On Sat, 21 Jul 2007 20:13:12 -0400, "Fred Mann"
> wrote:

>
>"Jim Behning" > wrote in message
.. .
>> On Mon, 16 Jul 2007 17:49:13 -0700, "Matt B." >
>> wrote:
>>
>> >"Fred Mann" > wrote in message
>> ...
>> >> Well, I finally got my catalytic converter all the way off. I had to
>cut
>> >> the
>> >> screws off with a dremel. Anyway, it's completely hollow. I'm not sure
>if
>> >> it's supposed to be like that. My concern is that the backfires blew
>some
>> >> of
>> >> the "guts" of the CC down the pipe and possibly cause a clog there or
>in
>> >> the
>> >> muffler.
>> >
>> >Shouldn't be hollow and yeah the guts could be plugging your mufflers.
>> >
>> >> Any thoughts?
>> >
>> >It's probably more than you wanted but could very well be time for a
>> >cat-back exhaust.
>> >
>> Old post to answer too. If it is completely hollow then somone
>> probably gutted it with a screwdriver. On my cars they tended to melt
>> down and chunks would break loose. Those chunks either rattled making
>> a noisy car noisier or the car would not run due to a corked up
>> exhaust.
>>
>> The converter is supposed to look like a honeycomb. But the grid is a
>> lot smaller than the honycomb you buy at the store to chew on. The
>> holes might be .5 mm in size. Maybe it is a bit bigger but it is
>> fairly small. You can hold a good converter up to light and see
>> through it input to output. A failed one meaning one that has clogged
>> or melted down will not pass light or you will see melted parts. Go to
>> any parts store and ask to see a new one.
>>
>> Do not put a new converter on until your car is running perfectly. You
>> will just destroy a converter in short order if the car is running
>> rich, lean, or if the camshaft or ignition timing is significantly
>> off. I prefered to get someone to attach a sniffing probe to the
>> sniffing port to make sure the mixture was correct before installing a
>> new converter. The procedure is in the Bentley. Since the converter is
>> hollow you could just exhaust sniff from the tailpipe. The challenge
>> is finding someone with an old style exhaust analyzer that will let
>> you work for 15 minutes.
>
>
>Well, it appears that timing was the main issue, so I adjusted it by trial
>and error since there are no marks on the wheel or a pointer in the timing
>hole. Anyway, I'm at about 85% full-power now. The engine still seems to
>miss a little bit, but it's not regular.
>I "fixed" the exhaust leak wih JB Weld and it worked fine for my trip
>downtown. The leak was limited to a small piece of missing gasket.
>The exhaust is a little smoky (sometimes not visible) and it kinda stinks.
>I'd guess this could be due to my timing being a little off? Also, would the
>converter help the smell. I'm certain that the fuel mixture has been
>adjusted, so it's probably off as well.
>Is there any way to test for proper amount of vacuum at the vacuum advance?
>I don't see this particular test in either of the manuals (I have a Haynes
>for this car and a Bentley for the older 79 Rabbit). If so, what should the
>reading be? I hooked up a meter and it moved, but it may be beyond the
>sensitivity of the guage. It read maybe 1 or 2 inches of vacuum when I
>revved it up.
>Just for the record, the car did not run as well with the catalytic
>converter removed. Besides being obviously loud as hell, there was probably
>an additional 10% power loss. I don't think I imagined it. So I guess a
>certain amount of backpressure is necessary? Moot point I guess.
>And here in NC, my car doesn't need to pass emission inspections, so I might
>put off buying a new converter ...
>I would like to formally thank everyone for their input. I read everything
>and I really appreciate it. Danke schoen.
>
Backpressure is a myth. Part of what a good exhaust system does in
enhance cylinder scavenging. One cylinders pulse helps pull exhaust
out of another cylinder. Second part is anti-reversion. You want the
exhaust to go out and stay out. The muffler and converter help reduce
the exhausts tendency to go the wrong way. The converter does two
things. One is it helps reduce the stink and polution. Second is that
it reduces the exhaust noise. A straight test pipe would be quieter
than the hollowed out converter. Well that is my guess.

Timing marks. There is a zero degree mark there. You just do not know
how to read it. Well I can't swear to that but that is what my owners
manual says. Here is how you find it. Get your rotor to point close to
number 1. Remove spark plug #1. Insert large screwdriver in #1 hole.
Slowly turn crankshaft paying attention to screwdriver rising. Keep
paying attention to screwdriver and watch it fall. Turn crank the
other direction to get it back to top dead center. Look in timing hole
which should be 1.25" or so big. If that hole is just 1/2" or 3/4"
then you have a plug that needs to be removed. There is a mark on the
flywheel. It is not close to the ring gear or the machined flat
surface but below that. If you are good at reading the rise and fall
of the screwdriver then you will see. You have to find it to confirm
camshaft timing. Until you find it you are wasting your time. The
manual also mentions making a mark 12 mm to the left if you want for 6
BTDC or 6mm to the right for 3 ATDC.

There is a pointer in the timing hole if you removed the plastic plug.
It would rather hard and unlikely for someone to chip off the timing
pointer. The pointer is just a nib. It is not some huge 1/2" big arrow
with a white tip on it. It is smack dab center of the threaded hole on
the side closest to the engine block. If you were looking at the
machined back edge of the block and you used a square against the
machined block and could read the center of the threaded timing hole
you should see it. I played a carpenter and tileman in another life. I
can usually see the center of something.

You need to get someone with a good camera to take a picture. I don't
have a Rabbit anymore so I cannot take a picture. Crummy pictures from
my Bentley.
http://www.brookridgemorgans.com/jim/timing2.jpg
http://www.brookridgemorgans.com/jim/timinghole.jpg

I test vacuum advance and retard with a small hand help vacuum pump
and a timing light. The newer Bently has the specs. Bedtime.