spanky

This sounds like the balance shafts to me. Even if the windows on the covers were lined up correctly with the O on the upper shaft and nothing on the lower shaft it still possible that when the gears were installed, one or neither of the shafts were rotated to the 12 noon position before the gears were slid into place . This is an easy fix but the only way to check it is to remove each gear and reinstall them with the shaft key pointed to the 12 noon position. Then you rotate each gear to its correct position/ alingment with the plastic cover markings/ notch. 1 o clock upper gear and 7 o clock lower gear.

EJZero1

Noticed over the past couple of drives, as I'm now much more conscious of it, that it seems the car must get good and warmed up before the noise starts up. On the way home from work today, started her up and headed out and the noise didn't happen. As I drove her longer the sound started and grew to what I now consider "normal". This leads me further down the heat shield trail, or at least something similar and as simple. Would seem to me that something down there has to heat up before it develops the properties that contribute to the vibration. I would think a balance shaft out of whack would make itself known regardless of the temp.

Thoughts?

EJZero1

A little update...

Sound is definitely coming from the cat converter. Took her out for a ride to get her good and warmed up (and rattling appropriately) then back in the garage. Had the little Mrs. hold her at 3500 RPM, rattling away, while I took a wooden dowel and did some prodding. Started at heat shield near the header with no findings. Eventually made my way down to the cat. Pushed the cat from the driver's side towards the passenger side and the rattling stopped. Released pressure, rattling returned, applied pressure, rattling stopped, released pressure...you get the idea.

So here's the deal now. There doesn't appear to be anything in contact with the cat to cause the rattling. Could the rattling be coming from the inside? Are there any other symptoms of a cat going bad? If it is indeed bad, does this adversely impact my performance? Should I be in a hurry to replace my cat?

A sincere thank you for inputs, previous and future!

EJ

944Ross

I don't know if these are monolithic cats, but I've had that kind pound itself to pieces internally. Once the mono gets a little loose in the casing, it just beats itself to death. On a Fiero I had, it got down to a baseball-sized chunk that went into the outlet and stopped it up completely! I had to wail on the converter to knock it loose.

Fishey

All I got to say is if your mechanic cannot tell the difference between the sound in the exhaust (or heat shield) from a sound in the engine bay. Well, I think its time to find a new mechanic....

Mark944na86

FWIW, whether the balance shafts are aligned properly or not, the engine vibration is greatest at around 3500 RPM. If your balance shafts were out of alignment, the vibration would be worse overall, but still greatest at that RPM range.

EJZero1

I am my mechanic, and through a deductive process I was indeed able to narrow the sound down to the source.

And for what it's worth, I tried firing myself, but I just don't listen. I'm such an a$$.

IGROWL

dhansen

I think Fishey was referring to the mechanic who said your rattling problem was the autotensioner and didn't realize that it was the cat. Hey I'm just trying to play peacekeeper!

Either way, I'm glad you found the source of the problem.

EJZero1

No worries here.

The shop is kind enough to keep sending me periodic reminders telling me about all the service they should be doing to my car. How nice...

Going to crawl under this weekend to verify the rattling isn't being caused by some contact I didn't notice before. Might go so far as to pull the heat shield to completely rule it out as a cause. Now that I know it's nothing catastrophic, it's really just a nuiscance to get rid of.

EJZero1

Reviving one of my own dormant threads...

Finally got the car to an exhaust shop for an inspection up on the hoist. A quick listen and a rev or two and they were able to report with confidence that my rattling sounds stem from my cat gone bad.

Their quote: $225, installed for a "standard" replacement (IMCO?).

My scenario: I'm not hell-bent on squeezing every drop of performance out of my non-turbo. I'll save that pursuit for later with an appropriately turbo'd ride. I do want to replace the cat and get rid of the annoying rattle and avoid potentially costly collateral damage in the future. So...

Anyone have any experience with IMCO? Good product?

$225 sound like a fair price?

Thanks much, in advance.

ernie9468

EJZero1 ___here is the beauty I was talking about in my pm. Honda S/S Cat. LOL take notice of the perfect weld on the back flange (was done six years ago & still looking good)don't know if I could do the same weld today been a while since I try my hand at it.

FRporscheman

Welding is like riding a bike, it always comes back to you quickly!

ZR8ED

Go find a universal performance cat at your local speed shop. $150.00. Not physically large either so you can fit them in tight spots if need be.