That knock was a main engine bearing

TonyT

Original poster
Member
May 6, 2012
108
In a previous posting I asked what a particular knock might be.

Mechanic just phoned and said it was a main engine bearing knock. Furthermore it was down four litres of oil. I *KNOW* I checked the oil the day before my 5 hour return trip when the engine was cold. The four circles in the red part of the dipstick all had oil in them. Yes, it was 4% away from needing the oil changed and it hadn't consumed any oil but I figure that was no big deal.

Furthermore at no time in my trip did any kind of engine oil low pressure light or warning go on. (Just the P0014 which is a different problem.) I know from reading postings here that the oil gauge is just a fake and there's just a switch.

This really irritates the heck out of me. Given that a replacement engine is going to be $2500 or so installed. Did I not read the dipstick properly? Did the oil suddenly leak out somewhere? Why didn't the oil pressure sensor tell me there was a problem?

So basically I don't trust the engine. I might spend the money on a replacement engine but I'm going to get rid of that vehicle soon. If I have a choice I will never, ever buy a vehicle that has just an oil pressure switch. But maybe they all do.

As you can tell from my posting I'm rather irritated!
 

gmcman

Member
Dec 12, 2011
4,656
TonyT said:
In a previous posting I asked what a particular knock might be.

Mechanic just phoned and said it was a main engine bearing knock. Furthermore it was down four litres of oil. I *KNOW* I checked the oil the day before my 5 hour return trip when the engine was cold. The four circles in the red part of the dipstick all had oil in them. Yes, it was 4% away from needing the oil changed and it hadn't consumed any oil but I figure that was no big deal.

Furthermore at no time in my trip did any kind of engine oil low pressure light or warning go on. (Just the P0014 which is a different problem.) I know from reading postings here that the oil gauge is just a fake and there's just a switch.

This really irritates the heck out of me. Given that a replacement engine is going to be $2500 or so installed. Did I not read the dipstick properly? Did the oil suddenly leak out somewhere? Why didn't the oil pressure sensor tell me there was a problem?

So basically I don't trust the engine. I might spend the money on a replacement engine but I'm going to get rid of that vehicle soon. If I have a choice I will never, ever buy a vehicle that has just an oil pressure switch. But maybe they all do.

As you can tell from my posting I'm rather irritated!
That sucks man....I feel for ya.

Just out of curiosity....how did he come to the conclusion it was a main bearing? I'm not saying he's wrong, I'm just questioning it if he didn't pull the oil pan. I honestly never heard a main go knock, knock, knock but I haven't heard this motor with a bad main either, usually it's a rod bearing and you can replace them yourself if they are bad....and the crank journal is ok, without removing the crank. I doubt this motor is any different but there is a webbing of a brace under the pan so it could be a hindrance.

As far as the dipstick is concerned, did you check both sides? There has been a couple times when the markings were covered and there was a straight cutoff line on the back side, about 1 qt down. I noticed this a few times when changing but doesn't happen often.

You may have been low on oil but still registering pressure, takes a dismal amount to trip the light, on older vehicles it was around 11 pounds but not sure what ours is. At that pressure it's already bad news.
 

triz

Member
Apr 22, 2013
746
I'm really surprised at that. These 4.2 I-6 are pretty bulletproof. The only way to lose that much oil is if you were burning it if you were not leaking it. You can check that by pulling the exhaust manifold off and checking with your finger in there. If its oily it might have been burning before it got to the cat, so you wouldn't see any white smoke.

I'm in shock. I've never heard that happen in these motors.
 

TonyT

Original poster
Member
May 6, 2012
108
No idea as to how the mechanic determined it was a bearing knock. A friend who I trust completely has lived in this town for 30 years and who worked for an auto dealer in town as the parts manager for about a number of years and is a very good back yard mechanic, and who knows a lot more people in town than I do. He tells me that outfit is a very good outfit and he sends everyone he knows over there. When I was listening to it myself it sounded like it came from about the center of the engine and not near the front like a timing chain or a water pump.

gmcman said:
As far as the dipstick is concerned, did you check both sides? There has been a couple times when the markings were covered and there was a straight cutoff line on the back side, about 1 qt down. I noticed this a few times when changing but doesn't happen often.
No I never checked the back side. When the engine is cold, in the morning, I pull the dipstick and look for oil in those four cavities on the red part of the dipstick. There has indeed been some oil in those cavities all this time. I am, of course, used to the straight metal type of dip sticks. Whee in the morning it's extremely obvious where the oil level is at. I never check the oil when it's hot unless it's after a lunch break on a 8 or 12 hour trip and the oil has time to drip down.

Maybe I should've checked the back instead so I could see a clear line. And maybe the oil stays in those indents when it's cold. So maybe I've been checking it wrong all this time. Maybe I should've pulled the dipstick when it was cold, wiped the dipstick clean, and put it back in and pulled it out again. Maybe it's been getting lower and lower all this time and I just assumed because there was some oil in the indents that all was well.
 

TonyT

Original poster
Member
May 6, 2012
108
triz said:
I'm really surprised at that. These 4.2 I-6 are pretty bulletproof. The only way to lose that much oil is if you were burning it if you were not leaking it. You can check that by pulling the exhaust manifold off and checking with your finger in there. If its oily it might have been burning before it got to the cat, so you wouldn't see any white smoke.
There certainly hasn't been much of a leak in the driveway but it's gravel. I'd think I'd notice that much of a leak but who knows. I'm not a mechanic so I'm not pulling off the exhaust manifold.

On the used replacement motor though I will get them to check the exhaust manifold for cracks and to check the bolts torque before replacing. As well as changing the spark plugs.
 

CaptainXL

Member
Dec 4, 2011
2,445
Yep whenever you pull the dipstick one side will usually be lower than the other. Go with the lower level side.

To the OP. It doesn't matter what kind of friend I have or weather I should take their word for it... Always have more than one quote for such expensive work. If you do decide to end up having them disect that engine without proof and they find nothing wrong then you are not liable. Dont sign anything stating they are without fault. Otherwise you will have no recourse. You should get physical proof.
 

gmcman

Member
Dec 12, 2011
4,656
TonyT said:
No idea as to how the mechanic determined it was a bearing knock. A friend who I trust completely has lived in this town for 30 years and who worked for an auto dealer in town as the parts manager for about a number of years and is a very good back yard mechanic, and who knows a lot more people in town than I do. He tells me that outfit is a very good outfit and he sends everyone he knows over there. When I was listening to it myself it sounded like it came from about the center of the engine and not near the front like a timing chain or a water pump.

OK, I remember this thread. Two things....did you ever remove the serpentine belt and run the motor to see if the noise went away????? Reason I asked this before is a bad water pump sounds EXACTLY like a rod bearing, this is the only motor I have heard make this type of water pump noise.

Second......you stated the main bearing was the culprit then just a bearing..did he say bearing, engine bearing, or main bearing? Big difference in a rod bearing than a main bearing. You could probably remove a main bearing and it still won't knock...but of course you would lose all your oil pressure so that's a moot point.

If it were me I would absolutely get a second opinion. At the very least pull the belt and try to rock the water pump pulley back and forth. I just went through this and mine was starting to get loose, no leaks, and now it's noticeably quieter.
 

TonyT

Original poster
Member
May 6, 2012
108
CaptainXL said:
Yep whenever you pull the dipstick one side will usually be lower than the other. Go with the lower level side.

To the OP. It doesn't matter what kind of friend I have or weather I should take their word for it... Always have more than one quote for such expensive work. If you do decide to end up having them disect that engine without proof and they find nothing wrong then you are not liable. Dont sign anything stating they are without fault. Otherwise you will have no recourse. You should get physical proof.
Does everyone have the dipstick with the red/pink thickened end on it? With the four indentions in the red/pink material? I've never seen that before. I'm very much used to the straight flat metal type.

Yeah, I'm going to talk to another mechanic I know who works for the GM dealer in town. Note that this is a small town. There is only one each of Ford, GM and Dodge dealerships. So when I say my friend knows the mechanics pretty goodl, well he does. He partied with them all when he was of legal drinking age and for years thereafter. :smile:
 

TonyT

Original poster
Member
May 6, 2012
108
gmcman said:
OK, I remember this thread. Two things....did you ever remove the serpentine belt and run the motor to see if the noise went away????? Reason I asked this before is a bad water pump sounds EXACTLY like a rod bearing, this is the only motor I have heard make this type of water pump noise.

Second......you stated the main bearing was the culprit then just a bearing..did he say bearing, engine bearing, or main bearing? Big difference in a rod bearing than a main bearing. You could probably remove a main bearing and it still won't knock...but of course you would lose all your oil pressure so that's a moot point.

If it were me I would absolutely get a second opinion. At the very least pull the belt and try to rock the water pump pulley back and forth. I just went through this and mine was starting to get loose, no leaks, and now it's noticeably quieter.

You could also just click on my user name on the left hand side and view my previous postings. No, I never did pull the serpentine belt. I'm no mechanic and don't have a clue how to do it or to put it back together again. I can't recall the mechanic/service writers exact words. And yes I will get a second opinion. Appointments take two weeks to get anything done so I have lots of time to track another guy down.
 

gmcman

Member
Dec 12, 2011
4,656
The belt is quick and easy, all you need is a long 3/8 ratchet or better yet, a breaker bar. There is a square 3/8 opening in the front of the tensioner, When I use a ratchet I have the handle facing at about the 1 O'clock position then rotate clockwise. Push the handle over until you can pull the belt off the alternator pulley then slowly let the ratchet come back to the left under spring tension. Be careful of the cam position sensor on the front of the valve cover.

There is a belt diagram on the air filter cover for reinstalling.

May not be the pump but it sure does make a knock when the bearings go.
 

silverunicorn

Member
Dec 4, 2011
327
triz said:
I'm really surprised at that. These 4.2 I-6 are pretty bulletproof. The only way to lose that much oil is if you were burning it if you were not leaking it. You can check that by pulling the exhaust manifold off and checking with your finger in there. If its oily it might have been burning before it got to the cat, so you wouldn't see any white smoke.

I'm in shock. I've never heard that happen in these motors.

I had the same thing happen. No lights or warnings.

Twice.

True story. No warning, had checked the oil about a week before it happened. no leaks, no visible burning of oil when driving.

I am not buying the BS that these are bulletproof, LOL.

On the rebuild of the replacement motor now, and hopefully that will last me as long as I have the truck.

Chris
 

TonyT

Original poster
Member
May 6, 2012
108
I've only driven the vehicle around town a few times since. The engine oil light now stays on after engine startup for about 8 to 10 seconds. It sure wasn't doing that before.
 

gmcman

Member
Dec 12, 2011
4,656
If the bearings are going, then you will begin to lose oil pressure. The oil pump only moves tje oil, it doesnt make pressure, tight bearing clearances make the pressure. You could have a partially clogged pick up screen also. Either way sounds like the oil pan needs to come off. This may encompass a complete rebuild or just new bearings. If its just the bearings then prolonged driving will ruin the crank.
 

TonyT

Original poster
Member
May 6, 2012
108
The mechanic shop is going to put in a used engine. I don't know of any place that does engine rebuilds. I rather doubt it would last the 120 miles to the nearest city where there might be some places. And I have no idea if any of those places are trust worthy.

Phoned one place in the city and he said he'd have to do some research but probably in the $5400-$6000 range.
 

CaptainXL

Member
Dec 4, 2011
2,445
TonyT said:

Well in the service manual or TSB (can't rightly remember) there is a troubleshooting step for when you have low oil pressure and or engine noise. One of the steps is to make sure the correct oil filter is used.

So really? Have you been presented with any other options besides replacing the engine? Gotten multiple quotes from GM certified mechanics? This could get unnecessarily expensive in a hurry.

Taking someone's word is one thing if you trust them however I would NOT if NO evidence of engine failure has been given to you. That would be insane.
 

gmcman

Member
Dec 12, 2011
4,656
Based on the sound of the knock, I'm still saying it's a rod and not a main bearing. I will try to explain it so you have a better understanding to what's going on.

When the oil is picked up, it is then pushed through the inside of the crank then onto the top of the motor. First it travels through the length of the crank and the bearings have a miniscule clearance around 15-20 ten-thousandths of an inch, that's .0015" and that's not exact but fairly close...didn't look up our motors specs.

Take a garden hose and turn it on, water just runs out. Now take your finger and try to plug the opening....what happens? The water sprays out under pressure. In your case, you likely have a leak somewhere and that's one of the bearings, allowing the oil to flow out and not build pressure.

This could have been caused by a few things but fact remains you have a knock. I can't imagine one main being worn causing that knock, main knocks are generally very deep sounding and takes more than one being worn especially on an inline 6 to make noise.

Here's a few diagrams, and you can see the crank is supported by 7 main bearings, if one is worn, the others next to it will support the crank but would lose pressure. The rods on the other hand have bearings also and if one is shot then you will hear it on every other rotation and at idle that's roughly 5 times per second, about what you are hearing.

If you are going to change the motor then the rest is moot, but just trying to help you explain. I would perform a compression test, dry and wet, and if everything checks out, the piston rings and cylinders are likely fine then it's onto the oil pan. If you end up just pulling the pan...major job BTW, then you may just need to change the bearings and worst case replace the crank. If you need to pull the crank then the front timing cover should come off also to replace the oil pump.

Sounds like a ton of work but likely far cheaper then an entire engine. I would suspect as long as you have been driving it you have likely beat a crank journal out of round and it may need a crank.

Pricewise a used motor is probably the cheapest, then onto changing the mains and rod bearings on your existing motor. Then most expensive naturally is a reman or new motor.

Based on the sound you may have or will shortly have a spun bearing, which is when one of the bearing halves rotates around to the other side and creates a monster gap, destroying that crank journal. Hoping for the best.
 

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gmcman

Member
Dec 12, 2011
4,656
CaptainXL said:
Well in the service manual or TSB (can't rightly remember) there is a troubleshooting step for when you have low oil pressure and or engine noise. One of the steps is to make sure the correct oil filter is used.

So really? Have you been presented with any other options besides replacing the engine? Gotten multiple quotes from GM certified mechanics? This could get unnecessarily expensive in a hurry.

Taking someone's word is one thing if you trust them however I would NOT if NO evidence of engine failure has been given to you. That would be insane.

I agree...a simple oil change may prove wonders, it's by far the cheapest. Using the factory filter just removes something out of place from the equation.
 

TonyT

Original poster
Member
May 6, 2012
108
CaptainXL said:
Well in the service manual or TSB (can't rightly remember) there is a troubleshooting step for when you have low oil pressure and or engine noise. One of the steps is to make sure the correct oil filter is used.

So really? Have you been presented with any other options besides replacing the engine? Gotten multiple quotes from GM certified mechanics? This could get unnecessarily expensive in a hurry.

Taking someone's word is one thing if you trust them however I would NOT if NO evidence of engine failure has been given to you. That would be insane.

The oil filter has been in for almost 15K kms. It was 4% away from needing an oil change. Don't forget that when I took it to the mechanic it was low 4 litres of oil.

Trouble is my appt to change the motor is on Thursday and it takes about two weeks to make another appointment as the mechanics are backed up that long. I could've easily taken it into the stealership for them to listen to a week or so ago but it's getting pretty late now for that to happen. That said I'll stop in there tomorrow and see if I can have them take a listen.

A good friend who is a mechanic and a car nut, and has lived here in town for 30 years and knows everyone, tells me that these are good people and many of the mechanics are from the GM dealer in town. Some of them retired, got bored and went back to work.
 

CaptainXL

Member
Dec 4, 2011
2,445
TonyT said:
A good friend who is a mechanic and a car nut, and has lived here in town for 30 years and knows everyone, tells me that these are good people and many of the mechanics are from the GM dealer in town. Some of them retired, got bored and went back to work.

Ok, I just hope these "retired" folk didn't retire before our model truck entered service. This Atlas engine isn't your father's engine. If ya know what I mean. lol.

Regardless of anyone's opinion, I would hope you understand the importance of seeing the damage first though. As proof...before any further work is done. Seeing how the engine might need work anyway and needs to come out then I hope they will take off the oil pan and check for damage first. Get something in writing if you can.

Also, a spun bearing would not cause a loss of oil like that. Did you ever find out what caused it? Was it something that crept up on you or did the majority of the oil disappear within a relatively short timespan? Is the oil filter and oil drain plug secure? When and where was the last oil change done?

Setting aside all of the above for a moment....what you really need to do first before spending a lot of money is remove the serpentine belt and hear with your own ears if the noise is gone. Don't care how you do it, get it towed, etc , etc (shouldn't be driving an over heating car anyway) just do it.

So I will say this again with emphasis...

A bad water pump will sound like a bad bearing! No joke.

If I am right then you will be thanking all of us. I am still fairly confident it's just the water pump. Back in your older thread you did mention that the coolant got up to 230 degrees. That's over spec and suspicious. Not indicative of a bearing failure at all. Are there any metal flakes in the oil?
 

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