In a message dated 8/4/00 7:13:24 AM Pacific Daylight Time, PAINTRIX@aol.com
writes:
<< I keep blowing the gasket that is between the exhaust manifold and the cat
conv on my still fully smogged B. I would think that this situation
occurs because I have not gotten the three bolts tight enough. With my
limited collection of tools I have a difficult time of accessing the three
bolts, the 1 on the block side I can only get from underneath the car and
even then I have a few swivel joints to get around the converter so I am
losing a lot of torque.
Anybody got some suggestions on what I can do to get better access
to the bolts? >>
Steve,
I have had this problem many times on my 1977 MGB. There are a number of
measures you must take cumulatively to prevent against the CC (catalytic
converter) gasket from opening up:
1) The mating surfaces of the manifold and CC must be flat. If there are
small blemishes, go over both of the surfaces with a file. If there are
gouges or groves in the surfaces, you might want to get them milled flat.
2) Use two nuts per manifold stud. The first nut should be the
silicon-bronze nut (5/16 - SAE) that Mike Singleton recommended. The second
nut should be a locking nut, it is typically about half as long as the first
nut, and is tightened down against the first to keep it from backing off.
3) You will need to remove the entire manifold and CC together to get those
mating surfaces cleaned and those nuts on there tight.
4) Use a CC gasket that was meant for the job, not just one that was cut out
of gasket material. The CC gasket is multilayered, and is much thicker than
a normal gasket to accept the flex of the exhaust system.
5) Make sure your manifold is in good shape. The late "horseshoe" manifolds
have a tendency to crack in the middle of the bend and through the threads of
the top CC stud. British Leyland redesigned the casting to incorporate a
reinforced horseshoe, but sometimes even those newer castings crack. Also
make sure the manifold studs are clean, not stretched, and you can run the
nuts down their length with only your fingers. You might want to replace the
studs, or chase them with a thread chaser. They should be studs, and not
bolts.
6) There is a stabilizing bracket from the transmission bellhousing to the
downpipe of the exhaust. Make sure it is on there and tight. This is the
last mounting from the exhaust to the drive train and should absorb all of
the flex from the exhaust back to the rear of the car; the next bracket
should be behind the first resonator. If the first bracket is not in place
the CC gasket must take the flexing.
7) Check the condition of the O-ring between the CC and the downpipe. If
this "doughnut" is rusted, corroded, or missing, replace with a new one.
Make sure the three studs (or bolts) that hold the CC to the downpipe are
clean and in good shape.
8) Make sure the exhaust hangers toward the rear of the car are in good
shape. The two hangers near the rear wheel (one in front of the rear
muffler, one behind [standard exhaust assumed]) have rubber bushings that can
rot out and "leave you hanging." In this case bailing wire is not
recommended because that allows the exhaust to swing and flex. The exhaust
should hang high and tight.
9) Sometimes the neck of the CC can come loose from the body of the CC. In
this case you will have to have the neck welded or buy a new CC (Moss, VB,
Proper MG, and many of the shop owners on this list have them for about $200).
I'm sorry for the long winded post, but most, if not all, of these
precautions must be taken to assure long catalytic converter gasket life.
Good luck to you, and feel free to ask me more questions about the late model
exhaust set up off of the list.
Steve Sanchez
1977 MGB
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