sTUPID Knock.. need help

[milenko1247]

So I started hearing a knock on my rebuilt engine. Its a 99 cobra with an aluminum block with forged pistons and rods. I also have an eaton swap on it and it seems to knock bewteen 1900-2900 rpms when it is under a load. so just reving it in the drive way there is no noise. Its not a loud noise so when the windows are down i can barely hear it, but with the windows up i can hear it even louder. But it is still not a loud tick. What is this, is this piston slap?? I didnt think it could be a spun bearing because it only happens bewteen a certain rpm . Oh yeah, the car has like 1200 miles on the new motor.

 

[01yellercobra]

Are you running headers? You might have an exhaust leak. Piston slap usually goes away when the engine warms up.

 

[milenko1247]

dang.. an exhaust leak would make a knocking sound?... also Im pretty sure it doesnt make the sound when it is cold

 

[milenko1247]

and i do not have headers, i have a bassani xpipe no cats and slp exhaust

 

[01yellercobra]

It can sound like a knocking and mess with your head.

 

[Bite Me]

It can sound like a knocking and mess with your head.

I agree. I had an exhaust leak on my chevy when I put some headers on and it sounded like a knock.

Just so happens that that specific RPM range is where my cobra sounds the worst exhaust note wise. It very well could be exhaust related. Hell its worth a look before you tear in to the motor.

 

[milenko1247]

Yes it is worth the look

 

[dadro77]

Mine was ticking at the same rpm. Spun bearing....

 

[droptopsnake01]

put your car in 4th gear at like 2k rpms and go up a hill. Thats a good way to check aswell. It could be alot of things.

Have you checked your oil?

 

[milenko1247]

if it was a spun bearing, wouldnt there be shavings in the oil?

 

[droptopsnake01]

if it was a spun bearing, wouldnt there be shavings in the oil?

Thats why I asked if he checked his oil...

 

[milenko1247]

I changed it 200 miles ago and no shavings... could a bad lifter make that noise only at a certain rpm

 

[Ande99SVT]

Mine was ticking at the same rpm. Spun bearing....

1800-2000 RPM range I had a knock, turned out to be a #2 bearing spun on my crankshaft.

Open the hood up while the car is running and listen between your head and intake manifold on both sides, if it sounds like it's near the rear of your heads then you just might have a spun bearing.

 

[milenko1247]

Its only when the car is under a load. So it doesnt make a sound when i checked under the hood and revved it in my driveway

 

[Ande99SVT]

It could be the start of one, maybe just not as severe as the one I had. To be honest I wouldn't drive it anymore and I'd take it to a mechanic ASAP just to get it checked out. With the range of RPM's it's in it definitely sounds like it could be a spun bearing.

Put your head near the drive side wheel well, does it sound almost like an exhaust leak?

 

[milenko1247]

I cant listen for the exhaust leak.. because it only makes the noise when the car is under a load

 

[Wynn]

I was a little nervous after reading this thread. I changed the oil yesterday and there was really no hint of metal shavings.. nothing unusual anyway. I went with M1 10w40 and it seems to have helped with the sound a little bit. I'm convinced that my motor's okay.. hopefully everything works out for you too.

 

[milenko1247]

Hey could it be my flywheel or clutch? I have stage 3 alum. flywheel, and puc clutch.... It kinda makes sense because the sound is only there when it is under a load. Yeah, I switch my oil to senthetic tooo qucik after my build and she smoked at every start up.. i need to switch back to the crapy crud stuff :banana:

 

[Wynn]

I don't think your clutch would make the noise under load though. Maybe at idle in neutral. Try having somebody push on the clutch while you listen underneath and see if the sound changes.

 

[01yellercobra]

If it's just under load I would lean more towards the exhaust leak. I've had that happen before. The load on the motor at idle wasn't enough to cause it. My spun bearing made noise all the time. No matter what load was on it.