OFFICAL WORD ON "KNOCK" FROM 5.3 AND 6.0L's

Zane · November 12, 2002

Well guys, this is to put to rest the utter rediculousness that someone started on PUTC. GM is NOT issuing a recall, and is NOT replacing engines on a wide scale effort.

Zane,
A condition called "carbon-induced cold start noise" has appeared in some

General Motors truck engines . The condition is caused by carbon buildup

on the pistons of 4.8L, 5.3L and 6.0L displacement GEN III V8 truck

engines, found in Chevrolet and GMC light- and medium-duty trucks and sport

utility vehicles. Upon engine start-up, this carbon can make brief contact

with the cylinder wall, resulting in a slight ticking noise that recedes as

the piston and cylinder warm up. The sound typically occurs during the

first 5-30 seconds of engine operation,

The cold start noise issue does not pose a performance, durability or

safety concern. Analysis of 150,000-mile and 300,000-mile engines that have

exhibited cold start noise shows no significant wear to the pistons or the

cylinder bores.

Since this condition does not represent a defect, but a carbon build-up

issue, it is not subject to a recall or customer communications campaign.

Customer concerns are being addressed through dealer service departments on

a case-by-case basis.

MiSdIrEcTeD_1 · November 12, 2002

Cool Mervz... Is that from the guy @ GM that you know???

Zane · November 12, 2002

Cool Mervz... Is that from the guy @ GM that you know???

Not the one that i'm guessing your referring to.

This was the NE Communications Director that i talked to this time.

I know many people at gm...

Dihappy · November 13, 2002

I understand the letter, however, id like to state that IMO that is total BS!

What a coincidence that this problem has been most evident in the new generation vortecs.

This is a mechanical problem and of course, GM will never fess up to that.

CapnDean · November 13, 2002

Thanks & Kudos to MervZ! Another example of professionalism on this board!

I am inclined to agree with their explanation of the knock. If it knocked continuously...then it would be a different issue. But as it is...I wouldn't be too concerned about it.

CapnDean

Beaux Duke · November 13, 2002

GM apparently doesn't have their ducks in a row.

Take a look at the document they gave me yesterday 11/12/02 that explains GM's position on the Cold Start Knock Issue

View Document # 650406

LarryE · November 13, 2002

till I experiece in or hear it in real life, I'll still throw the bs card on it.

still sounds like alot of ppl being over protective to me

bobc · November 14, 2002

That doc link, Beaux Duke, says the same thing as the 2001 Helm manual in the diagnosis section.

OK, so GM wants to make it clear to Zane that this is carbon build up and it's not a problem. Based on that, I'd like to hear answers to the three following questions:

1 - When will GM rectify the source of this abnormal carbon build up? (Excessive carbon build up in an engine is not normal, oil blow-by can do it, overly rich mixtures can do it, in both cases it can be prevented or corrected.)

2 - Why does the noise go away within 1.5 mins on a cast iron block that should not show any physical dimension changes until it's bloody hot? Modern high-silicon Hyperutectic pistons for all practical purposes do not grow or change dimensionally, certainly not enough to quiet a slap.

3 - If diagnosis of the problem suggests grounding the secondary circuit (ie, kill the spark) and note the lack of knocking doesn't that contradict the carbon build up/piston contact explaination?

I wonder what GM would say about running low-test gas in an engine and hearing knocking under load? Would they say this is normal and does no damage to the engine? Knock (preignition) vs Pinging (detonation) are very different animals. Preignition will hole or crack pistons, destroy spark plugs... etc. So, why is spark induced knocking ok at any time?

Inquiring minds wanna know.

bobc

thatboy092 · November 14, 2002

:angry: I took my car to the dealer for the knocking and the shopfore man said yes there was knocking and there is nothing they can do about it to correct it. When I was at the dealer there were 5 other trucks with the same complaint. He says that GM will respond to the problem and correct it if enough people bitch about it. He has a 5.3 and it does the same thing. I think GM is brush us off and saying that the knocking is normal.

check out these Consumer Complaints from NHTSA.

http://www.nhtsa.dot.gov/cars/problems/complain/central2.cfm

After reading that fill out the complain form. The more complaints maybe someone from GM will wake up!

http://www.nhtsa.dot.gov/cars/problems/ivo...OQ/VOQ/voq1.cfm

Thanks guys!

:thumb: nhtsa nhtsa

thatboy092 · November 14, 2002

sorry that link before didnt work. heres the site for the complaints. follow the steps (silverado) and click on engine. hope link works.

http://www.nhtsa.dot.gov/cars....Vehicle

goldnrod24 · November 14, 2002

Well, of course you've chosen to swallow GM's "official" words, hook, line and sinker. You are beholden to them for access to vehicles and other perks.

Your bias is obvious and should be disclosed prior to spewing factory propoganda and exploiting your ability to "pin."

Ridiculous, indeed!

Randy

Mervz-I think your post is ridiculous. All i did was post what GM's offical stance is. I don't want people running to their dealership demanding a new engine. Guess who they are mad at when the dealership says no? US!

Markeaux · November 14, 2002

My 01 Tahoe 5.3 20K/mi has a low DOK DOK DOK DOK whenever it idles, and that is cold, warm and hot - that does not fit the carbon buildup scenario but does fit a "piston, rod or other "lower" engine component" problem.

Beaux Duke · November 14, 2002

From the posts I've read here and at other forums it looks like GM Service Technicians may be using the "Cold Start Knock" problem to blow off all requests dealing with a tick, knock or tap.

I suppose there are some dealers who can spot the difference but it's beginning to look like a lot are taking the easy way out.

Go to a dealer and get it documented. Push the fact that it's making a noise continuously. You'll have to push the issue yourself if you want results.

CapnDean · November 14, 2002

to Goldnrod24:

Sure Mervz has accepted the GM explanation. He is also the chap that pressed GM for an official explanation.

So what gives? MervZ does a great job moderating this forum. Has gobs of patience, and is fair & accurate...often de-bunking the BS with accurate information.

Does GM give him a freebie? Nope. Betcha Mervz couldn't even get a $5 discount based on his task here (If he could get 'compensated' Ill bet there would be more folks volunteering to moderate!)

The accusation that MervZ is somehow paid to push propaganda is in my view an insult.

Of course he is biased toward GM trucks....He moderates the GM truck board! You think he should go moderate Ford's F-150 board too, so his credibility would suit ya?

Just my 2 cents.....again!

ClipperSkipper · November 15, 2002

Well guys, this is to put to rest the utter rediculousness that someone started on PUTC. GM is NOT issuing a recall, and is NOT replacing engines on a wide scale effort.

Zane,

A condition called "carbon-induced cold start noise" has appeared in some

General Motors truck engines . The condition is caused by carbon buildup

on the pistons of 4.8L, 5.3L and 6.0L displacement GEN III V8 truck

engines, found in Chevrolet and GMC light- and medium-duty trucks and sport

utility vehicles. Upon engine start-up, this carbon can make brief contact

with the cylinder wall, resulting in a slight ticking noise that recedes as

the piston and cylinder warm up. The sound typically occurs during the

first 5-30 seconds of engine operation,

The cold start noise issue does not pose a performance, durability or

safety concern. Analysis of 150,000-mile and 300,000-mile engines that have

exhibited cold start noise shows no significant wear to the pistons or the

cylinder bores.

Since this condition does not represent a defect, but a carbon build-up

issue, it is not subject to a recall or customer communications campaign.

Customer concerns are being addressed through dealer service departments on

a case-by-case basis.

You are kidding right? You expect consumers who purchase Thirty- odd thousand dollar vehicles to believe this?

Have you been to the GM piston-slap website? Read the threads on the Usenet and Ultranet and Mirc? A quote from

a buddy who built the thing:

Well, I don't know if this post on the pistonslap site is from a real good liar, but does seem to be in the know at any rate. Not a surprise unless you're a loyalist (for some godforsaken reason) to General Mistake....but it's interesting anyway.

Also, since General Mistake knows that crap sells when the blind are buying, don't really expect them to come to you and offer a legit fix, assuming (don't do that) a fix ever comes.

---------------------------

As a former employee of an automotive supplier that was involved in the design and development of Gen III and Vortec 8100 engines I can tell you that this is strictly an issue of the bean counters running GM, not the engineers. The Vortec 8100 is a perfect example. Take a 454, bore it slightly and stroke it a ton and you have the Vortec 8100. The problem is that the piston skirt is way too short(to keep the crank from running into the piston with such a long stroke). These pistons showed up all of the time with cracks, broken lands, cracked pin bosses, etc. Yes, reciprocating mass is the enemy of fuel efficiency and yes dyno testing is tougher than real life applications, but these motors were a disaster waiting to happen. The piston mass requirements were too low and the clearance requirements were too tight to make a robust engine without additional cooling of the piston. Furthermore, anyone who is impressed with the power output of these engines (Gen III and Vortec 8100) should understand that they do it by generating tremendous cylinder pressures, which means more heat. The engineering compromises for this are obvious: More piston mass in the skirt, less stroke, less cylinder pressure, or better cooling of the piston (or some combination of these). All of these solutions cost something. The best engineering solution was to cool the backside of the pistons with oil jets (rather than splash lubrication), something that many european engines with high cylinder

pressures do. Could add $50 an engine. Bean counters won't pay for it.

The customer apparently doesn't get the option to pay the $50 up front for a better engine. They get to pay $4000 down the line for an engine that sounds embarassing in a $30K+ automobile.

The same "bean counter" saga applies to the Gen III engines. Slightly different scenario, but suffice it to say the that GenIII piston was a real bugger. I don't know who "won" the contract to supply it to GM, but the design and development was trouble. Either way, the "find a way to make it cheaper" philosophy killed what was an exceptionally ingenious implementation of the "modern" pushrod engine.

It seems to me that anyone that dares to use the word "Motors" in their corporate title, ought to #### well make sure that the powertrain is solid. whether the AC works, or the power windows work, I don't care, but the damned thing oughtta run like a top. Anything less is a crime. Go get'em.

My $0.02.

Well done sir!

Updates from the piston slap website, and for God's Sake loose the carbon issue! Most of us are well educated adults.

Besides the 1952 Turnip truck is parked in my barn.

Here's the deal:

The Gen III engines were designed for torque, long stroke,

short piston skirts to accomadate the crankshaft throws.

OEM design specifications showed original cylinder bore to piston clearance of 1 mil (.001"). Production tolerances were showing from .002" to .0025" resulting in cold start, and oftentimes continuous piston slap after 15,000 miles.

Seems as if our little stroker motor has come up short.

No worries, it appears replacement blocks meeting the correct cylinder to piston specs have entered into a " Special Engine

Replacement Program has recently come into effect and several GM Dealerships are going ahead with this.

More news as developments continue.

Have a great one!