I Built an Engine From Scratch

I built this engine from scratch, and today I'm going to show you exactly how I built it. The first component I wanted to manufacture was the crankcase. I designed the part in SolidWorks and printed the pattern on a 3D printer. The printed model would later be used to create a mold, allowing me to reproduce the same shape as an aluminum casting. I started by preparing the molding mixture. For this process, I used finely sieved sand and mixed it with liquid glass at a ratio of 1 part liquid glass to 10 parts sand. Once the mixture was ready, I packed it around the printed pattern inside steel molding flasks. The sand had to be compacted carefully around every surface of the model. This allowed the molds to reproduce the geometry of the crankcase as accurately as possible. The completed mold was placed into the furnace. During heating, the printed plastic burned away, leaving an empty cavity inside the hardened sand. Once all the plastic had burned out and the mold had fully hardened, I removed it from the furnace. The next step was melting the aluminum. After the metal reached the required temperature, I poured it into the prepared mold. After the casting had cooled, I broke apart the mold and removed the finished aluminum blank. The basic shape was now complete, but the casting was still far from being a usable engine component. All critical surfaces and dimensions still had to be machined. I began the machining process on the lathe. The purpose of these first operations was to establish accurate dimensions and reference surfaces. For the remaining holes, I used a coordinate drilling machine. This allowed every hole to be positioned accurately relative to the main reference point of the component. First, I located the exact center of the crankcase. From that position, I moved the machine table by the required coordinates until the spindle reached the center of each hole. I first created a small starting point with a center drill. This prevented the main drill from wandering when it entered the material. I then drilled each hole to its final diameter. After drilling, I cut the required threads. I also installed locating dowels. These dowels ensure that the second crankcase half always returns to exactly the same position during assembly. The next step was manufacturing the second crankcase half. The procedure was almost identical. I prepared another printed pattern, created the mold, burned out the plastic, and poured a second aluminum casting. The casting then went through the same machining process until the second half was complete. With both crankcase halves complete, I could begin machining them as a single assembly. This was necessary because several critical features had to remain perfectly aligned across both components. The two halves were joined together using the locating dowels and mounting bolts. I moved the assembled crankcase to the milling machine. The first task was machining the main mounting surface for the cylinder. This surface had to be flat and correctly positioned. It determines the angle and height of the cylinder relative to the crankshaft. I also machined the mounting surface for the carburetor and reed valve assembly. Once the reference surfaces were complete, I returned to the coordinate machine. Here, I machined the main locating bore for the cylinder. This bore keeps the cylinder accurately centered above the crankshaft and piston. Next, I machined the mounting holes that secure the cylinder to the crankcase. I then drilled the mounting holes for the carburetor assembly. The final component in this section was the adapter plate between the carburetor and the crankcase. The next major component was the cylinder. This 3D-printed PLA pattern contains many internal passages, curved surfaces, and complex features. Producing this geometry with a conventional two-part sand mold would have been extremely difficult. The printed pattern allowed the complete shape to be created as a single, expendable model. During molding, it was important to compact the sand carefully around every channel and narrow feature. If the molding mixture failed to reach one of these areas, part of the geometry could be missing from the final casting. Once the pattern had been completely surrounded by the molding mixture, the mold was placed into the furnace. The plastic burned out, leaving the complete cylinder cavity inside the hardened mold. The mold was then ready for pouring. After breaking apart the mold, I was left with a highly detailed aluminum casting. Despite the complex geometry, the cooling passages and external features were reproduced successfully. I removed the gating and feeder system from the casting. These channels had supplied molten aluminum to the part during pouring, but were no longer needed after solidification. With the excess material removed, machining could begin. On the lathe, I created the main reference surfaces. I also machined the central bore that would later receive the cast iron cylinder liner. This bore had to remain concentric with the outer cylinder geometry and perpendicular to the mounting surfaces. Next, I moved the component to the milling machine. Here, I machined the mounting face for the exhaust system. I also drilled and tapped the opening for the water cooling fitting. This fitting would connect the cylinder water jacket to the rest of the cooling system. The next component was the cylinder head. The aluminum blank had already been cast, so I could proceed directly to machining. One of the most important features of the head was the combustion chamber. To produce its spherical profile accurately, I used a CNC lathe. The programmed toolpath created a smooth and consistent chamber geometry. The shape of the combustion chamber affects compression, combustion efficiency, and the movement of the fuel-air mixture near top dead center. For this reason, the profile needed to be both accurate and symmetrical. Next, I aligned and finished the mounting holes in the cylinder and cylinder head. The aluminum cylinder was then bored on the lathe to receive a cast iron liner. I designed the joint with an interference fit of approximately 5 hundredths of a millimeter. This allows the liner to remain tightly fixed inside the aluminum cylinder after assembly. I could now begin manufacturing the liner itself. The most difficult part was positioning all of the transfer and exhaust ports correctly. In a two-stroke engine, these ports control the movement of gases through the cylinder. Their height, width, and position directly influence the timing of the engine. Even a small error could change the way the engine runs. To create the ports as accurately as possible, I used a CNC milling machine. It machined each opening according to the coordinates defined in the model. After machining, I finished the remaining imperfections by hand. This included smoothing the edges and ensuring that the passages were free of sharp transitions. The liner was now ready to be installed. To install the liner, I used the difference in thermal expansion between aluminum and cast iron. The aluminum cylinder was heated, causing its bore to expand. At the same time, the cast iron liner was cooled, causing its outside diameter to contract slightly. This temporarily reduced the interference between the two parts. As a result, the liner could slide into the cylinder with very little force. The final result was exactly what I wanted. All of the ports in the cast iron liner aligned with the corresponding passages in the aluminum cylinder. The next major task was manufacturing the crankshaft. At a scrapyard, I found an old crankshaft from an unknown motorcycle. Instead of manufacturing the complete component from raw material, I decided to use it as the starting blank for my design. The existing steel forgings already had the strength and basic geometry required for a motorcycle engine crankshaft. I began by machining the crankshaft webs on the lathe. The old component was reduced to the dimensions required for my engine. Several original holes and features were no longer needed. I machined steel plugs for these openings, pressed them into position, and welded them to the crankshaft webs. After welding, I returned the components to the lathe. The surfaces were machined again until the plugs became flush with the surrounding material. This created solid blanks from which I could produce the new crankshaft geometry. The next operation was machining the holes for the crankpin. Their position had to be extremely accurate. The distance between the crankshaft center and crankpin center determines the stroke of the engine. Any difference between the two crankshaft webs would also make the assembled crankshaft run out of alignment. For this reason, I performed the operation on the coordinate machine. I then finished it with a precision boring tool. This allowed me to control the final diameter and position to approximately one hundredth of a millimeter. The final machining operation was creating the balancing cutouts in the crankshaft webs. These features reduce unnecessary mass and help compensate for the moving weight of the piston, connecting rod, and crankpin. A single-cylinder engine can never be perfectly balanced at every crankshaft angle. However, correctly designed counterweights can significantly reduce the vibration transmitted to the crankcase and frame. With all machining complete, I could assemble the crankshaft. For the connecting rod, I chose a component from a Yamaha DT. The crankpin, bearing, and connecting rod were positioned between the two crankshaft webs. The complete assembly was then pressed together. During assembly, the two main shafts had to remain perfectly aligned. After pressing, I checked the crankshaft for runout and corrected the alignment where necessary. The completed crankshaft was then balanced. This final adjustment helped reduce vibration and ensured smoother operation at higher engine speeds. The engine also required a mounting bracket for the electronic ignition system. I started with a solid aluminum blank and machined it to the required dimensions. The bracket had to position the ignition components accurately relative to the crankshaft. This determines when the spark occurs during each engine cycle. Incorrect positioning would shift the ignition timing and could prevent the engine from running correctly. At last, all of the main components were ready for final assembly. Before installing anything, I thoroughly cleaned every part. Machining chips, abrasive particles, or dirt left inside the engine could quickly damage the bearings, cylinder, and piston. I installed the bearings and oil seals into the crankcase. The sealing surfaces were cleaned and degreased before applying the sealant. Removing oil from these surfaces allows the sealant to bond correctly and helps prevent air leaks. This is especially important in a two-stroke engine, where the crankcase forms part of the intake and compression system. I positioned the crankshaft inside the first crankcase half. The second half was then aligned using the locating dowels and bolted into position. With the bolts tightened, the crankshaft could be checked for free rotation. Next came the piston. The complete manufacturing process for this custom piston is already shown in another video on my channel. For the final assembly, I installed the compression rings onto the piston. The piston was then connected to the connecting rod using the wrist pin and retaining clips. With the piston installed, I could lower the cylinder onto the crankcase. The piston rings were carefully compressed as the cylinder passed over them. Once the cylinder was seated, I could begin preparing the cylinder head installation. Before fitting the cylinder head, I manufactured the required mounting studs. I also machined flat seating recesses around the fastener holes in the cylinder head. These features are known as spot faces. They provide flat, accurately positioned surfaces for the nuts and washers. I also drilled and tapped the opening for the cooling system fitting in the cylinder head. Returning to the engine, I installed the electric starter. The cylinder and cylinder head sealing surfaces were prepared and sealed. The head was then placed onto the cylinder and tightened evenly. The ignition system was installed on the crankshaft. Its position was adjusted to provide the initial ignition timing required for the first start. Finally, I installed the spark plug. At this point, the engine was almost ready to run. To make testing safer and more convenient, I built a dedicated engine stand. The frame holds the engine securely while still allowing access to the starter, carburetor, exhaust, and cooling connections. I mounted the engine on four rubber vibration isolators. These mounts reduce the amount of vibration transferred from the engine to the stand during operation. With the engine secured, all that remained was connecting the supporting systems and preparing for the first start. Thank you for watching. If you enjoyed this project, consider subscribing to the channel. I'll see you in the next video.