Weird knock sound at idle only

[Jon89LE]

Geez its been awhile since ive posted on here. Im kinda liking the new site, but anyways, im starting to hear something on the motor and i cant tell what it is. It only happens at idle first off with the tach around 800. Its a knocking sounds but not a rod-knock sound. With rod-knock it gets louder as rpms increase but this sound disappears as soon as the rpms jump up. I was thinking maybe my oil isnt thick enough but that makes no sence. I have been using 5W30 since the motor was rebuilt 2years ago. The knock sounds like the bottom end is low on oil but it defenitely isnt. Anyone have any ideas? For a quick background on the internals, im running stock crank and rods with forged pistons, Crane Cam/Valvetrain with Comp rockers. Oil used is Mobil or Mobil1. Thanks for any help.

[RacerX11]

Does this happen with the engine fully warmed up? Forged pistons run larger clearances when cold, doue to the higher thermal expansion rate, so they can be noisier when cold. Cold piston slap can sound like a knock.

How many miles on the timing chain? A loose timing chain can knock against the timing cover, sounding very similar to rod knock. Stiffer valve springs and aggressive cam will wear out a stock stiming chain quicker.

Marty

[Jon89LE]

It happens when warmed up and idling. The chain was replaced with everything else in the rebuild about 35k ago. I cant remember what springs im running but they were the recommended ones for the Crane2030 which has .423" of lift at the valve. Off hand all i know is that the springs are single coil with damper and are less stiff than the LS1 springs. I didnt think that would be that aggressive to make any excessive wear. Would the slapping of the timing chain have a certain pattern to its noise or be random? Also, could this be an oiling issue at the oil pump with it not pumping out enough oil psi at idle? At idle the oil gauge reads a tad above the red spot, basically at the end of the white line but as soon as the motor spins up past 1500 it goes to around 60psi. I say around because the gauge likes to twitch eratically but when its somewhat steady, its there.

[RacerX11]

When my timing chain was knocking, it was a more random sound, not regular like a rod knock, but similar tone. If you are even a little worried about an oil pressure issue, I would invest in a mechanical gauge to check it out. Factory gauges and senders are not known for their accuracy.

Marty

[Jon89LE]

Your chain, when was it that you heard the sound? Was it at idle like my issue? What would happen when the motor was reved up, any vibration?

[RacerX11]

Mainly idle, occasionally higher, like when I would rev it up and let off. I don't recall any vibration. My noise started petty suddenly, right after a carb swap, so I was worried I had dropped something into the engine. I took it apart right away to find the problem, so I didn't drive the car at all with the noise.

Marty

[Jon89LE]

Alright, is there anyway to check the clearances on the chain, maybe to check if theres play in on the crank pulley? Is there a way i can mechanically check the oil psi?

[RacerX11]

check the chain = pulling the timing cover. For the oil pressure, buy a mechanical gauge that hooks up in the same location as the electronic sender.

Marty

[Jon89LE]

Alright, Thanks for all the help buddy.

[Jon89LE]

Alright, well as weird as this sounds all of my spark plugs were loose. I never noticed it because the wires normally vibrate a bit but i guess the 3700rpm 4hr drive home really did it. But after I went around and retightened them up the noise was still there, not as noticeable, but still there. I needed to do an oil change anyways so i got some 10w40 oil to see if its a internal/valvetrain issue or that timing chain. Anyone think this is a bad idea? And Marty, when your chain was knocking, did you feel any difference in the motor? Any missing sounds, roughness, etc.?

[gpse3400]

Hey Jon. If your oil pressure is normal then I'd go and see if your Torque Converter is loose. Just to be ont he safe side, I'd also hook up a mechnaical oil pressure gauge just to make sure nothing is truly wrong with the engine. You'd remove the oil pressure sender and hook the gauge up though there. 15-20 psi at hot idle is pretty safe.

[TheProfessor]

ive had noises like that before
sometimes the mounts sound like that when theyre blew out really bad
you can try to track down the location better putting an object like a wrench or screwdriver up to your ear and then put the other end up to different parts of the motor

[Jon89LE]

Lorenzo! How the hell have you been. I dont know if you still have the same AIM name but i never see you on. I just put in 10w40 and the car is much quieter. I dont here the rockers as much, but that random knock is still there, very faintly. All the mounts are new. I tryed the screwdriver thing but between having the cam and roller tipped rockers, its hard to tell where its coming from, although it does sound like its in the center/back of the motor, so i dont think its the timing chain slapping. Im going to take it to my mechanic down in Staten Island to have him take a listen for that and the DAMN CREEKING SOUND that i have on the front end! Its been happening since i did my springs.

[TheProfessor]

yeah actually a timing chain can be the culprit 9 times out of ten now that i thing about it

[Jon89LE]

Wouldnt a bad chain cause driveability issues?