18) You can now test whether the engine has any air leaks. Gently press the Piston Rod down for about 30 seconds: this forces air out of the Cylinder. Now, quickly (but gently!) pull the Piston Rod up. If the engine is properly sealed, the Piston will snap back to the down position. Air leaks will allow the Piston to remain in the up position. You can view brief video clips of a successful test by clicking here, and of a failed test by clicking here.
If your engine does not pass this test, you should re-seal around the Cylinder and/or check the Gasket/Piston/Washer assembly. You should not proceed further until the engine is properly sealed. Gasket/Piston/Washer problems can ususally be solved by re-seating the Piston and carefully tightening the Nuts. Cylinder leaks can always be fixed by carefully applying more adhesive around the edges where the Cylinder attaches to the Cap and the Crankcase: the only challenge is doing this without leaving a mess behind. Use a toothpick to apply the adhesive and wipe it clean immediately after application.
19) Slip the Upper Displacer Rod Bearing [S3] into the Upper Displacer Rod [S2], if this was not done by the manufacturer. Note that the Piston Rod [S4] is longer than the Upper Displacer Rod [S2]. Slip the Piston Rod Bearing [S5] into the Piston Rod [S4]. The two assemblies should look like this when you are finished:
20) The Crankshaft [S1] has a long straight section on one end (on the left in these photographs) and a short straight section on the other end. Slide the Upper Displacer Rod (shorter) assembly on from the long straight end of the Crankshaft (left) until it snaps into place on the first offset. Slide the Piston Rod asssembly on the Crankshaft from the short end (right) until it is in place on the other offset.
When you are finished with making this assembly, the Brass Tube should be enclosed with two pieces of rubber tubing that meet exactly in the center of the brass. If you have trouble doing this with the tubes dry, try wetting the parts with rubbing alcohol before assembling. A twisting motion works better than merely tugging at the Tubing. Do not use oil or soap: this will cause the Tubes to wander after the engine has been assembled, causing performance problems. This assembly is the Piston Connector.
22) If you have not done so already (during the epoxy assembly of the Cylinder Cap), trim the remaining rubber tubing to 1.25 inches (3.2 cm) and slip this piece onto the Upper Displacer Rod (shorter) until it comes close to the Upper Displacer Bearing, again using rubbing alcohol if necessary. Then slide the Piston Connector onto the Piston Rod (longer). The Crankshaft should now look like this:
23) The small grey plastic bearings installed in the Crankcase (see below) must be free from flash and other defects.
If necessary, ream them out by hand with either a 1/16 inch, #52, or a 1.5 mm drill bit. Install the Crankshaft in the Crankcase so that the Upper Displacer Rod is over the center of the engine and the Piston Rod is above the Piston. Later, when you are ready to run the engine, you will be tempted to oil these bearings. Do not do this. The engine runs much better with no oil on the bearings.
24) Place a small drop of adhesive inside each end of the 4.25 inch (10.8 cm) brass tube, the Handle [C4] of the engine. Install the Handle in the Crankcase using the two Rivets [C6] provided. Rotate the Handle 1/2 turn to ensure a good adhesive bond. Check the assembly carefully as it is drying to make sure that the Rivets do not back out of the brass tubing. Make sure there are no gaps between the Rivets, the Crankcase, and the Handle.
In some cases, the Crankcase may be wider than the Handle. In this case, you must use Epoxy to hold the Rivets in place. Use a rubber band to tighten the Crankcase against the Handle while the Epoxy is setting.
25) Fit the the reducers on the Crankshaft. The Short Reducer  goes on the piston end of the Crankshaft, and the Long Reducer  goes on the other end, with the larger end of the Long Reducer nearer to the Crankcase. If necessary, ream out one end of the Reducers by hand with a 1/16 inch , #52, or 1.5 mm drill bit. Tighten the Reducers on the Crankshaft using the supplied hex wrench. The Crankshaft should be able to slide laterally just a bit: if the Reducers are too close to each other, they will bind on the sides of the Crankcase. If you are not familiar with how hex wrenches are used to install set screws, the photographs below should help.
The photographs below show the Long Reducer and the Short Reducer being installed. The Short Reducer is installed on the end of the crankshaft closest to the piston and the Long Reducer is installed on the other end.
26) Press fit the rubber connecting tubes from the Crankshaft onto the metal rods coming up from the Piston and Displacer. Make sure that the Piston rod fits inside the Brass Tube inside the Piston Connector : the Brass Tube is necessary for the connection to be stiff enough. Use rubbing alcohol if you wish when putting the Rubber Tubes over the metal Rods. The connectors must be adjusted vertically with care.
The Displacer must move from the top to the bottom of the Cylinder, and must offer no resistance to turning the Crankshaft. The Displacer must strike neither the top nor the bottom of the Cylinder tube. The “rubber” Piston diaphragm must neither stretch nor compress as the Crankshaft is turned. If it is well adjusted, it should be slightly wrinkled at the top and bottom of its travel.
Similarly, the Piston diaphragm must move evenly above and below the horizontal plane of the Crankcase, and must offer no resistance to turning the Crankshaft. Not only must the rubber connecter neither compress nor stretch, but the diaphragm itself must never stretch. Adjust the vertical position of the connectors with care, especially the Piston connector.
Be careful not to bend the Crankshaft or tear the Piston diaphragm while adjusting the connectors. One way to protect the Piston diaphragm during adjustment is to hold the Piston Rod at the bottom with a needle nosed pliers, pressing the pliers against the Brass Washer. This ensures that you will not accidentally pull or push the Piston diaphragm too much, focusing the energy on the connectors.
Try to avoid leaving the connectors twisted such that the Piston diaphragm is twisted or torqued: when in the middle of its range, the diaphragm should be as relaxed and flat as possible.
27) It will be easier to check the engine setup after you have put the Propeller [S10] on. To do so, grab the Long Reducer with a pair of needle nose pliers (or, even better yet, needle nosed Vise Grips!) near the Crankcase. Spin the Propeller onto the Reducer until 4-5 threads protrude through the Propeller. Place a small drop of adhesive on the protruding threads and install a Brass Nut [S11]. Install the final Brass Nut on the Short Reducer with a drop of adhesive.
Above: Propeller installed on Long Reducer; Nut installed on Propeller; Nut installed on Short Reducer.
Getting back to engine setup, observe the motion of the rods on the Crankshaft as you slowly rotate the Propeller. Is it binding? If so, figure out where the binding is and adjust the connectors accordingly. Binding is usually caused by the Displacer hitting the Crankcase or the Cylinder Cap, or by the Piston being stretched. When you have everything working smoothly, spin the Propeller quickly by hand. The Propeller should spin about four or five revolutions before stopping.
Install the thermometer and Stirling Engine labels as shown below: peel the paper off the back, position carefully, and press firmly into place.
The easiest way to run your engine for the first time is to puts about 1 inch (2.54 cm.) of water in the bottom of a coffee mug, and microwave it until it is boiling vigorously. Be careful with the boiling water! Place your engine on top of the steaming mug for several seconds, then rotate the propeller in the direction indicated on the label.
To run your engine on ice, get a flat bowl and fill it with ice cubes. Place your engine on the ice cubes and rub it around carefully to make sure that you get good contact between the ice and the bottom of the engine. After about 30 seconds on ice, you should be able to rotate the propeller in the opposite direction that it turned when fueled by hot water and the engine should run.
Congratulations on successfully completing your Stirling engine! You have accomplished something that most people would not be able to do. The American Stirling Company is very interested in hearing of your success. Specifically we are very interested in your answer to either or both of the following questions.