Engine Squeal at speed

[eriesailor]

Hello all,

Maybe someone will have some ideas what this could be. My Atomic 4 runs like a top, except this squeal that starts in the low rpm range and gets louder in the mid-cruising rpm range. Occasoinally I can power past the squeal, or reduce the rpms to make it stop around idle speed, but have not been able to figure out what is causing it. I have tighten the alternator belt, which didn't change anything. I have also tightened the transmission as well, also with no results. One thing of interest is that if I tie the boat up at the dock and apply any rpm it doesn't squeal at all... Any ideas would be most appreciated, as I am losing my mind!

[Above & Beyond Yachts]

Does it sound like its the engine, or maybe the shaft. I would also suspect your raw water pump. The rubber impeller may be noisy if dry. Is the suction screen clear? That may be related to the fact it runs better in gear, when it's not moving through the water... less restriction.

[eriesailor]

Above & Beyond,

Thanks for your input. I forgot to mention that I did change the impeller too! The shaft didn't look scored or anything and the old one was in good shape. I will make a note to check for a difference in the water flow rate at speed.... hadn't checked that yet. If that is the case a larger screen may be the answer.

Do you know if the water pump is power through a chain or belt drive off the main crank? I was thinking if it's a belt that could be checked. Other than that my next guess would be to check the prop shaft... maybe it's rubbing on something?

[Rumrunner]

Engine Squeal...

I'm trying to figure out a similar problem I think. I've had the boat for three years. The first year the engine died at random, the cabin reeked of exhaust, I almost gave up. Cleaned the fuel lines from the filter forward, through the sediment bowl, and rebuilt the carb. Reseated the exhaust pipes. Engine runs like a top now, but it's still kills occasionally, often after running hard for a period of time.

Two examples: We left Manitowoc and motored at close to hull speed for two hours. Engine squeal develops, revs drop, engine dies, can't restart it. After sailing slowly home for a number of hours, engine starts, gets us into the marina.

Next example, we're crossing Lake Michigan headed home, as we get within four miles of Manitowoc the engine squeals, revs down. I pop it out of gear, engine revs up again, no power in gear. Temp gauge looks normal, engine doesn't seem overly hot when I open the cover. Set screw has been sheared off/worn down until it can't hold the prop shaft, and I don't have a spare. Get home eventually, buy a new set screw, get it moving, but now I have a horrible vibration, enough to make me not want to run the boat...

I hauled the boat last fall, and the yard told me that the cutless bearing is fine, (I had assumed that was part of the problem.)

So, I'm thinking it's an overheating packing gland that's binding up. If the engine is in neutral, should the prop spin fairly easily? (It doesn't.) Does that mean that the packing gland is too tight or over packed? How often do you have to repack a normal gland? (Bonus question, what size is the packing?)

Sorry to ask so many questions, but I can't trust the boat for longer trips, it keeps dying off when I need it.

Don, thanks much for putting this board out here, great community service.

John
Bristol 27, Nova

[Don Moyer]

There are at least three issues that can result in a squealing noise similar to the one you're describing:

1. A loose alternator belt (which you've already ruled out).
   
   
2. A bad bearing in the accessory drive. However, if the noise were coming from the accessory drive, I don't see how it (the accessory drive) would know if you were in the slip or not. So, on to the third possibility:
   
   
3. A harmonic produced as the shaft rotates within the cutlass bearing. Simplistically, in this model, the prop shaft becomes like a violin string as it is "drawn" radially across the surface of the cutlass bearing. Since you're getting a different result in the slip, I believe this is the most likely cause of your squeal. When Brenda and I had such a squeal, I simply readjusted one of the engine mounts a tiny bit, and the noise left.

Best regards,

Don Moyer

[dtinder]

"singing prop"

This is really grasping at straws. I commissioned a new Elco (electric) a few years back---during sea trials there was a noticable , variable pitch, variable amplitude squeal coming from somewhere in the drive train. We started with the motor and worked back thru the shaft log, stuffing box, cutlass bearing---etc. Checked all the normal stuff---at the dock---underway---etc, etc.
I checked all the clearances between prop tip, apature, keel, etc--no luck. We could alter the noise under certain situations----but couldn't eliminate it.
I checked with my Naval Arch. friend----he matter of factly stated that it was a "singing prop"----yeh right!!!!! Sure!!!
Per his instructions, I hauled the boat---using a Makita grinder with 16 grit---slightly tapered the (3blade 12X12) blade tips and reduced the diam. by 1/64th or so----No more "songs" from the drive train---Go figure!!!!!

[Don Moyer]

Dave,

Thanks for the reminder! I have heard of this phenomenon before, and in the future, I should probably list it as a long shot possibility when troubleshooting a squealing noise in the drive train. I wonder if the reason we don't hear more of "singing props" in the Atomic 4 fleet might be because it's more of a problem at RPM's higher than we're accustomed to experiencing in our engines.

Best regards,

Don Moyer

[eriesailor]

Thanks again to all who have given some input on the matter.

Don & Dave... I believe I once read something about resonance of the propeller, but didn't think it could make that much noise. I did notice that the shaft was fairly close on one side to the cutaway in the hull (about a 1/4 inch). I suppose if there is a bit of flex in the shaft or if the engine mounts are a bit lose it could cause it to rub?. When I lauch the boat this spring I will check to see how tight the mounts are and then maybe try moving the engine a little to see if it changes anything.... I will also give the prop a good sanding to see if that helps. Don, is the accessory drive propelled by a chain or belt? Obviously if it's a belt I could check that, but otherwise it would be a bearing if it sounds like it is coming from there.... I will have to try and pinpoint the sound as well this spring!

Rumrunner.... with regards to your stuffing box, it should drip a bit and especially when the boat is underway, otherwise it may be heating up and binding on the shaft. Don can correct me if I am wrong, but you should be able to turn the prop fairly easy by hand if the engine is in neutral.

Thanks again!

Eric.

[Don Moyer]

Eric,

The accessory drive is itself driven by internal gearing. A gear on the end of the accessory drive meshes with an idler gear, and the idler gear meshes with a small gear on the end of the crankshaft. It ends up being the case that the accessory drive rotates at the same RPM as the crankshaft.

Don

[eriesailor]

Don,

That makes sense and leads me to believe I a best starting with the driveshaft and prop. I will repost after launch this spring to let you know wihat I find.

Thanks again for everyones help.

Cheers!!

[jcbarger]

Greetings folks.

I'm sorry to dredge up this old thread, but this issue is one that has been frustrating me since last summer and I was wondering if either of you that was experiencing the squeal ever determined it's origin.

My problem: I have a high pitched squeal that starts after a few seconds of the boat being in gear (forward or reverse) and will bind up enough that it will shut down the engine if it is not quickly taken out of gear. If this happens and the engine is restarted, sometimes it will not go back in gear for a minute or two (I assume when it has cooled a little).

At the dock, I can go through the process of putting it in and out of gear until eventually the squeal will stop (about 5 minutes). Then i can go sailing. I have about a 10 minute motor out to my sailing area and usually the squeal does not reappear that day. However occassionally if I sail for a long time, it will happen on the way back in. I nurse through the same process and eventually it will quit squealing and I can return to the dock.

This problem first appeared last summer on a very limited basis. Over winter (i live in TX so we sail year around) the squeal never occured, but as soon as the water got over 75 degrees, the squeal came back. Now this might be completely unrelated but I wanted it out on the table.

I have owned the boat for 3 years now and the friend I bought the boat from said he had the same problem and just squirted grease into the cutlass bearing from the outside of the boat with a needle and the problem went away. But this to me seems a bit unlikely considering the cutlass is lubricated with water.

I would imagine this problem is either in the cutlass, the stuffing box or the accessory drive, but was hoping someone on here might have dealt with this and know the best way to trouble shoot the problem.

Thanks for any input.

Jeff

...may the wind be at your back, and it not be your own.

[lat 64]

same same

I'm GLAD you dug this up.
I just got te same sqeal this summer on my boat .
It seems to me to start to squeal after the boat catches up with the propellor.
I turn up the rpms on the motor and then the boat accelerates to a speed and the squeal starts singing. It sounds like Don's description of a harmonic.


Russ

[Al Schober]

These singing props and squealing cutless bearings are like old history - everyone's forgotten them! The classic book on mechanical vibrations by Timoshenko discusses these noises and emphasizes the importance of correcting them, as they "disturb the serenity of the fish". He 'tongue in cheek' glosses over the fact that they make submarines into targets.
The 'chisel' trailing edge on propeller blades is a common fix to propeller singing. Sparkman & Stevens even went so far as to put the same trailing edge on the keel of the Tartan 30 (chamfer to port).
The cutless bearing squeal is a different thing involving shafting rotary frequencies and stick-slip friction of steel against rubber, and is usually corrected by changing something. Or perhaps just spending money. You might just fix the squeal by jamming a $100 bill between the shaft and the bearing.

Al Schober

[ndutton]

I have a high pitched squeal that starts after a few seconds of the boat being in gear (forward or reverse) and will bind up enough that it will shut down the engine if it is not quickly taken out of gear.

Jeff,

I had the exact same symptom twice, one time after relaunching following a haulout and the other (here's the smoking gun) after adjusting the stuffing box.

Yup, you guessed it, in both cases the stuffing box was too tight, friction heating things up making them even tighter. To eliminate the possibility, I recommend loosening yours considerably, let it drip more than you ever wanted while you chase down this squeal. If the noise persists, at least you'll know for sure it's not the stuffing box. You can adjust it back later.

[jcbarger]

ndutton,

Thanks! I'll definitely check that today when I go out to the boat. I'll loosen it to see if that helps any.

I appreciate the helpful feedback.

I'll post back to let you know how it goes.