Chapter 25
Building a Belt Drive
Turbo:
Dick Datson has proposed that we all
consider building and testing a belt drive turbo.
Simply, this is a compressor section
from a regular exhaust driven turbo which is connected to a countershaft by a
wide belt. The countershaft, which has a larger diameter than the primary
shaft ,is then driven by the crankshaft at some effective ratio which will give
significant rpm at the compressor with modest crank speed. The advantage
of this is almost instantaneous power delivery. Dick's thrust is with
small engines here which could greatly benefit from a "touch of cold
boost" in specific situations, but which may not need such radical power
delivery at other times. He wants to test it in extreme use situations
by mounting it on boats with a jet drive. He has a prototype model which,
though crude, is a very flexible and appears to be something easily adaptable
to a variety of situations. It is quite simple and would be easily
repairable in the field. Since I have a few Chrysler TO-3 turbos (2.2
liter ), I decided to begin a buildup of one of these. Ultimately, it may go
into TurboStude alone, or as rapid spool up for the other turbo. I may
use it in the Bonneville project. I expect we will find that the optimal
turbo to use for this is a bigger one.
Tearing apart the used turbo:
These turbos have lived a hard life. The temperature swings are
incredible, and they do require some patience if they are to be taken down
without breakage. You may decide to restore the unit to its original
configuration, so damage to the turbine section might be a good thing to
avoid. I will describe what I have done in typical TurboStude diary style
as it happens over the winter of 03' while TurboStude slumbers in west
Minneapolis.
10/02 Taking the turbo apart and
beginning to make the new turbo-shaft.
My first step was to take as
much plumbing as possible off the unit including oil and water fittings. Use
wide and or box end wrenches for this as the brass fittings may mangle
easily. Once they are off, the turbine housing will be easier to clamp in
a vice.
Next I removed the exhaust
housing which holds the internal waste gate. This is done with 1/2"
wrenches, using 6 point box end whenever possible. It should be added
now that you should pre-soak all bolts with your favorite penetrating
solution. I use a substance called KANO KROIL, though I'm sure other brands will work. Once
these bolts are off, including the one just inside the exhaust outlet of the
turbo, the housing will come off exposing the turbine wheel. This has a
9/16" end on it which can be held still with a 6 point box-end wrench
while a 12 point 3/8" wrench twists off the nut on the other end of the
shaft (at the compressor end). Loosen this up, but not so much that the
compressor wheel is wobbling around.
Now, you can remove the
aluminum compressor housing which is probably held in place by about six
1/2" bolts ( Both the turbine and compressor housings can be twisted
around so that particular bolts have clearance for removal). CAREFULLY
take off the aluminum compressor housing and expose the delicate compressor
wheel. Inspect the wheel for broken vanes or signs of rubbing on the
housing. Wiggle the shaft to note lateral run-out. The wheel should
not be too difficult to remove once the 3/8" nut is out of the way (and
pre-soaked). Put it someplace safe. Now, a collar can be removed
which is held on by four 10mm bolts. This will uncover a spool shaped spacer held in place by a
"U" shaped collar.
Now comes the job of loosening
six bolts which attach the turbine scroll to the central cartridge
section. These are steel and the section is cast iron. They seem to
be 1/2" and may need some KROIL. Once loosened somewhat, the
scroll can be turned and the bolts can be removed the rest of the way. I
needed to actually drill a hole cross-wise to get more KROIL into the threads.
Even then, it didn't budge until I MIG welded an old wrench to the bolt
and slipped a 12" pipe over that for more leverage! Considering that
you probably will jettison the cartridge
section anyhow ( you will be permanently changing the shaft by cutting
off the turbine wheel), if the bolts don't come off, you could just grind
or torch off the bolt heads to save time.
Now that the whole thing is
apart, you can chuck the
shaft in a lathe and turn off the end near the turbine wheel.
This part of the shaft is fairly soft, and will cut with a hacksaw. I
left about two inches of the 3/8" part of the shaft.
Now, find a piece of 5/8" steel rod and drill a 2" deep hole in the
end that is an interference fit with the turbo shaft. The shaft mikes out
at about 5/1000ths larger than a 3/8" hole. You will need to use
your head (and patience) to make the two mate as an interference fit.
This is where the shaft and hole are within about 3/1000ths of one another
(shaft is bigger). To get this to work, you must heat up the 5/8"
rod on the drilled end. It will expand, and the chilled turbine shaft
should drop in. When the two equilibrate in temps, they will become close
friends.... It may be necessary to crossdrill a small hole in the 5/8" rod
about 2" down to let air out as the turbine shaft settles in.
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