Detroit Diesel Restoration / Dodge Conversion - Page 2


The oil pump has seen better days and has been replaced. The numbers written on the inner rotor were .001"s over the maximum allowable spec. Seven out of eight points were either at maximum clearance or beyond.
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The Roots blower essentially looked pretty good, but had some unusual wear between the bottom rotor and the engine side of the housing. On closer inspection, it appeared that the 4 mounting bolts that hold the blower to the engine block may have been over-torqued. Since these bolts are at the outer corners of the blower, it may have been possible for someone to crush the gasket at the corners while allowing the gasket to deform the center of the blower housing, pushing the housing into itself and into the bottom rotor. A very light surface cut in the mill (.003") of the engine-to-blower mounting surface seemed to prove the housing casting had, indeed, been distorted. Luckily, everything cleaned up nicely and still remained within spec.
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After the light remachining of the mounting surfaces, cleaning, painting, and seal replacements, the Roots is ready to assemble.
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The exposed rotors mounted in the front end plate showing the close proximity between the two. Average clearances throughout the interior of the blower are around .008". When taking into account that the rotors will be spinning an average 5000 RPM at normal road speeds, those close tolerances seem small!
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With the housing dropped down around the rotors, it can be seen how the air is drawn in one side, carried around the inside perimeter of the housing by the moving rotors and then expelled out the other side of the housing when the rotor "blades" come together. The rotors turn opposite each other.
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The near complete Roots, now shown with the gears mounted on the back end of the blower.DD39.jpg - 101887 Bytes

Before the front cover goes on, the thrust washer system is installed which holds the linear position of the rotors to within .002" of spec.
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Before the rear cover is installed, the drive coupling is installed on one of the blower gears. This spring loaded coupling presumably removes impulses generated by the blower from the engines' gear train.
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The final assembly to be disassembled is the cylinder head. The complete valve train is removed, cleaned up and ready to inspect. A lot of parts, to say the least! For the most part, everything looks good so far.
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Interesting design of this engine is the exhaust rocker arms setup for operating two valves simultaneously. The free floating "bridge" pinned to the end of the arm comes down on a pair of valves. My question would be: "What happens if a valve spring goes weak or breaks?"
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After the valves were reground and then lapped to the valve seats in the head, the head was sand blasted and washed up for paint prep.
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The valves in this engine are small! The valve heads only measure approx. 1 inch in diameter (4 valves of this size closely equal one 2" valve) with the stems measuring to .250 inches, which is just smaller than the chuck on my valve grinder can handle. So, I had to setup the lathe with the tool post grinder and do my valve grinding on the lathe.
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The valve seat inserts in the head were in really nice shape, but the valves themselves were pretty tough looking as shown in this comparison between an untouched and reground valve. All 16 valves required at least .006" of clean-up to remove all the pits. One valve head was also non-concentric with its stem, requiring nearly .013" to clean up.
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With all the work done and casting cleaned, the head gets both its coat of Detroit "Alpine" Green paint on the exterior surfaces, while the internal oil surfaces get a coat of Glyptal sealer. The Glyptal seals the pores of the cast iron, stopping any porous leaks that may be present, and allows for better flow of any particulate matter back to the oil pan for improved removal during filtering and draining.
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Finally, parts start to come back together with the installation of the valves.
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Most of the head is now back in one piece with most of the related hardware cleaned up. The injectors will not be installed until the head is reinstalled on the block.
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Close up view of one of the sets of rocker arms. The injector will be clamped into the copper tube in the middle of the valves.
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The wrist pin bushings in the rods are replaced and reamed to final size. The rods are rifle drilled to carry oil pressure from the crank journel to the gap between the bushings, a hole in the middle of the wrist pin, and also to the spray nozzle at the top of the rod. The oil between the rod bushings flows into the flutes in the bushings themselves, the pressure filled wrist pin forces oil out to the outer fluted bushings pressed into the pin bosses of the piston feeding the flutes of those bushings, while the nozzle spray cools the underside of the piston.
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The basic parts ready to assemble.
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Once assembled, spring steel discs are driven into the piston bosses to retain the pin and seal the pressurized oil away from the piston skirt.
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Between the wear from normal use and the rust from sitting for a lengthy time, the flywheel needed a clean-up turning in the lathe. This is the first pass of the process showing the emerging wear pattern in the clutch disc area.
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The second pass really shows the worn areas (rust colored patches). So far, .004" has been taken off the surface.
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Finally, it all comes clean with a total .007" removed from the clutch surface.
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After the con-rod/piston assembly, the new cylinder liners are paired up with the assemblies and everything is numbered accordingly.
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Pretty much the last parts to be cleaned up; the main bearing caps and bolts. These were bead blasted to remove the heavy surface rust.
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