Help me diagnose a noise 911 SC content

My Targa is making an odd noise that is present at idle but increases upon acceleration. The noise is coming from the area of the driver side of the engine. I thought it was valvetrain related but the idle screwdriver stethoscope test puts it coming from the front of the Catalytic converter. The sharp noise that you hear at the beginning of each rev is a slight example of the sound. It is constant under heavy acceleration. Any thoughts?

Here's my first ever YouTube video and it includes the noise:

There is no substitute

First thought is perhaps the cat is starting to come apart.

Could be some busted up platinum crap bouncing around the front of the cat, I've seen cats begin to disintegrate and make weird noises like that before. I've never wrenched on a 911 firsthand, but why not pull the manifolds and check? You know where the sound is coming from, investigate!

SlickDizzy wrote: Could be some busted up platinum crap bouncing around the front of the cat, I've seen cats begin to disintegrate and make weird noises like that before. I've never wrenched on a 911 firsthand, but why not pull the manifolds and check? You know where the sound is coming from, investigate!

I looked at the nuts and bolts and now I have to decide if I'm willing to actually give all that miracle rusty bolt remover crap another chance. They had better give up easy or they are gonna glow cherry red soon.

Josh,

Nice car!

I just checked out the video that I sent to you and it didn't seem to be doing it then. If you didn't save it, I can email the link (I've never posted on youtube).

If the stethoscope tells you it's the cat, I'm thinking that maybe it started to come apart on the trailer. Do you have any photos of how they had it strapped down? I wonder if a strap or chain was making contact with it.

Josh, the link to the video is in your mailbox.

it's an SC. Checked your head bolt torque lately?

It also sounds like you've got loose valves.(valve guides going?)

Woody wrote: Josh, Nice car!

Thanks, I know a guy.

Woody wrote: I just checked out the video that I sent to you and it didn't seem to be doing it then. If you didn't save it, I can email the link (I've never posted on youtube).

No worries, it wasn't there when I got the car. It is mainly present at cold idle and above 2/3 throttle. I didn't see throttle that heavy in the video so I cant rule that out, but the noise at idle showed up after owning it a few weeks so I assume they are just the same noise at different rpms.

Woody wrote: If the stethoscope tells you it's the cat, I'm thinking that maybe it started to come apart on the trailer. Do you have any photos of how they had it strapped down? I wonder if a strap or chain was making contact with it.

I didn't think about actual physical damage. The case looks good but that doesn't mean a couple of good whacks or a bunch of tiny whacks with a chain didn't happen.

I am actually hopeful. I went into this thinking best case was a locknut on a rocker loose and worst case being anything from a broken head bolt to rocker shaft walk. Now it might be as simple as a crappy cat.

This is the first time I tried the screwdriver stethoscope and it was really cool. You could hear all the different noises going on anywhere you wanted inside the engine.

tpwalsh wrote: it's an SC. Checked your head bolt torque lately? It also sounds like you've got loose valves.(valve guides going?)

Interesting, what gives the indication that the valves are loose?

A real mechanic's stethoscope works even better.

Kenny_McCormic wrote: A real mechanic's stethoscope works even better.

It is now on my must own list.

In reply to MrJoshua: It doesn't really sound like a sewing machine? It might be the camera angle, but there's a lot of "clack" in the audio feed. In my experience that's usually worn valve guides, or loose valve adjustments. There's not much else in a 911 engine that "clacks." Do you have any knowledge/documentation of a motor rebuild, or at least a head job?

Also you mentioned that it makes this odd noise under heavy acceleration as well. I'm sure you know, but for everyone else's sake, SC's are notorious for snapping head studs because they went to Dilavar(spelling?) vs steel. They tend to corrode, and break, letting the head bounce on the cylinder. (and there are 6 individual heads, and 6 seperate cylinders)

IIRC Woody did a valve adjustment when he had the car, but it may still be a loose valve tapping the cover.

You've probably already done it, but have you checked for exhaust leaks? Again, IIRC, there is a small triangle connection where the cat connects to the heat exchangers. I've seen that area rust in the past. And each heat exchanger has an exhaust gasket per cylinder.

When Josh first told me that there was a noise in front of the rear wheel, I suspected that the locknut had loosened on the number 3 exhaust valve and that it had gone out of adjustment. I'd still check that out, but the stethoscope seems point to the cat.

I didn't find any broken studs when I had the valve covers off. Broken studs on the exhaust side just fall out when you remove the lower valve cover.

For those playing along at home, here's what the area in question looks like:

Josh, looking back at this now, I remember that I had planned to remove the heat shield to get better access for the valve adjustment, but the bolts wouldn't budge and I left it in place.

Check for broken fasteners on the heat shield. I'd bet that the shield is what's making the noise.

The screwdriver/stethoscope on the valve covers was very much a "sewing machine" sound. I sampled the sound on the upper and lower valve covers from front to back. The clacking sound is a bit of the noise I was talking about. It was only audible through the stethoscope towards the rear of the Catalytic converter. I am hoping to get a few hours later this weekend with the car and get the heat shields and catalytic converter off. Fingers crossed.

That engine needs to go in that vanagon in the corner.....

DrBoost wrote: That engine needs to go in that vanagon in the corner.....

Lol-thats a Subaru Microvan. That would be one hell of a wheelie machine.

MrJoshua wrote:

DrBoost wrote: That engine needs to go in that vanagon in the corner.....

Lol-thats a Subaru Microvan. That would be one hell of a wheelie machine.

I stand corrected, but now my comment is ever moar better!!!!
DO EEET!!!

DrBoost wrote:

MrJoshua wrote:

DrBoost wrote: That engine needs to go in that vanagon in the corner.....

Lol-thats a Subaru Microvan. That would be one hell of a wheelie machine.

I stand corrected, but now my comment is ever moar better!!!! DO EEET!!!

This^, when guys are putting Subaru engines in Porsches?!

Woody wrote:

DrBoost wrote:

MrJoshua wrote:

DrBoost wrote: That engine needs to go in that vanagon in the corner.....

Lol-thats a Subaru Microvan. That would be one hell of a wheelie machine.

I stand corrected, but now my comment is ever moar better!!!! DO EEET!!!

This^, when guys are putting Subaru engines in Porsches?!

Can you flip the ring gear and make Porsche transmissions mid engine like you can ACVW?

Tap on the cat with a rubber mallet to see if the cat rattles.

sergio wrote: Tap on the cat with a rubber mallet to see if the cat rattles.

somehow I am not sure that cat will rattle

mad_machine wrote: somehow I am not sure that cat will rattle

You can always try.