Anybody else own a GM-Chevy 6.0L "knocker"

[OVERKILL]

Originally Posted By: NHHEMI
Originally Posted By: JetStar
Isn't the knock sensor going to retard the timimng regardless of the cause (piston slap or detonation)? I need to check to see if the knock sensor is active during warm-up or if it only becomes active after op temp is reached, or maybe closed loop?
I had a '96 GMC 1500 that I bought new that had this issue. Seems like it started at around 20K miles. It had 150K on it when I got rid of it. No engine work ever done on it. I always used M1 10W30 synthetic in it. Wish I could say the fuel pump was as reliable.


The piston slap issue has nothing to do with the Knock Sensor. There is too much play, with the engine cold, between the piston and the cylinder sleeve. Once the engine warms up, and things expand, the slop is gone and so is the noise.


But if the slap is hard enough, it COULD trigger the knock sensor. The sensor has no idea what the cause of what it picks up as "knock" is.

 

[tig1]

This is a chronic problem with these engines. A friend sued GM over this but lost his case. Oil will not cure this. It's design problem with the piston skirts.

 

[OVERKILL]

They are too short. And the bore clearance is too loose. GM fixed it later with coated skirts. Something Ford has been using since the early 90's.

 

[steve20]

didn't this all come about when The General stopped addressing manufacturing tolerances, and stopped fitting pistons relative to bore size? ie the biggest piston in the biggest hole, smallest piston in the smallest hole etc etc.
Wife has an 04 Tahoe with the 5.3-no piston slap whatsoever, and it has sat outside it's entire life 60K of short trip driving.
I've used a bunch of 5-30 synthetics and conventional oils, and it always sounds soooo much better on conventional oil

Steve

 

[OVERKILL]

I think it's just a characteristic of the very Ford-inspired LSx engines. They have very short pistons. This, by nature, makes them prone to slap due to to lack of lateral control, which the skirt provides. If they had forged pistons, it would be even worse due to looser piston-to-wall clearances.

Ford's modular engines have shorter pistons as well (compared to the Windsors) but not as short as the LSx ones. They also had coated skirts from day one IIRC.

 

[XS650]

Originally Posted By: OVERK1LL
I think it's just a characteristic of the very Ford-inspired LSx engines. They have very short pistons. This, by nature, makes them prone to slap due to to lack of lateral control, which the skirt provides. If they had forged pistons, it would be even worse due to looser piston-to-wall clearances.


There really wasn't a problem. It was just the customers "perception" that there was a problem.

 

[OVERKILL]

Originally Posted By: XS650
Originally Posted By: OVERK1LL
I think it's just a characteristic of the very Ford-inspired LSx engines. They have very short pistons. This, by nature, makes them prone to slap due to to lack of lateral control, which the skirt provides. If they had forged pistons, it would be even worse due to looser piston-to-wall clearances.


There really wasn't a problem. It was just the customers "perception" that there was a problem.


OUCH!

They are otherwise reliable engines though. And make good power.

Obviously, I'm not a GM fan, but still, I cannot knock (har har) the LSx series.

 

[Whimsey]

Originally Posted By: OVERK1LL
I think it's just a characteristic of the very Ford-inspired LSx engines. They have very short pistons. This, by nature, makes them prone to slap due to to lack of lateral control, which the skirt provides. If they had forged pistons, it would be even worse due to looser piston-to-wall clearances.

Ford's modular engines have shorter pistons as well (compared to the Windsors) but not as short as the LSx ones. They also had coated skirts from day one IIRC.


A friend had a 2001 F-150 with the 4.6 and he developed the cold start piston slap. It wasn't like Chevy's but it was there on start up in the cold temps. My 2002 F-150 does not have that problem. My 4.6 has an aluminum block and his 2001 has a cast iron block. I believe the pistons are aluminum. Maybe the expansion rates with aluminum pistons in a cast iron block helped cause that the "piston slap" where as mine being all aluminum didn't have that problem.

He took great care of the truck, so it wasn't from negligence but from design.

Whimsey

 

[OVERKILL]

You sure it wasn't the timing chain tensioner? They are known for it......

The pistons, like those in the LSx, are hypereutectic, which is a silicon/aluminum alloy. The exception being that all the Ford ones are coated, whilst the LSx ones are only coated in more recent years.

 

[XS650]

Originally Posted By: OVERK1LL
Originally Posted By: XS650
Originally Posted By: OVERK1LL
I think it's just a characteristic of the very Ford-inspired LSx engines. They have very short pistons. This, by nature, makes them prone to slap due to to lack of lateral control, which the skirt provides. If they had forged pistons, it would be even worse due to looser piston-to-wall clearances.


There really wasn't a problem. It was just the customers "perception" that there was a problem.




At least they were fasted than they were with various V6 gasket problems.

OUCH!

They are otherwise reliable engines though. And make good power.

Obviously, I'm not a GM fan, but still, I cannot knock (har har) the LSx series.


Yeah, my LS2 doesn't even have hint of a problem. GM does fix problems. It only took them a little over a year to start addressing the problem of C6 Corvette roofs blowing off. They somehow knew how to glue the roofs on so they wouldn't blow off on the C5 Corvettes, then forgot how on the C6 Corvettes. It must have taken them a year to get the C5 roof glueer to come back out of retirement.

When the roofs blow off of C6 Corvettes, you can hear the owners saying I "perceive that there is an unusual amount of wind going through my hair."

 

[OVERKILL]

HAHHHAHHAH

 

[Bryanccfshr]

[censored] picky owners...LOL

 

[XS650]

Originally Posted By: Bryanccfshr
[censored] picky owners...LOL


That's just your perception

 

[mstrjon32]

Originally Posted By: ThirdeYe
We have a GM 3.1 with the famous piston slap, I've tried all sorts of brands, synthetic, synthetic blend, conventional, 5W-30 and 10W-30, nothing really made a difference. It's still going now at over 75,000 miles though.


I sold a 1997 GM 3100 with 195K miles that sounded awful when cold, but still warmed up to a barely audible purr at idle. Pulled like new the day I sold it, and other than the [censored] intake manifold gaskets requiring replacement twice, never had any engine problems.

Tried a few different brands of oil and filters in it, none of it ever made a difference.

My 1999 Jeep 4.0L has 170K on it now, a bit of piston slap at start up that calms down once it's up to temp. Like the GM, it's annoying but I don't expect it to result in any longevity issues.

 

[edwardh1]

you'd think after building them for a few MONTHS GM would have gotten complaints and fixed whatever is wrong. Seems pistons 0.002 bigger would not cost that much.

 

[grease_monkey]

My mom's 03 chev trailblazer had the same problem. my dad used 1 quart of lucas and that took care of it.

 

[GMBoy]

I've got the 345hp version of the 6.0L in my 2006 Sierra Denali crewcab and while I have NO piston slap noise at all-- I did get the carbon problem around 15k miles. I did a Seafoam clean and that solved the carbon problem. Also, I now run Redline fuel system cleaner occasionally to keep things clean.

 

[bretfraz]

GM fixed the issue (for the most part) by the 2004 m.y. My Sierra has a slight CSK but using GC minimizes the noise a bit. "Thin" oils like Mobil One seemed to amplify it.

Don't know if its a big problem but it is a customer perception issue. I used to drive an '01 Sliverado 2500 with the 6.0L, towing about 8000 lbs, and that thing would rattle like an old diesel in the AM startup. Didn't affect engine performance and the motor hardly used any oil even with 80K of hard use on it.