describes C34 owners' exhaust system upgrade projects.
Please contribute yours!
Exhaust Riser Replacement
My wife and I are owners of "Flying Colors", Catalina
34, Hull #80. A "tech note" in the May 1997 issues
of Mainsheet reminded me that periodic inspection of the
exhaust riser was a good idea. To my surprise, cursory
inspection under the vanity in the head revealed soot buildup on
under the sink and on the interior side of the bulkhead to the aft
stateroom -- not a good sign. It was a surprise because
neither my wife nor I noticed or smelled diesel exhaust in the head
or the main salon.
With Mainsheet article in hand, I called Catalina and discussed
my options for replacement of the exhaust riser. Because hull
#80 featured a black-iron riser as original equipment, it was
recommended that I replace the riser with the black-iron version
($115). This recommendation was largely driven by the fact
that the stainless steel riser used on more recent Catalina 34s
results in the riser being centrally located between the interior
bulkhead of the aft stateroom and the aft bulkhead of the engine
compartment. (As I would later learn for "Flying
Colors", the output of the upgraded riser was about 3"
forward of the muffler input).
Ordering the riser was very straightforward, and was accomplished
by telefaxing critical information including the desired riser
material, hull number, and model year to Catalina. Catalina
advised me that the flange and gasket for mounting the riser on my
M-25 engine had to be purchased directly from the local Universal
To my delight, both the riser and the flange arrived within 7
days. However, as I would soon discover, the easy part of this
job was over. Examination of the existing flange revealed that it
was secured onto the exhaust manifold by three 9/16 nuts.
While the top two nuts were easily accessible, access to the bottom
nut was less than optimal and, of course, the bottom nut was the
most seriously corroded and required the most attention. To
improve access to the lower nut, I unfastened the heat exchanger
mounting bracket (with heat exchanger attached), and lowered the
entire assembly approximately 3 inches away from the riser. I
found that access to the lower nut was then best accomplished
through the large access panel under the aft berth.
However, after several applications of liquid wrench, various
wrenches, several sockets, and assorted vice-grips, I concluded that
the lower mounting nut had become an integral part of the boat’s
structure, and wasn’t going anywhere without greater leverage and
Discussing the situation with a few very reputable marine diesel
mechanics, I was consistently advised that my encounter with a
frozen lower nut was very common. The consensus opinion was
that I should remove the entire manifold with the riser still
attached. Once the assembly was clear of the boat, I was able
to remove the mangled nut by hammering a smaller socket onto the nut
and applying torque by using a 2-foot socket handle.
Persuasion worked! However, I soon learned that the entire
flange had seized to the manifold due to an extensive rust buildup.
A local engine shop was able to apply some heat with a blowtorch and
remove the flange from the manifold by using a small sledge hammer.
At this point, I employed the engine shop to clean the mating
surfaces of the manifold. I also took the shop’s
recommendation to remove the rusted mounting stud, and use a
stainless bolt for attaching the new flange (the other two studs
were in good shape). I had the shop screw the new manifold
into the new flange - a good decision since it took two men, a vise,
and two pipe wrenches to apply enough torque to screw the riser
sufficiently into the flange.
Upon returning to the boat, I remounted the flange/riser assembly
and utilized new manifold gaskets which my engine shop had been nice
enough to cut. At the recommendation of the mechanic, I
applied "Anti-Seize" to the nuts and bolt in order to help
preclude the future seizure of mounting nuts and bolt. Upon
remounting the manifold/riser assembly on the engine, I discovered
that the new riser was misaligned with the inlet port of the muffler
by about 3 inches. My choices were to remove the stainless
riser and order a black-iron riser, or replace the muffler; I
decided to replace the muffler. The boat’s muffler was the
original box-type waterlift which measured approximately
13"x13"x10". The muffler was screwed and
epoxied in-place on a piece of plywood which was form-fit to its
base. After removing the mounting screws and breaking the
muffler free from its foundation, I found that the height of the
inlet and outlet ports severely restricted the muffler’s egress.
Consequently, I cut-off the inlet and outlet tubes, and was able
to remove the muffler through the larger access port under the aft
berth. The new muffler which I selected was manufactured by Veralift,
and, similar to the old muffler, featured inlet and outlet ports on
top of the unit (not a commonly used configuration anymore – it
required a special order). However, unlike the old muffler,
the Veralift was cylindrical in shape, with a diameter of
approximately 8", and a height of 9".
Consequently, it was convenient to work with, and I would later be
able to install the muffler through the access door under the vanity
in the head (i.e., I would work right-side-up! What a
novelty!) As a foundation for the new muffler, I selected 3/8"
marine plywood and cut it to a dimension of 17" x 13".
I then aligned the plywood such that the 17" length ran
fore/aft and overhung the forward end of the old foundation by
3". I then screwed the plywood onto the old foundation;
the 3" overhang would allow for mounting the new muffler in
alignment with the new riser. With the new foundation in place, I
maneuvered the new muffler through the head-vanity access door and
reconnected all hoses.
As I started the engine and checked all connections, I realized
that my five-day adventure was almost over. The only other
action would be to retorque the flange bolts after a few hours of
Important: The opinions expressed here are those of the
individual contributors to this page, and not those of the Catalina
34 National Association or Catalina Yachts, Inc. Additionally, this
material has not been reviewed by Catalina Yachts, Inc. for
technical accuracy. This page's maintainer cannot guarantee the
accuracy of this information or the desirability of suggested
modifications or upgrades. Please obtain assistance from a competent
marine mechanic or boatyard prior to making any significant
modifications to your vessel.