Is my engine knocking?

[imjustauser]

Hi,

I got a 2002 Envoy 4.2 4x4 SLE 135k miles

The engine seems to be making a knocking type noise even with the serpentine belt off. Would love some opinions.

These videos are with the belt off.

The two videos of engine (belt off)

one with hood down inside cabin, other outside cabin.

It seems the mic gets overwhelmed when the hood is up and the noise is not captured properly.

Please help, thanks!

 

[mrrsm]

Some preliminary Questions... and some Observations:

(1) When did you "get" this SUV...? Any CEL or SES Lights on the Dash? Are you getting any PXXXX Power Train Codes on your Scan Tool read Out?

(2) If you are not the Original Owner... the vehicle is Remarkably Low Mileage... What did the Prior Owner tell you about the history of this vehicle? These engines can easily achieve 200,000 Miles of life.

(3) It would help if you avoid racing the engine above a Resting Idle any more until you can figure out what is really at issue here. Is the sound especially louder on the Exhaust Manifold Side due to a possible Crack in the Cast Iron?

(4) It would help if you would make another video of the engine idling for around 20 seconds or so. Leave the Hood UP and walk around the outside areas...and place the camera underneath ...around the Flex Plate to Bell Housing to Engine Block areas too:

(5) It sounds more like a possible Cracked Flex-Plate than a true "Piston Slap" or a Rod Knock. Listen to the Video below for the sound of a TRUE Rod Knock.

(6) If it turns out NOT to be a Cracked Flex Plate and you are Mechanically Inclined... Follow THIS Dude's Instructions and Procedures to determine is there is an actual bad Con-Rod Bearing Issue:

(7) Prior to doing the above ... Performing a Dry-Wet Compression Test will reveal any issues with Low Compression Bad Valves or Bad Rings. @gmcman 's procedures will give you the right idea on what to do:

Compression test

With the Voy getting up there in mileage, 287K, I want to do a lot of preventive maintenance in the next few months and freshen things up. One area is to replace all the lash adjusters but don't want to do this if the motor shows signs of being on it's last leg. This is my 2nd compression...

gmtnation.com

 

[Aroc]

I had the same noise which came from the bell housing flexplate area...turned out that after 152K miles the flexplate bolt holes became flexplate ovals due to the power cycles.
After a long trip the noise became unbearable so i replaced both the flexplate and torque convertor.
Truck runs quiet and shifts smoother now.

 

[imjustauser]

I had the same noise which came from the bell housing flexplate area...turned out that after 152K miles the flexplate bolt holes became flexplate ovals due to the power cycles.
After a long trip the noise became unbearable so i replaced both the flexplate and torque convertor.
Truck runs quiet and shifts smoother now.View attachment 108867View attachment 108866View attachment 108869

Did you also hear it from the valve cover area? When I listen to the valve cover with a metal rod I can hear it. I also tried listening on the bellhousing area but it is hard to figure out exactly where its coming from.

 

[mrrsm]

Pinning down the cause and origin for these sounds can be very difficult. Notice in the attached image that there is a "Modesty Access Panel" ...or a Circular Stainless Steel Plug located in the underside of the 4L60E Transmission Bell Housing.

You can simply *Pop* that Metal Plug Out with a Screw Driver and then just position your Cell Phone close enough to record any sounds emanating from inside that might give a better indication of having a Cracked Flex Plate ...or not:

 

[Aroc]

Did you also hear it from the valve cover area? When I listen to the valve cover with a metal rod I can hear it. I also tried listening on the bellhousing area but it is hard to figure out exactly where its coming from.

It originally sounded like it came from valve train area but after moving under vehicle and closer to bell housing the noise was from flexplate/torque converter area (removing the cover clip helps as mrrsm suggests).

 

[imjustauser]

Update: Switched out the old flexplate for a new one and still has a similar noise. Perhaps it is the beginning of rod knock? Would love to find out before dropping some $$$ on another trans for it. Hopefully it is another issue but im running out of ideas. Ill try out that rod knock test.

 

[imjustauser]

Some preliminary Questions... and some Observations:

(1) When did you "get" this SUV...? Any CEL or SES Lights on the Dash? Are you getting any PXXXX Power Train Codes on your Scan Tool read Out?

(2) If you are not the Original Owner... the vehicle is Remarkably Low Mileage... What did the Prior Owner tell you about the history of this vehicle? These engines can easily achieve 200,000 Miles of life.

(3) It would help if you avoid racing the engine above a Resting Idle any more until you can figure out what is really at issue here. Is the sound especially louder on the Exhaust Manifold Side due to a possible Crack in the Cast Iron?

(4) It would help if you would make another video of the engine idling for around 20 seconds or so. Leave the Hood UP and walk around the outside areas...and place the camera underneath ...around the Flex Plate to Bell Housing to Engine Block areas too:

(5) It sounds more like a possible Cracked Flex-Plate than a true "Piston Slap" or a Rod Knock. Listen to the Video below for the sound of a TRUE Rod Knock.

(6) If it turns out NOT to be a Cracked Flex Plate and you are Mechanically Inclined... Follow THIS Dude's Instructions and Procedures to determine is there is an actual bad Con-Rod Bearing Issue:

(7) Prior to doing the above ... Performing a Dry-Wet Compression Test will reveal any issues with Low Compression Bad Valves or Bad Rings. @gmcman 's procedures will give you the right idea on what to do:

Compression test

With the Voy getting up there in mileage, 287K, I want to do a lot of preventive maintenance in the next few months and freshen things up. One area is to replace all the lash adjusters but don't want to do this if the motor shows signs of being on it's last leg. This is my 2nd compression...

gmtnation.com

Also heres a recent video with a new flexplate

0 new items by Aaron

photos.app.goo.gl

 

[Mooseman]

That sure doesn't sound good. What you could also try while it's running is to unplug each coil and see if the noise changes on a particular cylinder. A borescope can also be useful checking and comparing all cylinders.

Another possibility is piston slap, which would be worse when the engine is cold.

 

[Dr.Fiero]

Mooseman beat me to it! As soon as I heard it I was going to say piston slap. If you hear it from a cold start, then after about 5 min's it has either gone away or is at least reduced... that's probably all it is. Still not good - but beats bottom end issues! Rod knock will not go away or reduce when warm (if anything it gets worse as the oil thins!).

Since my ~350K TB has started doing it, I just ALWAYS give it a good chance to warm up at idle before driving.

 

[mrrsm]

There is another Treatment called ACDelco Top Engine Cleaner to address this condition in High Mileage Motors that can be used to de-carbonize the Upper Cylinder Combustion Chamber and Trapped Compression Rings that is featured in several Threads:

https://www.amazon.com/dp/B007Q102AE/?tag=gmtnation-20

A.C. Delco Foaming Top End Cleaner....

Good Evening All, I've read about this procedure here on the forum. I'm wondering if it would be OK to do, regardless of if I have carbon build up or oil consumption. I have noticed a small amount of oil accumulated in the intake plenum. I do have a little piston "slap" that goes away upon...

gmtnation.com

Carbon cleaning the 4.2L LL8. Experiment

I have recently performed carbon cleaning on the pistons and valves using a method recommended by @MRRSM and I figured to document the experience for those who would like to pursue this in the future. The method involves pouring AcDelco Top engine cleaner in the spark plug holes. This is NOT a...

gmtnation.com

 

[imjustauser]

There is another Treatment called ACDelco Top Engine Cleaner to address this condition in High Mileage Motors that can be used to de-carbonize the Upper Cylinder Combustion Chamber and Trapped Compression Rings that is featured in several Threads:

https://www.amazon.com/dp/B007Q102AE/?tag=gmtnation-20

View attachment 108996View attachment 108997View attachment 108998View attachment 108999View attachment 109000View attachment 109001View attachment 109002

A.C. Delco Foaming Top End Cleaner....

Good Evening All, I've read about this procedure here on the forum. I'm wondering if it would be OK to do, regardless of if I have carbon build up or oil consumption. I have noticed a small amount of oil accumulated in the intake plenum. I do have a little piston "slap" that goes away upon...

gmtnation.com

Carbon cleaning the 4.2L LL8. Experiment

I have recently performed carbon cleaning on the pistons and valves using a method recommended by @MRRSM and I figured to document the experience for those who would like to pursue this in the future. The method involves pouring AcDelco Top engine cleaner in the spark plug holes. This is NOT a...

gmtnation.com

Actually, what we call a top engine clean is to remove carbon build-up on top of the pistons that can cause carbon knock and/or pinging due to pre-ignition. Usually what we would do is either removed the plugs and pour the solution into the cylinders or pull the vacuum line and put it into the top engine cleaner container, then start the car and let it run until it dies from the flood of cleaner. Then let it sit overnight and fire it up the next morning. It smokes like crazy for a while, more if the carbon build up was worse. The benefit of doing this is the carbon build-up can increase compression and cause a knocking noise at idle, and when accelerating hard the carbon is actually so hot it ignites the fuel before the plugs do and can cause severe engine ping.

What moman is talking about is what we call a upper intake and throttle body service which removes carbon buildup in the intake which causes airflow restrictions which results in low/erratic idle, which then causes all sorts of small problems at idle like ac not cool, lights dimming, power steering hard, etc all due to the idle not being high enough to turn the accessory drive belt fast enough to keep that stuff working right.

Found this in a forum, I might stick an endoscope down the spark plug holes and see if theres a bunch of carbon buildup. Hopefully this is the cause haha.

 

[mrrsm]

Unfortunately... after performing the ACDelco TEC Treatment... You will be faced with "The Prisoner's Dilemma" of NOT being able to Start and REV UP the Motor right away ...until AFTER the 4L60E is Re-Installed.

This is because Mechanic's should NEVER Rev any Engine when only the Flex-Plate is installed and the Motor is Operating in an Unloaded Condition with NO Torque Converter attached.

Ergo... You'll have to install the Transmission again before you can try to Blow Out all of the freshly dislodged Carbon Residue after bringing the Engine up to an Operating Temperature. :>(

 

[imjustauser]

Unfortunately... after performing the ACDelco TEC Treatment... You will be faced with "The Prisoner's Dilemma" of NOT being able to Start and REV UP the Motor right away ...until AFTER the 4L60E is Re-Installed.

This is because Mechanic's should NEVER Rev any Engine when only the Flex-Plate is installed and the Motor is Operating in an Unloaded Condition with NO Torque Converter attached.

Ergo... You'll have to install the Transmission again before you can try to Blow Out all of the freshly dislodged Carbon Residue after bringing the Engine up to an Operating Temperature. :>(

What happens when an unloaded engine is revved?

 

[mrrsm]

Internal Combustion Engines create forces that must be contained and coaxed at each Crankshaft Journal to prevent Harmonic Vibrations that will build up and eventually tear the Motor Apart. The Crankshaft Counter-Weights that are either Forged, Carved or Cast into their designs are meant to attenuate these "Pounding Forces" to some degree.

However, as the RPM increases... the accumulation of these vibrations grows exponentially and catastrophic damage can be the result when there is no mediation of this accumulated energy... and smoothing out their flow into steady momentum.

And so.. Engines are designed with necessary "External Loads" in mind in order to accommodate a certain amount of energy absorbing Mass... inertially Rotating ONLY in a Clockwise Direction.

Unfortunately, a Thin, Mild Steel Flex-Plate has insufficient Mass to allow the Rotating assembly Internals to flow their power with consistency and NOT allow the "Lash" in between all of the sub-components to literally "Bang Back And forth" and become a BACK-LASH working against these components.

The damage here can propagate rapidly in between the Small Spacing of the Mains and the Connecting Rods and their Babbitt Bearings that will ordinarily NOT occur if there is a Sufficiently Massive Object attached both at the Nose of the Crankshaft (where the Harmonic Balancer is necessarily attached there to Deal with the Excess Longitudinal Vibrations) and also at the Rear of the Crankshaft where it is the customary and popular prejudice to attach either a Flex-Plate Bolted to a Fluid Filled Torque Converter or a having a Heavy Fly-Wheel bolted onto the Crankshaft for mating up with Spring-Loaded Friction Clutch-Plate Based Transmissions.

These are the additional Mechanical Necessities bolted onto the ends of Crankshafts inside of ALL Engines in one form or another and are quite necessary to have installed there to handle these issues and not cause Excess Bearing and Vibration damage by literally pounding these engines to pieces.

Performing Un-Loaded Snap Throttle activities is an invitation to destroying your Motor. This "Toy-Like" version on a V-8 provides ample evidence of this reality and it follows on that the Physics being shown here are UNIVERSAL in their implication even for all of those "Naturally Internally Balanced" In-Line Engines 4 and 6 Cylinder Motors:

 

[imjustauser]

Thats a great explanation thank you and makes me wonder if its also bad to rev an engine with the clutch in. You seem like a very well versed individual. As for the top engine cleaner, it is hard to come by in Canada with the only available potential alternative being the Upper Engine and Fuel Injector Cleaner (88861803). Would this be a viable alternative or a completely different product?

Also when the motor is starting I notice that the starter makes a bit of noise when interfacing with the flexplate. Could this mean a flexplate spacer is needed or is this normal conisidering theres no belt or bellhousing to mask some of the noise.

Many thanks.

 

[mrrsm]

Yes... Thanks... I'm still learning...and We have Many More Folks here at GMT Nation ...who are a Whole Lot Smarter... than me... :>)

The Short Answer is... No.

Fuel Injector Cleaners evaporate far too quickly. The Foaming Version of ACDelco TEC is Very *Sticky* and while it DOES present the User with a Serious Danger from exposure to VOCs (Volatile Organic Compounds) ...Electronic Fuel Injector Cleaner is even more so.

Again... The Short Answer is... No.

Please note that others may suggest using the Chrysler MOPAR Spray (White Can with a Blue Mopar Label) Version, ostensibly similar in its performance to ACDelco TEC. But Trust Me... I have tried BOTH types and the MOPAR Stuff is like a Moon-Cast Shadow in comparison to the Very Bright Sunshine of the ACDelco TEC Solvent... so don't even bother with it.

The distinction here is that ordinarily, unless heavily modified and lightened for either Top Fuel or Pro Stock applications... Fly-Wheels with Friction Clutch set ups...are VERY HEAVY STEEL OR CAST IRON objects that will help to prevent the terrible shock of raising the RPM to a Near RED-LINE and then "Dropping The Clutch" and surprising the Gear Box with a sudden Surge of Power.

If you are familiar with the Clutch Plate Platter designs...they are NOT "Solid State" in between the Platters and their Internal Spline Centers...but rather have a series of Tightly Coiled Springs inserted to allow a little more "Give" once the Clutch Pedal is released and the two surfaces begin "Kissing" each other.

The Key Point here is the word MASSIVE...

If you are familiar with Gyroscope Designs... the Basic Principle behind their amazing stability is this:

"The More Concentrated and the Further away the MAIN MASS is from the Center of its Axis of Rotation at its Outer Orbit ...and the Faster it Spins... The MORE Stable the Gyroscope will be."

 

[mrrsm]

The only Rigid Portion of a "Flex-Plate" is found in the "Outer Fire Ring" as an attachment made as a Steel Hoop that has had its 'Starter Teeth' Hobbed Out and then Heat Treated before it gets welded to the Mild Steel Inner Platter.

The reason the Flex-Plate *wobbles around* so is because the Engineers intended that the Engine only be started AFTER the Massive, Sturdy Torque Converter is bolted up to it at a Separation Angle of 120 Degrees in between All Three of the 10.9 Hard, 15mm Bolts attached at those Three Thick Buss Pads. Doing so imparts additional strength and rigidity to the outer "Flexible Flex Plate" Ring Gear. :>)

 

[Aroc]

Update: Switched out the old flexplate for a new one and still has a similar noise. Perhaps it is the beginning of rod knock? Would love to find out before dropping some $$$ on another trans for it. Hopefully it is another issue but im running out of ideas. Ill try out that rod knock test.

A little history on solving the rattling noise on my Envoy.

It has been there since mid 2021 but barely noticable until i went back to old video when I had to replace a busted radiator.
The noise got progressively worse until i decided to address it by changing the flexplate bolts to ARP hoping to quiiet the issue, Did not help.
I then changed out the torque conveter since my truck transmission was slipping when transferring power in lower gears and hoped it would fix both issues. Torque conveter fixed the power transfer issue but on a long trip the flexplate rattle noise got so loud i had to go back in to replace it. I think the new torque converter accelerated the flexplate rattle.

If you have decent power through the transmission i would put it back together as is and check for other source of noises. BTW, how did the old flexplate look (any wear in the bolt holes?).

Hope this helps.

 

[imjustauser]

A little history on solving the rattling noise on my Envoy.

It has been there since mid 2021 but barely noticable until i went back to old video when I had to replace a busted radiator.
The noise got progressively worse until i decided to address it by changing the flexplate bolts to ARP hoping to quiiet the issue, Did not help.
I then changed out the torque conveter since my truck transmission was slipping when transferring power in lower gears and hoped it would fix both issues. Torque conveter fixed the power transfer issue but on a long trip the flexplate rattle noise got so loud i had to go back in to replace it. I think the new torque converter accelerated the flexplate rattle.

If you have decent power through the transmission i would put it back together as is and check for other source of noises. BTW, how did the old flexplate look (any wear in the bolt holes?).

Hope this helps.

Flexplated looked fine to me, no apparent cracks or ovalized holes. Im reusing the bolts though, (put blue wax loctite on them then torqued to 18ftlbs + 50 degrees).

 

[Aroc]

Well at least you elminated the flexplate as the issue,

BTW i replaced the 3 bolts (10.9 hardness) at the mounting pads to torque converter. Used blue permatex and torque to 45ft-lbs for those.