DIY Two-Stroke Engine Construction Methods

In article , "basilisk" wrote:

"durabol" wrote in message
...
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


my kawai h2 uses reeds and i believe has opposed cylinders. it ain't no
lawnmower.....

"basilisk" wrote

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.

Or you have each pair of cylinders and pistons moving outward and firing at
the same time, and have each opposing pair separated from the other opposing
pairs. It would still pump like regular single lung 2 strokes, then.

A 6 cylinder opposing pair would be an interesting 2 stroke engine. 3 power
pulses per revolution, and two pistons firing on each pulse. This concept
could mean that each pair could be designed basically identical, and bolted
together. You could add as many pairs as you wanted, to get the power
output you want. 6, or 8 or 10 cylinders! Cool! A 10 cylinder engine
should be as smooth as a turbine engine, but probably with the fuel flow to
match! ;-)

You could keep the cylinder sizes very small, and the engine very narrow but
long. This might be a concept to explore, I think.

If you wanted, you could have each pair rotated a little, somewhat like a
multi layer radial engine, for cooling mainly. It would probably make it
more complex than the benefits would justify.
--
Jim in NC

On Wed, 10 Mar 2010 07:24:54 -0600, "basilisk"
wrote:


"durabol" wrote in message
...
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

Or do like every 2 stroke multi-cyl engine in the past, and devide the
crankcase - basicaly X number of single cyl engines in a row.

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.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

On Mar 10, 12:37*pm, Tim Wescott wrote:
...
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.....
Tim Wescott

Like this:
http://picasaweb.google.com/KB1DAL/T...74948163130882
That's the right inboard engine of the B-17 "909", at an airshow in
Nashua NH. The cylinder cracked and they had to fix it to get home.

I happened to be standing under the wing when they set up the ladder
and made myself useful by taking the cowling pieces as they handed
them down, so by the time security roped off the area I looked like I
belonged there. Eventually the rest of the crew wandered off, leaving
just me assisting the crew chief to disassemble the head and fasten it
onto the good cylinder, then turn the prop while he set the valves. My
hands were too dirty to hold the camera most of the time.

Some day I'm going to make a model radial engine. First I might do a
pocket-sized one with valves timed to compress or run on air.

jsw

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.

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.

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
Control system and signal processing consulting
www.wescottdesign.com

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.

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:
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.

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.

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...

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

Tim Wescott wrote:

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.

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'.

I think all engine-driven aircraft have a window
of vulnerability on takeoff. Most general aviation
planes can't return to the runway straight ahead
and successfully land if they are higher than 200'
and can't turn around to return to the field unless
they are higher than 500'. Consider that the headwind
that you took off into is now a tailwind and you
can see how badly your day gets.

That's why takeoffs are *always* full throttle and
best rate of climb. You spend the least amount
of time getting through that zone.

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

Don't know. I was told that by someone whose knowledge
and experience were much greater than mine.

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?

Don't know for sure. I think the combination of
light weight and high drag bleeds off the airspeed
so quickly that you loose elevator authority
before you can put it to use.

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...