# DIY Two-Stroke Construction Methods

Discussion in '2-Stroke Aircaft Engines' started by durabol, Mar 6, 2010.

1. Mar 6, 2010

### durabol

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The two main methods for homebuilt construction would be casting vs. machining or some combination of both (probably the best option). Forging probably isn't appropriate for home construction (either the piston or connecting rod).

One method I have thought of is to produce a wax model of the engine with molds (to a fairly high tolerance to minimize machining) which is then cast using lost wax casting techniques. I planned to have an integral cylinder head/cylinder/half the crank case (this is for an opposed style engine). The only bolts would be to bolt the two halves together.

A completely machined engine would need a large block of aluminium to start with which I'm not sure how practical that would be. Perhaps lost foam casting could be used as a general model of the engine was made in foam and then cast and the resulting casting could be machined.

Brock

2. Mar 6, 2010

### Dana

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It would probably make sense to start with some components from an existing engine. Even many engine manufacturers do this; for example many PPG engines use a PPG specific crankcase with cylinder and moving parts from other applications (e.g. scooters).

An engine based on a bike engine, with a custom CNC'd crankcase eliminating the heavy gearbox, could make a great aircraft engine.

-Dana

Clothes make the man. Naked people have little or no influence on society.

3. Mar 6, 2010

### PTAirco

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If you do your casting at a small foundry, it can be surprisingly cheap. I remember getting a gearbox housing cast for a VW planetary reduction drive I was working on - it cost me about $80. That was a while ago though and making use of CNC equipment nowadays might be a good idea - shop rates around here are from$100-150, but these machines are fast. keep teh shape simple and the programming does not take long.

I concur with Dana that if something is available off the shelf and it suits the purpose, and the price is right - save yourself hassle and incorporate that.

4. Mar 6, 2010

### BBerson

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Another method would be welded sheet metal. A crankcase could be built up from scratch with 4130 sheet and bushings etc. using a MIG welder. It would need a final align bore after it cooled, but this probably is done with cast as well.

5. Mar 6, 2010

### PTAirco

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Yes, a welded crankcase is a perfectly good option - even in aluminium, if you're a good MIG or TIG welder. It would probably require less machining than a cast case and be a lot stronger too. A bit of sideways thinking would even let you do things you cannot accomplish with a casting, such as having re-entrant curves and not having to worry about draft angles etc.

It's also the only practical method used for the crankcases on many ship's diesel engines.

6. Mar 6, 2010

### wally

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I also think an aluminum weldment would be an easy way to assemble a 2 cycle engine crankcase. You can also find a lot of motorcycle and other engine parts and pieces that will move you along.

If you do go that route, be sure and put the finished weldment in an oven and warm it up for a while to stress relieve it before any machining. That way it won't warp during machining or later when running. Welding a big chunk like that can create some stresses.
Wally

7. May 16, 2010

### Von Richter

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Why go through all that trouble when great heavy duty lightweight blocks are available like the V4 and V6 Johnson-Evinrude blocks are so easy to come by in 100-161 cu in displacements? Von Richter

8. May 16, 2010

### WonderousMountain

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Casting...Forging....Machining....

There's a small aluminum foundry here we use for small part casting. Aluminum is diffucult to get right in large castings and I would not trust an engine cast here unless it was significanty overbuilt.

Pistons, rods, and cranks can be machined from small bar relatively easy. Casting these pieces would be a mistake that should not be made for a single engine aircraft.

I see no reason why a forge wouldn't be an option for someone with the appropriate funds. It would provide a better quality part, and the tool would be valuable for future projects. Or reproduction if you're trying to sell kits.

If I make an engine, it will be from 7075 bar, plate or something very similar. My dream is to build Uber miniature engines with power equivelent to a riding lawn mower.

Wonderous Mountain

9. Jun 30, 2010

### nathj

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If its cost your worried about try looking at the kawasaki 440a engine these can be picked up for around \$200-400 if you salvage from a jet ski. I was looking for a small 2 stroke engine then i found people useing 440a engines on the net and what do u know, i already had two of these engines in my garage.. and boxes of parts to boot. only prob now is finding a reduction drive kit, search ebay under js440 if your in the USA these engines and parts are EVERYWHERE!!

10. Apr 1, 2011

### haiqu

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Don't think I'd use any engine that had been in salt water. A ski-doo engine on the other hand ... hmmm.

11. Apr 11, 2011

### JMillar

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I've done some casting in aluminum. As a rule, I'd say that castings shouldn't fly if you can afford to avoid it. The strength you lose (or rather, the amount you have to derate by to ensure safety) means you gain weight compared to billet / forging / weldment. This is partially but not completely negated in industrial highly automated setups with large parts runs and very good process control.

12. Apr 11, 2011

### Tom Nalevanko

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The hydraulic cylinders for the Lancair IV (and Stallion) main gear legs are aluminum castings that are later machined. This seems to be a good design so castings can be the way to go in some situations. But for anything under a lot of stress, I will take a forging any time.

Blue skies,

Tom

13. Apr 11, 2011

### Dana

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Castings are OK if they're used appropriately. There is an additional safety factor that must be applied, the casting must be of good quality, and you might want to think twice about using it for anything critical like a major structural element.

-Dana

Mr. Cole's Axiom: The sum of the intelligence on the planet is a constant; the population is growing.

14. Jun 9, 2011

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