GM ENGINES KNOCK

Chris B. · Dec 28, 2003

Von!

Which engine do you have? I have a 2003 5.3 and I had better wear numbers using Mobil 1 10w30 but I had less miles on the oil then you do.
Do a search on "piston slap" and read up. My engine is quiet on M1, you might want to try it. You caould also stick with the Amsoil and see if the wear comes down in the next interval or 2. Really it is not that bad giving the mileage. These are tough engines and will the knock does not seem to hurt durability as there are many LS1 the knock like crazy with well over 100,000 miles.

Von · Dec 29, 2003

Thanks Chris,

What a bonehead! - I looked at other posts and put down all the info I could think of, but forgot to list the engine!! It is the 6.0 or 364 cubic inch gas V8.
I'm glad to hear the engines last even with the knock. Had me worried.
Von

Jared H · Apr 29, 2004

Any new news on this issue?

I took my car ('02 Z28) into the dealer for a listen to my "knock" several months back and got a "that's normal" for this engine and an explanation on shirt skirt pistons and how this phenomena(sp?) occurs.

FWIW ... my "knock" noise is definitely more noticeable in winter months and has seemed to disappear with the warming temperatures this spring/summer.

I've also noticed (last 2ea oil changes) that the "knock" noise was significanlty louder at startup after oil change than what I've heard in the past. All I've done differentl is to ensure engine oil was hot because I was sampling ... I think this may have impacted the oil pump's prime some how(fully drained when oil hot) making it harder to reprime with the new oil.

Typically I do not fill the new oil filter prior to installing it ... I tend to floor the gas pedal(cuts all fuel to the injectors) and turn the motor over a few moments to fill the filter prior to starting. I'll be pre-filling the filter from now on since I don't like what I've heard the on the last two changes.

Once oil pressure is established on the gage the noise is still there ... does not disappear until I rev the engine to ~2400rpm for 5-10sec ... once noise is gone I drop back to idle and the noise does not return. What I find interesting is the fact that if I don't rev the motor to ~2400rpm and just let it idle after oil change the noise does not go away and is very pronounced until engine rpms get up from either me driving it or reving the motor.

I don't view this "behavior" as normal ... although it may be "normal" for this motor nor do I believe it will noticeably shorten my engine life but I'd like to hear any comments or thoughts others may have on my particular issue as it relates to this thread topic.

Thx JHH

Link to my M1 0W40 oil analysis
http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=001469
Link to my M1 10W30 oil analysis
http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=001096#000003

[ April 30, 2004, 11:33 AM: Message edited by: Jared H ]

Motorbike · Apr 29, 2004

quote:

Originally posted by Jared H:
Any new news on this issue?

FWIW ... my "knock" noise is definitely more noticeable in winter months and has seemed to disappear with the warming temperatures this spring/summer.

Here you can read about how the enginneers aknowledge a somewhat excessive main bearing clearance causing cold start knock with the LS1 . The main clearance has been tightened up on the LS6 engine .

Read about the RPM limit concerns while there

Tech Article

G-MAN · Apr 29, 2004

quote:

Originally posted by Motorbike:

quote:

Originally posted by Jared H:
Any new news on this issue?

FWIW ... my "knock" noise is definitely more noticeable in winter months and has seemed to disappear with the warming temperatures this spring/summer.

Click to expand...

Here you can read about how the enginneers aknowledge a somewhat excessive main bearing clearance causing cold start knock with the LS1 . The main clearance has been tightened up on the LS6 engine.

I think you're reading too much into this statement:

quote:

For MY01, all Gen IIIs use a new main bearing that has reduced diameter variation. That allowed a slight decrease in main bearing clearance which reduces the potential for bearing knocks during starts in extremely cold weather from engines having bearings on the high-side of the variation.

What the guy is saying is that in some engines under extremely cold conditions there may be bearing knock if the bearings in that particular engine are on the high-side of the allowable variation. This is the exact same problem the GM 3.1 and 3.4 have with wrist pin variance and clearance. Neverhteless, the primary "noise" problem with both the LS1 and 3.1/3.4 is piston slap.

Motorbike · Apr 30, 2004

I disagree .

It says,
all Gen IIIs use a new main bearing that has reduced diameter variation. That allowed a slight decrease in main bearing clearance which reduces the potential for bearing knocks during starts in extremely cold weather from engines having bearings on the high-side of the variation

That means they knew they had a slight problem with the other generation motor so in designing a new bearing they also reduced the main bearing clearance vs the actual clearance of the previous design . They might have known about the knock through R&D or from the field . Regardless it is an upgrade .

While on topic I'll ask your opinion in three questions. Which is the case ,is a bearing made on the high and or low side on purpose or through production flaw ? The same question applies to the crankshaft journal diameter . If none, any or all of the above applies , what is the fix ?

[ April 30, 2004, 02:38 PM: Message edited by: Motorbike ]

RavenTai · Apr 30, 2004

my 8.1 slapper

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=3;t=001155

G-MAN · Apr 30, 2004

quote:

Originally posted by Motorbike:
While on topic I'll ask your opinion in three questions. Which is the case ,is a bearing made on the high and or low side on purpose or through production flaw ? The same question applies to the crankshaft journal diameter . If none, any or all of the above applies , what is the fix ?

It's not a production flaw, per se. To use the wrist pin problem with the 3.1/3.4 as an example, you could have wrist pins that were completely within spec, and pistons that were completely within spec, but if the wrist pin was on the small side of the allowable diameter (allowable production tolerance) and pistons with wrist pin holes that were on the large size of the allowable diameter (allowable production tolerance), then you had a problem in the form of a rather loud tic or knock, especially on start up in very cold weather.

Under the GM TSB that was issued for this problem, the "fix" was to install new pistons that had been pre-screened for wrist pin fit. Of course, the ultimate fix is to reduce the allowable tolerance so that even if you have a small wrist pin and a large wrist pin hole, it's not enough to cause a problem. This seems to be exactly what the LS1 engineers did with their bearing "problem."

mnztr · May 1, 2004

It's amazing that the 350 has been in production for so long and refined over so many years, yet here we are with these serious problems. It's just like the manifold gasket problems on the V6's. None of these engines are technologically advanced, or develop particularly high specific power outputs. GM has no excuse here I'm afraid, their quality and engineering are abysmal. How anyone can buy a Caddy over a Lexus or Mercedes is beyond me. Maybe there is some hope for Chrysler, looks like Mercedes engineering culture is being infused. The Hemi looks like a pretty decent engine.

sbc350gearhead · May 1, 2004

quote:

Originally posted by mnztr:
It's amazing that the 350 has been in production for so long and refined over so many years, yet here we are with these serious problems. It's just like the manifold gasket problems on the V6's. None of these engines are technologically advanced, or develop particularly high specific power outputs. GM has no excuse here I'm afraid, their quality and engineering are abysmal. How anyone can buy a Caddy over a Lexus or Mercedes is beyond me. Maybe there is some hope for Chrysler, looks like Mercedes engineering culture is being infused. The Hemi looks like a pretty decent engine.

The 350 is no longer made, and was last used in light trucks in 99 IIRC. The gen 3 engines are a vastly different design.

G-MAN · May 1, 2004

quote:

Originally posted by sbc350gearhead:
The 350 is no longer made, and was last used in light trucks in 99 IIRC. The gen 3 engines are a vastly different design.

Actually, the original small block 350 is still being made, it's just not used in any production GM vehicles. You can, however, still buy a 350 crate motor from GM. But as you have correctly pointed out, the GEN III small block engines are a completely different design, which unlike the LT-1 are not based on the original small block engines at all.

sbc350gearhead · May 1, 2004

G-man is correct, 350 replacement engines and GMPP engines are still being produced. I should have clarified that.

In fact GM produces engines for the aftermarket that were never installed in production cars such as a 383 sbc, and 502 and 572 bbc's.

mnztr · May 2, 2004

Yes but the engine is pretty much the same OHV 5.7 liter engine is it not? Considering all the experience they have with this type of engine, the problems are appalling.

XS650 · May 2, 2004

quote:

Originally posted by mnztr:
Yes but the engine is pretty much the same OHV 5.7 liter engine is it not? Considering all the experience they have with this type of engine, the problems are appalling.

It does have several things in common with the classic 350 SBC.

8 cylinders
Cylinders arranged in a 90 degree V configuration
IIRC, same bore spacing, but I'm not positive about that.
Close to 350 cubic inch displacement.

I do agree with your sentiment that they should get things right. It's not a complicated or revolutionary engine.

Unfortunately, GM has a long record of releasing engines to the public for beta testing without telling them they were getting engines that weren't fully developed.

Corvair
Vega
3.1 V6
Cadillac 8-6-4 V8
Chevy LT4 that had two factory recalls for valve gear problems. 2nd recall fixed the first recall.

I've owned two of those, fortunately after the problems were fixed.

G-MAN · May 2, 2004

quote:

Originally posted by mnztr:
Yes but the engine is pretty much the same OHV 5.7 liter engine is it not?

No, it isn't "pretty much the same." The Gen III engines don't have a single part in common with the "classic" small block engines. It was a totally new design from drawing board to production floor.

mnztr · May 3, 2004

Didn't they use the same bore spacing so they did not have to retool? What technological strides dod they try to make with this engine? Nothing really, just an old tech 2v OHV lump with modern engine management strapped on. Same old GM crap.

Patman · May 3, 2004

quote:

Originally posted by mnztr:
Didn't they use the same bore spacing so they did not have to retool? What technological strides dod they try to make with this engine? Nothing really, just an old tech 2v OHV lump with modern engine management strapped on. Same old GM crap.

It's not the same old crap by any means! The cylinder heads on the LS1 and LS6 are some of the best production heads ever built.

And where else are you going to find a 405hp engine (like the LS6) which can also knock down over 30mpg highway?

And just wait until the LS2 hits the streets late this summer, and the 500hp version the following year (which will most likely be labelled the LS7)

JohnBrowning · May 3, 2004

The fundemental design of the Gen III engines is not bad. They just leave too many comprimises in the design and then fail to exacute their design properly. Material selection,tolerance stacking and poor quality control plauge everything they make.

It just strikes me as odd that my 165HP I4 Toyota has forged steel rods, forged steel crank and forged aluminum pistons on a $17,000 car. While a $50,000+++ Corvette has to make due with sintered metal rods, cast crank and a horrable comprimised piston design built by Mahl. Mahl does almost all of GM's pistons includeing the 3.1 and 3.4!

G-MAN · May 3, 2004

quote:

Originally posted by JohnBrowning:
The fundemental design of the Gen III engines is not bad. They just leave too many comprimises in the design and then fail to exacute their design properly. Material selection,tolerance stacking and poor quality control plauge everything they make.

It just strikes me as odd that my 165HP I4 Toyota has forged steel rods, forged steel crank and forged aluminum pistons on a $17,000 car. While a $50,000+++ Corvette has to make due with sintered metal rods, cast crank and a horrable comprimised piston design built by Mahl. Mahl does almost all of GM's pistons includeing the 3.1 and 3.4!

Sintered rods are actually more expensive to make than forged and are stronger. As for the crank, I'll have to check, but I think the LS6 has a forged crank.

Patman · May 3, 2004

Nope, the LS6 uses a cast iron crank.

GM ENGINES KNOCK

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