jarcher

Hey guys,

Took the ol' girl out for a cruise today, got on the power when merging onto the highway and she started making some noises I didn't like. Please take a look at the video and let me know what you think.

It only seems to do it from 2500 to 3500 rpm range. At idle it sounds perfectly normal. It only does it when accelerating, sounds normal if the rpms are just hanging in that rpm range.

Motor is stock bottom end, medium cam, comp cam trunions, stock rocker bodies, new valve guides and exhaust valves. ARH headers/x-pipe with factory mufflers, vararam intake.

Link if video below doesn't work

UPDATE!!! - Pulled motor and took apart. Rods from cylinders 3 and 4 had worn out the CrN coating on the big end and chewed each other up. Picture on page 3

phipp85

Sounds like an exhaust pipe or muffler tapping on something solid. Get under the back and take a good look at the exhaust pipes that go over the axles and run alongside the differential case.

User Omega

I would be removing those comp trunion bushings regardless of what this is.

bambihunter

I agree with Phipp85 although I could not tell from the video much about the noise. If you had the modifications done very recently, I'd take that machine right back and have the shop go through and look for mechanical interference, rattles, etc. when the engine torques over. Might also make sure the motor mounts are at spec.

If the work was done long ago, then you should still check for mechanical sources of the rattle; given it only happens on acceleration I suspect something's bumping something it should not be. If you're not mechanically inclined, forget it. Find someone who knows what they're dealing with and pay them to preserve your expensive machine.

As for "comp trunnion bushings" I got no clue....stock rockers bodies? If you have CHE bushings, that's as good as it gets. If you have needle-bearing stocks or aftermarkets, I'm with the school that says get rid of 'em.

Bambihunter

Dan_the_C5_Man

It doesn't sound like valve train to me, from the video anyway..

Seems harmonic, as in it's only making the noise in that narrow RPM band / specific vibration frequency.

If it were a lifter or similar, you would expect the noise to continue / get worse through the RPM range.

Do you hear it when revving / holding it stead in that same RPM range in neutral (no load)? If not, that eliminates the VT as an issue, and points towards the motor shifting under load, and that movement causing contact (think weak or bad motor mounts allowing the engine to move).

jarcher

Thanks for the inputs guys. Give's me ideas to look for. I'm going to swap oil filters tonight and cut it open to see if there are metal shavings. That should tell me right away if its an internal or bearing issue. (I pray to god not!) The thing that leads me to believe its not exhaust or something rubbing is that it always starts making the noise at 2500 rpm even if I apply the throttle lower down. You'd think if the exhaust was hitting something from the engine torquing over that it would happen the instant I apply some load to the motor.

When there's no load it doesn't seem to make the noise. The only way it makes the noise when free revving is if I blip the throttle pretty aggressively. Would a collapsed lifter be rev range specific or would it be more of a ticking noise rather than the "chirping" sound that is happening?

The valve train has seen about 4000kms (yes I'm Canadian) without any noise up until now. I will check the motor mounts, the ARH exhaust system definitely has tighter clearances than the OEM so maybe if the motor is shifting more than it should. I'm still going to take the valve covers off and see how things are looking under there.

Dan_the_C5_Man

That's what I figured - my guess is the header is lightly tapping on the steering column shaft. Might be one or two other places to look as well.

jarcher

Ok,

So I checked for any possible clearance issues on the ARH exhaust. Everything seems to have plenty of room. I swapped oil filters tonight and cut it open. I could use some input though as this is the first oil filter I have ever looked at so I don't know what is deemed normal for the amount of metal to be found in the filter media. I can say that I did not find any big chunks. I know lots of guys use magnetic oil drain plugs that are often fuzzy with metal shavings when they do oil changes. See pictures below.

southspeed

I wonder if it could be in the oil tank. Mine had a crossover tube I think they called it that was rattling. Didn't sound exactly like yours but it did it only in certain situations like that. Do you have an msd intake?

jarcher

No I have the stock LS7 intake manifold, with a Vararam intake

jarcher

While I was under the car tonight I noticed an oily area under the car below the dry sump, I can't see exactly where it's leaking from but I can feel an oi leak on the back side of the sump tank that's facing into the fender. Looks like it might be leaking from just below where the bolts go around the perimeter of the tank just below where the dipstick goes in. Is there a gasket in there? How much pressure or vaccum does the tank see when under engine load. I know that we have the hoses from both valve covers and the intake that route back to the top of the dry sump.

Would there be any chance in hell that some sort of pressure or vacuum leak at the tank under load could be making that sound through a failed gasket? I'm just spit balling here.

southspeed

Does the sound seem like it's coming from behind the dash on the passengers side? Mine did and it was an o ring that's been known to wear out allowing a rattle. Again though, mine sounded different than yours but you never know. To me yours sounds more metallic.

User Omega

Oil tank rattle is rarely matched with RPM and almost always can be heard at idle.
https://www.youtube.com/watch?v=E7cN1zd1MAA

What is your oil pressure at idle after you warm the engine up? Oil temp at 180+ reading.

jarcher

My oil pressure at operating temp and idle is 40-50 psi

I took apart one of the comp cams trunnions last night, not very pleased to see this much wear after only about 2500-3000 miles. it was worn enough that I could catch my fingernail on it. What's the chance that I've got others that are worn worse, could definitely explain the metal flakes in my filter. Sorry for the out of focus picture

User Omega

Oil pressure is great.

There is a very good chance you have others worn just as badly if not worse. Without testing I would agree with you and assume the material in the filter is directly related to this wear. Although some will disagree, this is a common problem with the Comp "upgrade" and I would not use them again. I am also not clear on what these sound like when worn. Maybe someone can chime in and confirm or deny whether your sound could be directly related to this. I believe it is very possible.


For better results...
You could either send them off to CHE or install a set of Straubs yourself. I have read the Straub technologies bushings are holding up but I myself have never run them. I currently have CHE bushings installed.

jarcher

Thanks for your comments I actually ordered a set from Straub this morning. Once they get here I will install them and see if that fixes the sound I was having. Certainly a cheap and relatively easy thing to check out before starting to rip heads off the motor to chase things deeper.

User Omega

Good deal. Keep us up to date.

Unreal

Every single comp kit with over 3k miles that I've seen or heard of being inspected has at least that much wear, and I don't want a part polluting my car with metal shavings. Good catch. I hope more people pay attention and actually inspect their trunnions. Still waiting to see at least one person inspect and find unworn trunions.

MTPZ06

Shocker...another failed set of Comp trunions. Absolute JUNK.

Good move on the Straub kit.

Unreal

This was metal just from 1 snap ring groove from 1 trunnion. Now multiply that by 32...