Hi Chris, if you'd like I'd take you up on the checking it out, but I fear the postage would be a killer for you. I've just gone through your build log and this is what I see, and I'll try to keep it in order of priority. First, I have no confidence in your cylinder. Test tubes are not ground and lapped, so it is not round nor straight, I would almost guarantee. The fix is to machine a piece of polycarbonate or some other hard plastic to just barely fit in the cylinder, put some grooves to hold lapping compound, and I would rub rouge on it, lapping it longitudinally, while rotating the lap back and forth, and if the cylinder is true, you will get even lapping evidence throughout the cylinder. The best lap would be one longer than the cylinder, probably twice as long or a bit more. You can "prove out the cylinder by coating the piston with prussian blue, and pushing it down in the cylinder and pull it out taking care to avoid any turning or side pressure. If the cylinder is round and straight, you will get at least a 75% transfer of blue and it will be evenly spread with the 25% max, being spots disconnected from each other. Knowing the quality of test tubes from experience, I wouldn't even bother, but would lap the cylinder from the start, and if you can't get the one in place out, break it out, after you've lapped a new one, and are completely happy with it. Your lapping is done when you've got as near 100% cross-hatch as you can get, but you must ensure no dirt or dust gets in the lap. You can also turn a piston out of some plastic or metal, just for the use of testing your cylinder in place, making it just barely fit, and using it with the prussian blue. Secondly, once you are sure you have a perfect cylinder or as close as possible, you will need to turn a new graphite piston, but it will be easier this time, because your cylinder will be more accurate and a better gauge than the last. Your trunion in the piston should be as small as possible and aluminum for mass purposes. Third, you should have little discernable friction in the graphite displacer rod bushing unless it is cocked, or under pressure. Once reamed in line, there should be no discernable friction there. Fourth, your connecting rods should be loose enough on their pins to have no discernable friction there as well. The possibility of excess glue on the pin is something to investigate for and you should be able to feel any friction when turning the connecting rods around their respective crank pins, and there should again, be no discernable friction. If they are just a little snug, a bit of shaking side to side while rotating them around their pins should move sufficient metal to relieve any friction if there is no glue, and the pins are truly round. Next, the main shaft, with no connections, but rods freely moving, should be turned not by the wheel, which gives enormous mechanical advantage, but removes any slight "feel" you might get, but turn the shaft in your fingers by the end of the bare shaft, or somewhere in the middle, where your fingers can judge any force necessary to overcome friction. Again there should be no discernable friction here as well. There seemed to be some in the main shaft from your videos, but that is not as good as feeling it, so I may be wrong. A little loose is better than dead on, if you put your two respective "cranks" together with the main shaft running through both side plates of both cranks, and sawing out the middle of the shaft, once the pins were glued in, it should be in line. If you didn't do that, it is quite possible each crank is performing its own elipse, and causing the excess friction. If this is the case, I'd re-do the cranks, putting all the cheeks in their proper respective places on a single piece of shaft, gluing the pins in place at the same time as gluing the cheeks to the shaft, but only after getting all aligned and in proper timing to each other, and giving over night for the glue to set, so you don't disturb your accurate setup while cutting out the shaft between the cheeks of the respective cranks. At this point, I would mount everything but the flywheel, with the connecting rods attached to the displacer rod and the piston, and turn the shaft with your fingers pinched, to get the best feel of what actual friction you will have accumulated. It should almost be free enough to have momentum past spinning, even without the flywheel. If it does, then it is time to mount the flywheel and balance it. If it does not, as per my own experience, you must find where the friction has crept in, and it will be in one of the places you've just been through. It will most likely be a niggling little thing, such as a slight bend in a connecting rod or a pin where it connects to the displacer rod or the piston. Spinning it with light machine oil on the metal to metal bearing surfaces with a drill motor at a moderate speed so as not to bend the crank from the inertia of the displacer, should free up any friction in the shaft at this point. Once the flywheel is balanced to compensate for the mass of the displacer, it should run, as those are all the essential points absent the basic concept of a stirling, the sealing and good heat transfer. A "dashpot" made for many purposes in both electronics and in vacuum control circuits is commonly sold which is a ground, lapped and polished pyrex cylinder, with a fitted piston is commonly available here, I expect you can find similar there looking up "dashpot" as the key word, if you wish to avoid the work of fitting the power piston, however there is no reason you can't equal what they do, if you start right. For a new cylinder, I would put a piece of hard plastic round stock in the lathe with double the length of the cylinder sticking out, machine it to a snug fit and spin it in the lathe, working the test tube cylinder back and forth on it until is moves freely. I'd either split the plastic, or mill our a section half way through, in the middle of the working section of the lap, before using it, and take another piece already turned to the exact same size, and mill half of it away, and drill for two pins to hold the two parts in alignment, with the pins fixed in the main part of the lap, and then, once the cylinder tube is free on the lap, adding a piece of fine cigarette paper between the two parts of the lap to expand it, and continuing, doing this each time the cylinder gets free, before it gets loose, and continuing until you have an even lap as close to 100% as you are willing to work it. The displacer rod bushing should be reamed to exact size, and if it is a two part bushing, both parts in place for the reaming. That should eliminate any friction in it. I supect your piston and cylinder is the power issue, as you can probably tell. The lapping of the glass cylinder can also be done with a hardwood dowel, however I've had problems with warpage once I've cut one, because of grain patterns, that's why I recommend the plastic rod. I believe it is acetal or delrin I've used, not polycarbonate. Delrin is very cheap and easy to get, so I would go with it. I hope you can find some use in this, I'd hate to see you shelve a project with the labor in it, you will someday look at it and have to fix it anyway, that is my own experience.
jack
