4.2 Diesel and theory for resolution

[Lynn]

Hello all, 2004 Envoy, 225,000Km. A unit my son and my ex picked up without my involvement. It sounds like a diesel, hot or cold like many have reported. I pulled the intake, valve cover and replaced all the lifters.

First I pulled a few and found that they were solid, no springing action at all. One lash adjuster at #1 Intake was like new with 1/8" or so compression motion, the others solid, no movement, I speculate that they are full of crud.

So, I fashioned a simple valve spring "retainer" flat 3-1/2 in wide 1/4 in plate, fasted down at two COP mounts, roll the cam to compress springs, run two bolts down and hold both springs down, roll the cam , take out parts..

I did the process and replaced all with new. Fired it up, clattered like crazy for 20 sec then, back right where it was.

So the theory part. The length of new lash adjusters and the old were within .003 or each other. The new were of course had some movement. I believe that in the engine they were fully extended and then over time crud filled in adjuster and prevented any compressive movement.

What I am theorizing is that due to wear of all valve train part even when a new lash adjuster is installed the lash is too great. Hence the diesel clatter.

The cams and roller don't look too bad but there is some wear.

If I was to pull the lifters back out and put a shim under to take up some of the slack would that be too crazy? The shim I am thinking of will be like a star washer that will allow oil flow down the what I think may be a drain hole at the bottom of the adjuster bore.

I appreciate that this is a quick fix and valve job /rebuilt head would be the way to go but this is my 16 yr old sons and the risk of this vehicle making it through the winter unscathed is low (in my mind), in short I am not putting $3,000 valve job in a $2,000 SUV.

I am also trying to figure out how the lash adjuster work? Are they pressurized through the small hole on the side (as I believe) or does the oil gallery pressurize from the bottom of the adjuster? If it is the latter then my shim theory is a bust. I

have been looking for a drawing of oil galleries and flow but so far can't seem to find.

If the engine oils from the bottom of the lash adjuster (but I don't really think so) then I may have a clogged oil gallery problem.

Advice is appreciated..

L

 

[mrrsm]

Lynn…

While nobody appreciates someone who is being Clever and Resourceful when it comes to either inventing or re-purposing standard tools for “Specialty Jobs” more than I do... in the case of doing anything with Valve Train work on the GM Atlas LL8 4.2L DOHC Engine… the Tool of Choice is just about as ubiquitous as they come by as Clouds in the Sky...and you can get them on eBay for anywhere from $8.00-$15.00 +- S&H. This one tool that is better left to “The Boys from Kent-Moore”. Here is a pretty good sample of what eBay’ has as its “Port-au-Faire” on this item:

http://www.ebay.com/sch/i.html?_fro...TRC0.H0.Xen-47945.TRS0&_nkw=en-47945&_sacat=0

As for tearing into the upper head to replace the Roller Rockers and/or the “Valve Lash Adjusters” as they like to call these foreshortened “Push-Rod-Lifter” combos… After the work is all done… its a good idea to pull the IGN (Ignition Relay) #22 as per your Fuse Box Inside Lid Chart,,, and with a Freshly Charged Battery and Battery Charger nearby and at the ready to replenish it... after doing three of four 30 Second Engine Turnovers separated by a 5 Minute Cooling Periods in between … this will allow all 24 of these Metal Turds to ‘Plump Up’ Inside with Engine Oil… and NOT allowing the engine run until they get filled first is a much better procedure to follow.

The Roller Rockers in this engine look pretty flimsy and the VLAs have a history of snapping in half from Oil Starvation if they are allowed to spin ...and be doing so on both sides of the head at Half of the RPM of the Crankshaft. So running them Bone Dry and hoping they will improve in time and quiet down… comes with a big risk of damaging them. What applies here to avoid lunching this engine follows the old saying that goes:

“If you are NEARLY Correct… Then You are PRECISELY Wrong...”

You probably know this… but many people reading about topic may not and so it becomes one other Important Issue that bears mentioning here, This work should only be done when the Pistons are at the BDC (Bottom Dead Center) Position and/or when the Valve Lobes are exactly set on their Base Circles so that any Tightening of Kent-Moore EN-47945 Tool does not wind up putting Dents in the Tops of the Pistons or actually Bending the Valves and Valve Stems all to Hell and Gone if they just happen to run into the Tops of each Piston ...and have a disagreement.

This Tool does NOT allow for access to the Spark Plug Hole after the two High Grade Bolts are screwed down into the threaded Coil On Plug Holes… and so using a Special TDC Tool like THIS one First just before installing the Valve Spring Compressor… just makes Good Sense. This one is a bit Pricey… and yeah… I know...you can get away with using screwdriver down the Spark Plug Hole or you can call this one a Necessary Evil that warrants buying one these to be around and handy at times like these.

https://www.amazon.com/Innovative-Products-America-7886-Indicator/dp/B000FMSU9Q/ref=sr_1_1?ie=UTF8&qid=1478508990&sr=8-1&keywords=14"+tdc+tool



And Last but Not Least… There is just No Sugar Coating of your Notion of dropping a loose “Spacer” or "Shims" down inside what are essentially Two Horizontal Tubes with 24 Vertical Tubes “Waste Foam Casted” into them and then drilled out with better precision to allow Engine Oil to exit the Vertical Oil Column from the Oil Filter and then travel sideways down both sides of the Engine Head at up to 65 PSI on its way to nourish the VLAs and other needy Engine Parts in turn.

Please… Just think about it for moment… What would happen if your “Spacers” wound up getting “jarred loose” under the bouncy action of all those VLAs jumping up and down under the influence of the Twin Rotating Camshafts and suddenly slipped out from the base of the VLAs to get carried along with the Oil Stream and perhaps buried under pressure elsewhere deeper inside of the Oil Galleys ...or God Forbid… if any got pushed under Oil Pressure into the bearings of Rotating Assembly causing Oil Starvation. If that were to happen… Having a “Dieseling Clatter” from your Valve Train...would the LEAST of your problems. So… NO!… Please Don’t Do that... Okay? ;>)

Perhaps a closer look at the Roller Rockers for excessive Wear and Play would reveal a "Better Culprit" to examine as there is more motion and mechanical action happening with them than there is inside those VLAs. While you have them out...examine the Tops of the Valve Stems for any "Mushrooming" and Flattening as well for any excessive end play this phenomena would cause. With 225,000 Kilometers... Your son's vehicle is No Spring Chicken. Also... if you get this buttoned back up...Shoot a decent "Walk-Around Video" of the Top of the Engine so we can actually hear what you are hearing and confirm your suspicions or provide other ideas on what the sounds might otherwise be.

 

[DocBrown]

This is really much simpler and cheaper than all that. Live with the sound. When I had mine it started sounding like a diesel at around 75k. And yet it was the smoothest running engine I even owned. Couldn't feel the slightest vibration. Even at 160k when I sold it. Just listen to any GMT 360/370 with an I6, they all sound like that.

In other words I think you might trying to fix something that isn't really broken. Annoying maybe, but not broken.

 

[littleblazer]

Both of mine are noisy for the first 30 seconds or so because of piston slap, once they're up to temp I can't really hear them running. Very quiet. I haven't really heard the noise you are speaking of but I would guess it is valve clatter like? It won't hurt anything I would think either way. Just another quirk of the platform like @DocBrown was saying.

 

[DocBrown]

To qualify as littleblazer stated, it would not be as evident when it warmed up, but it was still noisy.

 

[Lynn]

To qualify as littleblazer stated, it would not be as evident when it warmed up, but it was still noisy.

Thanks all, I did soak the lash adjusters in oil and drenched the cams, rollers and lifters with oil before buttoning it up.

I am not clear of the issue with using shims, If I find a hardened part is my risk of disintegration low? Valve shims have been in use forever with success.

Doing nothing is an option of course and I am confidence that nothing serious is wrong after my digging around. I isolated the noise to top end, compression is good 165 - 170 psi - even across all 6. I will run a number of short oil changes with detergent and see if I can better the problem but in my heart of hearts I hate leaving it like this. I see risk of a greater problem if parts eventually break.

 

[littleblazer]

You could test oil pressure. It's a long shot but it could be running low and causing the issue.

 

[Lynn]

I pulled the oil switch out and put a gage in. McGivered up a 16mm X2mm pitch, 1/8 in NPT tap'd and remoted a gage..results.. 60Psi at an idle, 80 psi at 1,700???
Any thoughts, Plugged gallery('s).

 

[littleblazer]

I would think that is good...

 

[Mooseman]

If it was plugged, the bypass/pressure relief in the pump would bleed off the extra pressure. I wouldn't worry with pressure like that.