Engine Construction Part I
Crankshaft, Pistons, Heads & Eccentrics
4/20'/2006, last updated
These parts were machined in 2006 while
waiting for the investment cast parts to be produced. As documented
elsewhere, the investment casting effort fell through and these parts set for
over three years. The engine has now been successfully built.
The page was updated to show some minor chages and include the current
number for these parts.
|Crankshaft - HM100: The design information for the crankshaft
is in Engine Design I. The webs are made from 5/8" X 1.25" steel
bar stock. The closest size available locally was 5/8" X 1.5".
Two pieces were cut a little extra long and silver soldered together. The sides
of the combination were then milled to achieve the 1.25"
width. One end was also squared. The block was then
mounted in the vise on the mill and the mill indexing used to locate
and drill the two 3/4" holes. Photo shows the webs after the
holes were drilled.
The holes turned out to be a bit oversize. In
hindsight I should have drilled them 1/32" undersize and then used an
adjustable reamer to bring the holes to the desired size.
|The next step was to silver solder the pieces of
drill rod to the webs. The rod for the crank was cut extra long.
The main shaft rod was cut to correct length and the ends turned to
5/8" per the drawing before soldering the webs.
The slightly oversize web holes made it difficult for the solder
to flow into joints. Ideally, there should be about 0.002
clearance. The gap was maybe 0.005" or slightly greater.
The crankshaft was etched and the soldering operation repeated
several times until satisfactory joints were achieved.
Next, 1/4" holes (drilled undersize and reamed) were cross
drilled through the webs and drill rod. Pins of 1/4" drill rod were
put in the holes. The pins were cut about 1/16" long and the
excess on each end flattened with a hammer to retain the pins.
|The next step was to mount the main shaft in the lathe
chuck and turn the excess length of the crank shaft from the front
and back sides of the web. The radius and grooves were then turned on the
end of the webs.
The part of the main shaft between the webs was then sawed off
and the inside of the webs smoothed.
The final step was to use an end mill to cut the keyways in the
shaft. The photo shows the completed crankshaft.
|This shows the main bearings fitted to the
crankshaft. Thrust bearings are shown on the outer ends of the
man bearings. The initial plan was to use these thrust
bearings to give a finished appearance. However,
after i=the engine has been constructed its obvious thta these
bearings wouldn't be visible and a waste.
Eccentrics: The design information for the eccentrics is also in
Engine Design I. The eccentrics are 1.75" OD X 1/2" thick disks.
The only steel rod I had close to the required size was a length of 2"
OD 303 stainless, so stainless it was. I turned down about 1.25" of the end
of the rod to 1.75" and turned the end smooth. I then drilled a 3/32"
hole 1" deep in the end of the rod about 1/2" from the edge. A 9/16" disk
was then sawed off the end of the rod. The saw cut was then
turned smooth on the end of the rod and a second 9/16' disk sawed off
The disks were then chucked and the sides with the saw cuts turned
to achieve the required 1/2" thickness.
|The disks were then stacked on top of each other and
a roll pin driven in that 3/32" hole. The disks were then
mounted in the four-jaw chuck with about 1/4" sticking out beyond
the jaws. A dial indicator was positioned against the
part sticking out and the jaws adjusted such that the total throw
was 5/8". The indicator was also used to locate the extremes
and small marks were scribed on
the face at the extreme positions. The photo shows using the dial
indicator to position the disks in the chuck..
A 5/8" hole was
drilled and then bored to the required 3/4" diameter.
|The template shown on the right was made to position the
keyway relative the extreme positions. Unfortunately, I
subtracted 25 degrees from 90 degrees and got the 55 degrees shown
in the image. When I tried to time the valves I found the
valves opened about 10 degrees too early (DAH!). I remade the
eccentrics using the technique shown only using a 65 degree angle.
|A line was scribed on the face of the top disk
connecting the extreme position marks . The shaft hole was cut
in the template. Part of the template along the extreme line
was cut way so that the template could be aligned with the line
scribed on the front of the top disk. The template was then
glued to the disk. The broach bushing was inserted through the hole
in the template to help position the template.
After the glue set, the end of the broach was inserted in the
slot in the busing and the bushing was rotated such that the broach
was over the parallel lines on the template. The bushing was
then clamped to the disks to keep it from moving as shown in the
photo. The broach was
then removed from the slot and a press used to broach the
keyway in both disks at the same time.
|After the keyways were broached, the disks were
separated and the recess turned on the one edge. (Be sure to
check the drawings or photo to get the recess on the correct side.) Note that the
two eccentrics are identical.
|The eccentrics are mounted such that the recesses of
both eccentrics are next to the seam between the two eccentrics.
The key fixes the radial position of the eccentrics.
The setscrews (not shown on these eccentrics) hold the eccentric
|Cylinder Heads - HM110 &
HM111, Packing Gland HM112: The heads and piston rod rod packing
glad were the next parts machined. The design information for
the heads and gland is at
Engine Design III. The heads were turned from
a short length of 3" diameter 12L14 steel purchased online from
ASAP Source. The
12L14 contains a small amount of lead to make machining easier.
I turned the cylinder side of the head, cut off the thin piece with
the band saw and then mounted the 2.125" shoulder in the lathe chuck
and finished the other side.
Drilling the head bolts on the 2.625' bolt circle can be a
challenge. This time I turned a short piece of aluminum rod
to fit in the packing hole of one of the lower heads. It is retained
by a 10-32 bolt through the rod. The other end of the rod was
mounted in a 5C collet in a collet fixture centered on the rotary
table as shown in the photo on the right. That collet
fixture is essential fixed to the rotary table ---- an easy way to
mount things to the rotary table and have them centered. The
holes were marked with a center drill and the head was then removed from the
fixture and holes drilled through on the drill press. This head was then used as a
pattern to drill the holes in the other three heads. The
heads will be used as patterns to drill the holes in the cylinders
and crosshead guides.
The photo above shows the finished heads: the upper heads
on the left and the lower heads in the middle. The packing glands
shown on the right were turned from 1.75" diameter bronze rod that will
also be used for the crossheads.
Piston Rod HM121 & Crosshead-HM122: The design information for
the piston, rod and crosshead is in
Engine Design V.
The rod is made from 5/16" diameter stainless steel stock. The
Crosshead is fabricated from 1.75" diameter bronze bearing stock.
The first step was to thread the ends of the HM121 piston
rod. I was concerned that the threads be straight so that the rod
would be on the axis of the piston and crosshead. I turned the threads
to about 90% of the required depth and then ran a die (held in tailstock)
to finish the threads. I used a collet chuck for this operation to
get the rod centered accurately and to avoid marring the rod
|The crossheads were done next. A suitable
length of stock was chucked in the lathe and the shoulder on the end finished and the center hole
drilled and tapped. The rod was threaded into the crosshead using
high temperature Loctite (#672) to secure the joint. After the
Loctite set a 1/16 hole was cross drilled through the shoulder and
rod and a roll pin inserted to also secure the rod. The pin
will serve as a reminder to not remove the rod from the crosshead.
The rod was then chucked in the lathe and the crosshead turned to
the correct diameter, the end finished and the hole for the 4-40
setscrew in the end was drilled and tapped. I used a collet
chuck for this operation to center the rod as accurately as possible
and make sure the rod wasn't scratched.
The photo shows the crosshead and rod after this operation.
|The next step was to mill 3/8" off each side leaving
a 1" thickness.
The hole for the rod pin bearing was drilled after the sides were
milled. This hole is a little tricky since it intersects
the hole drilled for the rod. Bronze tends to grab the drill
and everything flies if it isn't firmly secured. I secured the
crosshead in a large drill press vise (using strips of aluminum
between the crosshead and the jaws). A
3/16" hole was drilled first followed by a dull 3/8" drill. The hole was
then reamed 1/64" at a time until the required 7/16" diameter
was achieved. The resulting hole is round and perpendicular to the
|The last step was to mill the slots in the sides of
the crosshead. The photo shows the finished crossheads
Main Piston-HM120: Brass,
bonze or stainless steel can be used for the piston. I decided
to use 3" diameter bronze bearing stock for the piston too. An entire piston except for the upper end was machined on
the end of the rod. A cutoff tool was used to make the grooves for
the rings. The stepped center hole was bored rather than drilled to make sure it was
centered. The center hole was tapped using the tailstock to hold
the tap. The piston was then sawed off the rod (band saw) and the
piston chucked so the upper end could be turned smooth.
The final step was to drill the two holes for the piston wrench.
The photo above shows the finished pistons, a set of rings
and the piston wrench. The wrench has a pair of pins (10-32 screws)
that fit in the holes in the upper end of the piston. The 1"
diameter hole through the wrench allows a deep socket to be used on the
locking nut. The process will be to install the crosshead and
rod through the crankcase and the piston through the upper end of the
cylinder. A ring compressor will help get the rings inside the
cylinder. A rod can be inserted through the hole in the crosshead to keep
it from turning. The piston wrench can then be used to screw the
piston onto the rod. The jam nut can then be fitted to the end of
the rod and a socket used to tighten it while the piston wrench keeps the
piston from turning.
The assembled pistons-rods-crossheads are shown in photo
above. Fabricating these parts was easier than expected.
The photo above shows the finished valves with rings and
valve rods. A short piece of 3/8" brass hex stock was silver soldered to the
stainless steel valve rod serves as the stop at the bottom of the valve.
A lock nut will be used at the top end. Stainless steel washers will
be used at each end of the valve. The lock nut will be tightened just
enough to remove most the slack but still allow the rod to move side to side
to match the rocker arm motion.
The lower end of the stem will be cut to length and threaded after the
valve linkage has been assembled so the correct length can be determined.