exhaust leak tap - Cannot affort rebuild, help please?

[sporqster]

For some time now, my wife's '79 911SC daily driver (113k miles, stock) has been making what I have decided is an exhaust leak noise. From reading an talking to owners of other 911's of this era, I suspected a pulled head stud, so popped the valve covers to check them- and they all are tight as can be.

So then I thought maybe the racket was coming from one of the exhaust header header gaskets- it's definately once cylinder, a tuf-tuf-tuf at idle. It also seems less pronounced once the engine is warm. Changing the header gaskets made no difference. I made a recording with the mp3 player- take a
listen

The car has reasonable power- actually more than I would expect from a car this old. It will light up street tires pretty easily and is reasonably fast autocrossing. I would have thought that a compression leak that makes that much racket would cost a lot of horsepower and cause the car to run rough. No?

Now the ugly news- I cannot afford more than about a $1000 repair right now. Just too tight on cash. I'm not afraid of getting my hands dirty, and have done some basic work on this car, adjusted valves, swapped a tranny, fixeds some electrical gremlins... and aside from this car I've rebuilt a Chevy motor with detailed instructions in hand, and it actually ran afterwards... But I cannot embark on a month long project with this car as it is the my wife's means of transportation to work, not to mention our autocross / track day car. Anything I do I would like to be able to do in a hard working weekend.

I would be led to the conclusion that I need to change the head gasket, but that doesn't seem to be a very popular topic of discussion on here, leading me believe that is an unlikely diagnosis. But I would think swapping a head gasket is a job a guy like me could probably handle, right? I realize it's not like changing the gasket on a Honda, but how bad can it be? What else should I just change because I'm in there? Is there a partiuclarly good write up I should be looking at? (I've got a Haynes manual, which is pretty vague)

I'd appreciate the help!

Thanks in advance!

[2.7RACER]

Sounds bad, like maybe a burned exhaust valve. Just a guess.
I would first run a comp check. It's going to be low somewhere.
Then do a leak down, just to understand whether it's valves or rings.
Either way you are looking at a tear down and repair.
Do the work yourself and maybe you can keep the cost under control.
Whatever you do, the Targa is going to be out of service for awhile.
$1,000 isn't enough.
Sorry, but this is my best opinion.

[dick911]

Yep, sounds familiar to me.

Sorry for my english, but here is my story:

I've had the same with my SC engine. Turned out it that the exhaust header-exhaust port (outlet port) connection had a tiny leak... Which made the same sound as I hear in your sample.

At that time I was not knowing that this tiny leak was causing this sound.
So took the engine in for a rebuild... After starting up this sound was there again; even with new gaskets !!!! Took off the complete exhaust system and flatten (is this the right word ?) all the connections. Put it on again with new gaskets and the sound was gone...

Why this story ?
First look at the cheap and easy things (like exhaust gaskets..) instead of broken headstuds etc. Try new gaskets again but with a bit of sealant.

Good luck,

dick911

[afterburn 549]

Ok Blah Blah You need to confirm/verify where the noise is comming from b4 you jump !! could be anything from a hole in exhaust to the dreaded stud, so look b4 you spend !! Seems like you could put it on rack or jacks and see feel get a temp probe and find it so no more guess work.
A burnt valve will have a miss with loss of pwr so I doubt that one. Where ever the exhaust is leaking out the temp will be much higher and a temp probe will pick it up

[BReyes]

Give your wife the Subaru. Ride to work with your cowoeker. Put the 911 on stands. Do a comp test/leakdown. Prepare for a rebuild.

Let her keep the Subaru. You will fix the 911 by winter.

If she will not give it up. We will still help you with recommendations for a tech and or advice.

Do not spend the money on dinners your 911 will need a lil bit more than that.

Regards,

[A930Rocket]

Use a piece of small diameter rubber hose to listen for the noise. Put one end in our ear and move the other end around the exhaust manifold, etc. You'll be able to hear any "leak" better that way.

[beepbeep]

Originally posted by A930Rocket
Use a piece of small diameter rubber hose to listen for the noise. Put one end in our ear and move the other end around the exhaust manifold, etc. You'll be able to hear any "leak" better that way.

Very good advice!

Also, check air-injection leaks...one of injectors might have developed a hole.

[fastfredracing]

Check the heat exchanger flanges where they meet the cylinder head, I have seen more than one set of thin flange h/e's on 3.0 sc's that were excessively warped, and would not provide an adequate seal, I had one set milled flat again, and that worked pretty well, but first confirm where the leak is coming from. A mechanics stetoscope works well, (cheap at sears), and if you do it when you first fire the engine, you can get around without getting burned for the first few minutes

[quattrorunner]

Yup, my guess is the flange to head is loose or warped, yup.

[JP911]

What condition are the heat exchangers in? Is it possible that there's a hole caused by corrosion somewhere close to the head?

[2.7RACER]

Sporqster,
Are you getting any of this? Are you reading our replies?

[A930Rocket]

Turned out to be an exhaust leak and it got to him I think....

Originally posted by 2.7RACER
Sporqster,
Are you getting any of this? Are you reading our replies?