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Old 12-27-2019, 10:35 PM   #1 (permalink)
BadDog
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Variable frequency clacking?

Sometime back I started a build that will probably be my last. Basically a 6.2 TD Suburban for back country exploration. But itís turned into something of an albatross. And my most recent problem has me a bit stumped.

Iíve now got the motor in, custom turbo plumbed, and drive train complete. I thought I was finally getting to the later ďfunĒ work of building out the rig. Then I started the motor for the first time with exhaust (previous run on stand before starting the build).

After priming the oil system, it actually started and ran pretty good for a first start. But within a minute or so, I started noticing a disturbing ďtickingí sound. It was variable/intermittent, and in a gas burner, if it were consistent, I would say it sounds a lot like a cracked piston. But on subsequent runs, the pattern persists. It starts sounding almost exactly like my other 6.2, but over a period of 10 to 30 seconds or so, it starts the variable frequency clacking sound, and it continues to get louder for another minute or so until it levels out. A few blips of the throttle, and it may (or may not) quieten. If it (at best almost) stops, another blip will bring it back. Another potentially relevant point is that it doesnít run well at all much off idle.

All but the core support is off, and standing alongside the running motor it sounds distinctly like itís coming from high on the front passenger side. I have a hearing problem that seems to prevent me from hearing it through a stethoscope, but a younger experienced friend confirms that itís coming from that area. He felt it was most clear from the front injector (#2). Thinking it may be a weak injector leading to intermittent pre-ignition, that lead to swapping out that spare injector, which had no effect. So, unless I happened to get a similarly failing injector, the injector doesnít seem to be the problem.

Some other background. I eliminated the mechanical lift pump in favor of an electric inline back near the tank. Pressure isnít quite what I hopped, but should be sufficient at ~3 psi. It also has a new professionally rebuilt injector pump. It also has all new valve train plugs, and initial inspection appeared to indicate the upper valve train was in extremely good condition.

It REALLY sounds to me like itís right below the valve cover. Maybe a previously missed cracked rocker? But it doesnít really sound like that either.

If no better suggestions turn up Iíll likely pull the valve cover next. But as we all know, on a 6.2, thatís not a trivial task as it is with a gas burner. This is made worse by the fact itís the passenger side with AC. And, I hate leaks beyond words to say. Since I did all the service and everything looked good in there, I used ďRight StuffĒ in a misguided effort to avoid the leaks this motor is so well known for. And now I have to get that tin-foil valve cover off in-frame. I dread that bad enough Iím seriously thinking I may pull the motor. But that makes ďcrank and testĒ much harder. There is no way I will hear it on the stand, though I suppose I could cobble up an exhaust, and maybe a primitive coolant system.

Anyway, Iím hoping the vast experience represented here will lead to a ďOh, itís thatĒ revelation that doesnít require major exploratory surgery. Sad that Iím considering pulling a valve cover major surgery, Iím seriously reconsidering my decision to go with a 6.2Ö

Please jump in with whatever you've got. Any suggestions MUCH appreciated.

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Old 12-27-2019, 10:55 PM   #2 (permalink)
BadDog
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I just remembered an audio recording I made of this to send my friend right after I first noticed it. The recording was made about 2' from the front passenger side of the block.

Oddly, listening to it on the computer, it sounds even more like something hitting the valve cover. I don't remember it being that clare standing next to it. Maybe it's the noise canceling mic of my phone? Anyway, I tried to attach, but the forum apparently won't allow wav files, so here is a link.

Audio of engine running

I also happened to think of one other potentially relevant point. The turbo is right there at the same location (Banks manifold), and I currently don't have the waste gate connected to anything (no boost gauge yet). One of my earlier thoughts was that maybe exhaust pulses were causing the little gate flapper (Holset Baby H1C) to bounce around. Even though I saw no movement, I wired it in the open position, but no change at all. So it's basically running as an NA.

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Old 12-28-2019, 08:11 AM   #3 (permalink)
sctrailrider
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Remove your belt and run the motor again for only a short time, if the sound is gone, check the crank pulley, their are 3 metal tabs in the center, if the pulley is wore out those metal tabs will hit and sound like that.. eliminate the items on the frond belt drive then go under the valve covers...
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Old 12-28-2019, 02:50 PM   #4 (permalink)
BadDog
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Thanks.

Sorry, trying to be brief, and typing a late night post, I didn't cover everything.

It has a new Fluid Damper, and one of the first things I did was pull all the belts to make sure it wasn't sound traveling from an accessory. I also thought maybe the untried vacuum pump. Not really, but I've been fooled before by sound traveling, and it was easy to swap.

What really gets me is that it seems largely random in frequency. A broken rocker or push rod should be more or less (or completely) steady. And in the recording, it's a lot more clear than standing beside it. But maybe that's just my hearing in that I have trouble distinguishing details (like voices talking to me) in even moderately noisy environments. Probably why I couldn't pick it up at all with the stethoscope.

I'm not really expecting some magic bullet here, but would hate to go to my next logical step only to find I overlooked something and didn't have to do all that. It's happened before...

So, I'm currently at your last point, pull the valve covers. And I'm REALLY hating my decision to put it together with Right Stuff. I just don't see any way I'm not going to have to destroy the valve cover to get it off, especially if I try it in frame.
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Tow rig: White '02 2500HD SWB Crew 4x4 D/A Juice/Attitude on 285/75-16

Toy truck: '85 C10 SWB Step 6.2 SM-465

Expedition (project): 85 K20 Sub 6.2/700R4/NP241 D60/C14 (both locked) camping/expedition outfitted.

Last edited by BadDog; 12-28-2019 at 02:51 PM.
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Old 12-28-2019, 03:35 PM   #5 (permalink)
legendman
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Bent push rod, maybe ?

Compression test? Is there a lot of blow by when you take the oil fill cap off?

If you loosen the injector line on the suspected cylinder does the noise go away?


Can easily hear the clacking in your audio link.


Does this sound the same to you?
This engine ended up having cracked pistons when I ripped it apart.






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Old 12-28-2019, 05:27 PM   #6 (permalink)
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I thought about bent push rod or related upper valve train sources. And I've experienced damage like that including a broken stud (not really possible on these), but never anything that was so intermittent. If it was mostly steady, like your clip demonstrates, then valve train or broken piston would be my guess.

One scenario in my head is a valve train damage such that the lifter isn't immediately returned to the lobe. Perhaps when it contacts the lobe it is fired upward hitting the rocker, but then may not fall back down immediately every time. Eventually the rattle/clatter/shake drops it back down, and it may hit once or a few times before another slow descent. Thereby explaining the intermittent nature.

Haven't done a compression test since installing, but did do one when I was evaluating the engine to go into the project vehicle. That was about 4 years ago (long before I found the donner body) and I don't recall the values. Based on expected values at that time (probably found here), compression was a bit low, but not unbearably so, and relatively balanced. And there is blowby, but not anything more concerning than I've seen on most any 6.2 (including my well worn C10).

I'm ashamed to say that loosening the injector didn't occur to me. Basically the same as pulling a plug wire. When the weather clears up a bit, I'll give that a try before choosing a path leading inside the valve cover. If it goes away, I'll have my answer regarding whether to even attempt to remove the valve cover in frame. That's the kind of potential boneheaded oversight risk that prompted me to post this.
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Old 12-28-2019, 05:42 PM   #7 (permalink)
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Also, it lights right off with no problem and idles smoothly. Another indicator supporting adequate compression and no completely dead hole. Getting stumbly above (something like) 1200 rpm would seem to support a fuel issue. Since it's a new/reman fuel pump, I don't have a valid reference for timing, but I've played with a range of timing going from major clatter at idle to getting hard to start and stumbling at idle (and didn't want to come up at all), so the current timing doesn't seem to have anything to do with this tacking, though it might be a bit low and thus contributing to the off-idle stumbling.

I also wonder if there could have been a mistake in the fuel pump that would do this (thus not changing with swapped injector). But from what little I know of it's function, can't imagine what that would be when it lights and idles so nicely. I was SO hoping it was just a weak injector popping unpredictably early.
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Old 12-28-2019, 06:07 PM   #8 (permalink)
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Need to break the injectors loose one at a time and see if the sound dissipates, As mentioned earlier.
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Old 12-28-2019, 06:13 PM   #9 (permalink)
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I had an engine sound quite similar. It was a broke valve spring. The piston was actually slapping the valve every so often. Not saying that's what it is but does sound close to it.

Spring was still there but a small portion was broke off.
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Old 12-28-2019, 09:15 PM   #10 (permalink)
BadDog
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Thanks. That certainly fits the observed sound and behavior.

And a smart person would already have cracked the lines to kill the cylinder. On a gas burner, pulling the wires to test the questionable cylinders is one of the first things I would have done, no idea why it didn't occur to me to kill the cylinder. I'll blame it on just getting too old, I've got no other excuse.

Now, anyone got a magic bullet for getting the right stuff to break loose? I know it's not the recommended path (including OEM), but I sure wish I had just used a gasket...

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Toy truck: '85 C10 SWB Step 6.2 SM-465

Expedition (project): 85 K20 Sub 6.2/700R4/NP241 D60/C14 (both locked) camping/expedition outfitted.
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