SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

weird engine noise

5K views 35 replies 14 participants last post by  chucklesR 
#1 ·
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?
 
#2 ·
Oh .. I know this one!

I know this one .. I've had it before...

Well something pretty close. This is what I did to repair.

First I installed one of these...



then.. these...



Then... this is where the tricky bit came in.. I started with installing this in the first pic....



But... to really make it go away.... I had to adjust the ...



Unfortunately.. that didn't do the whole job... so I needed to go to one of these... in replacement from the Mozart model above...



So now.. whenever I go on my boat. All of this automatically starts up and I don't hear any problems with the engine whatsoever.

you wouldn't believe what it fixed...! The noise from the neighbor's boat? Went away. The loud flapping of the big white things? Gone.

>>>>>>>>>>>>>>>

Slight Schreeching or scraping.... Have you checked the transmission? I guess the shaft could deform under load... and cause it.. so the bearings would be suspect. But I'd also dive into the tranny. What does the fluid look like?

I'm sure others will have better suggestions. (Hope you weren't offended by my post. Just a bit slow around here lately...) HAPPY NEW YEAR! :D :D :D
 
#4 ·
DUDE!!! I didn't know you had the Rammstein model. It Freaking Rocks!!!

I know this one .. I've had it before...

Well something pretty close. This is what I did to repair.

First I installed one of these...



then.. these...



Then... this is where the tricky bit came in.. I started with installing this in the first pic....



But... to really make it go away.... I had to adjust the ...



Unfortunately.. that didn't do the whole job... so I needed to go to one of these... in replacement from the Mozart model above...



So now.. whenever I go on my boat. All of this automatically starts up and I don't hear any problems with the engine whatsoever.

you wouldn't believe what it fixed...! The noise from the neighbor's boat? Went away. The loud flapping of the big white things? Gone.

>>>>>>>>>>>>>>>

Slight Schreeching or scraping.... Have you checked the transmission? I guess the shaft could deform under load... and cause it.. so the bearings would be suspect. But I'd also dive into the tranny. What does the fluid look like?

I'm sure others will have better suggestions. (Hope you weren't offended by my post. Just a bit slow around here lately...) HAPPY NEW YEAR! :D :D :D
 
#8 ·
Cavitation at the prop at moments of acceleration or chage in prop direction can cause such a noise and have nothing to do with the engine. Continuous cavitation can damage the prop, but if it only occurs at the moments you describe it may have no consequence. Station a crewmember at the stuffing box and see if they can determine if the sound is forward of them at the engine or aft at the prop. 'take care and joy, Aythya crew
 
#10 ·
As CP has said-IT WOULD HELP IF YOU MENTIONED WHAT BOAT< ENGINE AND TRANSMISSION YOU HAD when asking for assistance like this. Some engines, transmissions, and boats have known issues that are fairly common....and knowing that information makes it a lot easier to answer your question. It would also help if you said where the screeching/scraping sound is coming from.

BTW, yes, the engine can become misaligned under load since the torque put out by the engine is significant. IF you have a broken engine mount, that could allow the engine to move under load.

YOU REALLY SHOULD READ THE POST IN MY SIGNATURE, since you can't seem to figure out that more information in a post asking for help is generally better than less.
 
#24 ·
Actually, sailindDog, I know that more information is better. If you read back through posts I have initiated, you'll find that I "figured that out" a long time ago. However, since I was typing on a cell phone during a holiday party, I hope to be excused. Anyway, I'm sure you'll get over it-- you usually do.
 
#12 ·
JR...

Start your motor, and get your other half to reproduce the symptoms, however you do it.
Go round the motor listening carefully until you get an idea of where it's coming from.
Screeching is normally a belt drive issue, but it should not happen to the alternator belt if the batteries are well charged.
Check the belt tightness.
Which motor is it? Do you have a picture or a reference?
Is there enough lube in the gearbox? Sometimes a 'box can make a funny noise going on and off load.
Generally, if it is not a clattering, the motor should be fairly sound.
 
#14 ·
That's pretty much what I was thinking. I don't know of anything else that would make a screeching sound. I would definitely check to motor mounts. Also look around the pullyes on the front of the engine, is there anything in close proximity? Does it show wear that might be cause by rubbing against a pulley?

And as others have said, details of the engine and driveline would help as well.
 
#15 · (Edited)
On the basis that diagnosis involves eliminating the simplest possible causes first, then I would agree with those who advocate checking drive belts. If the alternator belt is the cause, then you should be able to reproduce the noise by starting with the engine at a fast tickover with no batteries connected, then switching in both batteries. The charging load on the alternator should result in a screech from the slipping belt.....

Good hunting

Stuart
 
#16 ·
Man, JR...., I have to go with Sailingdog & Cardiac and say, give some information, for crying out loud! It's not like everyone is right there in the boat with you.
 
#21 ·
Strain or just high rpm?:confused:

After the boat has set awhile or comming back from a motor?:confused:

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?
 
#23 · (Edited)
Might want to check the alternator shaft for play. Belt slippage will account for the "screeching", the faint "scraping" sounds like the alt fan may be coming in contact with the housing due to excessive shaft play, or just slopping around inside loose bearings. While you are at it, get out a straight edge and check to make sure that the alternator pulley is properly aligned with the crankshaft pulley.
 
#27 ·
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.)
 
#29 · (Edited)
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.
 
#33 ·
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?

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
 
#30 ·
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.
 
#31 ·
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.
 
#34 ·
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.
 
#35 · (Edited)
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?
 
#36 ·
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.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top