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Chapter 25: 10/02 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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