Anyone recognize this sound

[nairb]

Let my hmmwv sit for a few weeks and on startup immediately heard a new noise. This happens for the first minute or so, maybe only while the glow plugs are cycling? Once warmed up I drove it around for 10 minutes and didn't hear it again. Let it sit overnight and started up again and same thing, popping/clacking sound for the first minute or two then nothing. Almost sounds like marbles slamming together. Any recognize this or have ideas? Haven't had time to troubleshoot yet, first thought was maybe the belt tensioner so I'll pull the belt and check that out tomorrow.

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edit: from this second angle looks like the belt almost jumps off with the noise.

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[Coug]

watching the second video, you can see movement down low on the harmonic balancer and maybe belt movement on the fan pulley.
Extra load from the glow plugs pulsing for the afterglow is putting short extra stress on the belt system, and if everything isn't perfectly straight it ends up trying to pull things out of alignment.
I can't tell you what's actually wrong, but 99% sure there shouldn't be movement down there.

Check the harmonic balancer bolt would be the first thing to do I think.

 

[Mogman]

watching the second video, you can see movement down low on the harmonic balancer and maybe belt movement on the fan pulley.
Extra load from the glow plugs pulsing for the afterglow is putting short extra stress on the belt system, and if everything isn't perfectly straight it ends up trying to pull things out of alignment.
I can't tell you what's actually wrong, but 99% sure there shouldn't be movement down there.

Check the harmonic balancer bolt would be the first thing to do I think.

I think you nailed it!

 

[Retiredwarhorses]

check all bolts on all pulleys, ive seen the fan blade lightly strike the tensioner mouning bolt, I’ve also just had a fan blade hitting the fan clutch hose because the quick disconnect wasn’t plugged into the fan clutch, each time it hit it, it moved out of the way…till it struck it again.

 

[Mainsail]

Wait until it's dark outside and look for sparking? That's what it sounds like to me.

 

[gringeltaube]

.... you can see movement down low on the harmonic balancer and maybe belt movement on the fan pulley.

I watched it repeatedly and can't see any abnormal movement there- other than the camera shifting its position/angle.

 

[Mogman]

I watched it repeatedly and can't see any abnormal movement there- other than the camera shifting its position/angle.

It is the very beginning, you can even hear it snap each time the "pulley" moves back towards the engine, look at the very bottom of the fan blade.

 

[gringeltaube]

It is the very beginning, you can even hear it snap each time the "pulley" moves back towards the engine, look at the very bottom of the fan blade.

Ah... you guys are right, something is loose down there.
Just now I saw it, was looking at the wrong pulley.

 

[MarkM]

The snap seems to me to be the belt slipping out of the pulley track then snapping back into place.

Mark

 

[nairb]

Well, finally got around to checking it out tonight. One of the bolts for the generator mount had worked itself loose. I'm pretty sure it's one of the (many) loose bolts I found and snugged up when I first got the truck. Unfortunately I can't back it out far enough to get some loctite on it without removing the power steering pump. I marked it with some white paint and we'll see if it works itself loose again:


Poking around further, it looks like there is another bolt just to the left of that one that has snapped off inside the block (unless this is coming from the other side somewhere?). Looks like I'll get to use that expensive extractor again that I bought when removing stripped hub drain plugs:



In addition to all that, 3-4 of the fan blades are hitting the fan shroud lightly but enough to create some resistance. It looks like someone cut the fan blades down to make it fit but left a few too long.

Anyway, the sound was the belt jumping off and snugging up the one loose bolt fixed the belt jumping.

 

[Mogman]

You should of course repair the broken bolt and replace the fan., and make sure it has good clearance, that fan is likely out of balance and will kill the water pump eventually.

 

[Coug]

You have the old style serpentine belt, which means you probably have the old style generator bracket on the rear of it, that goes from the gen to an exhaust stud.

On my truck that exhaust stud broke, so nothing supporting the rear of the generator to the block.

This puts a lot of stress on the bolts on the front of the generator bracket (there are 3 of them, and on my truck 2 were sheared and the third was loose)

I tried to replace the stud with a higher grade one, but still snapped off again, so I upgraded to the newer style bracket that goes down to the engine block near the bottom, not the exhaust stud.

This thread should have the info you would need to do the same thing.

Sheared generator bracket bolts.

When I first got the truck(m1123, 200 amp generator) the stud on the exhaust that holds the rear generator bracket was sheared, and a couple of the front bolts were loose. It started making noise again, so I checked, and the exhaust stud is sheared again, and at least one of the front bracket...

www.steelsoldiers.com

 

[nairb]

Thanks Coug, good read. I think I'll upgrade it when fixing the broken bolt.

 

[87cr250r]

Your front crankshaft pulley appears to have failed. These are rubber driven and have a ball bearing on them.