DIY Two-Stroke Engine

durabol

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Mar 5, 2010, 8:56:42 PM3/5/10

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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

Tim Wescott

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Mar 6, 2010, 2:07:30 AM3/6/10

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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

cncmillgil

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Mar 6, 2010, 5:14:35 AM3/6/10

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Brock, you do have some ambition with a project like that. Sounds like
your basically re-inventing the wheel. Just my opinion, wouldn't it be
more cost effective & easier in the long run finding an antique wing
dinger & rebuild that? I've seen some pretty cool 2strokes over the
years. You've eliminated all those engineering variables that your
scratching your head about. When done, you have restored piece of
history, & may be $worth$ more that what you have into it? Again thats
just me, I dont like re-inventing the wheel. Some very smart guys
already did that. I like improving that wheel & making it spin faster.
The rotary wrankel engines have always intrigued me. Very simple,
compact, comparable with 2 stroke & can be made w/o a lot of
castings.

Good luck!

--
\|||/
(o o)
______.oOO-(_)-OOo.____________________
~ Gil ~
the HOLDZEM©® king
Member of
==American Toolmakers==
using the "old world" ways
with yesterdays technology
building
Tomorrows Dreams
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280451279735

Don Stauffer

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Mar 6, 2010, 10:22:28 AM3/6/10

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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.

PaPa Peng

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Mar 6, 2010, 11:24:00 AM3/6/10

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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.

sta...@prolynx.com

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Mar 6, 2010, 8:45:22 PM3/6/10

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On Mar 5, 6:56 pm, durabol <durabo...@gmail.com> wrote:

There's any amount of engineering info out there on two-strokes,
books have been written. They were a staple project in The Model
Engineer magazine for years, should you want to look that up. What's
UL use?

You'd be basically recreating a commodity item. Resurrect one from a
defunct snowblower, weed-whacker or Lawnboy and spend more time on
figuring out the project you want to drive. The engineering's done,
you aren't likely to improve on what's already been built. Want
overhead valves? Been done. Rotary valves, ditto. Fuel injection,
same. Separate lube system, been done. Opposed twins, flat fours,
square fours, Vs, Xs, Ws, all been done. Separate forced air pumping,
too. They basically suck thermodynamically except the one feature
they've got going is power-to-weight ratio, the small ones pump out a
lot of horsepower, usually at high RPM, for their size. For that you
can go with an existing engine and spend more time on the rest of the
project.

Stan

Jim Wilkins

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Mar 6, 2010, 8:59:45 PM3/6/10

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On Mar 6, 8:45 pm, sta...@prolynx.com wrote:
> On Mar 5, 6:56 pm, durabol <durabo...@gmail.com> wrote:

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

> > Brock
>
> ...What's UL use?
> Stan

I think UL here means UltraLight, a minimally regulated, tiny but
MANNED aircraft.
http://www.eaa.org/Ultralights/

I looked into it, flew a hang glider a few times, then gave it up for
the safer hobby of racing dirt bikes.

jsw

bizguy

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Mar 7, 2010, 12:36:28 AM3/7/10

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You could look at outboard motors as a starting point. In the past I
read of someone using a Mercury to get 100 hp in an aircraft.
Harold

jan olieslagers

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Mar 7, 2010, 8:51:46 AM3/7/10

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Jim Wilkins schreef:

> On Mar 6, 8:45 pm, sta...@prolynx.com wrote:

>> ...What's UL use?

> I think UL here means UltraLight, a minimally regulated, tiny but
> MANNED aircraft.
> http://www.eaa.org/Ultralights/

I thought the same, but should like to add that in several countries the
"ultralight" definition allows bigger planes, closer to the newer US
light sport aircraft definition.

jan olieslagers

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Mar 7, 2010, 2:34:10 PM3/7/10

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jan olieslagers schreef:

Come to think of it, several countries even allow them to FEMALES !

Nigel Eaton

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Mar 7, 2010, 6:04:37 PM3/7/10

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In article
<9446d3d2-3e78-45fc...@19g2000yqu.googlegroups.com>,
bizguy <bizol...@clear.lakes.com> writes

>You could look at outboard motors as a starting point. In the past I
>read of someone using a Mercury to get 100 hp in an aircraft.

That seems unlikely, to be honest. I've never met an outboard that
wasn't cooled by pumped water.

--
Nigel

When the only tools you have are an X3 mill, a
Colchester and assorted other stuff, every problem looks like a steam engine.

Ed Huntress

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Mar 7, 2010, 6:19:10 PM3/7/10

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"Nigel Eaton" <nig...@rcav8r.demon.co.uk> wrote in message
news:3C9hdkNF...@91.135.3.100...

> In article
> <9446d3d2-3e78-45fc...@19g2000yqu.googlegroups.com>, bizguy
> <bizol...@clear.lakes.com> writes
>>You could look at outboard motors as a starting point. In the past I
>>read of someone using a Mercury to get 100 hp in an aircraft.
>
> That seems unlikely, to be honest. I've never met an outboard that wasn't
> cooled by pumped water.
>
> --
> Nigel

There have been other uses of outboards that involved using a car-type
cooling system, with a radiator. A Bobsy SR2 sports-racing car of the 1960s
was very successful in the H-modified class using a Mercury outboard. I
think that was a 750 cc class.

--
Ed Huntress

cl...@snyder.on.ca

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Mar 7, 2010, 6:26:44 PM3/7/10

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I believe he's talking UltraLight Aircraft.

Why a two stroke? The commercially available ones are bad enough. I
hate even taking my chainsaw up a ladder - why would I want to fly
behind one???
A good, small, light supercharged 4 stroke or diesel??? Now that's
something completely different!!!

cl...@snyder.on.ca

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Mar 7, 2010, 6:28:28 PM3/7/10

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Like up here in Canada - 1238 lbs? as long as it stalls under 45 MPH.
It can have a Lycoming IO-235 in it if you want.

cl...@snyder.on.ca

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Mar 7, 2010, 6:30:22 PM3/7/10

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Had a 100HP Evinrude V4 I was thinking of putting in a plane - untill
I remembered all the problems I'd had with 2 strokes in boats, lawn
mowers, mototcycles, weed-eaters, and chain saws over the years.

cl...@snyder.on.ca

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Mar 7, 2010, 11:35:54 PM3/7/10

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On Sun, 7 Mar 2010 23:04:37 +0000, Nigel Eaton
<nig...@rcav8r.demon.co.uk> wrote:

>In article
><9446d3d2-3e78-45fc...@19g2000yqu.googlegroups.com>,
>bizguy <bizol...@clear.lakes.com> writes
>>You could look at outboard motors as a starting point. In the past I
>>read of someone using a Mercury to get 100 hp in an aircraft.
>
>That seems unlikely, to be honest. I've never met an outboard that
>wasn't cooled by pumped water.

Can be cooled very well with a radiator - the interface to connect a
rad instead of the raw water cooling was possible, but not simple.
There were "saltie" conversions that used a sealed cooling system and
a heat exhanger availble for some of the outboards of the period, but
they were not common. Very common with stern-drives (4 stroke)

Actually, there WAS a commercially available helicopter kit that DID
use the V4 Evinrude power head - and I believe I've seen refference to
the 6 cyl Merc "black max" in experimental aircraft use too.

cavelamb

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Mar 8, 2010, 7:54:28 AM3/8/10

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Nigel Eaton wrote:
> In article
> <9446d3d2-3e78-45fc...@19g2000yqu.googlegroups.com>,
> bizguy <bizol...@clear.lakes.com> writes
>> You could look at outboard motors as a starting point. In the past I
>> read of someone using a Mercury to get 100 hp in an aircraft.
>
> That seems unlikely, to be honest. I've never met an outboard that
> wasn't cooled by pumped water.
>

I had a really nice 5 HP Briggs and Stratton outboard on my previous
sailboat. It was air cooled. But it was the exception that proved
the rule...

http://www.duckworksmagazine.com/03/r/columns/cupp/06/index.htm
--

Richard Lamb
http://www.home.earthlink.net/~cavelamb/

Peter Fairbrother

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Mar 8, 2010, 11:38:11 AM3/8/10

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Without knowing anything much about ultralights (beyond they look fun
but dangerous) wouldn't the obvious source of lightweight engines in
that power range be motorcycle engines?

-- Peter Fairbrother

Anyolmouse

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Mar 8, 2010, 5:28:47 PM3/8/10

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"durabol" <dura...@gmail.com> wrote in message
news:4bba8908-a834-4ce7...@g28g2000prb.googlegroups.com...

How about a 2 stroke radial developed by Pontiac for their X-4 1,500lb
car in 1969.
http://www.popsci.com/archive-viewer?id=EyoDAAAAMBAJ&pg=43&query=homebuilt+airplanes

Popular Science has just released ALL of their archives for free
http://www.popsci.com/archives and found it while searching for
homebuilt airplanes.

--
A man is known by the company he keeps- Unknown

Anyolmouse

bod43

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Mar 8, 2010, 10:47:45 PM3/8/10

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On 8 Mar, 22:28, "Anyolmouse" <Anyolmo...@invalid.invalid> wrote:
> "durabol" <durabo...@gmail.com> wrote in message

www.deltahawk.com

Too big for ultralight I would guess but seems like
a very fine plan for a light aircraft engine.

160 hp and upwards

V4 two stroke diesel.

Has crank driven air pump + turbo.

No electrics *at_all* for engine operation.

Will continue running if air pump OR turbo fails.
Will run at about 50% power (check web site for details)
if all water is lost.

Seems a *very* fine thing to me.

Expected to be accepted as a FAA certified
aero engine this year.

200hp planned.

V8 in the future.