Bottom end noise: tap/light knock & chirp? Advice needed!

[cscmc1]

This one's been driving me nuts, guys. Under load, when accelerating, my M1009 makes a light chirp/knock (really more of a tap -- it's higher-pitched than a knock) . As soon as I let off the pedal, it's gone, and if I accelerate very modestly, it doesn't make noise. I can't replicate it in park or neutral. I have ruled out both alt belts, flex plate bolts, dampener, and don't think it's u-joints (they feel good and I greased them up with no change in the noise).

How far should I go to check this out? I see that someone's pried on the PS pump in the past to try to tighten that belt up; maybe it rubs a bit internally under load?

Am I being paranoid wondering whether it might be bottom end noise? Do they ever "chirp" The bottom end issues I've dealt with were all pretty low knocks.

Here's the thread I started a bit ago when I was trying to track down the noise:

http://www.steelsoldiers.com/cucv/92108-chirp-tap-under-acceleration-what-would-you-check-first.html

Thanks in advance!

 

[cscmc1]

I should add: I installed a mechanical oil pressure gauge and oil pressure seems to be good...

 

[SgtSnorkel]

Check the P/S mount for cracks and that all the bolts that hold the mount on to the block are there and tight . I had the same kind of noise , turned out I had one bolt missing and the others were loose . Hope this helps .

 

[cscmc1]

Check the P/S mount for cracks and that all the bolts that hold the mount on to the block are there and tight . I had the same kind of noise , turned out I had one bolt missing and the others were loose . Hope this helps .

Thanks -- I monkeyed with the PS pump last night and re-tightened everything I could find. Still no luck.

 

[rickf]

Sounds like a cracked flywheel. Pull the flywheel cover and look around the mounting bolts to the crankshaft.

 

[cscmc1]

Sounds like a cracked flywheel. Pull the flywheel cover and look around the mounting bolts to the crankshaft.

Thanks -- I pulled the cover to look at the flex plate bolts, but didn't look much further than that. I'll try to dig further. Are cracks generally pretty evident?

 

[MuleMac01]

Could be a bad lifter or cloged did you try running some motor oil additives?

 

[rickf]

Thanks -- I pulled the cover to look at the flex plate bolts, but didn't look much further than that. I'll try to dig further. Are cracks generally pretty evident?

Sometimes but not always. They will be around the flywheel bolts. A trick I have used in the past is to spray water up in there and let it sit for a day or two. If there are cracks you will generally see fresh rust tracks after a day. The longer you wait the better you will see the rust, up to a point. a week is going to be about it unless you keep wetting it but that is not really necessary. If it is cracked the cracks will rust up pretty quick.

Rick

 

[cscmc1]

Could be a bad lifter or cloged did you try running some motor oil additives?

I have not; I changed the oil (to Rotella synthetic) shortly after I got the truck, but that's all I've really done.

 

[cscmc1]

Sometimes but not always. They will be around the flywheel bolts. A trick I have used in the past is to spray water up in there and let it sit for a day or two. If there are cracks you will generally see fresh rust tracks after a day. The longer you wait the better you will see the rust, up to a point. a week is going to be about it unless you keep wetting it but that is not really necessary. If it is cracked the cracks will rust up pretty quick.

Rick

That's an excellent idea -- thank you!

 

[rickf]

A bad lifter will give a tap but not a chirp and generally it will tap under load and not. I have a bad lifter in mine, it comes and goes but it is always a tap and it does not matter about the load.

Rick

 

[cscmc1]

Thanks for all the advice, folks. I think that tonight I'll remove the PS pump belt just to rule that out -- it's the only belt I have no removed in my quest to isolate this noise. After that, I'll start poking around with the flywheel again. Whatever the case, I hope it's a simple fix. Hate to have the truck just sitting, and with 2 very young kids, time is at a premium at our house. Not a lot of free time to piddle around in the garage!

 

[cscmc1]

UPDATE: It's apparently not either alternator or the PS pump. I removed the belts for each and drove the truck, and the noise is still there. Time to check the flywheel!

 

[cscmc1]

Well, I'm at a loss. I pulled the inspection cover (finally) and see no cracks. I'll look again to be sure my eyes aren't playing tricks on me, but I just can't find a thing. I really need to find another 6.2 to compare the noise levels to. Maybe I'm just used to my VW and Mercedes diesels, which sound like sewing machines when running properly. I *AM* hyper-sensitive to noises, but a squeak/chirp with rpm under load concerns me. It's frustrating that I can't replicate it in park, or I'd be able to crawl underneath and just listen for the noise.

My fear is something internal, but this truck just runs like a champ. Thanks again for all the tips, guys. If you think of anything else I might check, please post here; I really do appreciate it!

 

[Hasdrubal]

Dont know if this would be applicable to your situation. I recently had my exhaust replaced, it was previously welded and now is clamped together. I now have a chirp, squeak type sound that is also load dependent. Wont do it in neutral or under light throttle loads. Trying to figure out a way to fix this. If I go underneath and move the exhaust I can get it to make the noise, under load its quite repetetive and noticeable when driving next to a wall.

 

[cscmc1]

Dont know if this would be applicable to your situation. I recently had my exhaust replaced, it was previously welded and now is clamped together. I now have a chirp, squeak type sound that is also load dependent. Wont do it in neutral or under light throttle loads. Trying to figure out a way to fix this. If I go underneath and move the exhaust I can get it to make the noise, under load its quite repetetive and noticeable when driving next to a wall.

Thank you for the suggestion! I have wondered whether my issue might be exhaust-related. I have been underneath and shaken/kicked at the exhaust and never can quite replicate the noise I am hearing, but I'm glad to hear it's not out of the realm of possibility that that's my issue.

In fact, last night I got underneath and sprayed penetrating oil on some of the clamped junctions on the exhaust, and on the studs at the manifold (the three that hold the flange of the downpipe in place). I'll look everything over and tighten what I can tonight and see if by any chance it helps. It sure would be nice to find that it's something so simple!

Thanks again...

 

[Hasdrubal]

In my case everything exhaust wise, nuts and clamps, is tight. If I grab the rear pipe and move it up and down it makes the noise, bloody annoying when the windows down. It seems to be from the clamped together sections. There is some play on the rubber mounts where the exhaust hangs, so I may try to tighten this up by putting some rubber pieces between the rubber and the metal bracket.

 

[fusioncow]

has anyone had any progess with this? I'm experiencing the same symptoms, but haven't gotten too far on the troubleshooting.

 

[cscmc1]

has anyone had any progess with this? I'm experiencing the same symptoms, but haven't gotten too far on the troubleshooting.

I checked my flywheel first -- no cracks there. I disconnected all drive belts, and that wasn't it, and I replaced the harmonic dampener (it needed it anyway) too. The squeak is still there. I really think that in my case it's the exhaust.

My truck is running great -- starting easily on these 35 degree mornings, and plenty of power -- so I'm not worried about it at this point.

Good luck!

 

[dependable]

Have many 6.2s, they all have their own sound. It could be nothing.

Another thing makes a 6.2 sound off is if a glow plug tip got ingested at some point. This may progress from mild engine rap to wrist pin failure. If you suspect this, taking the head off on suspect side would reveal the stamp of glow plug tip in top of piston. Replacing piston and wrist pin at this point can save engine.

As a general rule, if the sound is getting worse, look into it, if it is not getting worse and running fine, it might be fine. If you see metal flecks in motor oil, it is not good.