Idle Knocking

[malibuster]

Hello everyone. I'm new here and come from unitedmalibus.com I have a 2000 Malibu with a 3100 and have a knock at idle. It's kind of wierd because it seems to be worse when the engine is cold. When it warms up it's hit and miss and sometimes it's undetectable. Also when you get the motor up to higher revs, it seems to disappear.

Now my thoughts is that maybe I have a rocker arm hit the valve cover or something. It seems to come from the front drivers side of the motor maybe cylinder #5. Any ideas would be appreciated before I tear into it.

thanks,
Eddie

[talon2swords]

Could be any number of things. You'll probably have to make a youtube video w/ audio or something and post it here. Could be piston slap or something else.

I had a knocking in my 3100 engine. It got really loud on a cold start up. Finally the car started losing power. I didn't think it was the low end. I replaced the lifters and put in a metal lim gaskets. The noise was still there, but was less loud and gradually got less loud over time. The car still works for some reason. It's at least 10k miles later.

Sometimes the lifters may be starved for oil. Maybe the oil passages to the lifters are filled with sludge/gunk and need some cleaning.

I don't guess this kinda situation is the cam bearings, because I would think the car would stop working soon if that was the case.

My old LIM gasket was shot in a couple places too. Better make sure coolant isn't going into your oil or lifter valley. Sometimes the gasket is bad, but will not produce the mayonaise effect.

[geoffinbc]

It is the common piston slap situation. No damage will result from it. The reason you hear it when cold is because the pistons grow as they get hot and fit tighter in the bore.

[malibuster]

Ok so this is something to not even worry about?

Thanks guys for your help.

[SuzukiGhostRider]

Ok so this is something to not even worry about?

Thanks guys for your help.

No, nothing to worry about. It's a common problem even acknowledged by GM.

[malibuster]

I think I am going to add some Lucas Oil Conditioner. I've heard from other people that this can help to eliminate engine noise.

[torq455]

Lucas will just thicken the oil to "pad" the pistons. you really want the oil to get up there asap after a cold start. it's all "normal" for higher mileage. GM says if it goes away after 20 mins, then it's ok. my 97 lumina 3100 with 150K was almost diesel like when cold, but after 5-10 mins, you couldn't hear it. deep research provided an answer that ruled out the pistons. the noise was actually coming from excessive wrist pin clearance, and replacing the piston and pin was the answer. it's been awhile, but iirc, that came from a GM source, possibly a service bulletin.

[bszopi]

http://60degreev6.com/Articles/Pushrod/3x00_Maint/TSB/TSB04-3x00.html

[torq455]

haha! yes! that's the one! thanks Brad!