My angry pistons want out...........what's the best fix??

[wrenchead99]

hey all, I've done some searching but now seem to be more confused than ever. I have a 2000 Sierra 2500 with a 6.0L engine with that nasty piston knock. It's starting to get really bad so I'm wondering what are my options, especially the most cost-effective ones?? Simplest thing would be to drop in a used engine, which I can get one with 12k miles on it for about 1700.00. the problem is, will I still have the same problem later on, seeing as this engine will still have the same style pistons in it?? Now the big question is, Can I used a later style engine (03+) and only put the engine in without any other mods (ECM, etc.). I realize that I will have to use the later style flexplate for the 4L80E but will this not solve my piston issues completely?? Any good rebuild kits out there as well, in case I decide to go that route??


Thanks in advance for everything.

[GasGuzzler]

The base engines should swap from 2000 to 2003. Things like manifolds, hoses, sensors, throttle bodies, etc. need swapped over.

Are you sure it's a piston noise? 6.0's are the least common to have piston noise out of all the LS engines although piston noises are not totally uncommon.

Carbon knocks are a lot more common.

[wrenchead99]

pretty sure it's piston noise, but I could be wrong. Really hammers on cold startup and drive, no noise unless under load. Gets better as engine warms up, but is still noticeable when the engine is coasting. sounds like a bad rod bearing, but no debris in oil and oil pressure is good. What can be done to check if it's a carbon knock?? If it is a carbon problem, how do I cure it??

In regards to the engine swap, I realize all sensors, etc will need to be swapped over, but I still seem to remember something about the cranks being different lengths at the rear of the engine........

I need more education......

[r.barn]

Carbon can be removed using Seafoam sucked up thru a vac hose.
Disolves carbon off valves and combustion chambers.

Whats the deal with these Gen-III's and "piston knock" ?
Never heard of piston knock, just rod knock from bad bearing or bent rod.

[RedHeartbeat]

if you use seafoam be sure you just trickle feed it into the engine or you can bend a rod adding it too quickly. I prefer to add it before the throttle body or at the EGR port. Pour 1/2 - 1/3 of the can into the intake and shut the engine off for about 15 minutes. When you start it back up it should smoke like crazy an knock the carbon free.

The issue with the pistons is primarily due to very short pistons and skirts. The pistons rock a little bit from side to side in the bore. I believe GM has altered the piston design to reduce this issue in the later model vehicles and service parts.

[GasGuzzler]

Seafoam can damage O2 sensors too. Many have used it with no problems but...

I use GM Top Engine Cleaner.

[George C]

if using seafoam run it thru the vaccum booster line


what oil and what oil filter you using? my 4.3 blazer has that typical sound on cold start up

[GasGuzzler]

2500 may not have a vacuum booster or hose. My Denali does not because it has the 2500 style hydraulic booster. If there is no booster you can use the FPR vacuum line. It's small but it keeps from putting too much in too quickly. Cams are failure prone too, especially high mileage (200K+).

[wrenchead99]

has hyd. booster so I'll need to use another port. I've already de-carboned the engine once without any change in the noise Using a Wynns product which works well from my experience. Seafoam at the time was not available here, but I do believe it's carried now. Engine has 190,000 KM on it or 130,000 miles, so a cam issue may be unlikely but not impossible. Wouldn't a carbon or rod issue stay close to the same regardless of engine temp?? I'm still going piston noise because it almost goes completely away or is not as noticeable when warmed up. Typically I run QS truck semi-syn with a Wix Nascar filter, but the noise stays the same regardless of oil type used. Additionally, noise is not present for first 5-7 seconds of run time on cold (think overnight at -25, not plugged in) startup. In the couple of years that I've owned the unit, the noise has gotten somewhat worse, but now seems to have leveled out. Load does not affect it, as it sounds the same empty or when I'm pulling 30 foot travel trailer. I'm just sick of this thing sounding like a diesel all the time..........

[RedHeartbeat]

How about the possibility that it could be a failed rocker arm? The GM arms are notorious about losing bearings in the roller trunion and causing a knock noise.