I feel like one of the guys on American Chopper - ;>)
Started July 18, 2007
Originally, I was going to pay the $800 or so and have my exhaust system fabricated by one of the several companies that do it. Then, after some conversation with Bob Barrows, I was convinced to simply fabricate my own. The exhaust system is made from 1 1/2" EMT conduit, available from your local Home Depot or Lowes hardware store. For about $50 I picked up about 20 feet of straight 1 1/2" galvanized conduit and some 90 degree pre-bent angles of the 1 1/2" conduit. I will not have a muffler and my 4 exhaust pipes will run out of the cowling exit area with a slight downturn. (Caution: When welding galvanized steel, do not breath the fumes and have a well ventilated area with some air moving the fumes away from you).
The straight pipes were cut using a 14" cutoff saw with metal cutting disc
installed. The curved portions were cut on the bandsaw. Here
I am working on cutting one of the 90 degree angles to fit the cylinder head
better and come out at the correct angle:
I feel like one of the guys on American Chopper - ;>)
I started by cutting one of the 90 degree angles until it fit nicely against
the bottom of the front cylinder and pointed aft toward the opening at the
tunnel area of the firewall:
Once the fit was looking good, a 3' length of the straight conduit was tack
welded to the end of the 90 degree angle:
Note that the piece is cut to make the exhaust tuck up under the intake pipes
closely, keeping it all tight against the engine to allow clearance for the
engine cowling. The end that goes against the bottom of the cylinder head
was trimmed and shaped until it laid flat and was at the correct angle.
There should be only about 1/2" of clearance between the exhaust pipe
and the intake pipe of the rear cylinder.
With the first exhaust pipe roughed in and basically fitting well, it was
time to attach the mounting flange that bolts to the cylinder head (available
from Aircraft Spruce - P/N 33021). The mounting flange was bolted in place
on the head with no gasket. The pipe was slid up into the flange, held
in place where it goes and a mark was made on the pipe and flange with a
sharpie marker. Since I can't weld it in place on the engine, the mark
allowed me to remove the whole thing and put the flange back in place on
the pipe in the correct position, depth and clocking:
As you can see, I traced a line along the pipe where the mounting flange
meets it and also made a reference mark to make sure the clocking on the
flange was correct.
For now the mounting flange was just tack welded in two places to the pipe. Any adjustments needed can be made by heating the tack welds and moving the mounting flange as needed. When fitted back to the engine, it was just right.
For cabin heat, I have decided to go with a double heat muff that wraps around both pipes. To do this, the pipes must be parallel and 3/8" apart for at least 9". With that in mind, the exhaust pipe for the rear cylinder was made as described above but careful attention was paid to getting the pipes parallel and 3/8" apart. I clamped to two pipes together with a piece of 3/8" plywood in between them to maintain the proper spacing.
Here is the right side of the engine with both exhaust pipes just tack welded
for now:
Now, with it all tack welded only, I will check the fit of the bottom cowl to make sure that I have good clearance.
To check clearances, I attached the nose bowl and the cowling side
channels:
As you can see, I have plenty of clearance at the nose bowl and the side
channels.
With everything fitting and the clearance from the cowling and nose bowl looking good, it's time to take the exhaust assemblies off and do the final welding of the flanges and splice points of the pipes.
The pipes were then welded to the mounting flanges on the inside as shown
here:
Click here to go to Exhaust page 2