LS3 cold start Slap is driving me crazy!

[vombil]

In that case most likely lifters....
Piston slap on LS3 generally occurs on cold start, it's not audible at idle and it rattles for about 5 min or so, under light load until the engine warms up...

good to know - thank you. 5 mins seems like a very long time for it to be noisey. Mine is noisey for only up to 45-1 min max. Ive got 10x 5L 304's that do not make a peep on cold start even after not running for months. Not sure why the LS took such a drastic step backwards in this regard

 

[vombil]

I disagree, modern alloys (used to make pistons) expand less with heat so need less piston to bore clearances than older engines so there is no excuse for it. sure if you run forged pistons and heavy springs and solid lifters would I expect mechanical noises from the engine but for a stock factory engine you really shouldn't be hearing mechanical sounds.

LS motors have had issues with pistons/rings and oil usage from day zip because GM decided to make design compromises to try to increase efficiency. The fact that some people with VF/LS3's have whisper quiet engines and others have sowing machines clearly demonstrate that quality control was rather lacking at the engine production plant and then GM saying that excessive oil consumption/engine noise is acceptable is just pure horse ****.

Modern production techniques are supposed to improve quality and reliability, not make it worse.

totally agree. there just is no excuse for an old 304/8 bottom end from the 70's being, on average, quieter than something 50 years its junior. it's a smear and really just adds weight to the whole closure thing

 

[Mayuri Krab]

Mine only makes horrible sounds once in a while when 1st started, usually after it’s been parked for 2+ weeks...

Solution was to just drive it at least every weekend lol

 

[Skylarking]

I disagree, modern alloys (used to make pistons) expand less with heat so need less piston to bore clearances than older engines so there is no excuse for it. sure if you run forged pistons and heavy springs and solid lifters would I expect mechanical noises from the engine but for a stock factory engine you really shouldn't be hearing mechanical sounds....

Modern production techniques are supposed to improve quality and reliability, not make it worse.

Yep, it’s all in material science and modern manufacturing techniques.

I haven’t looked at forged pistons but even those do benefit from modern material sciences to control expansion rates so the old ideas aren’t as relevant... After all, forging is a process which results in stronger parts as compared to cast parts (material composition being identical)..

Its briefly discussed at the following link

https://www.jepistons.com/blog/2618-vs.-4032-material-differences

Guess I’m saying that just because a motor is high performance doesn’t mean it should sound like a 70’s bucket of bolts... if it does ,that’s simply lazy engineering and poor manufacture...

 

[lmfvf2ssredlineute]

engines may be in spec but on the border line, you may have a bore size thats at its upper limits still within tolerance , and the piston fitted to that bore at a lowest tolerance size, so you have a larger size bore and a smaller sized piston that been fitted , all within manufactures specs, add the modern low friction short skirt piston and that's the main difference between old 70-80s old pushrod v8s, the short skirt pistons will rock more in a oversized bore, that's the price for low friction and increased fuel mpg and more hp, as they say everything's a tradeoff

 

[Immortality]

engines may be in spec but on the border line, you may have a bore size thats at its upper limits still within tolerance , and the piston fitted to that bore at a lowest tolerance size, so you have a larger size bore and a smaller sized piston that been fitted , all within manufactures specs, add the modern low friction short skirt piston and that's the main difference between old 70-80s old pushrod v8s, the short skirt pistons will rock more in a oversized bore, that's the price for low friction and increased fuel mpg and more hp, as they say everything's a tradeoff

And therein lies the exact problem, Both item fall within individual machining tolerances but they do not meet spec as a unit. A piston at the small end of the spectrum in a bore at the max end of the spectrum equals excessive clearance. Problem is easily solved by matching pistons to bores but that requires another human to measure and match and that doesn't work in an automated assembly line where cost is the ultimate factor.

 

[abuch47]

> cost is the ultimate factor

welcome to modern world

 

[Immortality]

Of course it is, it still does not excuse what GM calls acceptable engine noise/oil consumption for all LS engines.

 

[Subju]

a

 

[bradp51]

What did I expect... a reasonably quiet powerful engine with reliability and long life... maybe it is the case and it’s just the fact one reads of all the problems on forums... but whatever the case, it’s not confidence inspiring

I think this point made by Skylarking is pretty relevant. I am pretty new to the forum and only have 13000 km on my car. So I am no expert. When you are on a forum we read all the faults people have.

Imagine this. How many posts would there be of owners of the VF LS3 the do not have problems. I am sure there would be many more stories of "good" no problem engines. Our impression of the LS3 may then change.

From my memory of owning older cars many years ago as a teenager, was that low oil would produce tappet noise until oil pressure built up. But I suppose that was my old LC 161 engine and my LJ 202 engine.