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#1
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DIY Two-Stroke Engine
For the last few years I have toyed with the idea of building a
homemade two-stroke engine for UL use. What keyed my interest was reading about homemade model aircraft engines and reading and watching a re-enactment of the Wright brother's first flight with a replica engine (not a two-stroke engine). Has anyone made a 2-stroke engine from scratch? One may need to cast aluminium, may need a lathe and milling machine with boring head and hone or perhaps the boring and honing of the cylinder and bearing journals could be farmed out. A commercial carburetor and piston could be used. Two-stroke engines seem simple enough that home construction may be possible, if not practical. A direct drive engine will be that much heavier when you take into account the weight of the drive reduction system. I have calculated the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm cylinder and crankcase wall thickness and a 1.25" dia crank. I have got some idea of port-time-area from the freeware computer program called "BiMotion". I'm not sure how good the data is for lowish speed engines but I guess it is a start. I have also worked up a spreadsheet for similar information. I don't think a reed valve system is needed for this engine since it is only going to operate at a fairly narrow rpm range and the port timing isn't critical. Piston ported valves offer similar performance to other induction types but only over a narrow rpm range which is what I have planned for the engine. I plan to build an engine with a restrictive exhaust to ensure no fuel escapes. I have heard that piston ported engines can spit some fuel out of the carb at idle but this doesn't seem like a major problem. Rotary valves via crank shaft induction (disk or drum valves as well) is an interesting idea but I don't think I need the critical timing they provide. I was planning on using the largest two-stroke piston (not a diesel piston) I could find and using the largest stoke that was reasonable, something like 90x105mm Brock |
#2
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DIY Two-Stroke Engine
durabol wrote:
For the last few years I have toyed with the idea of building a homemade two-stroke engine for UL use. Underwriter's Laboratories? What keyed my interest was reading about homemade model aircraft engines and reading and watching a re-enactment of the Wright brother's first flight with a replica engine (not a two-stroke engine). Has anyone made a 2-stroke engine from scratch? One may need to cast aluminium, may need a lathe and milling machine with boring head and hone or perhaps the boring and honing of the cylinder and bearing journals could be farmed out. A commercial carburetor and piston could be used. Two-stroke engines seem simple enough that home construction may be possible, if not practical. Certainly not practical in the "it saves you money" sense, but who cares? A direct drive engine will be that much heavier when you take into account the weight of the drive reduction system. I have calculated the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm cylinder and crankcase wall thickness and a 1.25" dia crank. I have got some idea of port-time-area from the freeware computer program called "BiMotion". I'm not sure how good the data is for lowish speed engines but I guess it is a start. I have also worked up a spreadsheet for similar information. I don't think a reed valve system is needed for this engine since it is only going to operate at a fairly narrow rpm range and the port timing isn't critical. Piston ported valves offer similar performance to other induction types but only over a narrow rpm range which is what I have planned for the engine. Piston porting isn't optimum at any speed -- crank-timed or reed valve induction is much better. But piston porting is certainly easier. I plan to build an engine with a restrictive exhaust to ensure no fuel escapes. I have heard that piston ported engines can spit some fuel out of the carb at idle but this doesn't seem like a major problem. Rotary valves via crank shaft induction (disk or drum valves as well) is an interesting idea but I don't think I need the critical timing they provide. I was planning on using the largest two-stroke piston (not a diesel piston) I could find and using the largest stoke that was reasonable, something like 90x105mm I'm still a home-built engine wannabe, but I'm working on it. Here are some resources: http://www.lindsaybks.com/prod/sub/engines.html http://www.modelenginenews.org/ -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com |
#3
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DIY Two-Stroke Engine
durabol wrote:
For the last few years I have toyed with the idea of building a homemade two-stroke engine for UL use. What keyed my interest was reading about homemade model aircraft engines and reading and watching a re-enactment of the Wright brother's first flight with a replica engine (not a two-stroke engine). Has anyone made a 2-stroke engine from scratch? One may need to cast aluminium, may need a lathe and milling machine with boring head and hone or perhaps the boring and honing of the cylinder and bearing journals could be farmed out. A commercial carburetor and piston could be used. Two-stroke engines seem simple enough that home construction may be possible, if not practical. A direct drive engine will be that much heavier when you take into account the weight of the drive reduction system. I have calculated the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm cylinder and crankcase wall thickness and a 1.25" dia crank. I have got some idea of port-time-area from the freeware computer program called "BiMotion". I'm not sure how good the data is for lowish speed engines but I guess it is a start. I have also worked up a spreadsheet for similar information. I don't think a reed valve system is needed for this engine since it is only going to operate at a fairly narrow rpm range and the port timing isn't critical. Piston ported valves offer similar performance to other induction types but only over a narrow rpm range which is what I have planned for the engine. I plan to build an engine with a restrictive exhaust to ensure no fuel escapes. I have heard that piston ported engines can spit some fuel out of the carb at idle but this doesn't seem like a major problem. Rotary valves via crank shaft induction (disk or drum valves as well) is an interesting idea but I don't think I need the critical timing they provide. I was planning on using the largest two-stroke piston (not a diesel piston) I could find and using the largest stoke that was reasonable, something like 90x105mm Brock There are several organizations for hobbyists building smaller (model sized) IC engines. Check out Model Engine Builder magazine (they have a web site. I suggest you build a model engine first. That would help answer the question of whether it is practical for you. Sounds like you may not be a skilled machinist yet, and I would become a master machinist before I bet my life on a homemade engine. |
#4
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DIY Two-Stroke Engine
On Mar 5, 6:56*pm, durabol wrote:
For the last few years I have toyed with the idea of building a homemade two-stroke engine for UL use. What keyed my interest was reading about homemade model aircraft engines and reading and watching a re-enactment of the Wright brother's first flight with a replica engine (not a two-stroke engine). Has anyone made a 2-stroke engine from scratch? One may need to cast aluminium, may need a lathe and milling machine with boring head and hone or perhaps the boring and honing of the cylinder and bearing journals could be farmed out. A commercial carburetor and piston could be used. Two-stroke engines seem simple enough that home construction may be possible, if not practical. A direct drive engine will be that much heavier when you take into account the weight of the drive reduction system. I have calculated the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm cylinder and crankcase wall thickness and a 1.25" dia crank. I have got some idea of port-time-area from the freeware computer program called "BiMotion". I'm not sure how good the data is for lowish speed engines but I guess it is a start. I have also worked up a spreadsheet for similar information. I don't think a reed valve system is needed for this engine since it is only going to operate at a fairly narrow rpm range and the port timing isn't critical. Piston ported valves offer similar performance to other induction types but only over a narrow rpm range which is what I have planned for the engine. I plan to build an engine with a restrictive exhaust to ensure no fuel escapes. I have heard that piston ported engines can spit some fuel out of the carb at idle but this doesn't seem like a major problem. Rotary valves via crank shaft induction (disk or drum valves as well) is an interesting idea but I don't think I need the critical timing they provide. I was planning on using the largest two-stroke piston (not a diesel piston) I could find and using the largest stoke that was reasonable, something like 90x105mm Brock I met a guy in Edmonton (St. Albert ) who made working models of historical engines such as the Liberty engine. Really beautiful piece of modeling and was featured in a modeling magazine. Its power/weight output was not enough to power a model plane. If your intention is to power a model plane you are much better off buying a model engine and tinker with that to boost its performance. Not much reward in building a two stroke engine from scratch. For a large two stoke you can modify a weedwacker engine (25 cc) A snowmobile engine powers those military drones. |
#5
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DIY Two-Stroke Engine
"durabol" wrote Has anyone made a 2-stroke engine from scratch? One may need to cast aluminium, may need a lathe and milling machine with boring head and hone or perhaps the boring and honing of the cylinder and bearing journals could be farmed out. A commercial carburetor and piston could be used. Two-stroke engines seem simple enough that home construction may be possible, if not practical. A direct drive engine will be that much heavier when you take into account the weight of the drive reduction system. I am assuming you meant to write "will _(not)_ be that much heavier", right? If so, when is the last time you saw a direct drive 2 stroke aircraft engine? Not me. Closest I can think of is a model airplane engine, and that is only practical because of the small prop sizes. If you put a large enough prop on a 2 stroke to soak up 50 hp, you will have to keep rpm's way down to keep from having a real noisy, inefficient prop. You keep the RPM's that low, and you now have a real inefficient 2 stroke engine. That is why all 2 stroke engines have gearboxes or belt drives to reduce prop speed. You might do well to consider a 2 stroke supercharged diesel engine. You make one of those, and make it scaleable by adding more banks of cylinders, and the flying world will beat a path to your doorstep. -- Jim in NC |
#6
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DIY Two-Stroke Engine
Suzuki built a 650cc water cooled 2 stroke twin for Arctic Cat. I think
that engine is about the ultimate in big bore 2 stroke twins... At one time I considered getting 2 of these and putting them in a small sports car like a Triumph Spitfire but I've since moved to a state that does emissions testing and that won't pass here... Suzuki just about ruled the 2 stroke motorcycle market with their rock solid reliable engines. You could count on a 75k miles out of a Suzuki triple when the other companies' bikes would only go 15 to 20k miles on a set of pistons... There were also some big bore 2 stroke dirt bikes. I know all the major players in the market built them but the one that comes to mind was a 500cc Husqvarna single. Sleeves, pistons ect are all available for these bikes could be used to build your own. The easiest way to go is to use someone else's engineering and machine work to build your engine. That way the major parts to make would be the cases, barrels and cylinder heads since the bike ones won't have adequate cooling. I imagine that a 1000cc 2 stroke opposed twin would be pretty cool and could be tuned to run at an RPM low enough for direct drive. However it's not a good idea to put a prop on a built up crankshaft like all 2 strokes use and a belt drive or some such would be required. I would highly recommend reading the 2 stroke tuners handbook if you can find a copy. I have a PDF version but it's too big to eMail. Also talk to Charlie at Superior Sleeve in Millwaukie, OR. Charlie has built more custom 2 stroke engines than just about anybody alive today... If you can catch him when he has time to talk, he will enlighten you a great deal. It's been more than 20 years since I was building high performance 2 stroke engines and I've forgotten a lot over the years... Good luck and keep us posted if you go on with this project. Tony |
#7
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DIY Two-Stroke Engine
On Mar 5, 6:56*pm, durabol wrote:
For the last few years I have toyed with the idea of building a homemade two-stroke engine for UL use. What keyed my interest was reading about homemade model aircraft engines and reading and watching a re-enactment of the Wright brother's first flight with a replica engine (not a two-stroke engine). Has anyone made a 2-stroke engine from scratch? One may need to cast aluminium, may need a lathe and milling machine with boring head and hone or perhaps the boring and honing of the cylinder and bearing journals could be farmed out. A commercial carburetor and piston could be used. Two-stroke engines seem simple enough that home construction may be possible, if not practical. A direct drive engine will be that much heavier when you take into account the weight of the drive reduction system. I have calculated the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm cylinder and crankcase wall thickness and a 1.25" dia crank. I have got some idea of port-time-area from the freeware computer program called "BiMotion". I'm not sure how good the data is for lowish speed engines but I guess it is a start. I have also worked up a spreadsheet for similar information. I don't think a reed valve system is needed for this engine since it is only going to operate at a fairly narrow rpm range and the port timing isn't critical. Piston ported valves offer similar performance to other induction types but only over a narrow rpm range which is what I have planned for the engine. I plan to build an engine with a restrictive exhaust to ensure no fuel escapes. I have heard that piston ported engines can spit some fuel out of the carb at idle but this doesn't seem like a major problem. Rotary valves via crank shaft induction (disk or drum valves as well) is an interesting idea but I don't think I need the critical timing they provide. I was planning on using the largest two-stroke piston (not a diesel piston) I could find and using the largest stoke that was reasonable, something like 90x105mm Brock There's any amount of engineering info out there on two-strokes, books have been written. They were a staple project in The Model Engineer magazine for years, should you want to look that up. What's UL use? You'd be basically recreating a commodity item. Resurrect one from a defunct snowblower, weed-whacker or Lawnboy and spend more time on figuring out the project you want to drive. The engineering's done, you aren't likely to improve on what's already been built. Want overhead valves? Been done. Rotary valves, ditto. Fuel injection, same. Separate lube system, been done. Opposed twins, flat fours, square fours, Vs, Xs, Ws, all been done. Separate forced air pumping, too. They basically suck thermodynamically except the one feature they've got going is power-to-weight ratio, the small ones pump out a lot of horsepower, usually at high RPM, for their size. For that you can go with an existing engine and spend more time on the rest of the project. Stan |
#8
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DIY Two-Stroke Engine
On Mar 6, 8:45*pm, wrote:
On Mar 5, 6:56*pm, durabol wrote: For the last few years I have toyed with the idea of building a homemade two-stroke engine for UL use. Brock ...What's UL use? Stan I think UL here means UltraLight, a minimally regulated, tiny but MANNED aircraft. http://www.eaa.org/Ultralights/ I looked into it, flew a hang glider a few times, then gave it up for the safer hobby of racing dirt bikes. jsw |
#9
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DIY Two-Stroke Engine
You could look at outboard motors as a starting point. In the past I
read of someone using a Mercury to get 100 hp in an aircraft. Harold |
#10
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DIY Two-Stroke Engine
Morgans schreef:
You might do well to consider a 2 stroke supercharged diesel engine. You make one of those, and make it scaleable by adding more banks of cylinders, and the flying world will beat a path to your doorstep. Hm. The flying world did not exactly beat any kind of path to the doorstep of www.dair.co.uk, though they did exactly that. Wilksh company wasn't far off, either, with equal lack of big success. |
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