'99 3100 Piston Slap

[IsaacHayes]

Wow, so I guess what I originally thought was lifters that hadn't pumpd up with oil enough is probably right. I don't have any of the "piston slap" sounds you describe. Inside the car you can not hear the motor at all.

If it's knocking that loud, no doubt you are tripping the knock sensor, and pulling timing. When the engine is cold, it ignores the knock sensor until the engine warms up IIRC. So you would get full power then.

That and a cold engine is getting cold air of course, and further suppressing real knock. But oil is thicker and pressures higher too when cold. My engine feels the same. Cold = decent difference in power.

[Joseph Upson]

I acquired the 2000, 3100 that's turbocharged in my Fiero for that reason I discovered after it was installed, I picked it up from a core shop in like new condition as if the car was purchased and the engine immediately swaped out. I have beat on quite a bit with 7 psi and high revs and the clacking sound hasn't gotten any worse over the past 3yrs though unlike many of yours it seems to always be there and then tapers down a little after it's warmed up. My guess is that it was on the extreme end to have been taken out with seemingly low mileage, everything was still silver inside.

I have read where GM states it's not a problem but I'm sure they are speaking in terms of dependability, I don't believe any of the individuals claiming that on the companies behalf would tollerate such a racket coming from their well maintained vehicle with low miles. I also read stories from customers that dealt with this annoying issue in GM vehicles with larger engines that after making enough fuss about it had it taken care of in warranty including one instance where the problem was fixed with a new vehicle.

Just do a search on the internet under GM piston slap and that will probably take you where you need to go for the run down on it.

Aw what the heck, here you go: http://www.pistonslap.com/

[knockknock]

Hey IssacHayes, I just noticed something else. Not sure if it's relavent to my case or not, but when the car is even warm, I get a constant light metallic ticking noise from the passenger side and I can hear it crisply right at the cover "3100 SFI". It's the same frequency as the "knocking" is, and speeds up just the same when I accelerate and dissapears when the engine decelerates.

Valve...Piston?

Side note: I wanted to flush the oil with some engine flush before I change it this weekend, is it safe or is the potential for engine damage great (90K, regular oil changes)? Any suggestions what to use? Iremember buying some and justrunning it through the oil in a neon before changing theoil and it killed off a weird noise thatcar was doing.

oh yeah,I've been to pistonslap.com before, i listened to the soundsample. I can hear the clacking whichi hearmy car do, but the "knock"my car has isn't in the sound file. heh

[Joseph Upson]

I recommend flushing the engine under one condition, just before you rebuild it to help pre clean the parts otherwise don't do it. Your regular oil changes alone don't warrant it, and in small print on the can it recommends removing the oil pan in some cases which means if you have enough build up in the engine you'll ruin it if you don't by clogging up the oil pump screen.

That stuff is cryptonite, and I saw first hand what it can do when a Jiffy Lube put it in an S10 and forgot to drain it.

You can use it without a problem, I just don't believe it is a wise thing to do without very good cause. I was warned against it and used it anyway. It didn't damage the engine but it removed the oil clot from my valve cover gasket and the oil quietly leaked out the back end of it over several of the many hills in Tallahassee Florida until the oil pressure gauge went to zero, an indirect assault, I learned quickly what was meant by the quote,

"Some times the dirt is the only thing holding it together".

[tractorman]

Joseph knows what he's talkin' about here. If an engine has 90K miles on it and the oil has been changed like it should, then there isn't much crud in there anyway. If there IS enough crud to warrant a flush, then you're going to have problems when that crud starts movin' around. Best to leave well enough alone.

[IsaacHayes]

Hmm. I defiantly don't have a knock sound. Only a desiel motor type sound on start up.

Your knock may be something else. Perhaps it's a worn bearing or something and once warm it expands and takes up the slack?!?!

[knockknock]

Yeah. I hope not. I am now leaning towards bearings, skirt slap, or something similar.

If you guys with the 3100 get really bored, listen to the oil pan with a dowel or screwdriver to your ear once. Silky smooth? or Cummins?

I am now 99% positive whatever I am hearing down there is the "knock" under light load when I take off. It happens every time it sits for 2+ hours. I thought originally the slap the 660s had didn't really come back the rest of the day after it's been ran.

So if that is in fact the piston/skirt slap, then case closed. If a diesel at the pan (when cold or warm) is bearings, time to drop it.

[Superdave]

I noticed the 3400 in my Z24 has a little piston slappage this morning... it's an '02 so no coated skirts for me

[IsaacHayes]

I'll try to listen to my pan and report back.

[knockknock]

Sorry, I know this thread became old but it didn't make much sense starting a new one.

Anyway, that "knock" I described has virtually disappeared. I just had my trusty mech shop service the transmission (MUCH smoother shifts...yet 2 - 3 still shifts hard sometimes, softer other times...any of you with 3100 mated to 4T60E notice that?). Dropped tran pan, new filter, cleaned & new gasket, ran 18qts thru and that was that. Came and picked it up the next day and that noise was GONE. Well, it was sort of there, but you had to listen directly for it with the door open and even then I think it was just an illusion and I was really hearing the real "piston slap".

Any clue??

[prophiseer]

Did you also have the oil changed while it was there? Tranny work won't cease piston slap noise. If you had the oil changed, and they used a higher viscosity oil than what you had in it (i.e. 10W-30 or 15W-30 vs. 5W-30), it can sometimes help quiet benign noises.

I have no idea how servicing the tranny would qiet the noise

[knockknock]

Hmm, not sure if you read the whole thread & replies or not, so I'll just sum it up for you:

Also: a side note, I was never really sure if I was distinguishing this noise from piston slap or not because I haven't had too much experience with these 660s. Hence a misleading title and initial content I suppose.

Purchased car, had valvetrain noise (tick tick tick) and piston slap (tak tak tak) then in Nov. 2005 there was a knock that was very rythmic, noticeable in the cabin, and got progressively worse. Changed viscosities of oil from 5W-30 to 10W-30, went through such brands as Quaker State, Valvoline, Mobil 5000, etc. with no change in intensity or duration of sound. Tried various additives such as MMO, Restore with CSL, and Gold Eagle StopLeak. Nothing. Used Purolator oil filters with the antidrainback valve, nothing really helped.

Noise would go away usually by the time it shifted to 2nd or 3rd. I could leave the car idle for a minute or two and it would still knock as I drove off and would dissapear then. Came back after car sat for 2-4 hours or more.

After the transmission service, that noise is gone. Leads me to believe that a bolt might have been slowly backing off somewhere, but I'm not too sure. Someone suggested to me a few months ago on another forum that a bolt could have been loose on the T/C or plate. Maybe it was, maybe it wasn't, but that's what I'm guessing it was.

Here is maintanence that was performed. Nothing helped the noise but as I said, it was maintanence and NOT and attempt to fix the issue. Just extra information.

Replaced transmission fluid & filter.
Replaced plugs and wires.
Replaced serpentine belt tensioner.
Replaced PCV valve.
Replaced fuel filter.
Replaced air filter (x2).
Cleaned fuel injectors.

Changed oil & filter every 2200-2800mi.
General tuneup

The noise still occured even with the serpentine belt off, which led me to believe it wasn't an accessory or anything belt-driven for that matter. I was convinced it was internal, but I have no clue what it was.

Anyone have any remote clues of any knocking or illusion of a "knock" than can be caused by something tranny related? ???

[prophiseer]

yeah, a loose t/c bolt or a cracked flew plate can cause a 'similar' noise; but usually you'd hear that kind of noise around shift points and under heavy acceleration.

so I take it what you just listed was all done at the same time? If so, replacing the plugs & wires, the fuel filter and cleaning the injectors might have eliminated the problem. It could very well have been spark knock that you were hearing (I doubt it, but still possible).

[torq455]

Sorry, I know this thread became old but it didn't make much sense starting a new one.

Anyway, that "knock" I described has virtually disappeared. I just had my trusty mech shop service the transmission (MUCH smoother shifts...yet 2 - 3 still shifts hard sometimes, softer other times...any of you with 3100 mated to 4T60E notice that?). Dropped tran pan, new filter, cleaned & new gasket, ran 18qts thru and that was that. Came and picked it up the next day and that noise was GONE. Well, it was sort of there, but you had to listen directly for it with the door open and even then I think it was just an illusion and I was really hearing the real "piston slap".

Any clue??

Since your tranny is shifting smoother, I'm thinking somehow the line pressure was high. Maybe the modulator that controls that was bad, or there was a vac leak. I've run w/o the vac line on and heard the same kind of noise. I plugge the vac line back in and soon the noise was gone. However, I did slightly dammage the pump. Running the pump at full psi will damage it.

[bwwelk]

I have a 01 GA gt and bought it nearly a year ago with 39,000 miles and around 41000 it started makin a noise like a piston was slappin so I took it to 2 different mechanics and both said that it was definitely piston slap and that almost all 3400's do it and to not worry bout it ... In fact 1st guy I talked to has a chevy venture with 3400 motor and he said it had a slappin sound in piston since they got it and it now has close to 130000 on it and it still is running fine other than timing chain recently broke..