DIY Two-Stroke Engine Construction Methods

On Thu, 11 Mar 2010 00:45:04 -0800 (PST), frank
wrote:

On Mar 10, 9:02Â*pm, Rufus wrote:
durabol wrote:
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.

As someone whom has done lost wax casting, I wouldn't recommend doing
that for something I was going to bet my life on...not without investing
LARGE amounts of capital in equipment - a centrifugal or pressure
injection foundry...sand casting (which I've also done) is a far better
alternative for casting a raw engine casing. Â*Make a durable wooden
master model, preferably of a hardwood.

In any event, you're still going to have to sleeve the cylinders with
some alloy of machined, durable steel - which will have to be hardened
and polished in some way and interference fit into the block or stud.
And you need to match coefficients of thermal expansion when choosing
your materials in order to keep it all tight - same goes for choosing
and tolerancing your bolts and every other component in direct
contact...which means you also need to do some thermal analysis and
figure out how hot, as well as how, your engine is going to run...

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

Again - big investment in big machines to insure uniformity of the
casting...which will kill the project (and the pilot) if you screw it
up. Â*Hot spots, porosity, voids...not that simple. Â*Best way to
spot/find/quality check castings involve die penetrant or x-ray.

Also - don't overlook the fact that you are going to have to heat treat,
case harden, or otherwise machine or post-work any part you produce
depending on choice and application of materials...I don't know what
kind of tools and resources the OP has at hand, but if he's starting
from scratch he better be prepared to spend the amount of money he'd
spend on a mid-size car in tooling just to get started with such a
project...make it a large luxury car, now that I think about it...

The far easier (and safer) alternative is to modify an existing engine -
like a motorcycle engine - strip it down and just build the parts and
accessories required to make it turn a prop. Â*And along the way one can
also machine it's component parts down to lighten it...run it on the
ground, if it breaks, you know you went too far.

--
Â* Â* Â* - Rufus (pilot, engineer, jeweler, model builder...yadda, yadda...)

Anything that flies a person has to be certified by the FAA anyway.
Especially homebuilts due to some fatal crashes early on.

Not true.
Experimental/homebuilt can use ANY engine - absolutely no
certification required.