strange engine or prop (?) noise

[John]

When I'm motoring forward, and the engine is running at between 1000 and 1150 rpm's, I get a warbling/chirping/whisteling noise. (I'm not sure how to describe it.) It doesn't change pitch as the engine revs up, but at around 1200 rpm's it disappears. The strange thing is this: When the boat is tied up at the dock and the engine is running, either in neutral or in forward, it doesn't make the noise; only when it's under way. At first I thought this might be because it only started to make the noise as the engine warmed up, and that was why it didn't make the noise initially. But after I took it out, listened to the noise, docked it and tied it up again (all the while leaving the engine running), I again couldn't get the noise.

Any ideas? A ghost maybe?

 

[Don S/V ILLusion]

Sounds like the trans damper plate

 

[Hermit Scott]

Don-please explain how a damper plate works and why one would make that noise? Is it the clutch looking piece?

 

[Pat T]

John because I have a Catalina 36 also and this has been a common problem. I have heard the sound described before as marbles rolling around a coffee can. I replaced mine, while on the hard. I waited a season before replacing it so I don't think you have to worry about things coming apart. It does requires pulling the transmission to access the damper plate. If you research the old Catalina 36 website you can find more info written about this issue.
Hermitt, I'll take a shot at explaining. The damper plate absorbs the initial shock the transmission shaft gets when all of a sudden the engine starts to spin the shaft from zero to 800 or 1000 rpm's. There are springs that take this initial shock in the damper plate. They become loose or worn out with time/use. This is the noise you hear. When under a load the spring are still under some compression so you don't hear anything. However when at idle there is no load on the springs and they are free to rattle around.
Hope this helps.

 

[Stu Jackson]

Have you opened up the engine compartment (stairs) and listened? Have you listened at the stuffing box? Have you installed a new cutlass bearing recently?

Could be as simple as a slipping alternator belt. A simple $10 alternator belt tensioner is a great tool to have, although with your engine pushing on the alternator is not hard to do, whereas on ours it's a necessity.

 

[Pat T]

I'll second the damper plate

Left off the title on the last post.

 

[Maine Sail]

Damper plate

This is a damper plate:

Don't be too quick to diagnose it as a damper plate that is a prety major job especialy in the water. It very well may be a damper plate but do try and rule out everything else first.

I had a similar noise and discovered it was my prop. Apparently the guys, when re-conditioning it, sharpened the blade tips to much. According to my prop shop they need to be squared off on the edges and not knife like. Apparently when the edge is to sharp it can create a noise at certain RPM. The next winter I had the blades dulled/squared off and the noise went away...

Could be stuffing box
Could be cutlass
Could be damper plate
Could be many things but you'll need to listen closely.

A damper plate tends to make a nasty metallic noise when it goes bad and clunks more when going in and out of gear.

 

[John]

Doesn't sound like that

From what's being described, it doesn't sound to me like it's the damper plate. Number one, the sound isn't anything like marbles rolling around; it's a whisteling or singing noise. Number two, from what was said, it sounds like you only hear it when the engine is not under load or when the load is suddenly chaged. That's not the case here; you hear it as long as the boat is moving and the tranny is engaged and the motor is turning at between 1000 to 1150 rpm's. Number three, and what is most strange to me, is that you only hear it when the boat is moving through the water; like I said, when it's running and the transmission is engaged but the boat is tied up at the dock you don't hear the noise. Strange, no?

 

[Maine Sail]

Not so strange

like I said, when it's running and the transmission is engaged but the boat is tied up at the dock you don't hear the noise. Strange, no?

Not so strange if it is a prop induced noise. Fixed to a dock you develop slip and moving through the water you have less prop slip. this could make a difference in your noise.. Just a thought..

 

[Mike Holibar]

The old singing propeller trick! I had this problem with Fyne Spirit. When we did the pre purchase sea trial the prop was slightly fouled and the noise was not evident. However after purchase while on the hard I had the prop polished and treated with "propspeed" an antifouling agent. When we left the slip at about 1000 rpm there was a horrendous screeching noise. It put me in mind of a bearing siezing up or running dry, I stopped the shaft and tried it by hand and it turned freely. I ran it up again and the noise returned and there was a notable vibration at the shaft which I thought might damage the seal. Thereafter we ran the engine either above or below singing speed. Later when sailing 3-4 knots with the shaft locked, the noise returned. I contacted the po who said this happened whenever the prop was clean. I replaced the propeller with a Kiwiprop and hey presto- the noise has gone. Maine Sail offers another good solution above. Good luck,

 

[mac1840]

Did you just put the boat back in the water? I've had a similar problem and it turned out that the shaft had a air pocket around it as the shaft seal wasn't purged of air after the boat was put back in the water. Harmonics will give you a nice vibration and noise at a specific speed which you can't get in the dockfor the reasons Main Sail pointed out. Purged the shaft seal, vibration and noise went away. Changes to the prop can also affect the harmonic of a shaft.

Mac.

 

[John]

nope

Did you just put the boat back in the water? I've had a similar problem and it turned out that the shaft had a air pocket around it as the shaft seal wasn't purged of air after the boat was put back in the water. Harmonics will give you a nice vibration and noise at a specific speed which you can't get in the dockfor the reasons Main Sail pointed out. Purged the shaft seal, vibration and noise went away. Changes to the prop can also affect the harmonic of a shaft.

Mac.

Nope, I didn't just put it back in the water. Also the noise has been there for some time now, but I think it's getting a little louder now. In any case, my wife noticed it for the first time when we last went out. The boat stays in the water 12 months a year. (Don't forget - this is California!)

As for purging the shaft seal of air - I assume you mean air in the packing gland? I recently changed this packing. The noise was present before I changed it, but is it possible that it's got something to do with that - air in the packing gland? If so, it seems to me it would have been purged when I changed the packing, no?

 

[sfgary]

Prop noise

I think it may be the prop out of pitch. I had Alameda prop check mine when I had a similar problem. They repitched it for about 70.00 bucks. The noise went away and I gained about 700 RPM. Good luck Gary

 

[John]

Does it have to be hauled to repitch the prop?

 

[Steve Dion]

John: You diver that cleans your bottom can take care of R/R the prop. I suggest that you take your prop to Killian Prop in Alameda. They are some of the "best" prop guys around. Ask them about the "non-slip tip" prop rebuild while you are at it.

The diver will need a prop puller to do this, but it should save some money by having them do it vs. a haul.

 

[Maine Sail]

If you can hit max RPM

Does it have to be hauled to repitch the prop?

John,

If you can achieve max RPM then your prop won't need a re-pitch. If it is the standard two or three blade Michigan wheel that came from the factory the pitch should be spot on. Your motor should be able to achieve max rated RPM at WOT. It is doubtful that a re-pitch would change any prop singing unless they also squared off the blade tips. If you can't achieve max RPM at WOT then a re-pitch would be necessary.

Again we don't know what is causing your noise and this is just a likely scenario. Get a mechanics stethoscope (a Doctors scope would make you deaf) and start trying to narrow down where the noise comes from with someone else at the helm and you listening..

The guy who gained 700 RPM was way, way over pitched. I am in the process of re-pitching and I'm only off, with my new prop, by 250 RPM..

 

[John]

Darn! It seems there are no easy answers. I've never revved up the engine all the way, and I don't know what maximum rpm is for my Universal M35-b engine, but it doesn't seem to have any problems revving up. I've gotten it up to around 25-2700 rpm's with room to spare, so to speak. We bought the boat 2 years ago, and the pitch was checked at that time and was fine. To my knowledge, we haven't hit anything or done anything that would change that. I'll take your suggestions about a stethescope.

 

[BobM]

Hmmm...packing gland related. I had a nice whistling/ringing sound at low RPM that I could not diagnose right after changing my stuffing box, packing, hose, etc...

Now I wonder if it wasn't some kind of air bubble as the stuffing box was initially too tight. It sounded like metal on metal and I assumed the shaft was hitting the log slightly due to mis-alignment. I loosened it up and definitely purged out all the air (water was everywhere...long story) and it went away.

 

[Steve Dion]

Here are some specs on your engine.

UNIVERSAL MODEL M-35 SPECIFICATIONS
Pictorial views of this engine at the bottom of this page.Horsepower30 @ 3200No. of Cylinders4Bore x Stroke2.96 x 2.76Cubic Inch75.5Maximum RPM3200Cruising Range (Approx.)2100-2600 RPMCompression Ratio21:1"Electrical Equipment12 Volt - 51 Amp W/Glow PlugsLubrication (Eng. Approx. Ots.)4.5 to 5.0(SAE 30 HD. (CD) or 10W40) CAUTION: FILL ONLY TO FULL MARK ON DIPSTICKLubrication (Trans.)FILL TO FULL RING ON DIPSTICK(Type AFT “A” or GM-DEXRON - II Do not mix different oils)Transmission Reduction2:1Coolant FWC (50/50 Solution Approx.)5 QuartsExhaust Flange 1 ¼” N.RT.Fuel Type #2 DieselFuel Filter P/N 298854Oil Filter P/N 300209Eng. Operating Temp. Degrees F. 165°to 195°Propeller Rotation Right HandWeight (lbs.)335 lbs.Injection Nozzle P/N 299517 & 299518Engine is governor controlled to prevent overspeed. It is recommended to carry the following extra parts should the need arise: V-Belt, Sea Water Pump Impeller, Fuel & Lube Oil Filters, 1 Qt. of Trans. Oil, 2 Ots. Lub. Oil and 1 Gal. 50/50 Coolant. All pictorial views and specifications subject to change without notice"

If the engine revs to the max rated RPM when in gear, there is no need to repitch the prop, like Mainsail said. It is just that the factory does not always have the "perfect" setup on props from the factory.

 

[mac1840]

Re: nope

Gary,
I'm also in Alameda but even us California people need to have a bottom put on every few years. We have a dripless seal on our shaft so when its pulled, purging the air out of the shaft tube is just one of those little things that needs to be done to make it run right. Once we purged the air, no harmonic vibration / noise from the shaft. Hope you find the source. Enjoy the 4th.
Mac