DIY Two-Stroke Engine Construction Methods

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 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" 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

"basilisk" fired this volley in news:J4Nln.198564
:

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
. 3.70:

"basilisk" fired this volley in
news:J4Nln.198564
:

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
. 3.70...
"basilisk" fired this volley in news:J4Nln.198564
:

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

In article , "basilisk" wrote:

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
.3.70...
"basilisk" fired this volley in news:J4Nln.198564
:

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


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.

On 3/10/2010 7:46 AM, in wrote:

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.

Suzuki built but never raced a 3 cylinder 50cc engine that was rated at
the highest output per liter on record for use with pump gas. However
to get to one liter it would have 60 cylinders...

Tony

basilisk wrote:
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
"basilisk" fired this volley in news:J4Nln.198564
:

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



Try modifying an existing engine...and don't go hard over on it being a
2-stroke. I've often thought of trying to construct a full 9 or 7
cylinder aircraft radial using Harley engine parts - hell, those engines
have more in common with an air cooled radial than about anything I can
think of other than a Pratt & Whitney.

For your ultralight purpose, a basic V-twin would probably do, and I'd
suggest the fuel injected HD 88B counterbalanced one...just to keep
things smoother. The straight Dyna or touring Twin Cam 88 is lighter,
but I'm not sure how much vibration it would produce if hard mounted.

Something else you could do is use Harley studs and design your own
crank and case to make a flat twin, if you just want to build an engine
yourself - that would be a neat project, too.

If you need to use a reducer, you can machine your own pulley plate and
use a wide primary belt. Given that you'll be mounting the engine
behind a prop, you may also ba able to get away with shaving the fins to
lighten it a bit.

I'd also suggest you hot-rod the motor to a high compression setup -
that and the fuel injection will solve some horsepower vs altitude curve
problems for you - or at least help minimize them.

--
- Rufus

On Mar 11, 3:20*am, Rufus wrote:
basilisk wrote:
"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
.3.70...
"basilisk" fired this volley in news:J4Nln.198564
:

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

Try modifying an existing engine...and don't go hard over on it being a
2-stroke. *I've often thought of trying to construct a full 9 or 7
cylinder aircraft radial using Harley engine parts - hell, those engines
have more in common with an air cooled radial than about anything I can
think of other than a Pratt & Whitney.

SNIP

--
* * * - Rufus

Worth noting:

there is a radial project out there with quite a few builders that
uses VW jugs and a custom crankcase and heads. Around 100hp if I
remember correctly.

There are also a couple of half VW engine projects with plans
available.

If you take a stroll around the national air and space museum you will
get a feel for the art that went into many of the early engines. The
old designers and machinists were a different breed, and their work
inspires awe in any mechanically inclined mind. It is worth noting
that many of the older radial and fan engine configurations used a pie-
wedge style crankcase, where the cylinder and the case were a single
piece, and the crankcase bolted together in pieces arranged in
circumference to the crankshaft.

With modern alloys and machining techniques, I've wondered if
returning to this style might be tolerable for a small engine today.
Lawn mowers are done similarly, and so I'd imagine an engine designed
in this fashion would scale up quickly from a production standpoint.

While building a new engine solely for art is a lofty goal, I can't
really see it for any other reason. What performance specs could you
be looking for that aren't currently available in a production engine,
or are not otherwise achievable by making minor modifications to a
production engine?

The engine of interest to me lately is the new subaru TDI boxer
motor. Wow that thing is fancy, and I'm hoping it makes its way to
the states some time soon. With modern boosting techniques I'd also
like to see the packard aero diesel configuration revisited, perhaps
integrating some of the features in the elsbett engines. .

If I was heading off in the scratch built direction, I would outsource
the casting process. There are many shops domestic and overseas that
can do short runs of castings based on a provided dxf file. It is
unlikely that a backyard foundry will ever get close to the level of
detail these shops can create. I would probably search far and wide
before starting to CAD the thing up.

Of course, thinking down the road, if ever I should build my own bird,
I'm thinking Rotec, or PZL Franklin. I'd like to go heavy kung fu into
engine design, but it is just way to much work, for way to little
optimization.

Thanks!