sissond

My wife has been driving the '96 more in the last few days since her DD developed a nasty brake fluid leak in one of the calipers and I'm waiting for parts to get here. When she came home last night and was backing down the driveway (about 110 feet) to the garage, the vette started making a creaking noise that sounded like a door hinge in need of lubricant. After a brief investigation, I thought the noise was coming from the rear of the engine compartment. I was thinking maybe the flywheel.

The speed of the creak was directly related to the RPMs of the engine and it did it in park as well Drive/Reverse. It was louder at idle in park than at similar RPMs while in drive.

This morning I decided to investigate to see if the noise was still there. The noise has turned into more of a metallic rhythmic scraping noise than a creak. Perhaps the noise would become more of a creak again if I let the engine warm up. But I did get the stethoscope out and started listening. The noise seems the loudest toward the center of the intake manifold. Back toward the rear of the engine it gets fairly quiet. So I'm no longer thinking flywheel.

Here's a link to a quick video I got with my phone that captured the sound pretty well.

I did replace the intake manifold gasket about 9 months/2,000 miles ago to fix a large oil leak. I realize that the noise could be radiating from anywhere, but it definitely gets louder toward the center of the manifold. Where should I start? I can think of a bunch of things that could be causing this noise. I'm not looking forward to possibly taking that manifold off again. There's too much crap in the way.

Advice?

antfarmer2

Speed sensor?

antfarmer2

Auto or stick

sissond

Auto

sissond

Do you mean the crank position sensor? I know they can make noises like this. I'll add that to my list of things to investigate.

kg4fku

video is private.

sissond

Sorry about that. It's public now.

sissond

I'm finishing up the brakes on the wife's DD right now. While I'm dirty and sweaty I'm going to start checking stuff on the Vette. Any other ideas from anyone?

mtwoolford

there's not very much in the intake manifold to cause that noise; I'd pull the valve covers and check that the rockers are all still centered on the valve stem...and based on my own experience that could be an issue; if further investigation warrants pulling the intake manifold, I'd pull each lifter in turn and inspect the roller for any sign of wear or damage, if the roller is damaged the corresponding cam lobe is shot...I know this from experience too.

desertmike1

this sounds like a valve train issue, or at least it has the right Frequency..

sissond

Yes, I'll gladly start with the rocker covers. I've done those gaskets too (everything leaked when we got this car) and it was much easier than the intake manifold.

For all the numerous repairs I've tackled in the past, I've never messed with rockers, valve stems, rollers, or much of the internals of an engine. I've gotten lucky and never needed to before. Most of my time has been spent on suspension, brakes, drivetrain, exhaust, cooling, and parts that bolt on to the engine. So this will be a learning experience for me.

Thanks for the advice.

-Doug

sissond

One more thing, this may be a silly question, I've seen this before on television but I'm not sure if it is okay to do on all engines. When I have the rocker covers off, is it okay to run the engine to try and find the noise?

Also, is it safe to say that I should not drive the car until I remedy this problem?

I'm thinking yes on both questions.

mtwoolford

running with the valve covers off? back in the bad old days, that's the way hydraulic lifters were adjusted (with varying degrees of success);
it'll make a bit of a mess but nothing too terrible;

driving a car with this problem, wouldn't want to drive too far, but a short hop for trouble shooting, probably not a problem; but then again you're the man on the scene, not me. Err on the side of caution.

sissond

That's my motto. Thanks for the advice.

pifo1964

Could you find out where the noise was coming?

sissond

Unfortunately, the more I listened the more I felt it's down deep in the block. I took it to a local Vette mechanic and he confirmed what I thought. And he says it does not sound like a spun rod at all. I agree after listeninig to some videos online of spun rods. So it's a mystery that would require a rebuild to solve.
Right now I'm keeping an eye out for affordable low mileage LT-1 engines. If I can swap a working motor out, I might attempt my first engine rebuild. But I don't want to even attempt the job and leave the car disabled for however long it takes me.

Tom400CFI

Did you ever pull the valve covers??wrong frequency. That noise would be 8x faster.

sissond

I did pull the covers and didn't notice any significant increase in the noise with the stethoscope. I was sort of hoping it would be in the heads as an excuse to get some better heads, intake, etc. No luck.

bow tie guy

cracked flexplate and exhaust leaks

a cracked flex plate will mimic bottom end noise
and the roller lifters, are noisy by nature, very noisy with thin oil on a hot day I might add.

I wouldn't run out and buy a used motor just yet

sissond

Would the flex plate make noise if the transmission is removed? Is the noise of a cracked flex plate from it interfering with the torque converter? The reason I ask is that the mechanic I took it to, disconnected the transmission to try and isolate the noise. The noise was there w/o it connected (according to him).