Shay Engine Machining
Nelson Riedel, Nelson@NelsonsLocomotive.com
1/14/2003, last updated 06/05/2004
These pages show some of the I techniques used to machine
Shay engine parts. The first engine parts machined were the cylinders,
crosshead guides and valve stem guides. These were done before I
though to take photos. The critical facing and boring of the
cylinders and crosshead guides was done on the lathe using a 4 jaw
chuck. The heads were also turned on the lathe. A drilling
template was very carefully fabricated and used to drill the attachment
holes in the heads, cylinders and crosshead guides. This
permitted these pieces to fit together in correct alignment.
|The next step was the machining of the crankcase
casting. First, the upper surface was milled flat to form the
reference surface. The rear mounting pads were than
milled flat to form a second reference surface. The slots for the main bearings
Much of the material
was removed using the drill press before the finial milling
operations. All four slots were machined at the
same time as shown on the right. This insured
|This photo shows finishing the bottom surface of
the crankcase to accept the bearing retaining caps. This
was done without changing the casting from the bearing slot
machining above to insure perfect alignment of the
The cast iron is an excellent material to work with. It
machines easily because it tends not to grab the tools;
the removed material comes off as small chips, or fine sand like
granules or a powder. There is however one drawback; the
debris sticks to hands and
clothes leaving a dirty black residue. After washing, the
residue is transferred to the bottom of a sink or shower where
it turns to rust in a few seconds, much to the displeasure of
the domestic staff.
|The final major operation on the crankshaft was
to mill out the holes for the connecting rods and #2 cylinder
valve eccentric blades. Rough holes were made on the drill
press and finished on the mill as shown on the right.
After the major machining over 50 holes had to be
drilled and tapped. Drilling templates were made for
the bearing caps and crosshead guides to insure all the holes on
mating pieces lined up correctly.
|The main bearing retaining caps were fabricated
from cold roll steel stock. The photo at the right shows
milling a recess in the caps. Note that all four caps are
aligned in the milling vise and the slot in the four caps is
done in one operation. This insured that all caps were
|The main bearings were fabricated from 1.75"
bronze bearing stock like that shown on the right. This
stuff is really expensive, going for over three dollars per linear
The first step was to cut off a piece the correct length for
each bearing. Then each one of these pieces was cut in
half as shown on the right.
Next, the pieces were machined flat and to the correct dimensions
in the mill. The final milling operations were done
on all pieces using the same settings to insure uniformity.
These blocks are shown in photo below.
|Next, the center holes were bored (slightly
undersize) and the ends faced in the lathe.
Recesses were then milled in the sides of each bearing.
The recesses matched up with the slots in the crankcase as shown
in the photo below.
The final operation was to ream the holes to the exact inside
diameter using a toolmaker's reamer fabricated from drill
rod. This long reamer passing through all the bearings
insured correct alignment. .
The crankshaft turned out to be less of a job than
initially expected. Kenneth provided explicit instructions on how
to make it. I ended up doing the job twice. The first time I
used drill rod for the main piece. I somehow got the throw for one
of the cylinders a little long. While there were some tolerances
designed in, I though this error was pushing the limits (piston striking
the heads) so I made a second
crankshaft --- the second one took no time at all. I used precision ground
stainless rod rather than drill rod on the second one. The photos
below are mostly from the first attempt.
This photo shows the raw materials: stainless steel
bar stock, rod and taper pins. (This photo is from the second attempt.)
The bar stock is cut and milled smooth and drilled to make
the webs. The crank rods are then pinned in place on the webs using the
taper pins. The webs are then installed onto the main shaft
and also pinned in place. The photo below show the middle crank in
The next photo show all three cranks in position,
Note that the eccentrics for the middle cylinder are installed before the
#1 cylinder crank is positioned on the rod.
The next photo shows the completed crankshaft after the
rod had been sawed out between each pair of webs.
Here is the crankshaft in place in the crankcase.
The connecting rods were machined from the three
pieces of stainless bar stock shown below.
Most of the work on the rods was done by milling and all
three rods were done at the same time wherever possible. The
photo below shows finishing the sides of the three rods held together in the
The photo below shows the nearly finished rods.
The next photo shows finishing the upper end of a rod
to the proper radius with a corner rounding end mill.
|There are a total of six bronze
eccentric straps, two for each cylinder. The first
step was to saw the part of the eccentric strap casting that
goes around the eccentric in half and machine the mating
surfaces flat. The outer sides of the straps were then
machined using the mill. The photo at the right
shows the six top halves held together in the vise and the top
being milled smooth and to the correct height using a fly
After this operation holes were dilled in both halves and the
lower holes tapped so that the two halves of each strap could be
held together with screws.
|The photo on the right shows
machining the side of one of the straps in the lathe. This
same setup was used to bore the inside and to turn a groove to
match with the eccentric.
|The valve reversing link and link blocks shown on
the right were some of the most difficult parts to fabricate.
The slot in the link is at a 4 inch radius and there is a mating
curve in the bronze link block that rides in the slot.
|The photo on the right shows the setup used to
mill that slot on the 4 inch radius. Before the slot was
milled the three links were silver soldered together. This
permitted three identical links to be machined. The outer
surfaces were machined on all three at the same time and the
holes also drilled through the three at the same time. The
three links were then fastened to a scrap aluminum plate with
screws. The aluminum plate was then secured to the lathe
faceplate which was then attached to the rotary table. ( Years
ago I made a fixture for the rotary table identical to the end
of the lathe headstock so that the lathe faceplate, chucks and
collets can be secured and centered on the rotary table.)
The links were then adjusted to the 4 inch radius from the
center of the table and such that the radius bisected the
links. The entire setup was then positioned under the
vertical milling head and the table rotated to make the curved
slot. (This is the only way I could think of to make that curved
|The next job was to machine the sides of the link
block to match the sides of the curved slot in the reversing
link. The setup on the right was used for this
operation. The first step was to machine the link blocks
to the correct overall dimensions and with a hole in the
center. A slot was then milled in the aluminum scrap, the
link block positioned in the slot and a hole drilled through the
scrap aligned with the hole in the block. The block was
then secured to the scrap with a small crew. The scrap was
then fastened to the faceplate such that the center of the block
was 4 inches from the lathe center line and orthogonal to the
radius. Both sides of the block were then turned to the
correct shape. The second and third blocks took little
effort using this setup. The blocks matched the slot in the link perfectly.