mdhegar

Hey everyone, I hate for this to be my first post but I have a problem I'm hoping someone can help me with. I have a '96 LT1 that is knocking during idle. The car has about 87K on the clock. The knocking goes away when I give it gas, even a little. While driving the car sound completely normal.

I've read a few things on the boards about the possibility of a flywheel, spun rod bearing, bearing knock or piston slap. It's happening right when I start the car, doesn't need to warm up, and continues even if it's warm. I always use Prem gas and just changed the oil but I didn't look for shavings or anything as the problem just came up.

The problem JUST came up. Yesterday the sound was pretty faint. Today however it's quite loud. I'm also noticing that it may be overheating a little. I'm not sure if that matters, could just be a little low on coolant.

I also read that some requested a video of the problem to hear it. I took one:

http://www.youtube.com/watch?v=opEVMM0pTCI

I'm thinking a proper diagnosis will need to be done by a mechanic with hands on but any help here is appreciated.

Thanks!
Michael

Guest47904

Sounds like either an exhaust leak or a loose plug to me.

shoebox

Sounds like a bearing to me.

DAVE00

How's your oil pressure? If it's a bearing your op might be affected. Also, pull your valve covers and check your rockers as it might be a loose rocker or bent pushrod.

bw_hunter

Sounds like a rod bearing to me.

Cam bearings regulate oil pressure so until the rods and mains get really bad it soesn't show up on the gauge....

LearJet

rev it way up and hold it there for a few minutes, the problem should be much easier to find after that. No seriously, stop driving and pull the valve covers off, if theres nothing wrong in there then your in need of a rebuild.

mdhegar

Thanks for the info everyone! Seems like the consensus is to remove the valve covers and check it out. Could be a rod bearing, pushrod or rocker. Seems like it's coming from the passenger side too. Oil pressure seems to be ok also. Does it make sense that the sound goes away during reving?

Did the video help at all?

thanks,
-m

blue 79 Z/28

i had this in my bbc drag car after only 1 weekend out. knocked like mad at idle but when i gave it gas it went away. turned out to be the flexplate. bolts backed out and caused play which oblonged the holes and make it bang around. thats an easy check, look there first.

greenmachinedriver

sounds like a loose flexplate bolt to me id pull the dust cover and give them a check at least before rebuilding.

bubba4

Try one thing before you take it apart. My 95 z28 had a knock only at idle when I got it and it sounded just like a rod bearing but the car run strong
with no noise off idle. Pull the belt off of it and crank it and see if the noise goes away. Mine turned out to be a broke rear A/C bracket. Hope it helps.

shoebox

Obviously, check all the easy things before going internal.

mdhegar

Great info everyone! I'll check those things out before getting drastic!

-m

mdhegar

Found the problem. I wanted to make sure to post the solution in case anybody else comes across this.

It ended up being the harmonic balancer! Since it was vibrating, the belt was slapping against the other pullies which caused the popping/knocking sound. The dissipating element in the balancer was half missing. I guess reving it up spun it faster reducing the vibrating and thus noise. I just replaced the whole thing. End of story.

Thanks everyone for your suggestions! Here's a pic of the balancer:

96capricemgr

That is great news, cheap and simple repair compared to the other alternatives.

shoebox

Proves the importance of a visual inspection.