Tim Wescott wrote:
Jim Stewart 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.

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.

I went back and read your first post to try to
get the big picture here. So what I think you
are saying is that you want to build an engine
that will be roughly equivalent to a Rotax 2-stroke
ultralight engine. I think the best advise I
could give you is don't. Despite the fact that
the Rotax engines are meticulously designed and
built, they still fail and have a 300 hour rebuild
interval. They have exotic coatings and metallurgy
to get the reliability that they have. There's no
way you'll even come close to their performance and
reliability in you garage.

Now if you want to build an engine, that's fine. If
you want to talk about building an engine, that's
fine too. I just have to say that you're taking
on a project with very, very small prospects of working
and a real steep downside if it fails in the air.

If you're interested in the design of the Rotax
engines, you can download the manuals he

http://www.rotax-owner.com/index.php...08&I temid=25


The line drawings of the engine, piston and cylinder
might be of interest.

I should mention at this juncture, that any time you say "never do that,
it's too hard for an individual" you're citing a rule that -- if applied
recursively -- is telling your audience "never do anything".

Agreed. Just the same, there are little steps and
big stumbles. I would offer much encouragement if
the goal was to build and fly a small 2-stroke on
a control-line model. Not much at stake and a good
prospect for succeeding. The last issue of Model
Engine Builder had plans..

http://www.modelenginebuilder.com/elmwood.htm

OTOH, I just finished reading the ATSM consensus
standards for light sport aircraft engine design.
Not gonna happen in a garage.

Raking over all possible difficulties so that someone can take them into
account, however, is more than a little bit helpful.