[blak dymondz]

honestly, the bearing going bad would sound logical or consistant to what im hearing... im not 100 on that though...im going to have it checked out this week (hopefully) but i feel you, i dont need the heat right now and it could wait, but i would rather address it before i NEED the heat this fall and im rolling @ in a car that sounds like crap. i hate that lol

its most likely the blower motor, mine makes noises in my 98, due to trash and i think the bearing is going out in it, but it still works, so ill keep using mine til i finally goes, lol.....

 

[FSTLS1TA]

The odds of an ls1 having piston slap are rare. There very well built motors. But they all have noisey valve trains. And when you add a cam it sounds like a sewing machine under the hood. Reason why is the rocker arms are a full roller rocker arm they only swing so far. And what happens is called a tap effect. That's when the valve train gets really loud with a cam install because now the tapping effect gets worse with bigger cams. So when a cam install happens most of the time aftermarket full roller rocker arms are used. So you can cut down on the valvetrain noise.

 

[GaryDoug]

The odds of an ls1 having piston slap are rare. There very well built motors. But they all have noisey valve trains. And when you add a cam it sounds like a sewing machine under the hood. Reason why is the rocker arms are a full roller rocker arm they only swing so far. And what happens is called a tap effect. That's when the valve train gets really loud with a cam install because now the tapping effect gets worse with bigger cams. So when a cam install happens most of the time aftermarket full roller rocker arms are used. So you can cut down on the valvetrain noise.

Well then my 1998 LS1 engine must be rare then, because it's been diagnosed by two shops as having piston slap in one cylinder. But it is temperature or warm-up related, not randomly occuring like the OP mentioned. Mine knocks from about 10-15 seconds after startup until 1-4 minutes later. The duration depends on the outside temperature, Colder (<40F) is longer. Warmer (>80F) is very short. It was explained to me that that is the time required for the piston to expand to a tighter fit due to the thermal expansion differences. The fix for now is that I let it warm up until it silences almost every start. The "official" GM answer is that 3 minutes or less of noisy knocking is aceptable. And it actually states that in the factory shop manual I purchased in about 2000.

 

[FSTLS1TA]

You have to remember not all engines are built the same. That's why you see some ls1 engines make great power and some make ok power than there are the freaks of natures that just make crazy power from the factory. Same with the internals. Now in the LS1 motors that came out in the 97-98's had issues that made the motor have a short life. But new castings of the block were made for the 99's and on.