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

On Mar 10, 1:45 am, durabol <durabo> wrote:
> ...
> 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) ...>
> Brock

What machine tools do you have?

Some WW1 engine cylinders were machined from SOLID steel forgings.
Casting can easily have internal voids unless well designed, because
the metal shrinks as it solidifies inwards. Aluminum is easy enough to
melt that you could cast a simple shape and then test it for strength
or cut it apart.

Or you could make a lawnmower engine and see how durable it is.

jsw

"durabol" <durabol34> wrote in message
news:df23
> 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.

Most two strokes are single cylinder that rely on crankcase pumping
action to move the fuel/air mixture, if you go to a multiple opposed
cylinders, you will have to provide a slave cylinder or roots type blower
to move the air.

basilisk

"basilisk" <basilisk> fired this volley in news:J4Nln.198564
$Hq1.121731:

> 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

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in
news:Xns9D3756B4152F8lloydspmindspringcom:

> "basilisk" <basilisk> fired this volley in
news:J4Nln.198564
> $Hq1.121731:
>
>> 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
>

That didn't come out right... They use a "divider" or partition of sorts
at the journal between con-rods, and reed valving for intake on each side
of the divider. The "skirt" just extends across the whole crankcase.

LLoyd

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message
news:gcom
> "basilisk" <basilisk> fired this volley in news:J4Nln.198564
> $Hq1.121731:
>
>> 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

durabol wrote:
[..]

In article <J4Nln.198564$Hq1.121731>, "basilisk" <basilisk> wrote:
>
>"durabol" <durabol34> wrote in message
>news:df23
>
>Most two strokes are single cylinder that rely on crankcase pumping
>action to move the fuel/air mixture, if you go to a multiple opposed
>cylinders, you will have to provide a slave cylinder or roots type blower
>to move the air.
>
>basilisk
>my kawai h2 uses reeds and i believe has opposed cylinders. it ain't no
lawnmower.....

In article <6ANln.46018$Jq1.17210>, "basilisk" <basilisk> wrote:
>
>"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message
>news:gcom
>
>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
>it's not so hard, it just costs a bit more. but it adds a lot of grunt.
the 750 i have puts out almost 90hp. dragster h2's running exotic fuels have
been dynoed at over 400hp!. they need to be rebuilt often, but what drag motor
doesn't.
the quest for hp is expensive but doable. honda built a tt racer that got 18hp
out of 50cc! the 8 speed gearbox got it up to 100mph.
read about the mv augusta racers, you wouldn't believe me.

someone 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.

Don't sneer at sand castings, particularly for aluminum parts. Rods and
pistons can be made from billet, or can be purchased from racing parts
suppliers -- racers often customize these parts, so if you can find an
engine with e.g. a similar rod you can order one from Carillo or whoever
"yea, I want a Honda XYZ rod, but make it 5" center to center and make
the big end take a bearing from a Kumatsu 30HP diesel".

For an absolutely "I'm only gonna build one ever" engine you could
fabricate the rough parts by welding or brazing, then stress relieve,
then machine. This is, I believe, how railway locomotive and ship
engines are often built, and I believe that there were automotive
engines built this way, too.

You're building an aero engine, right? And it's going to be air cooled,
right? If so, the advantages of separate cylinder assemblies probably
outweighs the disadvantages of trying to build a monoblock engine.
Trash a cylinder on a monoblock engine and you have to do a complete
rebuild. Trash one cylinder on an assembled engine and you just have to
replace one part.

Another of the advantages of separate cylinders is that you can build a
one-cylinder "research engine" to get the myriad of details worked out.
Then when you like the porting and combustion chamber shape and
cooling fin layout and piston design and ring lands and cylinder finish,
and etc., you can build the multi-cylinder engine of your choice.

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 here:

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

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

Jim Stewart wrote:
> durabol wrote:
>
> 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.

But he wants the performance and reliability in the air, not his garage!!!

(sorry, couldn't resist).

> 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.

You could probably make some weight/reliability trades, though -- for
one example, use iron cylinder liners and conventional steel rings
instead of sooper-dooper nitrited aluminum fancy-pants coatings.

And always fly within an easy glide of a landing strip...

Tim Wescott wrote:
> Jim Stewart wrote:
>
> But he wants the performance and reliability in the air, not his garage!!!
>
> (sorry, couldn't resist).

Good point nonetheless...

>> 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.
>
> You could probably make some weight/reliability trades, though -- for
> one example, use iron cylinder liners and conventional steel rings
> instead of sooper-dooper nitrited aluminum fancy-pants coatings.
>
> And always fly within an easy glide of a landing strip...

That's a given. The problem is an engine out on takeoff
climb. With an ultralight, it's very difficult to
impossible to get the nose down and airspeed up fast enough
to avoid a stall. Of course, you can (and should) carry a
rocket-deployed chute on your ultralight, but it's bad
form to have to depend on one.

Jim Stewart wrote:
> Tim Wescott wrote:
>
> Good point nonetheless...
>> That's a given. The problem is an engine out on takeoff
> climb. With an ultralight, it's very difficult to
> impossible to get the nose down and airspeed up fast enough
> to avoid a stall.

I did not know this -- I fly models, not ultralights. It's scary to
contemplate, though. I would consider a model that can't recover from a
sudden engine-out event to be more than a bit of a turd; I wouldn't want
to get _close_ to a full scale aircraft with that 'feature'.

Surely there are ultralights that don't exhibit this problem!

Is it a consequence of the draggy airframe on the usual ultralight? Or
are you thinking of the flavor of ultralights where you steer by
shifting weight, rather than with a movable elevator? Is there anything
you can do to mitigate the risk during takeoff, i.e. can you trade
climbing performance for safety by keeping the nose down and flying a
bit hotter?

> Of course, you can (and should) carry a
> rocket-deployed chute on your ultralight, but it's bad
> form to have to depend on one.

Or an ejection seat...