Dreaded knock sound is starting

[gmcman]

I have it all back together and took it for a drive....I'm not sure what is going on exactly yet but I believe I'm on the right track.

This is what I did today:

Replaced plugs

Replaced valve cover gasket, TB Gasket, Intake manifold gasket.

Throughly cleaned out the lash adjusters on cylinders 1-4 except for the front adjuster on Cyl1 as it was buried behine some phaser hardware.

Replaced lash adjuster on Cyl 1 exhaust side, 2nd from front. This is the adjuster that just felt all wrong, 7/64" travel compared to just about 1/16" on the rest...almost double and a weak spring, also had play in the bore of the adjuster...not the head.

At this point I put it all back together and started it up, first thing I noticed was a greatly reduced valvetrain chatter. Wasn't too bad before but I can hear a difference. After about a minute I started hearing the noise again but not as loud...never really "peaked" after about 4-5 min like before then settled again, but just stayed there at the level it did before when warmed up but just slightly louder than that.

I let the motor run for about 5 minutes and the noise kinda went in and out briefly but never went away.

I shut it down and changed out the CPAS before it got too hot and fired it up and the noise was the same. I started cleaning up and this took about 20 min, at this point the noise was getting much quieter and at times I had to bury my head in the wheel well just to try to hear it. Would come back and go away and before I left it was very quiet but I could hear a knock every so often.

Went to get gas then a cup of joe, in line I could always hear it echoing off the building in the drive-thru....I could barely hear it and only because I was listening for it, otherwise it's unnoticeable to the untrained ear.

Arrived home and I could hear it again but at a greatly reduced level. Not sure but I really wish I could have cleaned up the last 8 adjusters, may not be the reason but based on what the others looked like they need some TLC for sure.

I will get a video tomorrow hopefully and also put some miles on it. One thing's for sure....it runs a WHOLE lot better now, much more responsive and likely a combination of all the goodies. The intake gasket was flush with the manifold...very little sealing going on and I'm sure it was leaking slightly somewhere.

The motor sounds different too, hard to describe but it does..alot quieter.

I would keep the synthetic in there...only does it good. Some of those adjusters were so tight they are digging into the cam lobes.

 

[jlarson1966]

Did you remove the cams to get at the adjusters?

Thanks,

 

[Texan]

I followed this thread, and I can tell you that he did not remove the cams.
See his other thread on 03 May to see how he did the project.

 

[jlarson1966]

I don't see his 03 May thread can you give me more information?

Thanks

 

[Sparky]

If the came lobes have wear you might not be able to get rid of all the noise as there is now extra wear/play involved. Just my impression.

 

[Texan]

Thread title to see info.


"What tool to compress valve springs"

 

[gmcman]

Thread title to see info.


"What tool to compress valve springs"

Sorry for the delay, here's the tool.

Appears that you bump the starter and when the valve is compressed, you place this over the spring and secure it to the coil pack mounting holes. Then bump the starter again to raise the cam lobe leaving the spring compressed. Don't use the threads of the bolts to compress the spring, this would likely strip the threads or break the bolt.

To update this thread, there is still a knock but when warmed up it's very faint.Work has been very busy so not much time to tinker but I have tried a new oil filter which is the Fram Ultra Synthetic and while I did havethis discussion in another thread, I agree I'm not a fan of Fram but tried this filter as an experiment due to it's apparent higher flow characteristics.

The motor is quiet when cold but that knock shows up after about 2-3 minutes and gets rather worrisome then gradually disappears but never goes away.

I could be chaisng an exhaust manifold crack for all I know but it's just too steady at idle for me to believe that. Along with the plugging of the valve cover breather port which silences the knock is just baffling, which still tends to point me to an oil delivery issue or lash adjuster. Maybe it's creating so much negative crankcase pressure it's sucking down on the bottom of the piston taking up slack in the rod bearing to crank journal gap removing the hammering effect......not sure but sounds plausable.

Captain XL:

I did finally get 2 cans of the KW flush and will give it a try.

 

[gmcman]

Here's a video I took this morning, fresh oil with about 500 miles on it. Slight tick when cold but nothing like it used to be. The video is long, about 20 min but it's the entire warm-up cycle.

You can skip through most of it, I uploaded the entire cycle in case anyone needs to pinpoint a certain area. The knock starts to become more audible around the 2:30 mark and even more so 1 min later. From there through about 15 min it gradually diminishes but never goes away. After about 20 min, it's far less noisy as when I first started hunting down the noise but seems the noise at 2-4 min is more noticeable..not sure but, thanks for watching as it's the most boring vid I ever recorded.

Also, at the 20 min mark I moved the camera around that side of the motor to get closer to the engine.

https://www.youtube.com/watch?v=_qwThKqmFEc

 

[Pittdawg]

What does it sound like under load?

 

[gmcman]

What does it sound like under load?

Nothing different, in fact..if I rev it up the noise dissipates somewhat. AC on or off, in gear there is no pitch change.

I cut open my last filter today and this oil has 4400 miles on it. I can't say for sure if the large piece was from the snips I used to open it but other than that, I only found pepper-size specs of shiny metal here and there, some were salt-size specs and they were maybe 1 or 2 specs per 4 or 5 pleats, some were magnetic and the large piece was magnetic. Really tough to say if it came from the can opening or not but it was on the ridge of the pleat, not the trough so I want to speculate it was from the can.

 

[Texan]

Based on your 04 May post #41, it would me wonder about the front adjuster on Cyl #1 exhaust side.
I think that I would try the KW flush. Good luck.

 

[gmcman]

Does anyone know if the front exhaust lash adjuster can be removed in the same manner as the rest? I know with my homemade tool it couldn't but not sure about the correct Kent-Moore tool. I remember it looked like a PITA but maybe someone can chime in.

I did the KW treatment and after I filled it back up and let it run for a few min, I can say that there's a lot less overall noise from the motor....almost like a nice steady normal hum but the knock was still there.

The light tap was there but not as much, the knock didn't appear to be as loud but I will wait for a cold start.

Wouldn't piston slap be audible right after start up and not almost 2 minutes after?

I'll give it some miles and see what happens.

 

[gmcman]

The high oil PSI really surprised me. I believe that the oil pump
has a by-pass relief valve. I wonder what it's relief PSI spec is? Did you check how far the new lifter plunger would travel?

The high pressure really surprised me also, and what's remained constant over this entire investigation, is the fact when I increase the RPM's the noise goes away.

Tonight after the KW flush, and the new oil and filter, I turned the A/C on, put it in gear, no change in pitch. When I rev it up the knock only returns just before idle.

I put it in gear and powerbraked it up to about 1800 RPM's and it still sounded good, when the RPM's are raised there was no knock that I could hear.

I found this short summary about the oiling system and the oil pressure relief was mentioned.

Here's the link http://www.greatautohelp.com/operation/4200-oil-system.html

I highlighted the text in question and I wonder if there is excessive oil being redirected somewhere. The fact I plug the port on the valve cover almost completely takes the noise away makes this a worthwhile avenue to pursue.

 

[gmcman]

I wonder if part #18 could be the culprit? With my luck it could be the spring (#12) but if it is a spring then I believe the pan has to be removed to pull the front cover.

 

[Harpo]

At the description for part 018 in your pic it says "opening pressure 21psi nominal".

 

[gmcman]

At the description for part 018 in your pic it says "opening pressure 21psi nominal".

Yeah that could be the mystery.....it appears that the oil would only flow unfiltered if there was an issue with a pressure difference in a properly working system.

However what if the spring (#12) is bent or damaged....where does the oil go? Does it take more pressure to open the relief? That part I'm uncertain of.

 

[Texan]

I can not remember the maintenance history of your Envoy, but I wondered if the problem
could be from gunk/carbon build up in the oil system. In the old days on SB chevy's the normal
oil pump relief PSI was around 40 PSI on stock engines. I can not find the same info, for the I6.
I would have guessed 60 PSI max. The oil filter by-pass is only for a old clogged up oil filter.
I wish that somebody could confirm that the 80 PSI that your mechanical gauge showed
is normal. I think that I would run more KW through it.

 

[gmcman]

I spoke with someone on another forum who hot rodded their 4.2 and he said he would get around 80 when cold as well.

I'm curious how I can easily push it over 100 when cold.

 

[Harpo]

I've done some reading in my Hanes manual.
The only thing stated in there about oilpressure was "12 psi@1200 rpm (minimum warm engine)".


It also said to test the oilpressure "at the oilpressure indicator sending unit" if that maybe would give you a different reading,idk.

 

[gmcman]

I will have to look for a M16x2 adapter or maybe even have a local shop fabricate one. I though the GM manual states to use a sandwich adapter? Someone will need to verify that.

So here's a hot idle after returning from work, been driving about an hour. I took these clips with my camcorder right behind the front wheels next to the fender wells.

I did this in park and in drive, sure sounds like a manifold leak (would be nice) but the whole plugging the breather port on the valve cover kinda negates that theory...I would suspect anyway.

Anyway, just an update on the noise, hopefully I can get into it before the weekend but not looking promising.

https://www.youtube.com/watch?v=6GFeSOpth1U&feature=youtu.be

 

[gmcman]

The following morning after the last vid I went out to start the engine and I pretty much always let the motor warm for a minute or 2 before I drive it off...but this time I let it run a few seconds to get everything circulating then I wanted to capitalize on the initial higher oil pressure.

I held the RPM at 2K-2300 and was thinking if there's a restriction in the valvetrain, then maybe the added pressure may work to my advantage. Drove it to work and not much difference, hard to say. I repeated this after I left work and when I drove home I tried to keep the RPM's above 3K and generally between 4K & 5500.

When I arrived home the noise was much quieter and I really barely heard it on the passengers side.

This morning I should have recorded the noise but it was fairly quiet for about 5 minutes and it's never quiet for that long. Never had the hard knock sound but was more supressed. I listened through the stethoscope and the noise seems more pronounced at cyl 3 & 4 on the intake side of the valve cover, directly across on the exhaust side is far less noisy.

I also pulled coil pack leads at the height of the noise and there was absolutely no change in pitch or frequency of the knock, I was pulling up to 3 packs at a time and no change.

I think I'm going to pull the valve cover again, bite the bullet and replace all the lash adjusters. Push comes to shove and I need to rebuild the head later on or replace a motor, then I'm keeping the adjusters. Could be something else like a worn adjuster bore in the head but I will check that out also.

Will hit it again with more KW or some MMO first but it's really sounding like a valvetrain issue.

 

[Mounce]

When you put the engine cleaner in, have you raised the rpm's like you said you did in your last post? If not, maybe the higher pressure will help the additive in the process of removing a possible blockage? Just a thought.

 

[gmcman]

When you put the engine cleaner in, have you raised the rpm's like you said you did in your last post? If not, maybe the higher pressure will help the additive in the process of removing a possible blockage? Just a thought.

I did. However not knowing how the KW would affect the oil in terms of handling pressure, I didn't want to run it too high since it states to let it idle.

After the 3 min mark I raised the RPM's to about 1200 for about another 3 min then drained it out.


As far as today, I was home slightly under the weather but I did drain 1 quart and headed off to pick up a quart of MMO then 7 qts of Redline 5W-30. Reason for the Redline is it has a good deal of cleaning agents and uses group V base stocks. I was going to get some Amsoil Signature but this is readily avail for me and after speaking to a Redline rep, we discussed this in length and with price being the same I wanted to give it a try after I remove the MMO in a week or so.

I put on about 70 miles with 1 qt of MMO and I'm surprised at how well it appears to be working in such short order. Granted the noise is still there but it is much, much less in intensity and hopefully we are on the right track.

This is after 70 miles of driving with 1 qt substitute of MMO.

https://www.youtube.com/watch?v=kPsiQwN7ztQ&feature=youtu.be

 

[BVEN]

Is there an update as to the knocking or diagnosis? I have the same issue with my 2002

 

[gmcman]

Is there an update as to the knocking or diagnosis? I have the same issue with my 2002

Man, can't believe it was July that I last updated this....thanks for calling it out. Honestly work and other projects have consumed me, I wanted to post results but the noise kept changing and I was hoping for a steady change not one that was so fickle.

When I start it up now it's quiet, the noise builds slightly but never gets real loud. I have an oil change due and when I do I will post back. The noise is still there when hot but appears to goes away when I raise the RPM's above about 1200-1500. I want to say it's a lash adjuster, just the way it acts...definitely keep your oil changed and I would surely recommend synthetic or a synthetic blend due to the tight tolerances especially in the cam phaser.

 

[streetmaster42]

Sounds to me like a thrust bearing knock, the one that keeps the crank from moving from front to back, cause mine at 130K has the same noise, but I have to listen for mine.

 

[BVEN]

Thanks for the update. Have you dismissed the oil pump as being a possibility?
Thanks

 

[gmcman]

Thanks for the update. Have you dismissed the oil pump as being a possibility?
Thanks

Not completely but It"s looking like the pump is working properly. Sorry for the late replies been finishing up projects and work is crazy.

 

[BVEN]

Not completely but It"s looking like the pump is working properly. Sorry for the late replies been finishing up projects and work is crazy.

Okay, so I have been investing a lot of time into this issue of "ours". My symptoms are very similar to yours in reference to the knock and PCV being temporarily blocked silencing the knock. I have two new possibililies with a theory, I would like your (or anyone's) opinion on....
1. Timing: When the PCV is capped during idle, the crankcase pressure is retarding the intake timing?
2. Catalytic converter: The lack of the ability to expel exhaust, capping the hole would retard intake?

I could be completely off, just my uneducated theory. Thanks

 

[gmcman]

The cam timing is only on the exhaust, intake is not controlled. The only thing I can come up with in regards to plugging the vacuum port is either the increased crankcase vacuum is pulling down on the piston silencing a knock, or pulling more oil into the lash adjuster boss and taking up any space in the bad adjuster.

 

[BVEN]

I am going to the dealer tomorrow (hopefully) and having my PCM updated. I noticed there were a few issues that correlate with an update. After that, and hopefully with more insight from the mechanic, I hope to tackle the knocking noise. Are there any advisements before I bring it in?

 

[sunliner]

Yeah, I've had my Trailblazer for three years now (and my father in law drove it for a year before that) and mine has always sounded just like that. Aside from my well documented codes, the truck usually drives great.

I would swear that was my engine. When cold, it almost sounds like a diesel running but once warmed up, it's quieter but not completely gone. Been doing this for over two years and even changed my cam phaser and CPAS. I'm thinking the chain or adjuster is loose.

 

[gmac310]

I have a problem that is similar except I only have it when the engine warms and I rev it up to around 2500-3000 RPM. The weird thing is that it only does it in first and second gear or if I idle it in the driveway. If I accelerate aggressively so the cam phaser 'kicks in', it doesn't do it then either. I tried changing the oil, using some oil flush treatment and I even thought it might be spark knock so I tried some octane boost. Could it be a bad lifter or knock sensor?