Replacement motor

[opg4]

Its true guys GM is going to release a service bulletin for the 6.0's andthe 5.3's. Took my truck to my local dealer and the service guy verified my knock and now I am going to get a brand new motor by Christmas time. Not a bad Xmas present? He is going to order my motor tomorrow and should be in late next month. But it is true I seen with my own eyes the replacement 03 model motors. The dealer was doing 4 motors today as I post this message. Thankgod for the complaints. The 5.3's are going to get new pistons, The bulletin has been out for about2 weeks and should be out completely by another 2 weeks to all dealers. I will let you know if I have anymore info.

[Shaners]

Did you ask the dealer what is different from an '03 motor and the '99 through '02  6.0L motors?  Or will the problem come back?

 

Is this a recall or a TSB?

 

Hmm...  I've got a ton of questions.  I guess I'll have to wait on some answers.

[Shaners]

The bulletin has been out for about2 weeks and should be out completely by another 2 weeks to all dealers.

I don't quite understand this...  I thought all TSB's were on the GM "Network".  I have physically stood next to my service mgr as we linked to GM and found the TSB for my new 1-piece driveshaft.

 

I would think this info should be available to all dealers at the same time and I know that the service mgr's meet with their reps weekly for a group meeting.

 

Things are still a little cloudy in "Shaners" camp, but I sure hope it comes true...

[Stepside Z]

I am very interested to see what happens with this.

[Beaux Duke]

opg4, in case you didn't see my earlier post I'll ask it in this thread too.

 

What part of the country are you located?

 

What did you tell the dealer?

 

Did you just bring it in and let them listen to it?

 

If there's a "magic word" or phrase I'd like to know it before I go back.

[opg4]

I know it is hard to believe but it is true and I am going to get a new motor. Called the dealer friday and the service guy I am dealing with said he put my order in for the motor and should arrive bye mid December. I live in southern california. Will let you know if I get more info.

[normy01]

What mileage do you have to be under to qualify?

[bobc]

I've been following this piston slap/knock thread for a while.  Especially since the 2001 truck that I bought  2months ago with 44k miles revealed the cold start rattle now that temps are in the 40's during morning start up.  I call it a rattle becuase it sounds like valvetrain rattle to me, not a knock.  Maybe I have a different problem.  However... I'd like to add some info that I have from personal experience that really has me wondering about what the real problem is.

 

These new engines use hyperutectic pistons.  These pistons are a cast type piston that is much stronger than traditional cast pistons.  I have quite a bit of experience with Keith Black Hyperutectic pistons.  The benefits of these pistons are their *stability*.  Becuase of this stability they can be fitted reliably to a bore as tight as .00075".  That's freakin tight.  A testimonial to how stable these are is that they can be run that tight on an air cooled motor, which is going to show much more tendency to seize the piston or cause a piston scuff problem.  These Hyperutectic pistons are not new, they've been used widely in the auto industry for at least 10 years.  Harley has been using them since the early 90's.

 

Ok, that said, if this cold start knock is the pistons slappin around in the bores, the fit on these motors must be WAY out of whack.  Ever heard a set of forged pistons?  Those pistons are considered to be installed tight if fitted with .003" wall clearance.  Typical fitment is closer to .0045" and race motors will be fitted closer to .006".  Forged pistons expand far more than cast and take up much of this clearance, so they will quiet down when hot.  However a forged piston at .003" clearance will sound about the same as a cast piston at that clearance, which is quiet enough that only a very savvy motor guy is going to hear it.  Traditional cast are usually fitted .0015-.0025".

 

Hyperutectic pistons don't expand unless you use them in a hardcore application like nitro or blown alcohol motor.  That says to *me* that you should hear them clattering away like crazy for far longer than the 10-30 seconds most people experience if it's a piston fit issue...  Keith Black says fit the piston wall .0020-0040" in these serious high performance apps.   That's basically stock fitment for cast.  :-)

 

I also do not buy the short piston skirt argument either.  My stroker pistons have a skirt that borders on non-existent.  I also run these pistons in a dry sump motor, ie, very little splash oiling in the crankcase.  You won't hear these pistons slappin at all even set up at .003".   So that debunks this excuse that GM has stated in my opinion.

 

Sooooo.... Where is that noise coming from?  If the pistons are hitting built up carbon they should be makin noise all the time.  If they are hitting carbon that is thick enough to act like piston to head contact, the rod bearings ARE going to get damaged over time.  But the noise goes away so quickly that it's not likely carbon to piston contact.   Harley cylinders grow almost .100" when hot, but they are made of aluminum.  I've heard the pistons hitting the head on a Harley when the squish band is set below .020" and carbon has built up.  It stops if you let the motor warm up before you give it some throttle.  The sound is *not* a pretty sound by the way.  Cast iron motors V8 motors don't grow in height.  So I see no reason why the piston to head contact would change... toss that idea out becuase it should have been hitting before the motor was parked... and that 5w30 oil is much thinner when the motor is at operating temp than it is on cold start.  You should hear that piston rock and slap when the motor is hot if this was the case.

 

My suspiscion, (finally), is that this is a lifter issue.  The lifters are bleeding down when allowed to sit for a few hours and on the colder mornings the lifter takes more time to pump back up.   Hence the clatter.  Another interesting thing happens when the lifter bleeds down.  The valve lift is significantly less.  This is effectively like running to mild a cam in a high compression engine, this will create too high of  static compression ratio.  What that means is that you could effectively see the motor act like it's got way too much timing causing a knock.  When the engine is hot and sits for a little while and really heat soaks the air in the combustion chamber  and if the tappets bleed down, you'll actually see the mixtured light off before the spark can be delivered.  Basically "diesel" starting.  On a Harley that means the motor will actually try and start backwards, which is not pretty and sounds horrible!   In a V8 motor you will hear the motor ping/knock on startup becuase the other cylinders resist the attempt to spin the crank backwards.   Regardless, that's a huge load on the piston, crank and crank bearings.

 

I think GM may be finding crank bearing problems caused by the additional pounding on the crank at start up.  Remember after a night of sitting the crank bearings have no pressurized oil feed on the bearings which is exactly what makes them work.   Alternatively if the pistons are so loose in their bores that we hear them, longevity of piston seal will be a problem.

 

Anyway, that's my thought on this whole problem.   My apologies if I put anyone to sleep...  

 

Besides, all that said and done... I bought used so I'm screwed anyway... I seriously doubt the dealership or GM is gonna help me.  If they do I'll fall outta my chair.  I *do* wish that I'd known about this problem before spending a chunk of change buying this Silverado.  I would have steered clear... This is not exactly the best introduction to the GM product line after driving a Ford truck for 15 years without a single problem.  

 

I dunno.. as a couple guys I know say, JOIBO.  (just one idiot bikers opinion)   :-)

 

Later,

bobc

[gilbo]

here u go check out this thread, think the dealership doing this is out of miramar GMC, san diego

 

http://forums.pickuptruck.com/showfla....fpart=1

[asepgrad98]

bobc,

great post. eventually we will know the truth, you explaination soulds as plausible as any ive read yet :thumb:

[sgiangregorio]

Wow Bobc, thanks for the info! And I buy your explanation. I had a 1997 Kawasaki Vucan 1500 with a bad lifter. It sounded and acted exactly like what you describe. All I know is this, ,y 2001 Silverado with an 8.1L was ok when sold at 30,000, and so far my 2002 Tahoe 5.3L with 6500 miles is still ok. Fingers are crossed...  :thumb:

[bobc]

Thanks for the Kudos.  It will be interesting to see how all this plays out.  It sure would be nice to see GM admit to a design flaw or oversite and make good on replacement/repair vs continuing to say, "they all do that"...   Just becuase "they all do that" doesn't make it right...  Of course if they fess up publicly and do a recall for original owners still in the warranty period, everyone else is gonna be screwed.  Who'd willingly buy a truck with an acknowledged problem?

 

Here's to a killer outcome for ALL!  

 

Later,

bobc

[TxDoc]

The only "official" GM response that I have seen was from Truck Trend Magazine.

 

1-GM is aware of it.

2-It is not causing damage.

3-no fix is coming in the soon to be released TSB.

 

From Truck Trend:

"There've been a lot of complaints about cold-start knock in the Vortec engine family and most General Motor's customers are getting incomplete answers at dealerships. We've spoken with Matt Kester, assistant manager with GM Powertrain Product Comunications, about this situation. He said General Motor's engineers ARE AWARE of the problem and are currently in a RESEARCH STAGE. The cold-start knock involves the 4.8L, 5.3L and 6.0L V-8s in all applicable GM cars and trucks from '99 to '02. They believe the CAUSE IS carbon buildup on the circumference of the piston ABOVE the top piston ring. This interference is affecting the dynamics of PISTON TRAVEL and therefore causing a knock. It seems the problem begins after the first 12,000 to 15,000 miles and the knock will last between five and 30 seconds in temperatures below 50 degrees after a cold startup. The noise also seems more pronounced AFTER long trips and at lower temperatures. The use of a top engine cleaner will give only TEMPORARY results, IF ANY, and a replacement engine without modifications would most likely develop similar symptoms. We were also told that a Technical Service Bulletin is in the process of publication, which should provide and explanation of the condition, BUT NOT A FIX, and that carbon deposits and associated knock ARE NOT CAUSING ANY STRUCTURAL DAMAGE TO THE ENGINE. So,for now, don't let it bother you. We'll give you further details when the TSB becomes available."

 

 

Now, just an observation. I don't see any corporation replacing or fixing a large number of  motors  because of a noise that occurs at startup.  I have not seen anyone with an engine knocking at startup that failed. I have not seen anyone who was killed or permanently injured in an accident due to the knock.  Until some product liability lawyers, like my relatives get involved, I don't see the incentive for GM to do anything.  The labor cost alone has got to be high for one. And, deciding who has enough of a knock to be included would be difficult. Is 20, 30, or 25 or 5 seconds the threshold? What if 30 is and yours knocks for 28?--my luck.

 

 

I wonder, as I don't know, if they pay for the motor and the labor to install it, or does the customer pay for the labor?  Congrats to those who get a new one and hope everyone who wants one gets one.  I am staying tuned for details.

 

 

I would hope those with the problem would get it fixed and they would be happy.  I guess I am pessimistic about the nature of the problem being worthy to GM to fix a large number of motors without some pressing force. This is interesting, though.

[RyanbabZ71]

The noise also seems more pronounced AFTER long trips and at lower temperatures.

 

I disagree.  I do agree with the comment about the noise being louder in cold temps but not the long trips comment.  My truck runs smoother after long trips.  If i take a long trip the night before, the next morning i have almost no startup knock.  

 

I do agree with the following statement

 

 

 

associated knock ARE NOT CAUSING ANY STRUCTURAL DAMAGE TO THE ENGINE.

 

Why you may say?  How many engine failures have you heard of?  If it was causing damage we would definitly hear about trucks breaking down.  I know a handful of people with 5.3s and 6.0s with the knock and well over 80K miles and no problems

 

Until i see engine failure problems i wont worry

 

[bobsedor]

Does anyone know if the TSB is on the GM tech site where my dealer logs in?