Tensioner Pulley's

[jjoerger]

A few nights ago we stopped at a rest area and heard a noise coming from the front of our MBE4000 engine. It was a grind, pause, grind, pause type of sound. The AC was off and we could not tell where the sound was coming from. The noise went away but now there is a lot of vibration when the truck is idling or stopped at a traffic light. If the idle speed is bumped up it smoothes out. I am guessing we have a bad idler pulley or a bearing going out on something that is belt driven.
Any thoughts?

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[paullud]

The grinding sound combined with a rough idle is concerning, possibly the cam.

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[jjoerger]

No oil or power loss. Temp and volts reading normal. Alternator is new. Not the fan clutch. Oil pressure is normal.
I edited the OP to change the phrase from rough idle to vibration when idling.
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[Slo-Ride]

To many places and accessories to try and guess where the noise is coming from.
Take the belt off the tensioner and spin,shake,wiggle all the pulleys you can. Look for free play in any accessory pulleys. A tensioner that has gone out should be easy to find once the belt has been removed.
If you have access to a stethoscope that will help you narrow down the noise with the motor running.
It could becoming from many places including inside the accessory drive housing.

 

[BobWolf]

If you dont have a stethescope a screwdriver with a long skinny shank placed against the ear and probing the spots on the engine will work also tensioner, water pump crank and bearings. Juat be carefull of anything moving

Bob Wolf.

 

[tknight]

I've replace both idler pulleys on my mb motor in 350k miles not expensive and ez to change out 1 is squeaking now a little so I guess it's next to go!

 

[jjoerger]

Found a couple of chips missing on the top inside of the alternator pulley. Could that throw it out of balance enough to cause the vibratition?

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[paullud]

Found a couple of chips missing on the top inside of the alternator pulley. Could that throw it out of balance enough to cause the vibratition?

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I think the pulley is to small to cause vibration but it may indicate that there is something wrong with the bearings or internals of the alternator.

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[Jenny]

Found a couple of chips missing on the top inside of the alternator pulley. Could that throw it out of balance enough to cause the vibratition?

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We actually had a similar issue. The beaing in the alternator was bad, and another pulley. Once it was changed the vibrations did lessen some.

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[redytrk]

The fan clutch is also a source for this kind of noise.

 

[RETIDEPXE]

You say the alternator is new, make sure installed correctly, nice and tight. I've seen some strange things happen after repairs. If an accessory is loose, alternator, A/C compressor, and this is unusual, it will cause a rattle and grind as you describe.

 

[jjoerger]

Is there any reason I can't pull the belts, start the engine and see if it is still vibrating? The engine idles at 625 and there is quite a bit of vibration. At 690 it smoothes out.
If it were a cam or valve problem wouldn't I be seeing exhaust smoke, loss of power or increased fuel consumption?

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[mjmsprt40]

Is there any reason I can't pull the belts, start the engine and see if it is still vibrating? The engine idles at 625 and there is quite a bit of vibration. At 690 it smoothes out.
If it were a cam or valve problem wouldn't I be seeing exhaust smoke, loss of power or increased fuel consumption?

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If you pull the belts and start the engine, don't run it long. That belt powers everything including the water pump, so you have no coolant circulation while the belt is disconnected. No power steering, no alternator and so on of course. But, for a couple of minutes max, you might run the engine and if the vibrations are belt-driven, you'll know by their absence.

"Quite a bit of vibration" makes me think the fan could be the culprit. I could be wrong, but that's where my suspicions based on the description make me want to look first.

 

[Rocketman]

Of all the things that it could be, I would suggest checking the fan clutch very thoroughly. That is the one component that could cost you a lot of money if it turns the fan loose.

 

[Speedwagen]

Hmmm- new alternator, eh? Or reman?
Does it have a one-way clutch-type belt pulley?
If so, and your belt tensioner is bouncing around at idle and stops at a higher RPM,
I'd take the belt off and check to see if the alternator pulley is working correctly.
You can check it by hand- should only turn the innards one way and slip the other way...
Been there- done that

 

[jjoerger]

So, I got the truck home tonight and the vibration went away. Idling just as smooth as ever.
I have a feeling it will be vibrating again in the morning when it is cold. I still plan to check all the belt driven accessories tomorrow and everything else that was suggested.
Maybe it just wanted to come home for Christmas.

 

[jjoerger]

I found one bad tensioner pulley (the grinding sound) and the water pump pulley wiggles (the vibration). There is also minor evidence of coolant on the water pump housing. I'll put it in the shop after Christmas for a new water pump, tensioner pulley and 2 new belts.

 

[usafk9]

Count your blessings.....you found them early, and it's not a new engine!

Merry Christmas!

 

[xiggi]

Remember pulleys are regular maintenance on sprinters just like the belt.

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[SHARP327]

I had a tensioner pulley that I thought was squeaking so with the engine running I sprayed
some Liquid wrench lubricate (a little) on only the bearing area and the squeal lessened so I then had
it replaced and that was the fix.