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Discussion Starter #1
Sometime back I started a build that will probably be my last. Basically a 6.2 TD Suburban for back country exploration. But it’s turned into something of an albatross. And my most recent problem has me a bit stumped.

I’ve now got the motor in, custom turbo plumbed, and drive train complete. I thought I was finally getting to the later “fun” 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 “ticking’ 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 doesn’t run well at all much off idle.

All but the core support is off, and standing alongside the running motor it sounds distinctly like it’s 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 it’s 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 doesn’t 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 isn’t 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 it’s right below the valve cover. Maybe a previously missed cracked rocker? But it doesn’t really sound like that either.

If no better suggestions turn up I’ll likely pull the valve cover next. But as we all know, on a 6.2, that’s not a trivial task as it is with a gas burner. This is made worse by the fact it’s 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 “Right Stuff” 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 I’m seriously thinking I may pull the motor. But that makes “crank and test” 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, I’m hoping the vast experience represented here will lead to a “Oh, it’s that” revelation that doesn’t require major exploratory surgery. Sad that I’m considering pulling a valve cover major surgery, I’m seriously reconsidering my decision to go with a 6.2…

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

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Discussion Starter #2
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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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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Discussion Starter #4 (Edited)
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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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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Discussion Starter #6
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. :thumb:
 

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Discussion Starter #7
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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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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Discussion Starter #10
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. :confuzeld

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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Oddly enough, I will second the highly likely possibility of a broken valve spring! I put together a BMW R90S motorcycle this summer and I had one valve that kept ticking, sometimes louder, sometimes not. Thought it was bad adjustment or something. On my way to work one morning the valve broke... Caused some nice damage and I once again have to pull the bike back apart. I would say replace all of the springs on one side and go from there.

You can also run these engines with the valve cover off. Don't run it super fast as it will get oil all over, but it may help.

Trust me, you dont want to use a gasket. They weep. Cork or silicone, doesn't matter. I went through a big process getting the silicone valve cover gaskets made and available for these engines and they aren't that great because of the tin can valve covers....

Good luck!
 
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I like the killing the cylinder idea for a start. I'm wondering if it has the early style rockers which are prone to failure issues. I would definitely upgrade especially when adding a turbo.
 

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I like the killing the cylinder idea for a start. I'm wondering if it has the early style rockers which are prone to failure issues. I would definitely upgrade especially when adding a turbo.
The later pressed sardine can rockers are bad. My 94 developed lifter failures, common for this year, which caused clacking noises, then inlet manifold pulses. Most of the rockers, and push rods were destroyed, and a number of valve stems were mushroomed.
 

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Grancito I'm not sure what "pressed sardine can" rocker arms you are refering to. The early style cast rockers are prone to failure. Cast rocker failures were one many things that plauged the early 5.7 diesel. The later style drop forged rocker arms became the standard for later engines. I often buy used runners that the owner wants to pull and replace with a gas engine. Of the 150 or so 6.2 and 6.5 I've bought and built through the years I'd say a good 1/3 of the 6.2s had rocker issues which why the owner sold them and all of them had cast rockers. Ive never has a failure you describe although I have worked on engines which had simular failures but that was always do to another issue.
 

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Discussion Starter #15
I hope to get time to look deeper this weekend. Weather, holidays, and family can be such a distraction... :D

And mine has the steel rockers. It appears to be a '91 (mil surplus)
 

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been a while since your post, i had similar mystery valve train noise on rebuilt 6.2 after adding turbo. after chasing noise around i suspected low valve train oil pressure. sure i had all new bearings and oil pump, but it sure seemed to be 1 lifter or another that was intermittently ticking. i had run oil feed for turbo from side of engine by filter area and used 3/8” id line and elbow directly into t3 turbo. some websites for hopped up cars suggested installing different oil feed restrictors for one reason or another. i machined a restrictor for my oil inlet elbow (dont remember exact). this cured my lifter ticking problems. maybe your custom turbo is unrestricted also
 

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Discussion Starter #17 (Edited)
Thanks.

I've got the same -4 line as used in the Banks kits, though I do have the Baby H1C (less restrictive?), so hopefully that's not the issue. Everything I read about over oiling was more oil intrusion from the cartridge rather than oil starvation. Oil pressure reads at ~45 psi at idle.

Things have been moving slowly on my side. Between a series of bad weather days (including a rare Phoenix tornado doing significant damage on my rental property), holidays, family, and mostly grandchildren, I haven't fooled with the Suburban much.

However, yesterday the planets aligned and I got to spend a bit of time on it. I got it cranked and ran until I heard the distinctive tapping, then cracked the injector. Doing so destabilized the idle so much that with my hearing, I wasn't sure if it stopped or not. But after several repeats I was able to convince myself it was still there in amongst the general 6.2 clatter (now with a hard miss).

So, next step remains getting that ridiculous valve cover off after foolishly gluing it on with Right Stuff. If it were not so hard to get replacements, I think I would just use an hold hook can opener (as seen on utility knives) and cut the top off, then peel the lip off going around like perimeter. I fully expect to spend hours trying to get it off without ruining it, only to ruin it anyway and have to find a replacement. Too bad there are no cast valve cover replacements, or enough meat to add more fasteners (or fewer bean counters to produce such crap valve covers in the first place)...
 

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So, next step remains getting that ridiculous valve cover off after foolishly gluing it on with Right Stuff.

Using "the right stuff" is not "foolish", use something else like silicone and see, doing it again because of a leak not using the right stuff would be foolish...



New valve covers are cheap on ebay, I never attempt to reuse them and always replace with new... a oil leak will make you do it right the next time for sure...
 

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Discussion Starter #19 (Edited)
LOL, I actually agree. One of my biggest beefs with these in the past has been the near impossibility of stopping leaks. In fact, I passed on more than one at a good deal (years past) just because I didn't want to deal with a perpetual leaker. I'm just pissed that I now have to remove it right after putting it together "permanently". :facepalm:

Thanks for the pointer on ebay. Now to find my Leatherman with the hook can opener. Also kidding, but maybe not really... :(
 
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Discussion Starter #20
I wasn't thinking of ebay, expecting nothing but used and questionable. But just went for a look and found 2 "direct replacement" (aka aftermarket) new for ~$115 in this listing. I'm normally a bit skeptical of such parts, particularly when the OEM sucks to start with, and aftermarket isn't calling out "improved" or some such. And that's all that shows up as new other than later model with plug (most of those at >$100 each).

Is this what you refer to? Or am I missing some search term or part number that produces OEM covers at half the price? Yeah, but one can hope... ;)
 
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