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Discussion Starter · #1 · (Edited)
Does anyone have a suggestion about what this engine noise might be? I replaced the rattling flexplate with an updated one and the noise is still present. It sounds loudest through the transmission inspection port. The video is of the engine running with the transmission out of the car and the old (bad) flexplate in place. After replacing the flexplate (the new one doesn't wobble), I ran the car, also with the transmission out, including a complete warm-up and it did NOT make a knocking noise. After putting the transmission back in the car, the knocking noise returned again!

It doesn't sound consistent enough to me to be a rod knock, but it does sound similar to other rod knocks I've heard from 3.6L engines. The owner reported that he was revving the #$*&^ out of the car in gear shortly after starting it and that it was definitely not warmed up when the engine started making this sound all-of-a-sudden. He suspected an engine knock and parked the car immediately.

I plan to disconnect the torque converter and start it up again to see if it still makes noise when the TC is disconnected but the trans in the car. I am pretty sure it will, but is there another possible explanation? Thx
 

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...The owner reported that he was revving the #$*&^ out of the car in gear shortly after starting it and that it was definitely not warmed up when the engine started making this sound all-of-a-sudden. He suspected an engine knock and parked the car immediately...
Why doubt the above, as high revs on a cold motor is a sure way to increase the risk of bearing damage.

You dropped the the tranny and replaced the flywheel, meanwhile, the oil pan is close enough to slap you in the face and would have been a quick removal for bearing inspection with the transmission out, that would have cleared the source +/- up for you for sure.

It's not unusual for the knocking sound to all but disappear with the tranny removed, because now there's no load on the motor.

You've eliminated the flywheel as a source of the noise leaving two possibilities I can think of; crank/rod bearings, or the the crank thrust bearing (walking crank slamming against the thrust surface. Really tight belts would cause it on older chevy motors). You can get away with a thrust bearing clearance problem a lot longer than you can a crank/rod bearing problem.

What does the oil and pressure look like? Pull the filter and take a look.
 

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Discussion Starter · #4 ·
Why doubt the above, as high revs on a cold motor is a sure way to increase the risk of bearing damage.

You dropped the tranny and replaced the flywheel, meanwhile, the oil pan is close enough to slap you in the face and would have been a quick removal for bearing inspection with the transmission out, that would have cleared the source +/- up for you for sure.

It's not unusual for the knocking sound to all but disappear with the tranny removed, because now there's no load on the motor.

You've eliminated the flywheel as a source of the noise leaving two possibilities I can think of; crank/rod bearings, or the crank thrust bearing (walking crank slamming against the thrust surface. Really tight belts would cause it on older chevy motors). You can get away with a thrust bearing clearance problem a lot longer than you can a crank/rod bearing problem.

What does the oil and pressure look like? Pull the filter and take a look.
Thanks for the note back. Believe me, I thought about taking the oil pan off, but (a) it didn't look like that was going to be enough room to drop it with the cradle in place, (b) the noise was most audible (with a stethoscope) from the flexplate, (c) the visible wobble in the flexplate perimeter gear suggested that it wasn't right, (d) the flexplate rattled after I got it off, and (e) the noise was gone after I replaced the flexplate and ran the engine before putting the transmission back in. Also, hindsight is 20/20. I've dealt with motor rod knocks on way too many occasions and both rhythmically and consistantly, this one doesn't sound at all the same.

Oil pressure is really good - about 60 psi after startup. I haven't idled the engine for half an hour to get it fully up to temp, but it's steady in the 10-15 minute range.

I did wonder about the thrust bearing, but I've never personally seen or heard one worn out before. The engine has 80k on it, so I really don't expect a thrust bearing issue, but I agree that it's a possibility and maybe a better fit for the sound. I haven't checked the oil for sparkles as the owner said he just had the oil changed and if a bearing was failing, I'd have expected the shop to report on metal in the oil. Also of note: When I initially looked at the car, it was down about two quarts of oil from full (so maybe not the best shop for oil changes). Obviously, adding oil did not remedy the knock, but, assuming it is a rod knock, I have to wonder if that contributed to the knock.

I'll drop the oil and search for the sparkles.
 

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I haven't checked the oil for sparkles as the owner said he just had the oil changed and if a bearing was failing, I'd have expected the shop to report on metal in the oil. Also of note: When I initially looked at the car, it was down about two quarts of oil from full (so maybe not the best shop for oil changes).
I'd be curious about the conversation surrounding the oil change, if it was performed following the incident. Usually the oil is drained without much attention given to it, except someone looking for signs of a problem.

Two quarts low now, I wonder if it was low, or even lower before the abuse. High revs on a significantly low oil level could possibly have created a moment of cavitation long enough to damage a bearing from a low pan level.

The circumstances under which the knock occurred sure fits the sequence of events that can lead up to bearing damage. I've damaged main bearings in a GM 60 deg V6 before during a severe overheat, without damaging the rod bearings and noted that the main knock was higher in frequency (sounding with each ignition pulse), and lower in intensity than a rod knock. The recording sounds like a rod knock.
 

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Discussion Starter · #6 ·
I'd be curious about the conversation surrounding the oil change, if it was performed following the incident. Usually the oil is drained without much attention given to it, except someone looking for signs of a problem.

Two quarts low now, I wonder if it was low, or even lower before the abuse. High revs on a significantly low oil level could possibly have created a moment of cavitation long enough to damage a bearing from a low pan level.

The circumstances under which the knock occurred sure fits the sequence of events that can lead up to bearing damage. I've damaged main bearings in a GM 60 deg V6 before during a severe overheat, without damaging the rod bearings and noted that the main knock was higher in frequency (sounding with each ignition pulse), and lower in intensity than a rod knock. The recording sounds like a rod knock.
I have swapped out WAY too my 4.3L V6 engines with rod knocks!!! It's what they do. In fact, I've got a 4.3L right now that needs a replacement for exactly this reason. I tried just replacing the #1 bearing trick but that didn't work. I think that the previous owner ran it with the knock and ovaled out the rod. :-(

Anyway, back to the 3.6L: The oil change was done before the abuse. The abuser recognized he'd messed up and immediately parked the car.

Thanks for the opinion on sound aligning with a rod knock. Sadly I think I'm with you at this point. With this engine, is this fatal? Or are there any "cheap/easy" remedies that I don't know about. My thought on a normal fix is either swap the engine for a known-good, or overhaul the bottom end on this one. If it's a rod knock, I'd say, from the sound, that there are at least two and probably three bad/spun rod bearings. The owner (and really I'm not talking about myself in the third person here) can't afford much and he's been told he only has a few more months to live. I'm trying to help the guy out, but I think he might've buried himself on this one.
 

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I have swapped out WAY too my 4.3L V6 engines with rod knocks!!! It's what they do. In fact, I've got a 4.3L right now that needs a replacement for exactly this reason. I tried just replacing the #1 bearing trick but that didn't work. I think that the previous owner ran it with the knock and ovaled out the rod. :-(

Anyway, back to the 3.6L: The oil change was done before the abuse. The abuser recognized he'd messed up and immediately parked the car.

Thanks for the opinion on sound aligning with a rod knock. Sadly I think I'm with you at this point. With this engine, is this fatal? Or are there any "cheap/easy" remedies that I don't know about. My thought on a normal fix is either swap the engine for a known-good, or overhaul the bottom end on this one. If it's a rod knock, I'd say, from the sound, that there are at least two and probably three bad/spun rod bearings. The owner (and really I'm not talking about myself in the third person here) can't afford much and he's been told he only has a few more months to live. I'm trying to help the guy out, but I think he might've buried himself on this one.
That's a pretty horrible diagnosis (health) and one hell of a constitution. I can't imagine showing any concern whatsoever for a knocking motor in my car, knowing my life was about to end in months.

If there's considerable bearing damage, checkout car-part.com for a suitable replacement, unless the finding on inspection is remarkably promising for a bearing patch. If there's metal throughout the motor, the 3.6L just doesn't fare well with so many moving parts to hold contaminants. Usually when someone says the oil level ran low enough to cause an engine to malfunction leading to discovery of the condition, it's not long before things start going down hill. Due to the prognosis, perhaps an effort to patch it is in place if at all possible.

This motor is far from a cam in block V6 as far as rebuilding goes, it's pretty expensive by comparison to rebuild.
 

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Discussion Starter · #8 ·
If there's considerable bearing damage, checkout car-part.com for a suitable replacement, unless the finding on inspection is remarkably promising for a bearing patch. If there's metal throughout the motor, the 3.6L just doesn't fare well with so many moving parts to hold contaminants. Usually when someone says the oil level ran low enough to cause an engine to malfunction leading to discovery of the condition, it's not long before things start going down hill. Due to the prognosis, perhaps an effort to patch it is in place if at all possible.

This motor is far from a cam in block V6 as far as rebuilding goes, it's pretty expensive by comparison to rebuild.
Thanks for the assessment. I checked on car-part and there aren't any running 3.6L's in WA right now. One in Turner, OR, 4 hours away for $1.8k w. 110k on the clock. Looks like a GM reman is $3.9k. Someone's listing a whole car quasi-locally for $5500! Gaskets and bearings for an overhaul would run about $700 and machine shop work should be well under $400 on an 80k engine, but the labor to pull it, rework it and stick it back in makes a $2k used motor pretty attractive even if it'd cost $300 to fetch it.

I don't think the engine ran low on oil; I think they just didn't fill it with enough oil (i.e. properly). It was leaking a little oil out the lower left corner of the rear main, but otherwise the engine's quite dry underneath. Have you taken an oil pan off one of these in-situ? Do I need to drop the engine cradle or lift the engine up a bit with a cherry picker to get the oil pan off?

I've done DOHC rebuilds on Japanese and domestic engines. I wouldn't hesitate to do this one, but dude is on his veteran's fixed income and doesn't have the money for it. If it was the DI 3.6L, then I'd definitely think twice about diving into it. And I don't touch Diesels!
 

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Thanks for the assessment. I checked on car-part and there aren't any running 3.6L's in WA right now. One in Turner, OR, 4 hours away for $1.8k w. 110k on the clock. Looks like a GM reman is $3.9k. Someone's listing a whole car quasi-locally for $5500! Gaskets and bearings for an overhaul would run about $700 and machine shop work should be well under $400 on an 80k engine, but the labor to pull it, rework it and stick it back in makes a $2k used motor pretty attractive even if it'd cost $300 to fetch it.

I don't think the engine ran low on oil; I think they just didn't fill it with enough oil (i.e. properly). It was leaking a little oil out the lower left corner of the rear main, but otherwise the engine's quite dry underneath. Have you taken an oil pan off one of these in-situ? Do I need to drop the engine cradle or lift the engine up a bit with a cherry picker to get the oil pan off?

I've done DOHC rebuilds on Japanese and domestic engines. I wouldn't hesitate to do this one, but dude is on his veteran's fixed income and doesn't have the money for it. If it was the DI 3.6L, then I'd definitely think twice about diving into it. And I don't touch Diesels!
You should be able to drop the pan with everything in place for RWD. I recall a member doing this a few years back and do not recall mention of needing to raise the motor, in part due to the cradle design. Just be mindful of the cross bolts in the side of the block in the 6 bolt main caps. Some 3.6L motors use oil and it can be a little, or a lot.

The motor does not have to be from a CTS, all of the blocks should be interchangeable (the word is "are" over the net) for a given generation and year(s) with some boundary crossing, so you should be able to take a good front wheel drive motor and dress it with the appropriate parts from the bad RWD motor, including the harness from what some have apparently done. I know for example there are two additional bolts in the timing cover of the 2010 CTS DI motor vs. the previous, but that only amounts to a yr specific timing cover and the two additional bosses could be ignored for the use of the earlier cover that does not have them.

Try ebay with a zip code and miles adjustment for range. That is where I discovered some of the absolute best prices on LFX motors (2012 up), with low mileage motors as low as $400-500 dollars, there are $600-700 motors with free shipping, where if you can drive to the location, the shipping portion could be waived through use of best offer options. The LFX bottom half should also be an option to spread the resource range even further, although he would likely need to use 89 octane fuel at a minimum from the compression bump the domed pistons would provide, I would however, play it safe with an LY7 short block.

I'm not sure what it is about the individual exh port motors, LY7 and LLT (DI), but auto salvagers are very proud of them and ask the most for them, despite being worn out.
 

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Discussion Starter · #11 ·
Great info on all the swap possibilities. I've not worked on anything quite this new before. I take it that I can't do the old intake&accessories swap trick to run an LFX as an LY7 and leave the PCM alone, thinking it's still running the older LY7 motor.

I'll drop the oil and pull the oil pan over the weekend and check the rod bearings and crank rod journals. I'm going to be a bit annoyed with the guy in the mirror if it pulls down without moving the cradle. It's about $30 for a set of new bearings if the journals aren't smoked. I should be able to check the longitudinal play without even undoing the rod caps, but if I'm in that far, I'm going to pull them anyway.
 

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Great info on all the swap possibilities. I've not worked on anything quite this new before. I take it that I can't do the old intake&accessories swap trick to run an LFX as an LY7 and leave the PCM alone, thinking it's still running the older LY7 motor.

I'll drop the oil and pull the oil pan over the weekend and check the rod bearings and crank rod journals. I'm going to be a bit annoyed with the guy in the mirror if it pulls down without moving the cradle. It's about $30 for a set of new bearings if the journals aren't smoked. I should be able to check the longitudinal play without even undoing the rod caps, but if I'm in that far, I'm going to pull them anyway.
The later model GM cars starting with early 2000s on have become quite complicated and fastidious about control parameters and no, the complete motor swap across engine computer platforms would not work, given there are several additional functions that the direct injection PCM has over the port injected LY7.

That oil pan should come off without much trouble, I just recalled the oil pickup is attached to the pan and there's an O-ring seal in the pan rail, that seals it against the block so look into that and do not forget that detail. The baffle is also attached to the pan so there shouldn't be anything hanging below the bottom skirt of the block; main caps, oil pump etc... The timing cover and tranny bell housing might have a little compression bite on it.
 

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Discussion Starter · #13 ·
That oil pan should come off without much trouble, I just recalled the oil pickup is attached to the pan and there's an O-ring seal in the pan rail, that seals it against the block so look into that and do not forget that detail. The baffle is also attached to the pan so there shouldn't be anything hanging below the bottom skirt of the block; main caps, oil pump etc. The timing cover and tranny bell housing might have a little compression bite on it.
Thanks. I looked at it today. With the pickup attached to the pan, it should slide out pretty easily. I didn't notice the front cover bolts so I'm glad you mentioned them. I just replaced the rear main seal, so I'm going to have to redo that little bit of RTV when I put it back together as the bottom two bolts run through the pan. The rear main leak was through the vertical join between the block and the cover at the lower left. The seal itself was fine, as was the horizontal seal. Just not enough goop on the vertical when they put it together I guess.
 

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Discussion Starter · #14 ·
UPDATE:Oil that was supposed to have been changed "recently" was actually filthy and, upon further query, was changed 4000 miles ago. Two large sheared-off slivers of bearing-material in the oil pan. Lots of fine gray metal coating the bottom of the pan below the filthy oil.

#6 bearing spun and heavily eroded. Journal is smooth but marked. Rod cap is a little dark, but not blue. Rod is also marked but not scored.
#5 journal looks perfect but there is a small score on the bearing.

Repair plan: Repolish the #6 journal a bit. Replace all the rod bearings. Run the engine at idle for a couple of hours with a diesel oil, 20 ozs of seafoam and a new filter to try to clean out any remaining metal. Change the oil back to synthetic and add a new filter. I'd recommend changing the oil pump as well, but the owner can't afford it, so I'm limiting the amount my own money I'm throwing at it now. :-( Let no good deed go unpunished.
 

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Just an FYI, I had to change my oil at 298 miles and it was black as coal. That is nothing but the detergent working and doing its job. That being said, I'm certain that you already know this (I had to say it).
 
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UPDATE:Oil that was supposed to have been changed "recently" was actually filthy and, upon further query, was changed 4000 miles ago. Two large sheared-off slivers of bearing-material in the oil pan. Lots of fine gray metal coating the bottom of the pan below the filthy oil.

#6 bearing spun and heavily eroded. Journal is smooth but marked. Rod cap is a little dark, but not blue. Rod is also marked but not scored.
#5 journal looks perfect but there is a small score on the bearing.

Repair plan: Repolish the #6 journal a bit. Replace all the rod bearings. Run the engine at idle for a couple of hours with a diesel oil, 20 ozs of seafoam and a new filter to try to clean out any remaining metal. Change the oil back to synthetic and add a new filter. I'd recommend changing the oil pump as well, but the owner can't afford it, so I'm limiting the amount my own money I'm throwing at it now. :-( Let no good deed go unpunished.
I thought there was something wrong with the 2qts low after a fresh oil change story.
I believe your plan will work, except it's going back to the person that caused this problem to begin with. You will need to flush the cam actuator solenoids good because of the filtering screen they have, probably two or three times.

Don't touch that oil pump, they're flush mount fit, no seal and the concern is so high for proper installation that it is recommended that the original chain guide attached to it be left in place and the old guide shoe be removed only and replaced with the new. I have read at least one, maybe two stories of low oil pressure following oil pump replacement with timing chains. The crank has to be turned before it is torqued down to make sure it is centered and not binding on replacement.
 

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Discussion Starter · #17 ·
Don't touch that oil pump, they're flush mount fit, no seal and the concern is so high for proper installation that it is recommended that the original chain guide attached to it be left in place and the old guide shoe be removed only and replaced with the new. I have read at least one, maybe two stories of low oil pressure following oil pump replacement with timing chains. The crank has to be turned before it is torqued down to make sure it is centered and not binding on replacement.
I've built race motors for high-revving motorcycles with pretty tight tolerances, so I'm not really concerned about getting the oil pump just right. That said, I am good at heeding "if it's not broken, don't fix that bit" advice and the oil pressure at the sensor was really good. Although, apparently not good enough at bearing #6. If the parts come in, then I should have it back together tomorrow and we'll hear how messed up the connecting rod got. I'm hopeful that the bearings were soft enough that they took one for the team.
 

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I thought there was something wrong with the 2qts low after a fresh oil change story.
I believe your plan will work, except it's going back to the person that caused this problem to begin with. You will need to flush the cam actuator solenoids good because of the filtering screen they have, probably two or three times.

Don't touch that oil pump, they're flush mount fit, no seal and the concern is so high for proper installation that it is recommended that the original chain guide attached to it be left in place and the old guide shoe be removed only and replaced with the new. I have read at least one, maybe two stories of low oil pressure following oil pump replacement with timing chains. The crank has to be turned before it is torqued down to make sure it is centered and not binding on replacement.
I have sort of an unrelated question, but it was triggered by your next-to-last sentence. As I've discussed elsewhere, we had the timing chains changed in my wife's LY7, and the thing threw a rod a day later. The dealer says it was unrelated and it's the oil pump. Is it possible it's the oil pump and it IS related?
 

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Discussion Starter · #19 ·
Update: I replaced the #2 to #6 rod bearings this afternoon. #1 bearing looked perfect so I left it. Crank rod journals for #1 to #5 were perfect, so I left them alone. I ran some 600 paper over the #6 rod journal that looked a bit rough, and then did some polishing with some polishing paste. It was smooth to touch and under a nail before I started and slightly more even-looking when I was done. The bearings went in perfectly and the rod knock is eliminated. There were a few metal shards in the oil pickup tube as well as a bonus piece from the end of one of the cam chain tensioners. I also found a scrap of metal on the #2 bearing journal. I wasn't sure if that had been picked up in the oil or run through the oil pump. I took the piece of the tensioner as a sign that the cam chains should be replaced before they deposit more bits to block up the oil pickup. Oil pressure after coming up to temperature was about 25 psi and the engine ran quite smoothly.

To get to one of the forward bolts on the left side of the oil pan, I chose to undo the steering rack. To move it forward, I had to remove the steering intermediate shaft. That was less than exciting because it's supposed to slide and wouldn't budge! After some investigating, I discovered that this is a common CTS problem. I filed down the inside of the female and the outside of the male shaft until they'd slide against one another, added grease, and put them back into play.

I managed to convince the owner to spend on the cam chains and tensioners, so that job is next.
 

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Nice job. You've done a very good deed for the owner.
 
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