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

monstar

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soooo....in theory...

Does the engine oil type and viscosity play any part in how audible the noise is ?
Yes for all the mechanical friction noise, but my guess is that although quieter because of that, it will still make slight knock under same conditions.
 

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I wouldn't be concerned about piston slap more like slight knock because the engine is cold. It takes ages for the engine oil & trans fluid to get to optimum temp. Well after the coolant temp is at operating range. With normal driving this is around 10-15 mins in Qld but if in cooler climates could take longer. Maybe warm it up driving a bit harder up to about 4,000rpm or so and see if it's better. If still doing it I'd be looking at the tune
soooo....in theory...

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

It does somewhat. I've recently gone to the Penrite Enviro Dexos 2 from the hpr5. The top end noise isn't quieter on cold start up but it seems to get to temp quickly and is running 1 deg cooler on the hwy. The engine seems right on song. Sounds tuff as on cold starts too, noisy, rattling & lumping over roughly! Some folk around the local shops look in disgust when it pulls up. Freakin luv it when that **** happens
 

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I wouldn't be concerned about piston slap more like slight knock because the engine is cold. It takes ages for the engine oil & trans fluid to get to optimum temp. Well after the coolant temp is at operating range. With normal driving this is around 10-15 mins in Qld but if in cooler climates could take longer. Maybe warm it up driving a bit harder up to about 4,000rpm or so and see if it's better. If still doing it I'd be looking at the tune

You’re right on the money, the coolant gets to operating temperature in a few minutes but the oil takes much longer and around Sydney it’s about ten minutes winter or summer.

My Euros are equipped with oil temp and coolant gauges and with my Merc the oil temperature is also digitally displayed in the central display window and the numerals flash until the operating temperature is reached and until it’s reached it won’t let you go mental with the accelerator.



.
 

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We all love a nice short skirt on our slugs. But, they do have their disadvantages.
 

monstar

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I wouldn't be concerned about piston slap more like slight knock because the engine is cold. It takes ages for the engine oil & trans fluid to get to optimum temp. Well after the coolant temp is at operating range. With normal driving this is around 10-15 mins in Qld but if in cooler climates could take longer. Maybe warm it up driving a bit harder up to about 4,000rpm or so and see if it's better. If still doing it I'd be looking at the tune


It does somewhat. I've recently gone to the Penrite Enviro Dexos 2 from the hpr5. The top end noise isn't quieter on cold start up but it seems to get to temp quickly and is running 1 deg cooler on the hwy. The engine seems right on song. Sounds tuff as on cold starts too, noisy, rattling & lumping over roughly! Some folk around the local shops look in disgust when it pulls up. Freakin luv it when that **** happens
Haha same, 250 psi cranking pressure sounds like jalopy with increasing flat battery like “Wah wah wah err errr errrr... arr.... nah....” then BOOM! Surprises people with hideous farting, shaking, gotta run lots of random explosions - runaway - until vacuum builds to shut the bimodal flaps. Work park is underground concrete cavern full of golf cart mode hybrids and weeny crossover turbos gliding around, also perfectly amplifies monstar bangs, kapow and clangs over four or five levels! Old mate attendant wandered over the other day recommended a cheap place to get a service o_O
 

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Haha same, 250 psi cranking pressure sounds like jalopy with increasing flat battery like “Wah wah wah err errr errrr... arr.... nah....” then BOOM! Surprises people with hideous farting, shaking, gotta run lots of random explosions - runaway - until vacuum builds to shut the bimodal flaps. Work park is underground concrete cavern full of golf cart mode hybrids and weeny crossover turbos gliding around, also perfectly amplifies monstar bangs, kapow and clangs over four or five levels! Old mate attendant wandered over the other day recommended a cheap place to get a service o_O
Is that with or without bimodals open. Haha.
 

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We all love a nice short skirt on our slugs. But, they do have their disadvantages.

I seem to recall reading somewhere that the piston offset was also reduced in the evolution of the LS3. This was something to do with reducing the internal friction but had the side effect of increasing the piston slap. However, I don’t recall when the reduction in the piston offset occurred.
 

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I found these links which may be of interest: (chrisp yes there is a lot 'out there' and from my understanding, we are lucky having our LS V8s over the other comparable cost options for both performance and longevity).
The following link refers to LS1 and is reassuring to all LS owners and yes to my understanding the LS3's have seen improvements to what is a basic problem to most manufacturers; the links describe this popular forum 'problem noise' repeatedly discussed here and the US (other most likely have better info but I hope this info helps alleviate some concerns - I personally find just letting the car idle in the garage for a short time (couple of minutes) before driving off helps to quickly stop this driving cold noise than just driving slowly for a few minutes. I am not a mechanic, now only use 95 or 98octane fuel to reduce knock. I don't race the car so use the oil the manufacturer recommends (another popular forum topic) - Delco 1 5W30 oil and I prefer not to go thicker as there are more parts in the engine to consider than just catering for a few minutes of piston clearance chatter.
https://ls1tech.com/forums/generati...791-piston-slap-explaination-gm-engineer.html
SS Forum http://www.ssforums.com/forum/engine-technical-discussion/63498-piston-slap.html
AMW SS forum member provided this opinion: Okay, what worries me is that some of you don't have any "slap" in the morning, upon cold start-ups. However, I found this quote online from a GM engineer: The noise is an annoyance but will not hurt anything and the engine is fine. (see link for full comments).
Also re "Especially in cold weather starts, isn't piston slap *expected* and *unavoidable* in engines such as LS3 with hypereutectic pistons?
The whole point of hypereutectic is to increase the thermal stability...which is to say to REDUCE the coefficient of thermal expansion. In other words hypereutectic don't expand and contract very much based on temperature."
If you are getting piston slap in an LS3, it can be a worst case scenario of a piston on the smaller side of acceptable tolerance and a cylinder bore on the larger side of acceptable tolerance."
Hope this helps but if not, suggest do a search yourself and lodge any key recognized professional opinions found on this forum. Worth it to ease concerns I also had but are now comfortable with.
In brief as explained in the links above: "Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter skirts make them more prone to rocking.
Unfortunately, when the performance and fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.
The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm."
 
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monstar

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The following link refers to LS1 and is reassuring to all LS owners and yes to my understanding the LS3's have seen improvements to what is a basic problem to most manufacturers; the links describe this popular forum 'problem noise' repeatedly discussed here and the US (other most likely have better info but I hope this info helps alleviate some concerns - I personally find just letting the car idle in the garage for a short time (couple of minutes) before driving off helps to quickly stop this driving cold noise than just driving slowly for a few minutes. I am not a mechanic, now only use 95 or 98octane fuel to reduce knock. I don't race the car so use the oil the manufacturer recommends (another popular forum topic) - Delco 1 5W30 oil and I prefer not to go thicker as there are more parts in the engine to consider than just catering for a few minutes of piston clearance chatter.
https://ls1tech.com/forums/generati...791-piston-slap-explaination-gm-engineer.html
SS Forum http://www.ssforums.com/forum/engine-technical-discussion/63498-piston-slap.html
AMW SS forum member provided this opinion: Okay, what worries me is that some of you don't have any "slap" in the morning, upon cold start-ups. However, I found this quote online from a GM engineer: The noise is an annoyance but will not hurt anything and the engine is fine. (see link for full comments).
Also re "Especially in cold weather starts, isn't piston slap *expected* and *unavoidable* in engines such as LS3 with hypereutectic pistons?
The whole point of hypereutectic is to increase the thermal stability...which is to say to REDUCE the coefficient of thermal expansion. In other words hypereutectic don't expand and contract very much based on temperature."
If you are getting piston slap in an LS3, it can be a worst case scenario of a piston on the smaller side of acceptable tolerance and a cylinder bore on the larger side of acceptable tolerance."
Clearance.
Hope this helps but if not, suggest do a search yourself and lodge any key recognized professional opinions found on this forum. Worth it to ease concerns I also had but are now comfortable with.
In brief as explained in the links above: "Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter skirts make them more prone to rocking.
Unfortunately, when the performance and fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.
The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm."
Or you could take that 12 year old post relating to 15 year old in the GenIII pre-modern brittle silicone eutectic pistons, being slapped around when cold (not under load but audible stationary revving), as not relevant to the cold load noise being discussed here re the GenIV knock when cold.
But sure, above is an easy explanation, thinking GM's high-tech honing of new bores is literally pear-shaped, if that is your want. But I think it would stand to reason that clearance gets worse with use, and the engine becomes prone to excess oil consumption / needs replacement rings, right?
When is the last time you heard of an extremely high mileage GenIV needing new rings? Only time I read about that was hopelessly diagnosed. I've never needed to top the oil BTW, in more than 300k km hard use.
 

Immortality

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Or you could take that 12 year old post relating to 15 year old in the GenIII pre-modern brittle silicone eutectic pistons, being slapped around when cold (not under load but audible stationary revving), as not relevant to the cold load noise being discussed here re the GenIV knock when cold.
But sure, above is an easy explanation, thinking GM's high-tech honing of new bores is literally pear-shaped, if that is your want. But I think it would stand to reason that clearance gets worse with use, and the engine becomes prone to excess oil consumption / needs replacement rings, right?
When is the last time you heard of an extremely high mileage GenIV needing new rings? Only time I read about that was hopelessly diagnosed. I've never needed to top the oil BTW, in more than 300k km hard use.

It's probably a bit hard to compare your built engine to a run of the mill GM production line unit, I'd certainly hope your engine guy took a bit more care than the GM production line.

Stock GM engines are well known to breathe heavy and put lots of oil through the intake, I wonder what causes that? Worst part is it's not a problem restricted to the V8 engine either as the V6's are just as bad.

The other issue at hand is that some of these LS3 engines make horrible noises at start up where others don't. All things been equal (same engine/tune etc) they should either all do it or non do it. Just because a GM engineer says it's acceptable doesn't mean it really is, it just means GM doesn't care because to admit that this is a problem would potentially bankrupt the company repairing all those noisy LS engines out there.

People need to remember we live in a capitalist society where bean counters regularly over-rule the engineers to save a few dollars where ever possible to the point that they would rather pay out for a few dead people than recall a million cars because it's the cheaper option. Do you think the bean counters really care if the new engine is a bit noisy sometimes because they removed a few guys from the engine line, the guys that double check those piston bore clearances for example, they just pay some engineer a big bonus to say "it's all 100% a OK".
 
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