DESIGNING & BUILDING A STEAM ENGINE FROM SCRATCH
Just recently after having finished about a dozen different steam engines of various designs and sizes raging from a diminutive 1/4" bore " breath " powered miniature, several pivoting valve and oscillating cylinder engines, to a large horizontal mill style engine, I got the urge to design and build an engine of my own. Up until now, I was building them according to drawings and plans of engines originally built by other craftsmen. Half way through the list of projects I began to see how I could modify or improve a given engine component or maybe devise an easier technique, resulting in what I think is a better overall product. After many such changes and through close study of how to lay out the required porting to provide air or steam to the cylinder, I decided to begin building my own engine totally from scratch and except for set screws, cap screws and other bits of hardware, the number one primary criteria was that it had to be built entirely out of recycled material from the scrap yard. Before I get into the actual construction details on how I accomplished this, I must tell you that it not only looks, but it also runs great.
Some workers insist on working only after a detailed and finished set of drawings are happily in their hands. I usually also work along those lines, but in this case I didn't know what I wanted my engine to look. Well, I basically new how large my engine was supposed to be from what I had mentally designed on, so I decided to start with the building of the cylinder, cylinder head, inlet port, valve chest and valve only after very rough sketches were made. These five components make up the basic power portion of the engine. After having built an engine with a similarly sized cylinder and valve arrangement, I chose a 5/8" bore and 3/4" piston stroke coupled with a 1/4" valve stroke. I began building the cylinder by sawing off a length of 1-1/4" round aluminum rod about 2-1/2" long which after some work would become the basic cylinder body. After facing both ends clean I reduced the length to a final 2-1/4". I switched to the four jaw chuck and with the aid of a test dial indicator I centered it to within .0005". The cylinder bore was started by spot drilling, drilling to a .250" all the way through. I then continued to drill with larger drill bits, to a depth of 1-5/8"and a 1/2"diameter, leaving a conical bottom matching the drill tip. The .250" diameter portion of the hole was reamed to a 9/32" final size so it could accept a equal diameter brass sleeve with a bore of .250" to act as a piston rod guide. I had also wanted to sleeve the cylinder bore with some very true running thin walled brass tubing to prevent any possible taper possibly introduced during the final boring to size to interfere with the piston action. The outside diameter of the sleeve I was using, (also surplus) was 23/32" so I carefully bored the hole a few thousands at a time until the sleeve just slid into the bore with a bit of friction. I was using a telescoping hole gauge to constantly check my progress until I was about ten thousands away. The final refining was done attempting to slip the sleeve into the bore until the proper fit was reached. I really do not know what the exact final diameter was and can only guess that it was within 1/2 a thousands under size considering the sort of fit I got. The bore did not go all the way through the cylinder but was finished with a square shoulder at the bottom end of the cylinder. After pushing the sleeve until it hit bottom, I took a slight cleaning pass across the face ( top of the cylinder ) to bring the slight excess of the sleeve flush with the top cylinder end. I reversed the cylinder blank end for end and tuned down the bottom 1/2" to a 1" diameter, forming a square shoulder. This narrower portion will be pressed into the cylinder mount with the shoulder fitting flush on the mount's surface. Two small #55 to #60 holes are drilled through the bottom end of the cylinder at either side of the piston rod guide sleeve to vent the bottom portion of the cylinder. This is needed because the rod guide or sleeve is such a close fit to the piston rod that it tends to create a vacuum situation as it moves up and down. I made the cylinder head out of a 1/4" thick slice of the same diameter rod used for the cylinder. After facing off both sides, a shallow 1/32" deep stepped shoulder was created by facing from the edge toward the center until the diameter of the raised shoulder just fit the cylinder bore. I shaped to top side of the head to form a flat ring around the perimeter for the mounting bolts and a chamfered, raised dome on the middle. I put a tiny center spot with a # 00 center drill and removed it from the chuck. I put two small dabs of CA glue to the surface top edge of the cylinder and attached the cylinder head to it until it set. After re-chucking and centering the cylinder / head to within .0005" I took a slight turning cut at a relatively fast feed and the slowest carriage feed to create a nicely polished surface between the two parts. This trued up the head to the cylinder body so you could barely detect the joint between the two. Using the dividing / indexing plate on the head stock of my TAIG ( home made ), I indexed off for six equally spaced # 43 holes which I drilled with my cross slide drilling rig ( also home made ) to a depth of 3/8". The holes were drilled through both the head and cylinder at the same time, ensuring perfect alignment later. The portion of the holes passing through the cylinder head were enlarged to a #33 clearance size for the 4-40, 3/8" cap screws used to install the head. Needless to say the remaining portion of the holes ( #43 ) were tapped to 4-40. I put a line across the head and cylinder joint so I could return the two part to their exact position after separating them. In order to separate the head from the cylinder I applied a very low flame to the edge joint to effectively melt the CA glue joint apart. You MUST make sure you have plenty of cross ventilation as the fumes given off are very dangerous to the mucus membranes of the eyes. Soak and scrub the parts in acetone to remove any excess glue and gunk from all surfaces and wash is some hot soapy water. Screw the two parts together and put a scribe mark running along the center of any two adjacent screw holes. You will need that index mark later as you start to mill the flat vertical slot along the side to accept the face of the valve chest. The piston was next and while I was building the prototype, I thought I would also sleeve the piston with the next smallest size tubing. I unfortunately didn't have any so I did it the tried and true way by turning and fitting a piston made from light weight aluminum. Unlike most pistons that use a wrist pin through them, I decided to make this one as one solid piston and rod unit so the rod could pass, be guided and kept in position by the .250" diameter piston rod sleeve previously pressed into the bottom portion of the cylinder. To make a piston itself, I began with a piece of 5/8" aluminum rod about 1-1/5" long, chucked it, center drilled, drilled and reamed to .250", .25" deep. I parted off the piston blank to a bit over 3/4" long to allow some material for facing off the top. I prepared a 2" long piece .250 diameter stainless steel ( if you can get it ), brass rod ( actually prettier ) could have been used as well, and after facing and slightly chamfering one end, pressed the piston blank all the way into the rod. If it is a bit loose, use a bit of CA glue and let it cure. Now you can turn the piston to the correct diameter ensuring that the rod and the piston are running along the same central axis. Take a reading of the cylinder bore with a small telescoping gauge and begin to turn down the piston. When you are about .015" away, begin to a use the cylinder itself to check the fit. Reduce the diameter of the piston by taking only .001" off the diameter per pass, ( that means advancing the cross slide .0005" per pass ). You should reach a point when the piston almost fits if you force the issue, please don't. Use a 400 grit piece of silicon carbide paper to remove the last smidgen of metal and at the same time polish the piston so you achieve a perfect slip fit. The correct fit is one that allows the dry piston to freely drop through the bore and yet cause it to float if you plug up one end of the cylinder with your finger. The piston will still drop but it might take a couple of seconds to do so. After oil is applied. it will have an even better seal. At this point the top of the piston is faced, chamfered and touched up with 400 grit. You definitely do not want any burrs on the edges to ruin your cylinder bore. As a method to retain some oil inside the cylinder you should turn three or four closely spaced grooves about 1/16" apart along the length of the piston to a depth of about .003" to .005". Not too critical but try not to go too deep on these. Fit the piston and rod through the top of the cylinder, checking for any binding or stiffness. Correct by polishing the rod on the lathe to just reduce the diameter ever so slightly. When everything is fitting just right, allow the piston to drop to the bottom dead position and mark the protruding piston rod to a point 1-1/8" from the bottom edge of the cylinder. Take it back out and after wrapping two full turns of masking tape around the piston, chuck it in a three jaw chuck with soft jaws. Reduce the length of the rod to the mark previously made and chamfer smooth. Set up the milling machine and clamp the piston horizontally on a milling vise and cut a perfectly centered, .0625" wide horizontal slot perpendicular to the pivot hole and 1/4" deep. Locate for a centered #43 vertical cross hole, 1/8" in from the bottom edge. Drill the hole, going all the way through the slot to act as a pivot hole for the crank connecting rod screw. Tap the hole for a 4-40 thread. The next thing to set up for would be the machining of a flat vertical slot along one side of the cylinder to accept the valve chest, but first we need to make the valve chest itself.
Lets talk a little bit about the interaction between the valve, the valve chest and how it admits and exhausts air or steam into the cylinder at just the right times to operate the engine. In so called single action steam engines, which by the way, are the simplest ones for the beginner to start with, the piston receives power a trifle after the piston has passed the top dead center position or twelve o-clock and it's just beginning to come down. On a simple engine, the single port to the cylinder will both admit the steam or air in and also exhaust it out. This seemingly impossible event can take place if a valve with two strategically located ports is allowed to pass along the single port at just the correct times in the power / exhaust cycles. The valve operates up and down inside a sliding fit bore through which the intake/exhaust port are located about 3/16" down from the top end. The valve itself will have a notched area facing the port so when it is positioned in the exhaust mode, air being pushed out of the cylinder by the piston moving up can escape through the port and around the notch. During the complete exhaust cycle, right after the piston has reached top dead center and the last bit of air or steam has been evacuated from the cylinder, the valves exhaust notch will have by now slid beyond the cylinder port thus sealing it shut. A few more degrees of rotation later and the intake circular slot or in some cases a transverse hole will begin to slide toward the hole to begin allowing air or steam to enter the cylinder to send it on its way down again on the power portion of the cycle. A flywheel of just diameter and weight will impart the much needed amount of momentum to smooth out the engine's movements. The timing of the valve, that is the conditions that synchronize the valve notches and or holes, so they pass by the cylinder port at just the right times to insure smooth running is controlled by the eccentric. A disk with an off center pivot hole to impart the required horizontal motion to the valve via the connecting rod. So basically speaking, the intake hole or in some case a circular notch around the valve should just be coming into view as one sights into the air intake hole on the valve chest as the piston reaches top dead / twelve o-clock position while the exhaust notch on the valve should just begin to peak through when the piston has reached the bottom dead center / six o-clock position. This rather difficult concept will become clear when we reach the valve timing stage in the project. To get started, we need to prepare a block of aluminum 1/2" x 5/8" and a length that goes from the cylinder head / cylinder joint to the bottom edge of the cylinder at the point where the mounting shoulder begins. Take some careful caliper measurements between these two points and after surfacing the block to the correct cross sectional dimensions, finish it to length by chucking it on a four jaw chuck as centered as possible and face off both ends. The valve bore is to be drilled and reamed for the best operating results. We do not want any leaks here! If you wish to try your hand at sleeving once again, you can drill and ream to accept brass tubing with an inside diameter equal to the valve's as your sleeve ( same as the piston rod guide ). No matter what method you choose, the final bore of our valve chest is to be .250". If the valve chest blank was centered as close as possible during the facing operation, you can proceed directly with the boring. If not, measure the widths, divide by two and scribe cross two marks along the end face. Where the two scribe marks intersect, that's where your center point is. With the aid of a pointed wiggler and a test dial indicator you can now center the workpiece to within .0005". Center drill, drill and ream to either .250" final bore ( no sleeve used ) or to the next tubing size of 9/32". Insert, and if needed glue a long enough piece of 9/32" brass tubing with an inside diameter of .250 ( hobby shop type brass tubing ) so that it sticks out about 1/32" beyond both ends of the valve chest. Finish by facing both ends flush and lightly counter sink by hand to remove the burr created during facing. The last operation to perform calls for a .125" diameter reamed, transverse hole to be located on center and through the valve bore .1875" down from the top edge of the valve bore, completely through the valve chest assembly. The hole will cross the upper part of the valve bore from right to left, at right angles and centered along the 1/2"width. At this point you should begin to mill the vertical flat on the side of cylinder to accept the face of the valve chest. Place the cylinder horizontally on a vise and jack up as needed to mill the flat. I like to clamp it along the sides with some soft aluminum packing to prevent marring the surface of the cylinder. The flat should fall in between the two adjacent head bolts you placed that mark on earlier, if for nothing else than esthetics reasons. Once the location is found, remove the cylinder head for this operation. Cut the flat in several .010" deep passes with a centered 1/2" diameter end mill along the length of the cylinder until the flat is as wide as the valve chest face. Check as you go by directly placing the valve chest against the flat. If the end mill is truly 1/2" in diameter and it is centered along the long axis of the cylinder, you can cut one last pass to create a slight slot along the length that will house the valve chest face in a neat flush fit. Lap the face of the valve chest that will go against the cylinder on a sheet of 400 grit paper laying on a sheet of glass to get a very flat and scratch free surface on it. Coat the lapped surface of the valve chest with some epoxy or CA glue and clamp it against the cylinder flat until cured. Make sure that everything is in perfect alignment and flush with the top and bottom edges of the flat. After curing you can continue to drill and ream the .125" port hole by simply passing the drill bit and reamer through the already drilled hole on the valve chest so it emerges inside the cylinder bore. Clean off the burrs that were made as the drill and reamed emerged through the cylinder liner.
The valve itself is next on the agenda and it is made from either a length of .250" diameter drill rod or brass rod. It's your preference which material you wish to make the valve from. Begin by chucking the piece of rod, facing and slightly chamfering one end to insure that absolutely no burrs or corner sharpness that can quickly ruin your valve bore is allowed to remain on it. The valve blank is set up on a milling vise, preferably the kind with a horizontal "V" groove on one of the jaws. Set the rod so about 1/2" of the faced end protrudes clear of the jaws at both ends. With an edge finder chucked to the milling machine spindle, locate the side edge of the rod and after compensating for the diameter of the tip of the edge finder tool, advance the carriage exactly 1/2 the diameter of the rod as measured. Do not take it for granted and actually measure the rod with some calipers or a micrometer. The center of the spindle should now be located right over the center line of the rod. Find the edge of the faced end of the rod and in the same manner locate a point .325" from the end. Drill a .125" through hole at that point which will become your steam inlet port. Move the carriage exactly .250" away from that point to locate the spindle at a point .125" from the edge. Use a ..250" diameter end mill and begin to cut a horizontal flat across the first .250 of the valve end. We placed the spindle .125 from the end so by using a .250: diameter end mill you will automatically remove .125" to the right and .125" to the left giving you a .250" final width slot. By bringing the end of the mill so it just touches the un-milled surface of the rod, you can then make as many shallow passes, removing material until you have advanced .125", reaching the middle of the rod. This is the slot that will become the exhaust port. Move the carriage over and begin to machine the end that will connect to the valve rod. To accurately measure the 2.00" distance between the center of the intake port hole and the center of the valve rod pivot hole, I chuck a pointed rod of about 3/16" diameter ( so long as it is larger than the hole ) to the spindle and center it over the intake port, adjusting it until it can be seated right inside the hole by lowering the spindle a bit. I raise the spindle back up and after noting my reading on the carriage longitudinal dial, I move it the correct amount to the opposite side ( 2.00") to locate the second hole. The pivot hole is also a through hole with a #44 bit. What we want here is a clearance size hole for a 2 -56, 1/4" long set screw that will pass through a matching but threaded hole on the end of the valve rod. Set up a slitting saw and arbor to mill a .0625" wide centered horizontal slot and proceed to mill it to a depth of at least 3/16" pass the cross hole. This will ensure an adequate amount of clearance later for the valve rod end. All that is left to do is to face off the bottom end of the valve ( the slotted end ) to a point .125 from the bottom edge of the pivot hole. De-burr and polish the perimeter by running on the lathe with 600 grit paper until a perfect fit into the valve bore is obtained. We have just completed the power end of the engine and can put it aside for now so we can begin concentrating on the crank shaft, eccentric and both piston and valve rods. The material for the crank shaft can again be drill rod or brass. This is entirely left up to the builder. I myself made the entire crank shaft, crank disks, crank journal and eccentric out of solid brass for looks if nothing else. Practically speaking, brass makes a good shaft material and does tend wear and run real well against brass or better yet bronze. The crank shaft was made to a diameter of .250" which I thought was plenty hefty for this engine, although in retrospect, 5/16" would have been even better. Prepare a 5-6" long piece of .250" rod by facing and center drilling both ends with a #2 center drill bit. Make sure that the end of the rod is not protruding any more that about 1/8" out of the jaws to prevent any possible flex and maintain concentricity of the two center holes. Remember that the outside diameter of the rod will not be machined in any way so the two center holes must be as accurate as possible to begin with. Put the rod aside for now and prepare to make the two crank disks. I made my crank disks out of 1-1/4" solid brass bar stock as well since I meant to hard solder all of the crankshaft components together. I began with a short piece of the stock about 1-1/2" long and face off one end. To mark the offset for the journal, you just measure from the center, out a distance equal to 1/2 the stroke length you are trying to achieve. In my case, I wanted a 3/4" stroke so I measured out from center 3/8" or .375". You could use a steel ruler, but I used my calipers set at that distance. A center punch mark on that spot and you are ready to begin drilling and reaming the central crank and journal holes. Hold the rod in a four jaw chuck and true it to the center point as indicated by the little nib left after facing off with the help of a wiggler held on the tail stock drill chuck and a tool post held dial test indicator. Center drill, drill and ream to .250" to a depth of at least 1/2". Shift the work piece laterally by adjusting the independent jaws until the .375" off set punch mark is centered and drill and ream that point to .1875". I could have also used my horizontal drill rig which is installed on top of the cross carriage so holes can then be drilled at any point away from center on a workpiece by simply shifting the unit along the " Y " axis with the cross slide. Now you must part off the two slices for each crank disk with a parting of cut off tool to a thickness a bit over 3/16" each. After the two disks are loose, you should face the surfaces to clean off any cut off tool marks and bring them to .1875". You can slip the .250" shaft through the central hole and put it aside for now. The width of the piston rod crank journal straps is .1875" so use a piece of the same rod stock you will use for the journal to set the distance between the two disks. Prepare a 3/4" long piece of .1875" brass rod by facing and chamfering both ends. Insert the journal through the off set hole to align the two cranks disks. Place the second piece of rod on the opposite side to set the width between the disks and slide the disk sandwich so that the middle of the area between the two disks is 1/2" to the right or left of the center of the crankshaft. Set it down on some non flammable material without disturbing the disk's positions. I use a concrete block for this job and it works great. Heat the disks and the crank evenly with a torch and apply the solder to the joint so it flows into it. Allow to cool without disturbing it. When it has fully cooled, mount it between centers on the lathe and face the outer surfaces only the bare minimum to clean them up. Now is the time to turn the outside surfaces as well. Do not cut off the central shaft section just yet. Solder is plenty strong for this operation but I like strengthen the joints as much as possible so I drill transverse holes and pin the joints. I set the crank/ disc assembly on the milling vise, griping it by the sides of the disks. aligning it so the journal is at twelve o-clock and in line with the drill spindle. I spot drill and drill out the hole through the middle of the edge of the crank disk with a # 60 drill bit going deep enough to not only pass through the journal but also the middle portion of the main crank. #60 drill rod pins are driven, aided with a dab of CA glue and filed flush. Now you can saw the center part of the crank to leave the journal by itself between the top crank disks. I used a slitting blade and arbor on the spindle while I held the assembly by the crank shaft with a drill chuck set up on my special tool post. After aligning the carriage, and slitting saw blade so it was cutting almost flush with the inside left surface of the left disk, I advanced the cross slide forward and the saw blade cleanly cut through the waste portion of the crank. I shifted the carriage to the opposite side to cut the remaining piece of crank as close the right inside surface of the right disk. I did not have to do any filing on any of the cut surfaces as they were smooth enough. You can mount the crank between centers and polish it as it spins on the lathe with 400-600 grit papers. The next item will be the eccentric.
I made my eccentric out 3/4" diameter brass rod by first chucking a piece about 1-1/2" long on the four jaw chuck. After facing one end, I took a light turning cut to true up the circumference. A trough has to be machined around the circumference of the eccentric over which the eccentric straps wrap around. They are kept from moving laterally by having two shallow raised steps on either side of the trough. To make this, I first measure .062 from the edge and by using a very narrow square ground tool bit I plunge it in the work ever so slightly, to begin creating the .062" wide step on the right side. I move the cutter to the left until the width of the slot is about .070" wide. I continue deepening the slot or trough until it is .624". I take the same cutter and slightly plunge it in to mark the position of the left .062" step. Measure .125" from the center spot to mark the position for the crank shaft hole. Off set the work as before, and drill and ream the crank shaft hole. Rotate the almost finished eccentric so the off set hole is at the top or twelve o-clock position and drill and thread a 6-23 centered hole for a set screw. Set up the parting tool and part off a bit past the left side mark just made. Face the newly parted face clean and insert the 6-32 x 3/16" set screw into the locking hole. Take very close measurements with outside calipers around the piston rod and the valve ( each .250" diameter ) Subtract .500" for the reading to arrive at the center to center distance between the two. The eccentric must be slid and locked opposite the crank disks so both center distances between the two are the same. This will ensure alignment when you get ready to assemble the connecting rods to them.
The crank shaft needs a pair of bearings to rotate in and these were made by machining two 3/8" thick aluminum pedestals, approximately 1-1/2" wide x 2" tall. The corners were cut off at 45o were a pair of 6-32 set screw hole were drilled and tapped. These two set screws will retain and lock the bronze bearings that held in two matching holes. The bearing supports are drilled on the underside for two 10-32 cap screw holes each one inch apart on center and also centered along the width of the bearing support underside. The bearing holes themselves are best drilled by stacking the two supports in perfect alignment of the bottom edges and one of the sides. After clamping them securely, they are drilled and reamed .375". Put a mark on the two side edges that you used as a reference to help later when it comes time to mount them on the base. I am using some great 7/16" diameter, very hard aluminum bronze rod material that I obtained at the scrap yard for my bearings. This stuff cost a fortune is it has to be purchased from a metals company. By being able to buy it in "scrap" form ( actually in the same form it is sold as new ), you can really save a lot of money better saved to buy good tooling. To make these, just chuck the rod so about 1" protrudes through the chuck jaws and center drill, drill and ream to .250" to a depth a little more than an inch ( plenty for both bearings ). Face the end and begin reducing the diameter until a perfect slip fit into the bearing supports is obtained. The bearing supports are 1/4" thick so the bearings need to be cut off about 1/16" longer to allow about a 1/32" over hang at both sides of the support. Part these off and finish by taking facing cuts with a small chamfer on all edges especially the inner bores. Insert the bearings so the there is a equal amount of overhang on either side and lock them in position with the two set screws on each corner of the supports. Locate the center point on the top edge of the support and punch the mark. Drill a #60 hole that runs down and through the center of the bearing to allow oil to the bearing and shaft. Enlarge the hole for about 1/4" and thread for a 5-40 thread leaving the rest of the hole as a #60 hole. The oil cups are simple item made out of 1/4" brass rod. Face and chamfer the ends. Drill them with a 3/16" bit 3/16" deep to make the oil reservoir and follow through with a #50 drill for about 1/2". Measure about 1/4" from the top edge and begin to turn until you reach .125" in diameter for a full 1/4" or so. Part off the oil cup, maintaining the full 1/4" length of the .125" portion. Reverse chuck, griping by the oil cup and thread the narrow end with a 5-40 die held on a tail stock die holder. Once the first few threads are well established, reverse the die and continue to thread to the base of the oil cup. Chamfer the bottom edge of the oil cup a bit and you are now ready to screw them into the bearing supports.
The piston rod bearing caps and the eccentric straps are next. I made the piston connecting rod and bearing caps by taking a 1" long piece of 3/16" thick and 1/2" wide. The bolt holes that hold the two caps around the journal are drilled by clamping the stock vertically. After finding the two adjacent edges and centering the spindle at a point .125" from each edge, that is, from the left and right edges, drill the two # 44 holes to a depth of at least 3/4" ( #44 is the clearance size for 2-40 screws ). Now you can slice each of the bearing caps off with a slitting saw and arbor on the spindle or milling machine. I like to use the lathe spindle/slitting saw method to slice these halves. I clamp the stock with the drilled surface toward the spindle, to the cross slide, jacking it up on spacers to bring it to the approximate lathe center and squaring it to the lathe axis. To set the depth stop to produce two equally dimensioned halves, first advance the carriage so the face of the stock is touching the teeth of the blade. Set up a dial indicator to the right of the carriage on a magnetic base with the tip of the plunger bearing on the side of the carriage. Set the dial to zero. Back off the cross slide so the work is clear off the blade and advance the carriage toward the head stock until the dial indicator displays the distance equivalent to the width you need, which in our case is 5/16" or .3125". Add to that the thickness of the slitting blade you are using to compensate for the saw kerf. Slide the depth stop so it bear against the carriage and lock it at that setting. You can now cut as many bearing cap halves as you want, all of them being the same width. After each cap is sliced off, back up the cross slide and advance the carriage to the stop and you are ready for the next one again. Once I have finished slitting the two caps, I bolt them back together with two 2-56 bolts and nuts in the same orientation they were sawn. I chuck them on a four jaw chuck as centered as possible so we can drill and ream the crank journal hole to .1875". Take a cleaning facing cut and then a second facing cut stopping short of the hole to create a thrust bearing. do this on both sides to finish that portion of the work. The width of the straps must be a few thousands narrower that the space between the crank disks to provide lateral clearance. Remove the bearing cap assembly and clamp it vertically so the top half can receive a central .125" hole where the rod will be soldered to. This hole only needs to be about 1/8" deep. Test the fit and clearances by installing them around the crank journals. The fit must be a free running fit. No slop allowed here. I did not provide a means for drip oiling but a drop of a good machine oil on the edge of the caps, allowing it to seep into the journal is all you need for several hours of running. The eccentric straps are made in exactly the same manner, excepting the size of the stock material is larger as well as the bearing hole which in this case needs to clear the .625" eccentric journal diameter. The same diameter connecting rod hole is made on the top strap, where the connecting rod is to be soldered into.
The base of the engine is made out of 1/4" thick aluminum plate. The dimensions are more or less left up to you as it is not that important to the engine's operation. The mounting holes for the bearing must be accurately located and in pretty much perfect alignment to each other. Set the crankshaft with the eccentric installed on it and hold it next to the upper cylinder assembly to check that the crank journal and eccentric center lines are in line with the piston rod and the valve centers. Slide the eccentric right or left as needed to achieve this ver important alignment. The crank shaft assembly should sit centered between the bearing supports but without either the crank disks nor the eccentric touching them. The two flywheels on the outside of the supports will keep the crank from shifting laterally. Locate the mounting holes and proceed to drill and counter bore them for 10-32 cap screws. I find the drilling the screw holes over size allows enough play to adjust their alignment during the installation of the supports and crank. Begin mounting everything and adjust as necessary so the crank spins freely. Four 6" long vertical supports are needed to hold up the cylinder assembly and connect to the bottom engine base. I made them from solid 3/8" brass rod which I simply pass through four matched pairs of holes going through the top cylinder plate and the bottom plate, gluing them with CA or epoxy glue. My supports have a nicely tapered and pointed tops for good looks. The distance between the top plate and the bottom plate is 5-1/2". The rod connectors are made out of 1/4" rod and end milled to create a central tongue that will insert into the slots at the end of the piston rod and valve. Cross drill them to #44 for the pivoting set screws. Cut them off to a 3/4" length, facing and chamfering the cut ends, drill and tap them to a 5-40 thread to a 1/2" depth. Install them to the piston and valve, making sure that they free pivoting. Rotate the crank shaft so the crank journal is at the very top of its rotation and take a caliper reading to the piston rod connector with the piston also at its uppermost position. Cut a piece of 1/8" diameter brass rod 1/4" longer than the measurement taken. Face it and thread it for at least 5/8" to a 5-40 thread on one end. Insert the rod's un-threaded end into the top of the crank strap and solder it in place. Disconnect the pivot connector from the piston rod and screw it into the threaded end of the rod for about 1/4". Re-connect the pivot and test to see if the crank revolves smoothly without the piston hitting the cylinder head. If it does, just disconnect it again and screw the pivot in, a couple of more turns and check it again. As soon as nothing is binding, or hitting, you have completed the job. The valve connecting rod is made in the same manner. After the rod has been soldered to the eccentric straps, screw the valve / pivot into the top of the rod while the valve is in the valve chest bore adjust the valve by screwing it in or out until the intake hole is in line with the intake hole of the valve chest at the top of its motion. At the bottom of its motion, the exhaust slot on the valve should fully expose the valve chest port. The same single port can serve as an intake and exhaust port. The timing of the valve and cylinder is very simple to do. Decide in which direction you want the engine to turn and turn it so the piston is located at top dead center. Loosen the eccentric set screw and rotate it in the same direction so that as you look into the air / steam inlet hole on the valve chest you can just begin to see the edge of the cross / intake hole on the valve. Lock the screw and you are done with that job. The very last thing to make are two fly wheels. This is left entirely up to you as they can be of any design. I used stainless steel because I happened to have some and in a polished state they look great and never tarnish. My flywheels are 2" diameter each and about 3/4" thick. Nothing fancy here, I just turned them, making sure I machined a thrust bearing on the inside of each one to minimize the contact surface against the bronze crank bearings. A thorough polish job and they are done. Installation was done with locktite adhesive. A cousin of the regular CA glues but much slower drying. Lateral play on the crank should be not exceed 1/64". Check your fit constantly as you go to prevent any binding problems before it's too late to conveniently do something about them. The engine will need an inlet tube to connect a length of rubber tubing to provide air or steam to the valve chest. This should also be soldered to the inlet hole of the valve chest. Lubricate all moving parts with a good medium viscosity machine oil. Insert the air tubing into the inlet tube and set your air compressor to about 5-10 psi. Give the flywheel a flip so that it is past the top dead center position in the direction of rotation and your engine should begin to run happily at a pretty good clip making a nice " puff - puff "sound. The breaking in of this engine calls for plenty of lubrication and several 15 - 20 minutes periods of continuous running at different speeds ranges. A total of one or two hours of running followed by a thorough scrubbing with plenty of hot water and dish washing soap to remove all traces of grease and oil will do wonders in the appearance of the engine after breaking in. Dry and polish it with a soft towel and begin thinking about a nice display base for it. I made mine out of a piece of walnut I had left over from a previous project. My engine will run very smoothly at a nice slow 120 rpm, using only about 4-5 psi of air pressure. Pretty good for a single action engine. I also made a small stainless steel pulley so I could drive a small 12 volt DC motor ( out of a model HO locomotive ) to act as a small electric generator and light up a small bulb. This way the engine is not just spinning along without a reason to live. The faster the engine turns, the brighter the bulb will burn. Another possibility would be to use the engine to turn a slightly larger motor, generating a bit higher level of power to operate an electric gadget of any kind needing less power for it to run. Maybe a little electric fan.