #8
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- - That pretty much eliminates the whole engine and the front half of the tranny as the problem. There is only the back half of the tranny and the prop shaft, stuffing box and cutlass bearing and the propeller. Sometimes you have to think out of the box. If the prop is damaged or out of balance, it can set up a harmonic that travels up the shaft. Or it can put a uneven load on the cutlass bearing; stuffing box; or even the aft end of the tranny.
- - Running the engine in gear with the prop shaft separated away will eliminate the aft end of the tranny. And - when you separate the flanges - grab the prop shaft half of the flange and see if there is any movement at all between the flange and the prop shaft. Normally the prop shaft has a zero clearance fit in the flange. Any prop load on the system causing the squeal would be much lower on the probability scale than the shaft/cutlass/stuffing box. Depending upon the distance from your propeller to the nearest hull obstacle, you might be able to move the shaft far enough out of the boat to see if there is any obvious scouring, glazing in the cutlass bearing section. Or you may dislodge a foreign particle from the cutlass that was causing the problem (we call that "magical disappearance" of the problem).
- - The prop shaft is primarily supported by the cutlass bearing at the prop end and the transmission and flange at the other end. Disconnecting the flange will allow the prop shaft/flange to sag and move about in relation to the tranny flange. There is a small collar on the prop shaft end of the shaft/flange that slides into the tranny/flange. The alignment procedure is to just mate the two flange halves to get that collar into its recess. There will be a millimeter or two gap still between the flat round surfaces of the two parts of the flange assembly. Insert some of the bolts and nuts to keep the two parts rotating together but not enough to put any closing pressure on the two parts of the flange. Then take your feeler guage measurement on opposite sides of the flange and compare. The should be as close to equal as possible. Also rotate the whole shaft and tranny assembly 90 degrees and redo the measurements. Any misalignment would show up as a consistently larger or smaller measurement - left, right, top or bottom as your rotate the flange assembly.
- - Installing a "DriveSaver" disc - if you have clearance for the propeller to move aft about an inch or two - may also fix the problem. The "DriveSaver" will correct for minor mis-alignment of the engine/prop shaft and also absorb vibration. And installation will move the prop shaft back an inch which might just move the piece of shaft that might be causing the squeal away from its previous position.
- - A personal plug for the "DriveSaver" it saved my butt twice. With a dead stop of the engine due to snagging something with the propeller, the "DriveSaver" will absorb a lot of the shock torque in sudden stoppage and save the tranny and engine. Another "saved-you" aspect was when I snagged a long nylon line that my prop line cutter cut loose - but the remainder of the line wrapped around the exterior prop shaft setting up a heavy drag load - the DriverSavor deformed and helped save the shaft and bearings. It is a large orange plastic disc about an inch thick that mounts between the two parts of the flange assembly.
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Old 05-10-2009, 18:50   #9
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I had considered a drive-saver when I reinstalled the engine, 2 years ago. I would likely have to get the shaft machined about 1/2" shorter to install one, as I would not want to increase the distance from the strut to the prop, by more than the recommended amount.

Forgot to mention - the damper plate did look OK when we had the trannie apart 2 years ago. Of course, it did not look "as new" being 25 years old, but showed no major wear or concerns.

I did have the prop taken down this past winter, from a 15"x10" to a 14"x9", as it was overpropped. This work was done by a very well repected commercial machine shop, who work on props as large as will fit in the bays at the shop. The part owner is the guy who did the work, and is was extremelel knowledgable. I dove to have a look a few weeks ago and there was virtually no growth on it.
I am not aware of hitting any debris, etc, that would have damaged it. Now that I think of it, it did have the squeal last year, so it could not be any damge to the prop this year!

I ma leaning toward the shaft alignment causing a wearing on the stuffing box, or cutlass. Will check further when it is out of the water, in a few weeks.
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Old 05-10-2009, 19:53   #10
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Best of luck.
Let us know.

After thinking about you saying you can "hear it in the hull" or something like that, it makes me think it may be down stream of the tranny.
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Old 05-10-2009, 19:57   #11
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- - One by one the possible causes are eliminated and as the noose tightens the real culprit hopefully can be identified. If the engine runs in neutral at all rpm's and does not squeal then the dampener plate is probably fine - although 25 years old is a might old. The springs start to loose their strength. Just keep a wary eye open for a failure there at some other time.
- - Try to do the prop shaft alignment while the boat is in the water - - taking a boat out of the water and putting it on jackstands with blocks under the keel will change the shape of the boat. A boat is designed to be evenly supported by the water pressure/displaced water which is touching the entire underwater hull. Versus jackstand and keel blocks which only support at a few distant parts of the hull. We never tune rigging while a boat is out of the water. We can install rigging but the tuning must be done after the boat has been in the water for period of time.
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Old 07-10-2009, 22:42   #12
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Whats known as a 'singing' prop alter prop blade tip profile very common in bigger props. Some times can be heard if below in a nearby vessel or ear pressed up on side of dinghy or diving closeby, also check shaft end float at g-box rear thrust bearing is there any in--- out movement between fwd & rev?
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Old 08-10-2009, 05:30   #13
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I have not checked the gap - I assume you mean play, or the ability to push / pull the shaft fwd or reverse a bit. Should it be completely non-moving, or is a bit of play acceptabe? How much?
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Old 09-10-2009, 02:46   #14
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there should be zero movement at gear box rear bearing if movement found check gear box rear coupling nut has not backed off. Some older style boxs are fitted with double sided thrust bearings these will become very noisey if a 'Hardy Spicer or a 'scatra' joint has been installed.
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Old 13-10-2009, 16:17   #15
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There is no play in the propeller shaft! I do think that the engine to stuffing box alignment may be out a bit, causing the shaft to rub more on one side of the stuffing box. I did loosen off the engine mounts, but there is not alot of room to move it, side to side. I will likely wait until it is oun the hard, in about 3 weeks, and then I will have a look at it this winter (indoor storage).

I will take off the stuffing box, and coupling, to look for signs of wear in either (ie from metal rubbing on metal). I will then be able to take my time and align the engine for next year, with the final check being on the water.
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