Can anyone diagnose this sound from alternator area / alternator belt ?

[aidancoughlan]

Once or twice recently we've noticed an unusual high pitched sound for a short period after starting the engine. The other day, after starting the engine to get across a shipping lane, we noticed the same noise for a longer period (that's when this video was taken), shut the engine down and sailed back to port. On restarting the engine, same noise, but found it diminished at low revs (800-100 revs), so got back into harbour OK. I called the local mechanic who was on the marina to take a look, and about an hour or two later, he came over & I started it for him ... and no noise. He tightened the belt anyway (he said it was a bit loose - and it was a bit).

The recent history is that the boat has had 800 mile delivery trip, and the belt was really, really loose when she arrived (with a lot of black dust in the area). I tightened it considerably after arrival, but it has obviously slackened a bit more.

However, I'm not sure if this is the belt ?

• I've never had a belt screeching before on car or boat, so I'm not really familiar with the noise , though a belt noise seems more like a squeal from what I can gather
• Although I didn't find/show him the video until after tightening the belt, and was dubious about whether the sound would translate accurately on phone video , the mechanic didn't seem convinced that this was a belt noise.
• The noise has been intermittent - sometimes after startup (diminishing after, or at low revs), and sometimes not - she ran for hours without a noise the other day back to our home port. Why would a belt noise be intermittent ?

I've become aware that spraying water/wd40 on a noisy belt confirms a belt issue if the noise goes away when sprayed - will try that at next opportunity ?
Another suggestion someone made locally was alternator bearings, does that sound a likely candidate ? Our summer cruise is only a number of weeks away, should I pick up a spare alternator as a precaution, or take it out for inspection at an auto shop or go ahead and replace it ? (£100-£120)

Hopefully this video & sound will play.... many thanks for any input.

[video]https://photos.google.com/share/AF1QipNIDxZh-4AaqKN1LkLUvdVJgaHJzmyPcwX2oQbfuBJ8Wwu15hzwI2i28ME KRagkjQ?key=dlJfVGt5am5vSjVFcGNGZjZLaHB1RVVVaXMtSS 1n[/video]

 

[Mikedefieslife]

Alternator belt slipping a little under heavy load. Mine would do it occasionally when the batteries were down. Happen once on passage at night. I wasn't about to stop the engine at silly o'clock in the morning, so just gave it a little spray from time to time stop the squeak. Once at my destination I changed the belt, and all was right with the world.

 

[MM5AHO]

The video is really short, doesn't make it easy, but this sounds to me more than a belt, perhaps a bearing in the alternator. Take the belt off and hand turn the alternator slowly to feel for roughness in the bearing. (not foolproof test, but if rough there's a problem). Try changing the belt if its been slipping and there's rubber off then its worn anyway, so a new one won't cost a lot. Tighten properly and run again to see.

 

[VicS]

Once or twice recently we've noticed an unusual high pitched sound for a short period after starting the engine.
Hopefully this video & sound will play.... many thanks for any input.

The circumstances you describe suggest a slipping alternator belt but a cogged belt produces an unmistakable squeal ( like a piglet) if it slips. That is not what I hear in your video. You dont say if it is a cogged belt or not.

If it keeps going slack after tightening beware........ It'll break soon!

Take the belt off and spin the alternator by hand to feel and listen to the bearings.

Its not driving the raw water pump so run the engine for a shot while with the belt off and listen , but watch the temperature.

Run the engine and listen to various likely points like water pump and alternator bearings etc with a "listening stick" or an engineers stethoscope.

Eventually replace the belt with a cogged one if its not already cogged. ( they last for ever and squeal like a piglet if they slip.)

 

[RichardS]

The video is really short, doesn't make it easy, but this sounds to me more than a belt, perhaps a bearing in the alternator. Take the belt off and hand turn the alternator slowly to feel for roughness in the bearing. (not foolproof test, but if rough there's a problem). Try changing the belt if its been slipping and there's rubber off then its worn anyway, so a new one won't cost a lot. Tighten properly and run again to see.

I agree with Geoff ... 110%.

Richard

 

[Graham376]

That's not belt squeal, which usually only happens on acceleration or when heavy alternator loads come on. I would have the alternator checked by an auto electrical repairer, they can run them up to speed in test rig. If you want to rule out the alternator and check the engine water pump bearings, get an emergency fan belt and cut it to fit just from the crankshaft pulley to the water pump pulley.

 

[ghostlymoron]

Sounds like bearings to me but could be alternator or water pump. I it were the belt slipping, you'd see some black powder around probably.

 

[chrishscorp]

I have to agree it doesnt sound like belt slip, if it has been dusting then it would be worth gettting another belt anyway and changing it to see if it makes a difference, cogged are good as Vic has suggested. That is cheap and quick and will rule out the belt.

It does however sound more like its a worn/dry bearing lets hope were wrong.

 

[anoccasionalyachtsman]

Late to the party as usual, but I had an alternator sound exactly like that when a bearing failed. Cheap fix if you can find a convenient practitioner.

 

[Mikedefieslife]

If it's not belt sleep though, then why did it magically stop when the OP sprayed the belt?

 

[anoccasionalyachtsman]

If it's not belt sleep though, then why did it magically stop when the OP sprayed the belt?

He hasn't tried it yet.

 

[Mikedefieslife]

Ah, I was getting ahead of myself.

 

[aidancoughlan]

Wow, this forum is fantastic. Not been here regularly for a long time, and amazed at the depth of experience and willingness to help.

So, my plan now is to ....

• Try reproduce the sound first over the weekend, and if it re-appears be ready to spray some water/WD40 to see if it stops it ==> belt if so.
• If no success with WD40 test, consider alternator /water pump... in this order
  .....remove the belt and try turning the alternator by hand to see if it's obviously rough. If so... ==> remove & trip to alternator man.
  ..... try running engine for a short time (watching alternator temperature) while the belt is off to see if the noise persists. If the noise persists... ==> try "listening stick" (with a long screwdriver) to identify if its alternator or water pump ?
  ....... try rotate pulley wheels etc. by hand to check them too.
• If no success identifying so far, will try the emergency belt bypassing alternator idea , to see if the noise is present with just the pump on the belt. I'm confused/unsure about whether the water pump is driven by the belt, or not (VicS says its "not driving the water pump", but @Graham376 suggests (below) to put an emergency belt to the water pump pulley, but not the alternator. Will try find out more about the engine arrangement over the weekend (its a Yanmar 3JH5E).
  
• If I have no progress at all (ie. can't reproduce it, or identify the source), I'll definitely replace with a cogged belt anyway .... and will try get hold of the mechanic again.

Many thanks on the suggestions , very much appraciated. I'll report back on how it goes (and try and get a better video if I can reproduce it long enough).

@@MM5AHO - The video is really short, doesn't make it easy...

Yes, that's true - sorry folks... I thought I had taken a much longer video, but butterfingers on the touchscreen phone ensured otherwise!.

Alternator belt

@Mikedefieslife - Alternator belt slipping a little under heavy load. Mine would do it occasionally when the batteries were down

Maybe it is the belt, but it didn't sound like a belt noise to my untrained ear (hence the query), and the batteries were fully charged, and no heavy electrical load present.

@MM5AHO - The circumstances you describe suggest a slipping alternator belt but a cogged belt produces an unmistakable squeal ( like a piglet) if it slips. That is not what I hear in your video. You don't say if it is a cogged belt or not.

@RichardS - I agree with Geoff (ie MM5AHO ). ... 110%

Yes, although I'm not familiar with it, I tend to agree it doesn't sound like belt squeal that I hear on youtube videos. It's not a cogged belt as far as I recall, but I do believe the spare I have on board is a cogged one. I'll definitely try replace the belt , its done a lot of mileage & left a lot of dust anyway and I suspect could do with replacing even if its not the source of the noise.

@MM5AHO - Try changing the belt if its been slipping and there's rubber off then its worn anyway, so a new one won't cost a lot. Tighten properly and run again to see.

@VicS - If it keeps going slack after tightening beware........ It'll break soon! ...... replace the belt with a cogged one if its not already cogged. ( they last for ever and squeal like a piglet if they slip.)....

@chrishscorp - if it has been dusting then it would be worth gettting another belt anyway and changing it to see if it makes a difference, cogged are good as Vic has suggested. That is cheap and quick and will rule out the belt

Thanks all, sounds like good advice, will do ... as above.

Alternator bearings

@ chrishscorp - I have to agree it doesnt sound like belt slip ....It does however sound more like its a worn/dry bearing lets hope were wrong.

I fear you may be right, but thanks for the vote in that direction ... I;m leaning in that direction now too.

@MM5AHO - this sounds to me more than a belt, perhaps a bearing in the alternator. Take the belt off and hand turn the alternator slowly to feel for roughness in the bearing. (not foolproof test, but if rough there's a problem). ..

@VicS - Take the belt off and spin the alternator by hand to feel and listen to the bearings. Its not driving the raw water pump so run the engine for a shot while with the belt off and listen , but watch the temperature.Run the engine and listen to various likely points like water pump and alternator bearings etc with a "listening stick" or an engineers stethoscope.

Thank you both, turning the alternator is now definitely high on the list of the next steps!.
I don't have a listening stick (just googled it), but I've seen videos of mechanics trying to listen to various components with a long screwdriver. Something to be careful with obviously !
I guess the point about temperature is to do with the temperature of the alternator itself (it would be running free faster than normal, is that what you mean ?).

@anoccasionalyachtsman - I had an alternator sound exactly like that when a bearing failed. Cheap fix if you can find a convenient practitioner.

@Graham376 - That's not belt squeal, which usually only happens on acceleration or when heavy alternator loads come on. I would have the alternator checked by an auto electrical repairer, they can run them up to speed in test rig. If you want to rule out the alternator and check the engine water pump bearings, get an emergency fan belt and cut it to fit just from the crankshaft pulley to the water pump pulley.

OK, thanks both for the vote towards getting the alternator checked, good to hear an auto guy may be able to test & fix it. That's an interesting idea on the emergency belt (I think there is one on the a boat from the previous owner). I'll try rotating the alternator first to see if its rough, and the "listening test" first, but this sounds like a good way to check if its the water the pump in isolation of the alternator.

@ghostlymoron - Sounds like bearings to me but could be alternator or water pump. I it were the belt slipping, you'd see some black powder around probably.

Hmm, yes - there was actually a lot of black dust from the delivery trip, but belt has been tightened (twice) since, and it seems the consensus on the sound points away from the belt itself.

 

[Graham376]

. I'm confused/unsure about whether the water pump is driven by the belt, or not (VicS says its "not driving the water pump", but @Graham376 suggests (below) to put an emergency belt to the water pump pulley, but not the alternator. Will try find out more about the engine arrangement over the weekend (its a Yanmar 3JH5E).

I was assuming the engine has a cooling water circulation pump driven by fan belt, not the raw water pump.

 

[VicS]

I was assuming the engine has a cooling water circulation pump driven by fan belt, not the raw water pump.

The belt drives the engine coolant circulation pump.

The raw water pump, which you can see below the alternator, is not driven by the belt . The OP has misquoted me in post # 13. I actually said that the belt is not driving the RAW water pump.

Because the raw water pump is directly driven, the engine can be run, without fear of damage to the exhaust system, without the belt being in place provided an eye is kept on the engine coolant temperature.

 

[keithb]

I think thats a metallic bearing noise, probably alternator. I routinely rebuild alternator with new bearings and raw water pump with new bearings and seals when i buy a boat. Easy to do on bench at home, cheap parts (specialist bearing suppliers) and minimises failure risk in service.
I suspect you also have the yanmar belt issue, the general advice is to ensure no rust on pulleys (usual culprit crankshaft one), fit cogged belt and check pulley alignment is reasonable, eye usually enough - to make sure someone hasnt put alternator on incorrectly.

 

[earlybird]

I'd say that was a bearing noise. but just might be the alternator fan hitting the body. Also, you seem to have either a very worn belt or one incorrectly sized. the belt should more or less fill the V-grooves of the pulleys. If your belt is repeatedly slackening, with lots of black dust, you may have pulleys with corroded v-grooves. This is not too easy to see, as the belt polishes the corrosion, but it is death to belt life. A session with emery-cloth is called for.

 

[aidancoughlan]

So...hot down to the boat this evening, and had the same noise from the alternator area. The noise didn't appear initially, but starter to appear with increased revs.
Tried the spray test (with water), and the noise appeared/disappeared on spraying, returning soon after. The video makes it sound like the engine noise was reducing, but in reality the only change was in the screeching noise.
From previous posts (hopefully) this all sounds like the belt.
I removed it and tried twirling the alternator pulley and the other pulley (coolant pump ?), both rotated OK no obvious friction or anything I can identify as a rough movement/bearing noise.

Checking pulleys...

Running engine again with screeching noise ...

The belt looked fairly tired to be honest - cracked in places... and the pulleys look a bit rusty as can be seen in the video.

This is the belt removed..


I will try sand the pulleys down with wet & dry, and replace the belt with a cogged one and see how it goes. Fingers crossed that was all it will need .

Many thanks for all the input. Will update with the results when I get a chance to get back to it.

 

[VicS]

The belt looked fairly tired to be honest - cracked in places... and the pulleys look a bit rusty as can be seen in the video.
I will try sand the pulleys down with wet & dry, and replace the belt with a cogged one and see how it goes. Fingers crossed that was all it will need .
Many thanks for all the input. Will update with the results when I get a chance to get back to it.

Obviously belt needs replacing and pulleys cleaning but also check the alignment.

To me the alternator appears to be out of line with the pump pulley in the second video but it might be an illusion.

Listen to the alternator as I suggested in #4

 

[ghostlymoron]

The belt looks like it could fail any minute so replace it and see what's the difference.