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Go Back   SailNet Community > On Board > Gear & Maintenance > weird engine noise
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Thread: weird engine noise Reply to Thread
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Topic Review (Newest First)
12-29-2008 07:30 PM
chucklesR I'd go with cutlass bearing. Your repower put in a more powerful engine with more torque, from the prop / keel picture the rest is original to the old system.

Simplest solution usually works, check what changed and of those things that changed which can cause the symptoms.
If it made noise in neutral it would be the motor/belts etc..if it was the tranny the tranny would be making the noise, shredding and being obvious (screwed by now and unable to shift perhaps). Simple way to check is to take a sample with the dip stick, wipe it on a clean white cloth and look hard for metal bits.

Torque shifting friction to one side of the cutlass bearing; maybe.
12-29-2008 05:29 PM
craigtoo Is there anyway to verify that the prop is properly seated and mounted to the shaft? Perhaps under loads a misalignment results in uneven loading of the shaft? (maybe you've already done this...)

Barring that, I come back to the tranny because problems they are something you can hear from the cockpit. Gear Oil Sample?
12-29-2008 04:18 PM
jr438234606
Quote:
Originally Posted by timebandit View Post
First thing I would check is to be sure the mount bolts are still tight.
Mount bolts are all still very tight. No appreciable vibration coming from engine or shaft when in gear at different RPMs. Still seems to be aligned.

I did notice a little gear box oil getting past the seal on the dip stick and dripping down the side when at high RPMs. This is why I think there may be too much oil in the gear box.
12-29-2008 04:16 PM
SEMIJim
Quote:
Originally Posted by jr438234606 View Post
Here are some thoughts i had:

...

Shaft is bent slightly, and only gives a problem under heavy load.
A bent shaft would cause problems, particularly vibration, at all speeds and under all loads. You can check run-out with a dial indicator, but it's very tricky to do, because any attempt to grab and turn the shaft will tend to deflect it.

Shaft alignment is another story. It could be that. Was shaft alignment checked after the boat was splashed, following the re-powering?

Quote:
Originally Posted by jr438234606 View Post
Prop is cavitating.
Prop cavitation doesn't sound like a "scaping" sound, to my ear. I don't know quite how to describe it. Besides: A cavitating prop usually results in a sudden increase in engine RPMs, as if part or all the load had suddenly been removed. Also: You don't experience the thrust you're attempting to apply.

Jim
12-29-2008 04:03 PM
timebandit First thing I would check is to be sure the mount bolts are still tight.
12-29-2008 03:59 PM
jr438234606 The sound is not sustained. It only makes the sound when the engine is thrown into a heavy sudden load. For example, when coasting forward, and then suddenly throwing the engine into reverse at cruising RPMs. In this case, once the boat slows, and gradually starts moving backwards, the sound stops.

The way I discovered this was when I use reverse to slow the boat--like when coming into dock. I went and checked things out on my lunch break. it appears that I may have a little too much gear oil in the gear box. I'm going to verify this, but I wouldn't think this would cause the sound.
12-29-2008 02:57 PM
NOLAsailing Well, it stands to reason you'll get the most torque when the motor is in gear, so I'll stick with my suspicion of the motor mounts until you do your visual inspection and find out other wise. To be honest, though, if that's not it, I'm not sure what would cause the sound.

Another thought - Is the sound sustained when your revs are up or does it occur only when you power up. If it's sustained, I would look at the coupling, stuffing box and cutless bearing. If it occurs only at the moment you rev and then is mostly quiet, I would go back to looking hard at the mounts.
12-29-2008 02:49 PM
jr438234606 Thanks for that. Here is some additional info:

Engine is new.

It's more like a scraping sound. It's not a belt. I figure it must be the shaft.

It only happens when motor is under strain, in gear, not just reved up in nuetral.

Engine was perfectly aligned at install.

Engine beds are original, but with slight modification aft.

I have not done visual inspection, but plan to today.


Here are some thoughts i had:

Torque is shifting engine, shaft is eating into cutlass bearing.

Bearings in gear box are bad.

Shaft is bent slightly, and only gives a problem under heavy load.

Prop is cavitating.
12-29-2008 02:44 PM
NOLAsailing
Quote:
Originally Posted by bubb2 View Post
Did you do the installation. If not, I say warranty and I would be on the Phone.
I had the same thought. I see the boat is out of the water at Sintes in your photo. Did they do the work? If so, they'll certainly make it right.

If Northshore Marine did the work, then good luck!
12-29-2008 02:42 PM
NOLAsailing
Quote:
I've noticed that when I put a strain on my engine, I hear a strange sound. It sounds like a slight screeching/scraping sound. It's not very loud, but it still concerns me. It happens when I put the prop under considerable strain. For example, if Im moving forward and throw the engine in reverse. Or, if I power forward from stand still. I'm worried that the engine Is twisting because of the torque and possibly flexing the shaft. Could the shaft be putting too much pressure on the cutlass bearing because of this? Would the engine temporarily misalign under the load?
I would normally associate a screeching sound with a belt. As this is a new engine, are you certain the water pump and alternator belts are tight enough? There should be about 1/2" of deflection with moderate finger pressure. Another way of telling if your belt is too loose is if you see a lot of belt residue (fine black dust) around that area.

You say it's a screeching/scraping sound though - that's a little confusing to me which is why I suggested earlier if you could identify the region it's coming from. That may make an "internet diagnosis" easier.

To specifically answer your questions above:

If the engine is improperly mounted, it will temporarily misalign. If this was an older engine, I would suspect the rubber component of the engine mounts were worn. The motor's torque will cause it to jump when revved. This is easy to check. Just watch the motor as someone revs the motor up. If there is an issue, you'll see it lurch noticeably.

If that is what's happening, then yes, you are at risk of damaging the cutless bearing, as well as the stuffing box and the coupling.

It looks like you modified the engine bed to accommodate the new motor. When was this done? At the install or after some period of use. How have you measured the alignment?

(I've said this before, but I'll say it again now - gorgeous boat.)
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