DIY Two-Stroke Engine

For the last few years I have toyed with the idea of building a
homemade two-stroke engine for UL use. What keyed my interest was
reading about homemade model aircraft engines and reading and watching
a re-enactment of the Wright brother's first flight with a replica
engine (not a two-stroke engine).

Has anyone made a 2-stroke engine from scratch? One may need to cast
aluminium, may need a lathe and milling machine with boring head and
hone or perhaps the boring and honing of the cylinder and bearing
journals could be farmed out. A commercial carburetor and piston could
be used. Two-stroke engines seem simple enough that home construction
may be possible, if not practical.

A direct drive engine will be that much heavier when you take into
account the weight of the drive reduction system. I have calculated
the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and
it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm
cylinder and crankcase wall thickness and a 1.25" dia crank.

I have got some idea of port-time-area from the freeware computer
program called "BiMotion". I'm not sure how good the data is for
lowish speed engines but I guess it is a start. I have also worked up
a spreadsheet for similar information.

I don't think a reed valve system is needed for this engine since it
is only going to operate at a fairly narrow rpm range and the port
timing isn't critical. Piston ported valves offer similar performance
to other induction types but only over a narrow rpm range which is
what I have planned for the engine. I plan to build an engine with a
restrictive exhaust to ensure no fuel escapes. I have heard that
piston ported engines can spit some fuel out of the carb at idle but
this doesn't seem like a major problem. Rotary valves via crank shaft
induction (disk or drum valves as well) is an interesting idea but I
don't think I need the critical timing they provide.

I was planning on using the largest two-stroke piston (not a diesel
piston) I could find and using the largest stoke that was reasonable,
something like 90x105mm

Brock

durabol wrote:
For the last few years I have toyed with the idea of building a
homemade two-stroke engine for UL use.

Underwriter's Laboratories?

What keyed my interest was
reading about homemade model aircraft engines and reading and watching
a re-enactment of the Wright brother's first flight with a replica
engine (not a two-stroke engine).

Has anyone made a 2-stroke engine from scratch? One may need to cast
aluminium, may need a lathe and milling machine with boring head and
hone or perhaps the boring and honing of the cylinder and bearing
journals could be farmed out. A commercial carburetor and piston could
be used. Two-stroke engines seem simple enough that home construction
may be possible, if not practical.

Certainly not practical in the "it saves you money" sense, but who cares?

A direct drive engine will be that much heavier when you take into
account the weight of the drive reduction system. I have calculated
the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and
it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm
cylinder and crankcase wall thickness and a 1.25" dia crank.

I have got some idea of port-time-area from the freeware computer
program called "BiMotion". I'm not sure how good the data is for
lowish speed engines but I guess it is a start. I have also worked up
a spreadsheet for similar information.

I don't think a reed valve system is needed for this engine since it
is only going to operate at a fairly narrow rpm range and the port
timing isn't critical. Piston ported valves offer similar performance
to other induction types but only over a narrow rpm range which is
what I have planned for the engine.

Piston porting isn't optimum at any speed -- crank-timed or reed valve
induction is much better.

But piston porting is certainly easier.

I plan to build an engine with a
restrictive exhaust to ensure no fuel escapes. I have heard that
piston ported engines can spit some fuel out of the carb at idle but
this doesn't seem like a major problem. Rotary valves via crank shaft
induction (disk or drum valves as well) is an interesting idea but I
don't think I need the critical timing they provide.

I was planning on using the largest two-stroke piston (not a diesel
piston) I could find and using the largest stoke that was reasonable,
something like 90x105mm

I'm still a home-built engine wannabe, but I'm working on it. Here are
some resources:

http://www.lindsaybks.com/prod/sub/engines.html
http://www.modelenginenews.org/

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

durabol wrote:
For the last few years I have toyed with the idea of building a
homemade two-stroke engine for UL use. What keyed my interest was
reading about homemade model aircraft engines and reading and watching
a re-enactment of the Wright brother's first flight with a replica
engine (not a two-stroke engine).

Has anyone made a 2-stroke engine from scratch? One may need to cast
aluminium, may need a lathe and milling machine with boring head and
hone or perhaps the boring and honing of the cylinder and bearing
journals could be farmed out. A commercial carburetor and piston could
be used. Two-stroke engines seem simple enough that home construction
may be possible, if not practical.

A direct drive engine will be that much heavier when you take into
account the weight of the drive reduction system. I have calculated
the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and
it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm
cylinder and crankcase wall thickness and a 1.25" dia crank.

I have got some idea of port-time-area from the freeware computer
program called "BiMotion". I'm not sure how good the data is for
lowish speed engines but I guess it is a start. I have also worked up
a spreadsheet for similar information.

I don't think a reed valve system is needed for this engine since it
is only going to operate at a fairly narrow rpm range and the port
timing isn't critical. Piston ported valves offer similar performance
to other induction types but only over a narrow rpm range which is
what I have planned for the engine. I plan to build an engine with a
restrictive exhaust to ensure no fuel escapes. I have heard that
piston ported engines can spit some fuel out of the carb at idle but
this doesn't seem like a major problem. Rotary valves via crank shaft
induction (disk or drum valves as well) is an interesting idea but I
don't think I need the critical timing they provide.

I was planning on using the largest two-stroke piston (not a diesel
piston) I could find and using the largest stoke that was reasonable,
something like 90x105mm

Brock


There are several organizations for hobbyists building smaller (model
sized) IC engines. Check out Model Engine Builder magazine (they have a
web site.

I suggest you build a model engine first. That would help answer the
question of whether it is practical for you. Sounds like you may not be
a skilled machinist yet, and I would become a master machinist before I
bet my life on a homemade engine.

On Mar 5, 6:56*pm, durabol wrote:
For the last few years I have toyed with the idea of building a
homemade two-stroke engine for UL use. What keyed my interest was
reading about homemade model aircraft engines and reading and watching
a re-enactment of the Wright brother's first flight with a replica
engine (not a two-stroke engine).

Has anyone made a 2-stroke engine from scratch? One may need to cast
aluminium, may need a lathe and milling machine with boring head and
hone or perhaps the boring and honing of the cylinder and bearing
journals could be farmed out. A commercial carburetor and piston could
be used. Two-stroke engines seem simple enough that home construction
may be possible, if not practical.

A direct drive engine will be that much heavier when you take into
account the weight of the drive reduction system. I have calculated
the weight of an 80x80mm bore and stroke 2 cylinder opposed engine and
it was a bit under 40lbs which should give about 1hp/lbs. I used 10mm
cylinder and crankcase wall thickness and a 1.25" dia crank.

I have got some idea of port-time-area from the freeware computer
program called "BiMotion". I'm not sure how good the data is for
lowish speed engines but I guess it is a start. I have also worked up
a spreadsheet for similar information.

I don't think a reed valve system is needed for this engine since it
is only going to operate at a fairly narrow rpm range and the port
timing isn't critical. Piston ported valves offer similar performance
to other induction types but only over a narrow rpm range which is
what I have planned for the engine. I plan to build an engine with a
restrictive exhaust to ensure no fuel escapes. I have heard that
piston ported engines can spit some fuel out of the carb at idle but
this doesn't seem like a major problem. Rotary valves via crank shaft
induction (disk or drum valves as well) is an interesting idea but I
don't think I need the critical timing they provide.

I was planning on using the largest two-stroke piston (not a diesel
piston) I could find and using the largest stoke that was reasonable,
something like 90x105mm

Brock

I met a guy in Edmonton (St. Albert ) who made working models of
historical engines such as the Liberty engine. Really beautiful piece
of modeling and was featured in a modeling magazine. Its power/weight
output was not enough to power a model plane.

If your intention is to power a model plane you are much better off
buying a model engine and tinker with that to boost its performance.
Not much reward in building a two stroke engine from scratch. For a
large two stoke you can modify a weedwacker engine (25 cc) A
snowmobile engine powers those military drones.

"durabol" wrote

Has anyone made a 2-stroke engine from scratch? One may need to cast
aluminium, may need a lathe and milling machine with boring head and
hone or perhaps the boring and honing of the cylinder and bearing
journals could be farmed out. A commercial carburetor and piston could
be used. Two-stroke engines seem simple enough that home construction
may be possible, if not practical.

A direct drive engine will be that much heavier when you take into
account the weight of the drive reduction system.

I am assuming you meant to write "will _(not)_ be that much heavier",
right?

If so, when is the last time you saw a direct drive 2 stroke aircraft
engine? Not me. Closest I can think of is a model airplane engine, and
that is only practical because of the small prop sizes. If you put a large
enough prop on a 2 stroke to soak up 50 hp, you will have to keep rpm's way
down to keep from having a real noisy, inefficient prop. You keep the RPM's
that low, and you now have a real inefficient 2 stroke engine. That is why
all 2 stroke engines have gearboxes or belt drives to reduce prop speed.

You might do well to consider a 2 stroke supercharged diesel engine. You
make one of those, and make it scaleable by adding more banks of cylinders,
and the flying world will beat a path to your doorstep.
--
Jim in NC

Suzuki built a 650cc water cooled 2 stroke twin for Arctic Cat. I think
that engine is about the ultimate in big bore 2 stroke twins... At one
time I considered getting 2 of these and putting them in a small sports
car like a Triumph Spitfire but I've since moved to a state that does
emissions testing and that won't pass here...

Suzuki just about ruled the 2 stroke motorcycle market with their rock
solid reliable engines. You could count on a 75k miles out of a Suzuki
triple when the other companies' bikes would only go 15 to 20k miles on
a set of pistons...

There were also some big bore 2 stroke dirt bikes. I know all the major
players in the market built them but the one that comes to mind was a
500cc Husqvarna single. Sleeves, pistons ect are all available for
these bikes could be used to build your own. The easiest way to go is
to use someone else's engineering and machine work to build your engine.
That way the major parts to make would be the cases, barrels and
cylinder heads since the bike ones won't have adequate cooling. I
imagine that a 1000cc 2 stroke opposed twin would be pretty cool and
could be tuned to run at an RPM low enough for direct drive. However
it's not a good idea to put a prop on a built up crankshaft like all 2
strokes use and a belt drive or some such would be required.

I would highly recommend reading the 2 stroke tuners handbook if you can
find a copy. I have a PDF version but it's too big to eMail. Also talk
to Charlie at Superior Sleeve in Millwaukie, OR. Charlie has built more
custom 2 stroke engines than just about anybody alive today... If you
can catch him when he has time to talk, he will enlighten you a great
deal. It's been more than 20 years since I was building high
performance 2 stroke engines and I've forgotten a lot over the years...

Good luck and keep us posted if you go on with this project.

Tony

Morgans schreef:

You might do well to consider a 2 stroke supercharged diesel engine. You
make one of those, and make it scaleable by adding more banks of cylinders,
and the flying world will beat a path to your doorstep.

Hm. The flying world did not exactly beat any kind of path to the
doorstep of www.dair.co.uk, though they did exactly that. Wilksh company
wasn't far off, either, with equal lack of big success.

"jan olieslagers" wrote in message
...
Morgans schreef:

You might do well to consider a 2 stroke supercharged diesel engine. You
make one of those, and make it scaleable by adding more banks of
cylinders,
and the flying world will beat a path to your doorstep.

Hm. The flying world did not exactly beat any kind of path to the doorstep
of www.dair.co.uk, though they did exactly that. Wilksh company wasn't far
off, either, with equal lack of big success.

I suspect the two cylinders with 4 pistons is a bit unconventional, and will
have to work all the harder to prove itself.

I think the web page is about 10 years old, since much activity has taken
place. It looks like it is a bit heavy when you add all it needs to run in
an airplane, too. How about price? No mention of that, on the current
pages.
--
Jim in NC

"Morgans" wrote in message
...

I suspect the two cylinders with 4 pistons is a bit unconventional, and will
have to work all the harder to prove itself.

2 pistons per cylinder is not unconventional in the stationary diesel world.

Vaughn

On Mar 6, 2:44 pm, "Morgans" wrote:

If so, when is the last time you saw a direct drive 2 stroke aircraft
engine? Not me.

McCullough made two-stroke opposed four-bangers for miltary target
drones in several different sizes. Many of those were sold surplus and
found their way into several homebuilts and a lot of Bensen
Gyrocopters. I once owned one; the vibration was awesome, as was the
fuel consumption.

http://www.combatairmuseum.org/engin...ch0-100-1.html
http://media.photobucket.com/image/M...ctoshow026.jpg

And here's a video of one powering a Hummel Bird:

http://www.youtube.com/watch?v=ITB_dxbCTUk

Dan