got a 2001 ls1 which does 2 things,
1st when the season is cold the number 1 piston does some slight light knocking during start up for a few min until it warms up. iv reserched this on internet and dealer and found out its due to the material the piston is made dosent sit right in cylinder until it expanse from heat. dealer told me this same thing i found out on internet of course i dont take everything i read in the internet to heart but as good to know stuff. this piston knock thing has never affected the performance of the car.
2nd this ls1 has had the oil eating problem which i know alot od ls1 have that nearing the 3000 oil change mark the low oil light is coming on and you got top it off right before the next oil change.
where i leave right now the weather at night gets to around 55-60 which is around the time the engine does its piston knock during cold start up. the other day went ot start it arond 4am weather around 59 deg and the piston knock was pretty severe sounded like the piston was rattling (no literally) around or bad valve train noise. but it was coming from the number 1 piston area. i know ls1 pushrods are not the best at high rpms but car hasnt been reved up past 3000rpms in the 4o miles a week it gets drive in the past few month due to gas.
iv have this problem all time with the knock in cold weather and the low oil light coming on just drive home and add oil never had problem until this time
always use royal purple 10w-30, idles fine, oil pressure is normal, no overheating but then again didnt leave it on long enough to get the temp up. car is due for and oil change and the low oil light had just come on was moving car from driveway to garage. car had been running fine with no signs of this.
has anyone had this problem before with the severe piston knock? or any info that might help before i start tearing it down and banging head to the wall.
waithing for payday to change the oil

I'd check compression on #1 and a couple others for a baseline. I've been told LT1's can do this also because of the Hyperutectic pistons in them. A compression test may show signs of a problem.

If anything has passed thru the motor it may have ended up in the #1 cylinder to. Anything small and hard can embed itself into the piston or head and make all kinds of noise.

compression test yes, gonna do that when i change the oil. didnt think of that when something happens to one of my cars especially when i already got 2 other cars down up in jack stand i start geting fustrated cause i start jumbling all cars at once and start getting tunnel vision at situation.
if there is for some reason something passed in there (which would be my first time encountering this) what would be the easiest way to maybe get it out without removving the head if it hasnt wedged between piston and cylinder, maybe removing plug and blowing air in there.
the only thing its a rytemed knocking noise like it has always when its cold but all of a sudden louder if somethung had passed through and tapdancing in there it be off beat.

if comp test points toward worn rings would rings be severe worn enough that it make the piston knock on cylinder walls?
car has only 63k
well on payday gonna start with oilchange and take it from there
ill keep posted
if you have any more thought, suggestion, info or visions from heaven keep me posted

Yes, i have heard of this. I do not remember what the problem is, but it is common. I will see if I can find it.

Matt

Yea, I've read about this too, seems like it was a wrist pin. I think there's a TSB on it.

You originally said that the knock went away after a few minutes once the engine warms up. Is this still the case or has something new happened ?
The later LS1's all seem to have this problem including the oil consumption, My `98 never really did. although I do get some ticking in the engine on initial start up during the cold months it never has been an issue.

9t8w66 mine also does the ticking on initial sstart up in the cold month to and had never been and issue either.

let me rephrase it the normal knock i first described its had since day one on initial start up - is more of a ticking like 9t8w66 said his ls1 does (for anybody else thats had this normal problem, as a refrence point)

9t8w66 its still the case now the ticking is louder but, but i didnt leave it long enough to see it ticking went away. nothing new has happened as in driving habbits havent rev up past 3000 due to gas prices and onley drive it bout 40 miles a week.

i remember the oil consumption was having something to do with a hose or pipe that runs underneath the vally plate where the knock sensors are located, passing oil and the fix is to replace it with the same pipe kit from an ls6. got that on a stack of papers in my desk, ill dig it up and post for everybody else info.

A compression test will only determine if theres a bleed off problem (Bad rings or bent valve).
IMO you need to drive the car more spirited to aid in determining the problem. If the engine is warm and the noise persists and increases with rpm it could very well be valvetrain related. It's pretty unusual for an auto equipped car to bend pushrods and a collapsed lifter would most times throw a code and flash the SES light.
If you drive it and the noise goes away then it's probably just the regular piston slap isssue and there isn't much you can do about that short of replacing the engine.

havnt driving it right now cause the low oil light on and needs oil change, gonna drive it a bit as soon as i change the oil see if it was the regular tapping it was doing during the winter month and maybe this time around it decided to do it louder, maybee the oil broke down to soon but its royal purple then again it was a brutle hot summer.
ill keep it posted
just got back from this season powerlifitng world championship in reno and ill be in offseason lifting till around march and now can devote my time and money to my cars had some bolt ons for the ls1 laying around to try and hit the 12s this winter and bang this happens, dang it.

I sometimes hear a ticking sound on my 2000, ecspecially in cold weather, never been an issue though. I think in LS1 Tech there is a big writeup on this, they said it was because in the LS1 the pistons were not ''individually hand fitted to each cylinder'' as in the case of the previous small blocks because of cost constraints. Leave it to the General to skimp in an area as crucial as this! If it is louder/worse than normal I would definently do some more checking though. Dave

This is what I was talking about
http://www.pistonslap.com/

my 98 ticks every morning on initial start up. and yes mine uses oil even after a bottom end rebuild. i've read somewhere that the oil leaves via the intake yet i have no leaks no smoke or any residue in the intake. if the low oil light is on for goodness sake add some oil to it. my oil light never came on and under hard and i do mean hard acceleration the engine starved itself for oil and i spun a rod bearing. they won't run long with no oil.