Trouble Shooting 8.1 Squeak/Squeal

Hampton

Hampton

Air Defense Dept
TECHNICAL Contributor
Nov 26, 2006
7,628
Panama City, Fl
Boat Info
2008 44 Sedan Bridge
Engines
Cummins QSC-500's
Straight Drives
My port engine has had some belt noise for almost a year now, or so I thought. I replaced the serpentine belts on both engines about a year ago. The port has been squeaking a little, intermittantly since about then, if not earlier. At Idle, the frequency of the squeak is a little more than 1 squeak per second. It's worst at idle when I first start up. Then, as it warms up, it lessens.

Well, this past weekend, the intermittant squeak became a constant one, and is starting to sound a bit like a squeal.

Nothing is leaking. There isn't any sign of belt wear. I think it's either the idler pulley, the water pump (the one like a car has), or possibly the alternator. Where would you guys start, or how would you trouble shoot? Start taking stuff off left/right and swapping it?
 
If you don't have a stethescope, take a long screwdriver and put the tip on each accessory while holding the handle end to your ear (I know sounds ridiculous, but it works). This will help you isolate the offending accessory/pulley.

No need to say "be careful". It works great on a car engine leaning over the grill, but it may not work in the bilge with engine accessories facing aft.
 
carterchapman said:
If you don't have a stethescope, take a long screwdriver and put the tip on each accessory while holding the handle end to your ear (I know sounds ridiculous, but it works). This will help you isolate the offending accessory/pulley.

No need to say "be careful". It works great on a car engine leaning over the grill, but it may not work in the bilge with engine accessories facing aft.
Click to expand...

Exactly. I am aware of the technique, but a bit fearful. Maybe I'll try it using my hand as my ear so that I can closely monitor my body wrt to moving parts.
 
I would remove the belt and very briefly run the motor to see if the squeak remains. If it does not, start spinning the pulleys you can to see if it is one of those.
 
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keokie said:
I would remove the belt and very briefly run the motor to see if the squeak remains. If it does not, start spinning the pulleys you can to see if it is one of those.
Click to expand...

Not a bad idea. Any objections?
 
If they do not squeak when spinning by hand listen closely for any roughness in the bearing, if a bearing is bad you should be able to hear something. I have had an alternator on a car load up so heavy on start up that the belt would squeal real bad, so do you have a meter to check the output amps on the alternator. If the alternator is charging that hard there should also be signs of the batteries boiling water out. Probably a pulley bearing.
 
John,

Another thought -

I've not had a problem with GM serpentine belt tensioners - I assume that's what Mercruiser uses - but another thought is to spray WD-40 or silicone lube on each pulley shaft - one at a time, then start and listen after each one is sprayed. See if you can isolate it that way.
 
We had the same squeeking noise. Assuming the belt layouts are similar between 496 and 8.1 versions, there are 3 idler rollers. Speaking from memory, two on the raw water pump bracket and one on the alternator. One of these was making noise.

We were having the impeller and belt replaced and went with replacing the rollers at the same time. It added about $75 to the bill but ended the problem.

Henry
 
"I would remove the belt and very briefly run the motor to see if the squeak remains"

This is what our mechanic did to isolate a squeal. We have multiple belts so he was able to start with the alternator one.
 
Good words. I like the WD-40 one too. I've seen that quiet a pulley (temporarily) before, so I know that could isolate the problem child.
 
Started port motor today - squeaking. Climbed back over stbd to the area behind port w/can of WD-40 with small tube inserted in spray nozzle. Sound appeared to come from the side of the motor near center of bilge. Sprayed each pulley, 1 at a time - no changes. Put a tiny squirt on the inside of the belt - instant quiet, for a few seconds. Loosened belt - quieter, but too lose. Tightened belt - louder. Put screw driver on pulley mounts, alternator, water pump and listened to handle - all bearings good. Also spun every wheel while the belts were off. No squeaks. The alternator pulley seems to have a tiny wobble in it when spun by hand. When running, you can't see it, even at a slow idle (650 RPM). It's not loose.

Swapped serpentine belts stbd - port. Both are quiet. So, fixed for now. The port belt didn't like the port pulleys. The question is, which will begin to make noise first - port or stbd belt? It really is fixed for now, but something made the port belt start squeaking at some point in the past. I imagine there's a burr on one of the port pulleys that wears on the belt, though no signs for this were apparent. Maybe it was too tight and stressed the belt, but then why doesn't it squeak on the stbd side?

The squeak was consistent with one revolution of the belt, not any pulley. One belt revolution = one squeak.

If it starts back up, I'll let you know, but the fix was very apparent and immediate.
 
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Hampton, If you can get a belt tension gauge and check the tension on the 2 belts, you may find the spring is weak in the tensioner, I take it that it is the spring loaded type.
 
midway said:
Hampton, If you can get a belt tension gauge and check the tension on the 2 belts, you may find the spring is weak in the tensioner, I take it that it is the spring loaded type.
Click to expand...

Nope - you adjust it manually by tightening a bolt attached to the alternator bracket which rotates the alt to pull the pulley further out to the side.
 
Do you have a power steering pump on your engines? Sometimes the bearings inside them get noisy as well.

Doug
 
Are the pulleys slightly rusted up from the harsh environment? If so, a little sandpaper may help.

Doug
 
douglee25 said:
Are the pulleys slightly rusted up from the harsh environment? If so, a little sandpaper may help.

Doug
Click to expand...

No, they look new, but thanks for the words. Like I said above, all is quiet on both sides right now, just from swapping the belts port/stbd.
 
I had the same problem and found the culprit the same way you did. I found that the belt was slipping on one of the idler pulleys. I used fine sandpaper and sanded the area of the pully that the belt was riding on and the squealing has yet to return.
 
Update because I stumbled on this thread again by accident: No squeals in one year after swapping Serp belts Port/Starboard. Who could have known?
 
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