GM ENGINES KNOCK
- Thread starter Terry
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Terry, which GM engines are you referring to with "knock"? Nearly all GM Duramax engines have a "snapping" type sound, almost like a tappet or belt...
What specific knock, what engine models?
What specific knock, what engine models?
Not related to lower end knock of the LS1 but some reasons for oil burning and piston slap
The LS1 uses a 3.66620 stroke and a 3.8796 bore with a 6.100 rod that makes for a very aceptable 1.6841 rod ratio. But it came at a cost. They stacked the piston rings and reduced the tension of the rings over a LT1 by 30 percent. Why the reduction in ring tension? I am clueless.Did they not test these motors prior to putting them in between the fenders of a car?Certainly they did but supect it was a money/time issue. Just my opinion.
When they moved that ring set up 1.5 mm they knew they were going to have some piston rock with the use of the slipper skirt style piston generally known for poor oil control.The piston weighs 434 grams which is pretty light for a street motor,it came at a cost though.
They have also used a thinner ring set than the normal 5/64 used on the small Chevy and others. I cannot find out the actual width of the ring but think it to be probably a 1/16 top and second ring which is usually reserved for race motors. That there and the combinations of the 30 percent less spring tension plus a little piston rock is going to burn some oil.I have found the static compression of these engines but do not know the nominal compression which might help in knowing why they reduced the ring tension
The piston speed is not a factor on the LS1 motor. At 6000 RPM it is moving a mere 3662 feet per second.
The fix? Spread the rings back to normal and use the KB method of running the oil control ring through the piston pin hole with a pin in the piston to stop rotation plus a different skirt for less rock, clearanced for the rod and to get the ring tension back up to the norm and a more streetable width for oil control.A 5/64 ring with proper tension will not flutter at 6500 rpm if all else is correct.
Other ways to fix would to be to use a shorter rod and custom piston except that would decrease the dwell time at or near TDC and effect computer/injector timing
bandaid? 10/30 dino oil or 30wt is climatically possible because running a slick oil w/o much ring tension and or nominal compression will let oil get by into the combustion chamber
It is not exactly a "shaker motor". The rod ratio proves that but if rounded off a bit it is 3.700 stroke-3.900 bore which is getting close to being a square 345.69 ci motor as opposed to the 350 Chevy which is 3.480 stroke-4.00 bore and used a 5.700 long rod which is a stroked 327 motor.
They were reying on relative good cylinder head flow to off set this and gearing to offset the affects of that long rod and the power band a rod of that length in a motor of this size is usually operated in. In my opinion they would have been much better off to use a 5.700 Powdered Metal rod and a bit larger bore with a better piston design.
I understand GM has offered a "fix" for this in a new piston and or ring set. Can someone tell me what this consists of? Hopefully it did not include the new style tapered face ring?
These are just some thoughts I have without digging into it all too much as I doubt I will ever own one of these motors so no more digging for info and of course,opinions will as usual, vary
Is this a terrible engine? I don't think so but in my opinion they could have bettered it.
Lower end knock and high copper content of the oil? Spells quality control to me"imo" as some engines do not have this problem,I would like to see one of these checked for balance and the align bore of the block. It might lay in the type bearing used as well or a bit of both,betting someone will get inside one of the engines and figure it all out soon.A job not so easily done on those cars I hear to pull a motor that is
[ August 25, 2002, 09:55 AM: Message edited by: dragboat ]
The LS1 uses a 3.66620 stroke and a 3.8796 bore with a 6.100 rod that makes for a very aceptable 1.6841 rod ratio. But it came at a cost. They stacked the piston rings and reduced the tension of the rings over a LT1 by 30 percent. Why the reduction in ring tension? I am clueless.Did they not test these motors prior to putting them in between the fenders of a car?Certainly they did but supect it was a money/time issue. Just my opinion.
When they moved that ring set up 1.5 mm they knew they were going to have some piston rock with the use of the slipper skirt style piston generally known for poor oil control.The piston weighs 434 grams which is pretty light for a street motor,it came at a cost though.
They have also used a thinner ring set than the normal 5/64 used on the small Chevy and others. I cannot find out the actual width of the ring but think it to be probably a 1/16 top and second ring which is usually reserved for race motors. That there and the combinations of the 30 percent less spring tension plus a little piston rock is going to burn some oil.I have found the static compression of these engines but do not know the nominal compression which might help in knowing why they reduced the ring tension
The piston speed is not a factor on the LS1 motor. At 6000 RPM it is moving a mere 3662 feet per second.
The fix? Spread the rings back to normal and use the KB method of running the oil control ring through the piston pin hole with a pin in the piston to stop rotation plus a different skirt for less rock, clearanced for the rod and to get the ring tension back up to the norm and a more streetable width for oil control.A 5/64 ring with proper tension will not flutter at 6500 rpm if all else is correct.
Other ways to fix would to be to use a shorter rod and custom piston except that would decrease the dwell time at or near TDC and effect computer/injector timing
bandaid? 10/30 dino oil or 30wt is climatically possible because running a slick oil w/o much ring tension and or nominal compression will let oil get by into the combustion chamber
It is not exactly a "shaker motor". The rod ratio proves that but if rounded off a bit it is 3.700 stroke-3.900 bore which is getting close to being a square 345.69 ci motor as opposed to the 350 Chevy which is 3.480 stroke-4.00 bore and used a 5.700 long rod which is a stroked 327 motor.
They were reying on relative good cylinder head flow to off set this and gearing to offset the affects of that long rod and the power band a rod of that length in a motor of this size is usually operated in. In my opinion they would have been much better off to use a 5.700 Powdered Metal rod and a bit larger bore with a better piston design.
I understand GM has offered a "fix" for this in a new piston and or ring set. Can someone tell me what this consists of? Hopefully it did not include the new style tapered face ring?
These are just some thoughts I have without digging into it all too much as I doubt I will ever own one of these motors so no more digging for info and of course,opinions will as usual, vary
Is this a terrible engine? I don't think so but in my opinion they could have bettered it.
Lower end knock and high copper content of the oil? Spells quality control to me"imo" as some engines do not have this problem,I would like to see one of these checked for balance and the align bore of the block. It might lay in the type bearing used as well or a bit of both,betting someone will get inside one of the engines and figure it all out soon.A job not so easily done on those cars I hear to pull a motor that is
[ August 25, 2002, 09:55 AM: Message edited by: dragboat ]
My son's 01 GrandAM 3.4:
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=000016
What is the definition of LS1- a 350?? Does the GM 3.4 exhibit this problem. Copper was through the roof on my first analysis.
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=000016
What is the definition of LS1- a 350?? Does the GM 3.4 exhibit this problem. Copper was through the roof on my first analysis.
MolaKule
Staff member
Dragboat,
Lighter ring tension = lower frictional losses.
Higher ring position = better combustion.
Narrow ring width's = lower frictional losses.
BTW, You have a personal message.
Lighter ring tension = lower frictional losses.
Higher ring position = better combustion.
Narrow ring width's = lower frictional losses.
dragboat -
I have a 5.3 with lower end knock (audible if you stand by driver's side wheel well) for about 10-15 seconds upon start-up, hot or cold. Copper was 21 per Blackstone. It's strange that if you restart the engine within 2-3 minutes after turn-off, there is no knock.
In your opinion, what quality control issues may have contributed. Do you think I would be better running dino or synthetic with the lower end knock? Thanks!
[ August 25, 2002, 02:05 PM: Message edited by: robert ]
I have a 5.3 with lower end knock (audible if you stand by driver's side wheel well) for about 10-15 seconds upon start-up, hot or cold. Copper was 21 per Blackstone. It's strange that if you restart the engine within 2-3 minutes after turn-off, there is no knock.
In your opinion, what quality control issues may have contributed. Do you think I would be better running dino or synthetic with the lower end knock? Thanks!
[ August 25, 2002, 02:05 PM: Message edited by: robert ]
Patman
Staff member
It's funny you should mention this, because with the 94 Grand Am GT that I had (3100 engine) it had a cold start knock, but if I started the car and moved it from the road to my driveway for instance, but then let the car sit for even 5 or 6 hours later before restarting, it would not knock on that restart. Weird. I tried switching to Amsoil 10w30 and it didn't help, I even put in Duralube (yes, I didn't know better!) thinking it might help. The only thing that helped was trading that car in!
Patman
Staff member
Al, the LS1 is the 5.7 engine (346ci) that comes in the Camaro, Firebird and Corvette. The LS6 in the Z06 Vette is also pretty much the same engine internally, just with better heads and a bigger camshaft. They also have iron block versions of the LS1 which go into some of the larger GM trucks, but these engines are not designated as LS1s though.
dragboat, for the LS1 I understood the fix is both pistons and rings. The pistons have a shorter skirt and polymer coating to reduce cylinder chaffing.
Beyond slap, with higher-rpm driving the rings would float and oil consumption went through the roof. The new rings reduce this but I don't know their makeup. Believe the sequence and size changed which mandated new pistons anyway. Not sure how the shorter skirt helps other than reduced mass.
The larger problem with their v6's & truck motors (covered by GM TSB 01-06-01-005) probably has different fixes or just the warranty extension.
Seems like GM's having a tough time making it from the lab to production lately.
My knowledge of the situation is limited to what I've read in the news and on the net.
David
Beyond slap, with higher-rpm driving the rings would float and oil consumption went through the roof. The new rings reduce this but I don't know their makeup. Believe the sequence and size changed which mandated new pistons anyway. Not sure how the shorter skirt helps other than reduced mass.
The larger problem with their v6's & truck motors (covered by GM TSB 01-06-01-005) probably has different fixes or just the warranty extension.
Seems like GM's having a tough time making it from the lab to production lately.
My knowledge of the situation is limited to what I've read in the news and on the net.
David
The Verizon work truck I have is a 2001 3500HD with the 8.1 oil burner. It has finily slowed its taste for oil after 22k miles. It too has a cold piston slap noise. Our fleet has a 6000 mile OCI and I was topping off about 4 to 5 quarts in that OCI. We use the required 5W30 Valvoline.
We have a 98 Buick Century with the 3.1 at 135K miles that has bad cold piston slap. Its gotten worse when we started going to "Great America" (Shell) auto service. I might change my service provider. DaveJ
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=000671
99 Chevrolet Venture 3.4
Engine has always had a cold start knock which goes away after it is warm. Now at 77k.
Intake gaskets replaced at 58k and the engine has a warm idle or just above idle knock that can only be heard from inside van.
99 Chevrolet Venture 3.4
Engine has always had a cold start knock which goes away after it is warm. Now at 77k.
Intake gaskets replaced at 58k and the engine has a warm idle or just above idle knock that can only be heard from inside van.
They stacked the piston rings and reduced the tension of the rings over a LT1 by 30 percent. Why the reduction in ring tension? I am clueless.Did they not test these motors prior to putting them in between the fenders of a car?Certainly they did but supect it was a money/time issue. Just my opinion.
Just as Ford is going to SAE 20, GM has their engineering tricks. I read an article in which a GM engineer was bragging (and rightly so) about how their 3.8 V6 had the lowest frictional losses in the business. This directly translates into better MPG.
Another article discussing Corvette motors with oil consumption problem- engineer said they did not intend the ring setup to deal with owners keeping the tranny in a lower gear much of the time causing a hi-RPM, hi-manifold vaccum condition.
The fix is a new piston and ring combo for ONLY those who request it, as the orig setup is not seen as defective and operates OK for most owners - only designed for different operating conditions. This is one of the few times I agree with GM.
Exactly.quote:
Originally posted by MolaKule:
Dragboat,
Lighter ring tension = lower frictional losses.
Higher ring position = better combustion.
Narrow ring width's = lower frictional losses.
BTW, You have a personal message.
Just as Ford is going to SAE 20, GM has their engineering tricks. I read an article in which a GM engineer was bragging (and rightly so) about how their 3.8 V6 had the lowest frictional losses in the business. This directly translates into better MPG.
Another article discussing Corvette motors with oil consumption problem- engineer said they did not intend the ring setup to deal with owners keeping the tranny in a lower gear much of the time causing a hi-RPM, hi-manifold vaccum condition.
The fix is a new piston and ring combo for ONLY those who request it, as the orig setup is not seen as defective and operates OK for most owners - only designed for different operating conditions. This is one of the few times I agree with GM.
"Another article discussing Corvette motors with oil consumption problem- engineer said they did not intend the ring setup to deal with owners keeping the tranny in a lower gear much of the time causing a hi-RPM, hi-manifold vaccum condition."
Wouldn't hi-rpm running have low vacuum?
Idling has the highest vacuum...
Wouldn't hi-rpm running have low vacuum?
Idling has the highest vacuum...
Vacuum drops when engine is under load. At high rpm in lower gears, there is virtually no load, and the rpms stay close in relation to the throttle position.
If you go over to the gm-trucks.com form you can read all about the "knock" problem with the engines in the new trucks.
My 5.3 has it, not as bad as my friends 6.0 but it will knock on start up and go away in a minute.
I have had every UOA posted on here with both my truck and my wifes venture.
At least for now, knock on wood, both vehicles don't use any oil and the truck has 43k and the venture has 36k. That is no oil, not even up to 10k miles. That is about the time the oil filter is changed out for the extended drain.
It is amazing how loud that knock can be. My friends 6.0 is so loud you can hear it a few feet away from the truck.
There have been a few that said they got chevy to give them an extended warranty up to 100k on their engines because they have a knock. I didn't get one and will just wait it out and see.
My 5.3 has it, not as bad as my friends 6.0 but it will knock on start up and go away in a minute.
I have had every UOA posted on here with both my truck and my wifes venture.
At least for now, knock on wood, both vehicles don't use any oil and the truck has 43k and the venture has 36k. That is no oil, not even up to 10k miles. That is about the time the oil filter is changed out for the extended drain.
It is amazing how loud that knock can be. My friends 6.0 is so loud you can hear it a few feet away from the truck.
There have been a few that said they got chevy to give them an extended warranty up to 100k on their engines because they have a knock. I didn't get one and will just wait it out and see.
My 98 chevy with the 350 has had cold start knock. I really have not noticed it much since switching to Chevron Supreme but according to my dealer, this is common with this engine and its the old generation Vortec 350.
Wayne
Wayne
Nice post dragboat! I think you meant 3662 feet per minute though...
[ December 06, 2003, 01:13 PM: Message edited by: jsharp ]
(Gen II V8's)IF they would put some skirt on their pistons and lower the rings a lot of issues would solve them selfs. Adding about 30% more skirt area, incresing ring tension and lowering the rings would take care of most of this. I would also like to see either better material or improved coatings. The ring materail is very low quality. I have seen pistons with rings already rusting and they have not even been installed in the engine yet.
The high copper seems like a harmonic issue caused buy out of ballance internals to me. I can not think of any means that direct friction could cause this levels of copper we see in these enignes unless lead and tin wear also high. I can not imagine this much copper is from the cam bearings!
I am begining to wounder if we are not seeing the results of slopy assembly, just in time deliver of parts from the low bidder and a hit or miss quality control program?
WHile I belive that GM can design a competent engine I do not belive they can build one. Between the bean conters sabotage and the heavy reliance on human labor for assembly I think they are doomed.
In terms of the 3.1 and 3.4 V6's you would cry if you saw how cheaply made these pistons are!! The pistons are poorly cast from low quality aluminum. The ones I looked at that failed a quality inspection had very poor machineing. The rings are so close to the piston crown that any carbon at all on the tops of the crown works it way down into the rings almost right away. The skirt was almost non-exsistent! The piston was extremly thin in all area's. THe oil control ring has been turned into an almost useless apendage in a quest to reduce friction. The rings were also very thin.
Just for a contrast and comparison. My $17,000 Toyota Camry has Forged steel crankshaft,Forged Rods and pistons. The pistons are resin coated. The rings are heat treated stainless steel with crome coating on top ring( they are low tension though). The valves are one piece design and have undercut steems and are polished. The are differential heat treated and conatin a lot of nickle, cromeium and titanium. If my memory is correct they are sodium filled on the exhaust side. Most of the other valvtrain componets are CNC machined from billets and are then polished to a very fine finish. The few casting in this engine are also finished with presision. The valve springs are high silicone content. The sleves are cast steel not cast iron. GM is simply not willing to put this level of material cost into their engines not even engines for Cadilacs or Corvettes. The Lexus V8's have titanium rods and the pistons and rods are matched to .001 of a gram for all 8 pistons!
To date we have not heard of any Lexus engines developing a piston slap or rod knoc issue. We have not heard of any oil consuption issues with them either. They appear to tuen in low wear number reguardless of what oil is used or wich weight is used. This can not be an acident and it must be a function of design!
The high copper seems like a harmonic issue caused buy out of ballance internals to me. I can not think of any means that direct friction could cause this levels of copper we see in these enignes unless lead and tin wear also high. I can not imagine this much copper is from the cam bearings!
I am begining to wounder if we are not seeing the results of slopy assembly, just in time deliver of parts from the low bidder and a hit or miss quality control program?
WHile I belive that GM can design a competent engine I do not belive they can build one. Between the bean conters sabotage and the heavy reliance on human labor for assembly I think they are doomed.
In terms of the 3.1 and 3.4 V6's you would cry if you saw how cheaply made these pistons are!! The pistons are poorly cast from low quality aluminum. The ones I looked at that failed a quality inspection had very poor machineing. The rings are so close to the piston crown that any carbon at all on the tops of the crown works it way down into the rings almost right away. The skirt was almost non-exsistent! The piston was extremly thin in all area's. THe oil control ring has been turned into an almost useless apendage in a quest to reduce friction. The rings were also very thin.
Just for a contrast and comparison. My $17,000 Toyota Camry has Forged steel crankshaft,Forged Rods and pistons. The pistons are resin coated. The rings are heat treated stainless steel with crome coating on top ring( they are low tension though). The valves are one piece design and have undercut steems and are polished. The are differential heat treated and conatin a lot of nickle, cromeium and titanium. If my memory is correct they are sodium filled on the exhaust side. Most of the other valvtrain componets are CNC machined from billets and are then polished to a very fine finish. The few casting in this engine are also finished with presision. The valve springs are high silicone content. The sleves are cast steel not cast iron. GM is simply not willing to put this level of material cost into their engines not even engines for Cadilacs or Corvettes. The Lexus V8's have titanium rods and the pistons and rods are matched to .001 of a gram for all 8 pistons!
To date we have not heard of any Lexus engines developing a piston slap or rod knoc issue. We have not heard of any oil consuption issues with them either. They appear to tuen in low wear number reguardless of what oil is used or wich weight is used. This can not be an acident and it must be a function of design!
Forged steel pistons? While interesting it must be a typo.
Iron would be cool because it would swell at the same rate as the block.
Cast pistons and iron rods work very well. What it amounts to is GM slapping together junk to compete with Fords junk cammers.
The GM motors that I have built seem to have no problems at all. Cast or forged pistons.
Just my 2 centomos worth, now I'll get back to reading all this good stuff.
Cast pistons and iron rods work very well. What it amounts to is GM slapping together junk to compete with Fords junk cammers.
The GM motors that I have built seem to have no problems at all. Cast or forged pistons.
Just my 2 centomos worth, now I'll get back to reading all this good stuff.
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