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#61
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DIY Two-Stroke Engine Construction Methods
"bigegg" wrote in message
... two words: burt munroe as an example of home-cast/home machined engines. -- bigegg but he started with a manufactured engine, he didn't build it from scratch. He also had a LOT of failures before he got everything working, are you willing to do that with an AC engine ?? -- Remember Altitude is more important than Attitude |
#62
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DIY Two-Stroke Engine Construction Methods
On Mar 16, 4:48*pm, durabol wrote:
Thanks for the responses. -I planned to have one carburetor (and crankcase) for both cylinders. Shared carb and crankcase locks you into simultaneous firing of the two opposing cylinders -I have access to a lathe and a milling machine but I don't have that much experience with them so I'll have to learn as I go or get someone else to do the machining -I do plan to build the engine in a modular way so I suppose I could add more cylinders. -I do have some experience with lost wax casting although not with much success. The engine casting that I had envisioned may be too complicated for the simple gravity casting techniques I was planning. I also worry about hot tears of the cylinder as the aluminium cools and casting decent heat fins. -For the cylinder I was planning on just an aluminium wall since I have heard "cheap" lawn mower engine can get 500h on them. I though that the bearings in the engine will probably need to be replaced in a few hundred hours anyways, so the bore could be resized then. Those are four stroke engines, with no large holes in the cylinder walls trying to swallow the rings with every stroke. They are also generously lubricated with splashed oil from the crankcase, which you won't have in a two stroke. Remember that the only lubrication in a two-stroke is what's mixed in the fuel, or the tiny quantities that are injected directly into the lower end bearings, (if you have an oil pump like some two-stroke street bikes) where it's then mixed with the fuel/air charge. Brock Please get a copy (or download) of Gordon Jennings "Two Stroke Tuner's Handbook" before starting. It was my 'Bible' when I did two stroke performance development for a living. |
#63
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DIY Two-Stroke Engine Construction Methods
On Mar 18, 2:47*pm, Grider Pirate wrote:
On Mar 16, 4:48*pm, durabol wrote: Thanks for the responses. -I planned to have one carburetor (and crankcase) for both cylinders. Shared carb and crankcase locks you into simultaneous firing of the two opposing cylinders Not necessarily. What you describe is commonly called a 'boxer' configuration. You can also alternate the cylinders. That can simplify a lot, for instance the cylinders can be joined to a common, rigid scottish yoke. That will also vibrate horribly and probably shake itself apart. But people have tried it, google for Bourke engine, which has a small cult-like following on line. Maybe if you configured a Bourke with multiple banks of 2-cylinders each, rotating each bank around the crank by 360/n degrees, where n is the number of cylinders, that would smooth out the vibration issue. The result would be a sort of 2-stroke radial. |
#64
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DIY Two-Stroke Engine Construction Methods
On Mar 17, 2:32*am, Tim Wescott wrote:
... With some pretty fancy metallurgy you can use an aluminum cylinder wall. * It's how the Chevy Vega was done, and it worked great -- except when it didn't. ... Which I thought was all of the time. I never heard of a Vega engine that lasted past 50,000 miles, or Vega body that wasn't rust perforated after it's second winter in the rust belt. Had it been built to last the Vega would have been a great little car. -- FF |
#65
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DIY Two-Stroke Engine Construction Methods
Fred the Red Shirt wrote:
On Mar 17, 2:32 am, Tim Wescott wrote: ... With some pretty fancy metallurgy you can use an aluminum cylinder wall. It's how the Chevy Vega was done, and it worked great -- except when it didn't. ... Which I thought was all of the time. I never heard of a Vega engine that lasted past 50,000 miles, or Vega body that wasn't rust perforated after it's second winter in the rust belt. Had it been built to last the Vega would have been a great little car. There's an interesting Wikipedia article on the origins of the Chevy Vega. Apparently it was designed by GM corporate engineering, and shoved down Chevy's throat. Chevy wasn't allowed to make _any_ engineering changes, they were very grudging about building the thing, and that was a huge part of the problem. Apparently the wear point on the Vega engine wasn't the cylinder walls at all -- it was the valve guides*. But the oil leakage** got blamed on the cylinder walls because who could believe in an aluminum cylinder bore? For it's size it's certainly a damn strong engine. * Which were as new and innovative as the rest of the engine, just wrong. If you're going to make something that's new and innovative, identify the parts that _need_ to be new and innovative, and do the _rest_ of the thing with old reliable technology. Then when that works, go back and innovatize the rest of the thing, one system element at a time. ** "Fill er up and check the gas while you're at it!" -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com |
#66
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DIY Two-Stroke Engine Construction Methods
On 3/30/2010 10:22 AM, Tim Wescott wrote:
There's an interesting Wikipedia article on the origins of the Chevy Vega. Apparently it was designed by GM corporate engineering, and shoved down Chevy's throat. Chevy wasn't allowed to make _any_ engineering changes, they were very grudging about building the thing, and that was a huge part of the problem. Apparently the wear point on the Vega engine wasn't the cylinder walls at all -- it was the valve guides*. But the oil leakage** got blamed on the cylinder walls because who could believe in an aluminum cylinder bore? For it's size it's certainly a damn strong engine. * Which were as new and innovative as the rest of the engine, just wrong. If you're going to make something that's new and innovative, identify the parts that _need_ to be new and innovative, and do the _rest_ of the thing with old reliable technology. Then when that works, go back and innovatize the rest of the thing, one system element at a time. That was only 2 of the trifecta of problems with that engine. The last problem was the Vega engine cooked it's oil to a tar like sludge in a short amount of time. I've also heard that and oil cooler didn't help much because part of the problem was in that oil pooled in the cylinder head too long and picked up too much heat there. Tony |
#67
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DIY Two-Stroke Engine Construction Methods
On Tue, 30 Mar 2010 10:22:34 -0700, Tim Wescott
wrote: Fred the Red Shirt wrote: On Mar 17, 2:32 am, Tim Wescott wrote: ... With some pretty fancy metallurgy you can use an aluminum cylinder wall. It's how the Chevy Vega was done, and it worked great -- except when it didn't. ... Which I thought was all of the time. I never heard of a Vega engine that lasted past 50,000 miles, or Vega body that wasn't rust perforated after it's second winter in the rust belt. Had it been built to last the Vega would have been a great little car. There's an interesting Wikipedia article on the origins of the Chevy Vega. Apparently it was designed by GM corporate engineering, and shoved down Chevy's throat. Chevy wasn't allowed to make _any_ engineering changes, they were very grudging about building the thing, and that was a huge part of the problem. Apparently the wear point on the Vega engine wasn't the cylinder walls at all -- it was the valve guides*. But the oil leakage** got blamed on the cylinder walls because who could believe in an aluminum cylinder bore? For it's size it's certainly a damn strong engine. Totally not true. The only fix for the extreme oil burning was to sleeve the block - and that is not required for valve guide problems. When they were running well they WERE very torquy engines, giving the impression they were a lot bigger and "stronger" than they were. * Which were as new and innovative as the rest of the engine, just wrong. If you're going to make something that's new and innovative, identify the parts that _need_ to be new and innovative, and do the _rest_ of the thing with old reliable technology. Then when that works, go back and innovatize the rest of the thing, one system element at a time. ** "Fill er up and check the gas while you're at it!" |
#68
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DIY Two-Stroke Engine Construction Methods
On Mar 11, 3:20*am, Rufus wrote:
basilisk wrote: "Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message .3.70... "basilisk" fired this volley in news:J4Nln.198564 : you will have to provide a slave cylinder or roots type blower to move the air. Some variants use a cylinder skirt with reed valving. LLoyd You're right, *I didn't really consider that before posting. I supposed it could be worked out but that looks hard to do in a completely bottom assembled engine, just my 2 cents worth, I'm not an engine specialist. basilisk Try modifying an existing engine...and don't go hard over on it being a 2-stroke. *I've often thought of trying to construct a full 9 or 7 cylinder aircraft radial using Harley engine parts - hell, those engines have more in common with an air cooled radial than about anything I can think of other than a Pratt & Whitney. SNIP -- * * * - Rufus Worth noting: there is a radial project out there with quite a few builders that uses VW jugs and a custom crankcase and heads. Around 100hp if I remember correctly. There are also a couple of half VW engine projects with plans available. If you take a stroll around the national air and space museum you will get a feel for the art that went into many of the early engines. The old designers and machinists were a different breed, and their work inspires awe in any mechanically inclined mind. It is worth noting that many of the older radial and fan engine configurations used a pie- wedge style crankcase, where the cylinder and the case were a single piece, and the crankcase bolted together in pieces arranged in circumference to the crankshaft. With modern alloys and machining techniques, I've wondered if returning to this style might be tolerable for a small engine today. Lawn mowers are done similarly, and so I'd imagine an engine designed in this fashion would scale up quickly from a production standpoint. While building a new engine solely for art is a lofty goal, I can't really see it for any other reason. What performance specs could you be looking for that aren't currently available in a production engine, or are not otherwise achievable by making minor modifications to a production engine? The engine of interest to me lately is the new subaru TDI boxer motor. Wow that thing is fancy, and I'm hoping it makes its way to the states some time soon. With modern boosting techniques I'd also like to see the packard aero diesel configuration revisited, perhaps integrating some of the features in the elsbett engines. . If I was heading off in the scratch built direction, I would outsource the casting process. There are many shops domestic and overseas that can do short runs of castings based on a provided dxf file. It is unlikely that a backyard foundry will ever get close to the level of detail these shops can create. I would probably search far and wide before starting to CAD the thing up. Of course, thinking down the road, if ever I should build my own bird, I'm thinking Rotec, or PZL Franklin. I'd like to go heavy kung fu into engine design, but it is just way to much work, for way to little optimization. Thanks! |
#69
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DIY Two-Stroke Engine Construction Methods
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