Cold start rattle on LS3 - piston slap :) Engine replaced

[Ron Burgundy]

As some of you might know i was investigating cold start noise on my LS3. Rattles for only a few minutes until it reaches the operating temperature. Two holden dealerships said it was not a concern and a lot of people here had different theories.

Today I ended up consulting Sonny from Autowerks....and for those who are not familiar, he is one of the best and most reputable engine builders and tuners in NSW.

He saw the videos I took and told me he knew exactly what the issue was.

EXCESS PISTON TO BORE CLEARANCE - aka infamous piston slap.

He knew this as they came accross two LS3 engines with identical issue. One of them was brand new crate engine LS3 that they purchased. Holden did not acknowledge the issue so they ended up pulling apart brand new LS3.

The found that piston to bore clearance which is meant to be .002 was .006 and after adressing the clearance issue the engine was quiet as a mouse.

He also strongly advised not to let Holden pull it apart as they are not really engine builders and would probably make other things worse.

He took his time to look at this and talk to me free of charge. He at no point suggested for them to fix it and for those who know Sonny...he is one of the most honest guys and he provided advice without any self interest.

He said that it will generally not affect the performace and longevity of the engine but as the engine wears and tolerances increase the noise will get worse.

I am now stuck with this as I dont want Holden to pull it apart. I might start the process of insisting to have the engine replaced but I suspect I will not get very far.

The issue is not common on LS3 but some engines are slighly out of spec. from the factory...

For those who did not hear my engine on cold start I will paste some links in the post below.

 

[Ron Burgundy]

 

[monstar]

Ron, I like Sonny and yep he’s honest. However the information about the noise being piston slap because pistons to bore on some LS3 is opinion, not correct. Sonny does not turn spanners btw, taps the keyboard and is fairly well on top of the HP Tuners. When was Marranos I had full exhaust, OTR and Sonny flashed the tune, including trans tune which was radical but magic.
It is because you are putting engine under load when cold, when it is striving to be able to combust at all. That is knock you hear, that is all.
Here is my engine showing clearly that piston to bore is huge, massive. Yet I don’t get knock under load when cold because I modified the tune.

Now it’s doesn’t take a scientist in engine building to see there is more than a couple of pubes piston to bore, and I don’t have knock when starting. Because I don’t try and drive with an intake valve temperature less than 50°C.
Doesn’t matter how fast one thinks a 200kg aluminium heat sink should take to heat up the intake valve (never mind rest of rig) loading up a cold LS is mechanical masochism. Because finding acceptable combustion without knock is chasing a moving target.
Anyways I realise most everyone will quote the easy answer, a mechanical quality fault and careless attention by the largest engine builder. But consider how the problem was diagnosed in this case then repaired to become whisper quiet on cold start (before IVT > 80°C). Must have been removed, tear down, TPP honed and new pistons, rings right? To custom spec. I’d guess the tune was altered too.
Thing is if you want less knock under load when cold you need to riches the bejeezus out of it, and ain’t nobody gonna approve emissions from that tune, certainly not Holden.
If I were you I’d ask Sonny to have the thing tuned and spin the wheel RE warranty.

 

[Ron Burgundy]

As usual, thank you for your ongoing input with this mate. You always seem to push me the other way when I think I have an answer. What I found interesting in my conversation with him is that he said the noise was gone on LS3 once they sorted clearance issue. In any case...whichever theory is correct it is unlikely to have any negative effect on this engine.
My only question is.....if it is tune related...why is it that only some engines make this noise and others don't...
Btw. When my warranty is out I will be doing CAI and tune with Sonny

 

[monstar]

Why some more noisy than others because sure there are different clearances, cross sectional area and volumes, component / seal matching, injector characterisation, barometric environment, more so casting than honing... but the mandatory one size fits all stock tune stops compensating for such individual variance (fuel mainly) within absolutes of emissions, and safety (longevity within warranty). i.e. simple answer is to have engine high idle rich, which leaves huge unburned fuel like old days, wears engine prematurely.
Perfect tune is with feedback from each cylinder - EGT, knock, lambda, spark capacitance, cylinder pressure, injector spray pattern, shrouding at different load and RPM. Most race cars don't have this, all we got is one or two microphones on block, a narrowband for each bank, MAP and MAF, coolant thermometer and a dual core 32 bit processor to imagine what's going on!

 

[Smashfist]

Holden's position to dealers is that piston slap to a minor extent is characteristic of the LS engines and they won't be issuing authority to replace engines unless it's excessive. If it goes away shortly after starting I wouldn't worry about it, just don't go flog it cold.

 

[monstar]

Holden's position to dealers is that piston slap to a minor extent is characteristic of the LS engines and they won't be issuing authority to replace engines unless it's excessive. If it goes away shortly after starting I wouldn't worry about it, just don't go flog it cold.

He means the car, Ron

 

[Ron Burgundy]

He means the car, Ron

 

[Davison]

Mine is the same as the videos you posted. No big deal, I just let it warm up.

 

[Ron Burgundy]

soooo....in theory...

Does the engine oil type and viscosity play any part in how audible the noise is ?