DIY Two-Stroke Engine Construction Methods

"bigegg" wrote in message
...
two words:

burt munroe

as an example of home-cast/home machined engines.

--
bigegg

but he started with a manufactured engine, he didn't build it from scratch.
He also had a LOT of failures before he got everything working, are you
willing to do that with an AC engine ??

--
Remember Altitude is more important than Attitude

On Mar 16, 4:48*pm, durabol wrote:
Thanks for the responses.

-I planned to have one carburetor (and crankcase) for both cylinders.


Shared carb and crankcase locks you into simultaneous firing of the
two opposing cylinders


-I have access to a lathe and a milling machine but I don't have that
much experience with them so I'll have to learn as I go or get someone
else to do the machining

-I do plan to build the engine in a modular way so I suppose I could
add more cylinders.

-I do have some experience with lost wax casting although not with
much success. The engine casting that I had envisioned may be too
complicated for the simple gravity casting techniques I was planning.
I also worry about hot tears of the cylinder as the aluminium cools
and casting decent heat fins.

-For the cylinder I was planning on just an aluminium wall since I
have heard "cheap" lawn mower engine can get 500h on them. I though
that the bearings in the engine will probably need to be replaced in a
few hundred hours anyways, so the bore could be resized then.

Those are four stroke engines, with no large holes in the cylinder
walls trying to swallow the rings with every stroke. They are also
generously lubricated with splashed oil from the crankcase, which you
won't have in a two stroke. Remember that the only lubrication in a
two-stroke is what's mixed in the fuel, or the tiny quantities that
are injected directly into the lower end bearings, (if you have an oil
pump like some two-stroke street bikes) where it's then mixed with the
fuel/air charge.

Brock

Please get a copy (or download) of Gordon Jennings "Two Stroke Tuner's
Handbook" before starting. It was my 'Bible' when I did two stroke
performance development for a living.

On Mar 18, 2:47*pm, Grider Pirate wrote:
On Mar 16, 4:48*pm, durabol wrote:

Thanks for the responses.

-I planned to have one carburetor (and crankcase) for both cylinders.

Shared carb and crankcase locks you into simultaneous firing of the
two opposing cylinders


Not necessarily. What you describe is commonly called a 'boxer'
configuration.

You can also alternate the cylinders. That can simplify a lot, for
instance
the cylinders can be joined to a common, rigid scottish yoke. That
will
also vibrate horribly and probably shake itself apart. But people
have
tried it, google for Bourke engine, which has a small cult-like
following
on line.

Maybe if you configured a Bourke with multiple banks of 2-cylinders
each, rotating each bank around the crank by 360/n degrees, where
n is the number of cylinders, that would smooth out the vibration
issue.
The result would be a sort of 2-stroke radial.

On Mar 17, 2:32*am, Tim Wescott wrote:
...

With some pretty fancy metallurgy you can use an aluminum cylinder wall.
* It's how the Chevy Vega was done, and it worked great -- except when
it didn't.
...

Which I thought was all of the time. I never heard of a Vega engine
that
lasted past 50,000 miles, or Vega body that wasn't rust perforated
after it's
second winter in the rust belt.

Had it been built to last the Vega would have been a great little
car.

--

FF

Fred the Red Shirt wrote:
On Mar 17, 2:32 am, Tim Wescott wrote:
...

With some pretty fancy metallurgy you can use an aluminum cylinder wall.
It's how the Chevy Vega was done, and it worked great -- except when
it didn't.
...

Which I thought was all of the time. I never heard of a Vega engine
that
lasted past 50,000 miles, or Vega body that wasn't rust perforated
after it's
second winter in the rust belt.

Had it been built to last the Vega would have been a great little
car.

There's an interesting Wikipedia article on the origins of the Chevy
Vega. Apparently it was designed by GM corporate engineering, and
shoved down Chevy's throat. Chevy wasn't allowed to make _any_
engineering changes, they were very grudging about building the thing,
and that was a huge part of the problem.

Apparently the wear point on the Vega engine wasn't the cylinder walls
at all -- it was the valve guides*. But the oil leakage** got blamed on
the cylinder walls because who could believe in an aluminum cylinder
bore? For it's size it's certainly a damn strong engine.

* Which were as new and innovative as the rest of the engine, just
wrong. If you're going to make something that's new and innovative,
identify the parts that _need_ to be new and innovative, and do the
_rest_ of the thing with old reliable technology. Then when that works,
go back and innovatize the rest of the thing, one system element at a time.

** "Fill er up and check the gas while you're at it!"

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

On 3/30/2010 10:22 AM, Tim Wescott wrote:

There's an interesting Wikipedia article on the origins of the Chevy
Vega. Apparently it was designed by GM corporate engineering, and shoved
down Chevy's throat. Chevy wasn't allowed to make _any_ engineering
changes, they were very grudging about building the thing, and that was
a huge part of the problem.

Apparently the wear point on the Vega engine wasn't the cylinder walls
at all -- it was the valve guides*. But the oil leakage** got blamed on
the cylinder walls because who could believe in an aluminum cylinder
bore? For it's size it's certainly a damn strong engine.

* Which were as new and innovative as the rest of the engine, just
wrong. If you're going to make something that's new and innovative,
identify the parts that _need_ to be new and innovative, and do the
_rest_ of the thing with old reliable technology. Then when that works,
go back and innovatize the rest of the thing, one system element at a time.


That was only 2 of the trifecta of problems with that engine. The last
problem was the Vega engine cooked it's oil to a tar like sludge in a
short amount of time. I've also heard that and oil cooler didn't help
much because part of the problem was in that oil pooled in the cylinder
head too long and picked up too much heat there.

Tony

On Tue, 30 Mar 2010 10:22:34 -0700, Tim Wescott
wrote:

Fred the Red Shirt wrote:
On Mar 17, 2:32 am, Tim Wescott wrote:
...

With some pretty fancy metallurgy you can use an aluminum cylinder wall.
It's how the Chevy Vega was done, and it worked great -- except when
it didn't.
...

Which I thought was all of the time. I never heard of a Vega engine
that
lasted past 50,000 miles, or Vega body that wasn't rust perforated
after it's
second winter in the rust belt.

Had it been built to last the Vega would have been a great little
car.

There's an interesting Wikipedia article on the origins of the Chevy
Vega. Apparently it was designed by GM corporate engineering, and
shoved down Chevy's throat. Chevy wasn't allowed to make _any_
engineering changes, they were very grudging about building the thing,
and that was a huge part of the problem.

Apparently the wear point on the Vega engine wasn't the cylinder walls
at all -- it was the valve guides*. But the oil leakage** got blamed on
the cylinder walls because who could believe in an aluminum cylinder
bore? For it's size it's certainly a damn strong engine.


Totally not true. The only fix for the extreme oil burning was to
sleeve the block - and that is not required for valve guide problems.
When they were running well they WERE very torquy engines, giving the
impression they were a lot bigger and "stronger" than they were.


* Which were as new and innovative as the rest of the engine, just
wrong. If you're going to make something that's new and innovative,
identify the parts that _need_ to be new and innovative, and do the
_rest_ of the thing with old reliable technology. Then when that works,
go back and innovatize the rest of the thing, one system element at a time.

** "Fill er up and check the gas while you're at it!"

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!

wrote:
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!


Well said. And not only might I outsource the castings, I'd also be
inclined to outsource heat or chemical treatments, or forgings.

Particularly since I'd be staking my life on the end product...I've
become a lot more safety minded since I became a jumper...

--
- Rufus