Sasquatch6

Okay so heres the latest problem with my girls c4 nightmare.
it has a random knock. And i mean random. It starts knocking as soon as it starts but its inconsistent. It doesnt keep pace with the motor, it literally sounds like something is bouncing off the pistons randomly. Pulled the valve covers and adjusted valve lash and checked the lifter arms and springs, fine. Pulled the oil pan and cant see any visible scarring. I found very trace amounts of metal shards in the oil (but still scary). Im at a loss. I have no idea what could be causeing this. And im asking for any help anyone can give me. What else should i look at? Has anyone ever had this issue before?

C409

..... Anything loose on the motor ? brackets , mounts , etc . , starter motor ? how about a bad A.I.R. pump ? A/C compressor ? exhaust system pre-cats ? flywheel/flexplate ? Check for anything that might be rattling around on the engine .....

Bfenty

it's happening at idle? Can you pinpoint the location by starting it in neutral then going up front with a stethoscope?

Sasquatch6

Yes it happens at idle, it sounds like its coming from the passenger side underneath the valve cover but i cant see anything out of the ordinary. What was weird is when i went to put it on ramps, i put it in drive (its an auto by the way sorry for not mentioning that) it idled down and the noise stopped. But when i gave it gas to get on the ramps it started again, put it back in park and it was still there.

Bfenty

are you idling high? Where is your idle RPM at? You might take a look at your spark plugs. In a recent thread someone posted a nice graphic that I'll add to this post, showing what spark plugs are telling you. You may have already checked these things, I'm assuming nothing.

A video might help people here diagnose the issue with you. Think you could take a 30-second clip?

cv67

try starting it without the belt

may check for an exh leak at the manifold and the pipe that comes off it going to the intake. Somtiems when cold youll hear it clack then quiets up some as it gets warmer

whalepirot

Belts can mimic all sorts of sounds. Candle wax or different sprays on it can quickly eliminate that possibility.

Why would hydraulic valves need adjusting?

Oil pressure good? Change it recently? Try, perhaps a higher vicsosity.

With no info in your profile and no mileage you'll not get the best feedback!

Sasquatch6

Sorry for the lack of info, its an 85 l98 flat tappet. I'll take the belt off and record a clip of it running hopefully tonight, as i also need to check some stuff out on my trans am.

Sasquatch6

And the oil pressure is about 60 lbs. It was changed about 2,000 miles ago. But it'll have new oil in it when now when i put it all back together.