2000 Silverado - "Piston Slap" - Page 2

gmtech · 01-12-2006, 03:54 PM

Its not a problem I'm a gm tech for 20 years + now own a 2001 z71 and yes it knocks worse when could but the factory rep brought around a video showing some fleet vehicles with 300k+ on them that were torn down and you could still see the cross hatches in the cylinders. There are replacement pistons as they have come out with replacement pistons for the 3.1 engines which also have the noise but i'm not going to go into my own engine with 84k on it that is running perfect and no leaks to replace the pistons which I know the 3.1 replacement piostons still make some noise and have not heard how the 4.8/5.3/6.0 pistons are doing. If yopu complain about it to a gm rep they will give you in writting a 100k milage warranty on the engine. These engines are bullet proof. My advise is to leave it alone. As far as some bullitens speaking of a carbon knock noise if you buy a good grade of fuel you won't have this problem. I burn nothing but BP ultra the top grade and when i have torn down my friends engine for a concern and he used nothing but the BP unltra the engine is spotless inside.

speadphreak · 01-12-2006, 06:20 PM

As someone who has built many sbc's. Any time you have any kind of piston slap it is something to worry about. When there is a noise of this kind its caused by a piston that is smaller than the cylinder. Normally this is caused by the cylinder becoming out of round as the crank goes round and the rod goes back and forth it can cause the piston to tilt(usually on an engine that hasnt had the oil changed religously the wrist pins can become glazed and stiff) once the oil gets flowing things loosen up and the noise goes away. If youve have ever seen a badly worn engine and bore gauged the cylinders youd would understand whats happening the cylinders will be round at the top and ovaled at the bottom. The ovaling will be widest side to side (the way the piston tilts) anybody that tells you that this is ok should be smacked it may be common but it is not correct. Of course to fix requires an engine rebuild, basically boring the cylinders oversize and replacing the pistons. Go to the dealer and raise **** till they repair it. If they give you grief go to a reputable engine machine shop get dcumentation to what they say and then go back to the dealer if they still refuse call the GM warranty division direct. If that doesnt help you call a lawyer. It may seem like more of a nuisance but it means your engine is wearing prematurely.

speadphreak · 01-12-2006, 06:46 PM

No offense meant about the smack thing gm tech you hadnt posted when I was writing, but I stand by the statement that somethings wrong cross hatches or not somethings not clearancing correctly on the bottom of the cylinder I have never seen an engine that was bored correctly and true the whole length slap it just wont happen.

72'CaminoKid · 01-12-2006, 08:36 PM

i'm agreeing with you buddy ^^^^^

shopratles · 01-12-2006, 08:41 PM

This is kind of comparing apples and oranges, but my 1982 Harley has had piston slap since new. Guess what - 24 years and no rebuild yet. Also my '02 Trans Am (LS-1) really used to knock (even when new). I have to agree with GMTech, as long as the fluids look good and the knock goes away it is probably ok.

gmtech · 01-13-2006, 04:09 PM

The noise is because of the type of pistons which have no skirt and are what they call hyperconnectic sp they use them is race engines and they are a low friction piston and they are small in diameter in design and need heat to make them fit the cylinder. Seeing as how every single 3.1,3.4,4.8,5.3,6.0 engine that uses them make the noise There can not be that many cylinders out of round. On race engines inwhich they were designed for noone hears the noise over the loud exhaust but they are a true and proven design and have had no durabilty issues that i have seen.

gmtech · 01-13-2006, 04:23 PM

Here is the description of the pistons from the gm manual The pistons are cast aluminum. The pistons use two compression rings and one oil control ring assembly. The piston is a low friction, lightweight design with a flat or recessed top and barrel shaped skirt. The piston pins are chromium steel, have floating fit in the piston, and are retained by a press fit in the connecting rod. 6.0L LQ9 applications will have full-floating pistons/pins retained by internal clips. The connecting rods are powdered metal. The connecting rods are fractured at the connecting rod journal and then machined for the proper clearance. The piston, pin, and connecting rod are to be serviced as an assembly.And here is the 1 of the bullitens that addresses the concern Some of the above vehicles may exhibit an engine knock noise that begins in the first several thousand miles/kilometers of use. The knock noise is most often noticed during initial start-up and typically disappears as the engine warms up. The noise is usually more noticeable on the initial start-up when the temperature is below 10°C (50°F) or if the vehicle has not been used for several days.
This noise may be caused by an interaction between the piston and the cylinder wall. GM Powertrain Engineering, and an analysis of engines returned with this condition, has confirmed that the noise is not detrimental to the performance, reliability or durability of the engine. The noise does not have any effect on the longevity of any of the engine components. The other bulltien also talks about carbon build up.

chevyguy · 01-13-2006, 06:27 PM

As you all know,I am not a big fan of engine noises and leaks, but GM tech is right here. I have built quite a few race engines with the skirtless pistons and it happens sometimes. The old thoughts about slap were talking about pistons with skirts, the newer lower friction, less weight pistons dont have those skirts so It can happen and shouldnt be a problem.

Itstali25 · 01-13-2006, 09:31 PM

well i'm not gunna lie, i've never seen CG steer anyone in the wrong direction, so i'm gunna go with him on this one........

a5150joseph · 11-18-2006, 03:57 AM

Yeah, my 2001 knocks a bit too in the morning. They insist it is normal. I've had no engine problems in mine, i have 86,000 miles and still running strong.

01-12-2006, 08:36 PM	#14
72'CaminoKid Senior Member Join Date: Jun 2005 Posts: 2,329	i'm agreeing with you buddy ^^^^^ __________________ 99 suburban xlt 96 silverado 91 wrangler (my baby ) 08 Honday shadow 750 (my mistress)

01-13-2006, 06:27 PM	#18
chevyguy Senior Member Join Date: Sep 2005 Location: ALABAMA Posts: 3,160	As you all know,I am not a big fan of engine noises and leaks, but GM tech is right here. I have built quite a few race engines with the skirtless pistons and it happens sometimes. The old thoughts about slap were talking about pistons with skirts, the newer lower friction, less weight pistons dont have those skirts so It can happen and shouldnt be a problem. __________________ When i die, i dont want to walk gracefully thu the pearly gates and turn in a unused body. i want to go sliding thru sideways and turn in a body that has been completely used up.

01-13-2006, 09:31 PM	#19
Itstali25 Senior Member Join Date: Jul 2004 Location: Southern Missouri Posts: 708	well i'm not gunna lie, i've never seen CG steer anyone in the wrong direction, so i'm gunna go with him on this one........ __________________ http://www.cardomain.com/ride/644045 Trucks are just cars when they grow up!!! If your gunna get a truck....Get a TRUCK!!

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01-12-2006, 03:54 PM	#11
gmtech Senior Member Join Date: Dec 2005 Location: farmville Va Posts: 348	Its not a problem I'm a gm tech for 20 years + now own a 2001 z71 and yes it knocks worse when could but the factory rep brought around a video showing some fleet vehicles with 300k+ on them that were torn down and you could still see the cross hatches in the cylinders. There are replacement pistons as they have come out with replacement pistons for the 3.1 engines which also have the noise but i'm not going to go into my own engine with 84k on it that is running perfect and no leaks to replace the pistons which I know the 3.1 replacement piostons still make some noise and have not heard how the 4.8/5.3/6.0 pistons are doing. If yopu complain about it to a gm rep they will give you in writting a 100k milage warranty on the engine. These engines are bullet proof. My advise is to leave it alone. As far as some bullitens speaking of a carbon knock noise if you buy a good grade of fuel you won't have this problem. I burn nothing but BP ultra the top grade and when i have torn down my friends engine for a concern and he used nothing but the BP unltra the engine is spotless inside.

01-12-2006, 06:20 PM	#12
speadphreak Full Member Join Date: Dec 2005 Location: NW PA Posts: 37	As someone who has built many sbc's. Any time you have any kind of piston slap it is something to worry about. When there is a noise of this kind its caused by a piston that is smaller than the cylinder. Normally this is caused by the cylinder becoming out of round as the crank goes round and the rod goes back and forth it can cause the piston to tilt(usually on an engine that hasnt had the oil changed religously the wrist pins can become glazed and stiff) once the oil gets flowing things loosen up and the noise goes away. If youve have ever seen a badly worn engine and bore gauged the cylinders youd would understand whats happening the cylinders will be round at the top and ovaled at the bottom. The ovaling will be widest side to side (the way the piston tilts) anybody that tells you that this is ok should be smacked it may be common but it is not correct. Of course to fix requires an engine rebuild, basically boring the cylinders oversize and replacing the pistons. Go to the dealer and raise **** till they repair it. If they give you grief go to a reputable engine machine shop get dcumentation to what they say and then go back to the dealer if they still refuse call the GM warranty division direct. If that doesnt help you call a lawyer. It may seem like more of a nuisance but it means your engine is wearing prematurely.

01-12-2006, 06:46 PM	#13
speadphreak Full Member Join Date: Dec 2005 Location: NW PA Posts: 37	No offense meant about the smack thing gm tech you hadnt posted when I was writing, but I stand by the statement that somethings wrong cross hatches or not somethings not clearancing correctly on the bottom of the cylinder I have never seen an engine that was bored correctly and true the whole length slap it just wont happen.

01-12-2006, 08:41 PM	#15
shopratles Senior Member Join Date: Dec 2005 Location: Texas Posts: 172	This is kind of comparing apples and oranges, but my 1982 Harley has had piston slap since new. Guess what - 24 years and no rebuild yet. Also my '02 Trans Am (LS-1) really used to knock (even when new). I have to agree with GMTech, as long as the fluids look good and the knock goes away it is probably ok.

01-13-2006, 04:09 PM	#16
gmtech Senior Member Join Date: Dec 2005 Location: farmville Va Posts: 348	The noise is because of the type of pistons which have no skirt and are what they call hyperconnectic sp they use them is race engines and they are a low friction piston and they are small in diameter in design and need heat to make them fit the cylinder. Seeing as how every single 3.1,3.4,4.8,5.3,6.0 engine that uses them make the noise There can not be that many cylinders out of round. On race engines inwhich they were designed for noone hears the noise over the loud exhaust but they are a true and proven design and have had no durabilty issues that i have seen.

01-13-2006, 04:23 PM	#17
gmtech Senior Member Join Date: Dec 2005 Location: farmville Va Posts: 348	Here is the description of the pistons from the gm manual The pistons are cast aluminum. The pistons use two compression rings and one oil control ring assembly. The piston is a low friction, lightweight design with a flat or recessed top and barrel shaped skirt. The piston pins are chromium steel, have floating fit in the piston, and are retained by a press fit in the connecting rod. 6.0L LQ9 applications will have full-floating pistons/pins retained by internal clips. The connecting rods are powdered metal. The connecting rods are fractured at the connecting rod journal and then machined for the proper clearance. The piston, pin, and connecting rod are to be serviced as an assembly.And here is the 1 of the bullitens that addresses the concern Some of the above vehicles may exhibit an engine knock noise that begins in the first several thousand miles/kilometers of use. The knock noise is most often noticed during initial start-up and typically disappears as the engine warms up. The noise is usually more noticeable on the initial start-up when the temperature is below 10°C (50°F) or if the vehicle has not been used for several days. This noise may be caused by an interaction between the piston and the cylinder wall. GM Powertrain Engineering, and an analysis of engines returned with this condition, has confirmed that the noise is not detrimental to the performance, reliability or durability of the engine. The noise does not have any effect on the longevity of any of the engine components. The other bulltien also talks about carbon build up.

11-18-2006, 03:57 AM	#20
a5150joseph Full Member Join Date: Nov 2006 Posts: 10	Yeah, my 2001 knocks a bit too in the morning. They insist it is normal. I've had no engine problems in mine, i have 86,000 miles and still running strong.