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  #11   Report Post  
Old October 23rd 15, 06:50 PM posted to rec.crafts.metalworking
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Posts: 1,829
Default Mount a 2 stroke upside down?

John B. wrote:
On Thu, 22 Oct 2015 15:58:43 +0000 (UTC), Cydrome Leader
wrote:

wrote:
Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a
2 stroke bicycle engine upside down. Maybe upside down and backward.
If I did this the carb would need to be inverted because it is a float
bowl type carb. I suppose I could use a pumper type carb instead but I
don't know if I have one that is suitable as far as fuel and air flow
are concerned. Besides, small engine pumper carbs tend to be kind of
on/off devices in that they idle OK and and run wide open well but
don't do so well in the mid range throttle settings. I suppose I could
buy one but I'm cheap. So, if there is room to invert the carb what
else do I need to worry about? Will the crankcase tend to get too hot
since it will now be above the cylinder? And lets say that the engine
is not only inverted but also turned around. Now the engine will be
rotating the wrong way to drive the bike forward. Since the engine is
a two stroke it seems to me that I will only need to change the
ignition timing. I think this can be done simply by broaching a new
keyway in the spinning magnet flywheel. The ignition is a fully
electronic CDI type with no points. I assume the ignition works by
sensing the voltage rise in the magneto primary winding as there is no
other provision for detecting the position of the flywheel magnet.
Have I missed anything?


Is rebuilding an engine really the easier option here? I just can't
imagine that it is.

I have a bike with an engine strapped on. It's a decade old Golden Eagle
kit with the drive ring and belt and a 25cc Redmax weed wacker engine. The
only engine problems have been gas tank leaks from that ethanol **** in
the gas. It starts in negative temps, or with old gas. Very solid little
engine.

It sounds like you're going for the engine mounted inside the triangle of
the frame and not something strapped over the rear wheel though. The fake
motorcycle style is all I see these days. Never come across another belt
drive bike like I have yet.


The "Whizzer" motor bicycle, and motor kits for bicycles, was made
from around 1939 until about 2009 and there are some NOS still
available.


That's the style of kit I see in Chicago. I still prefer the leafblower
type as you just put a plastic bag over it and nobody knows it's a bike
with an engine.

  #12   Report Post  
Old October 23rd 15, 07:27 PM posted to rec.crafts.metalworking
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Posts: 223
Default Mount a 2 stroke upside down?

On Thu, 22 Oct 2015 09:03:57 -0400, Ed Huntress wrote:

On Thu, 22 Oct 2015 00:00:13 -0500, Tim Wescott
wrote:

On Thu, 22 Oct 2015 08:53:44 +0700, John B. wrote:

On Wed, 21 Oct 2015 14:01:25 -0700, wrote:

Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a
2 stroke bicycle engine upside down. Maybe upside down and backward.
If I did this the carb would need to be inverted because it is a float
bowl type carb. I suppose I could use a pumper type carb instead but I
don't know if I have one that is suitable as far as fuel and air flow
are concerned. Besides, small engine pumper carbs tend to be kind of
on/off devices in that they idle OK and and run wide open well but
don't do so well in the mid range throttle settings. I suppose I could
buy one but I'm cheap. So, if there is room to invert the carb what
else do I need to worry about? Will the crankcase tend to get too hot
since it will now be above the cylinder? And lets say that the engine
is not only inverted but also turned around. Now the engine will be
rotating the wrong way to drive the bike forward. Since the engine is
a two stroke it seems to me that I will only need to change the
ignition timing. I think this can be done simply by broaching a new
keyway in the spinning magnet flywheel. The ignition is a fully
electronic CDI type with no points. I assume the ignition works by
sensing the voltage rise in the magneto primary winding as there is no
other provision for detecting the position of the flywheel magnet.
Have I missed anything?
Thanks,
Eric

Model airplane 2 stroke motors are frequently mounted upside down and
run all right although if you flood one it might be a bit more
difficult to start and chainsaw run all right upside down.

As for running backward, I'm not sure of the efficiency as some modern
2 strokes use some pretty exotic porting that may be rotation
directional in nature. I'm leaning on model engine experience but some
glow plug designs of model engines seemed to run in either direction
with no problems and other, different in design, wouldn't seem to run
backwards at all.


The rotation direction thing is what Ed was referring to -- most model
airplane 2-strokes have intake ports that are timed by the crank, and
that lead the piston by a considerable amount. This makes the engine
prefer to run in just one direction. Cox reed-valve engines are
direction agnostic, as are the really old piston-timed engines.


I'd really like to see the engine the OP is talking about.


Me, too -- Eric, can you post a picture someplace, or a link to the
seller's website?

Chances are
that it's a piston-port engine, as most bike motors have been since the
beginning. My old O&R bike motor is a cross-scavenge, piston-port engine
-- the basic 2-stroke design that powered everything including
lawnmowers and ancient washing machines, and was used in all sorts of
applications where you're after low cost and smooth running, rather than
performance.


Weed-whacker and chainsaw motors are, to my knowledge, piston timed,
with the intake port to the crankshaft opened and closed by the skirt of
the piston rather than by the crank or a rotor attached to the crank.
So, they'll run pretty much the same in either direction, once you get
the spark timing sorted out.


I think that both piston-port and reed-valve intake have both been used
in chainsaws.


I could see that -- chainsaws have a bit more need to be high performance
in a small package than a lot of other 2-stroke applications. I suppose
I wouldn't even be surprised at a crank-timed one (I'm kind of surprised
that crank-timed 2-strokes only seem to be ubiquitous in model airplane
use, and even there the really big ones are piston-timed, either because
they've been repurposed from weed-whacker engines, or because they've
been re-designed from such engines).

Either one will allow an engine to run in either
direction, given the ignition timing issue discussed before.



--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
  #13   Report Post  
Old October 23rd 15, 08:56 PM posted to rec.crafts.metalworking
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Posts: 12,505
Default Mount a 2 stroke upside down?

On Fri, 23 Oct 2015 12:27:13 -0500, Tim Wescott
wrote:

On Thu, 22 Oct 2015 09:03:57 -0400, Ed Huntress wrote:

On Thu, 22 Oct 2015 00:00:13 -0500, Tim Wescott
wrote:

On Thu, 22 Oct 2015 08:53:44 +0700, John B. wrote:

On Wed, 21 Oct 2015 14:01:25 -0700, wrote:

Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a
2 stroke bicycle engine upside down. Maybe upside down and backward.
If I did this the carb would need to be inverted because it is a float
bowl type carb. I suppose I could use a pumper type carb instead but I
don't know if I have one that is suitable as far as fuel and air flow
are concerned. Besides, small engine pumper carbs tend to be kind of
on/off devices in that they idle OK and and run wide open well but
don't do so well in the mid range throttle settings. I suppose I could
buy one but I'm cheap. So, if there is room to invert the carb what
else do I need to worry about? Will the crankcase tend to get too hot
since it will now be above the cylinder? And lets say that the engine
is not only inverted but also turned around. Now the engine will be
rotating the wrong way to drive the bike forward. Since the engine is
a two stroke it seems to me that I will only need to change the
ignition timing. I think this can be done simply by broaching a new
keyway in the spinning magnet flywheel. The ignition is a fully
electronic CDI type with no points. I assume the ignition works by
sensing the voltage rise in the magneto primary winding as there is no
other provision for detecting the position of the flywheel magnet.
Have I missed anything?
Thanks,
Eric

Model airplane 2 stroke motors are frequently mounted upside down and
run all right although if you flood one it might be a bit more
difficult to start and chainsaw run all right upside down.

As for running backward, I'm not sure of the efficiency as some modern
2 strokes use some pretty exotic porting that may be rotation
directional in nature. I'm leaning on model engine experience but some
glow plug designs of model engines seemed to run in either direction
with no problems and other, different in design, wouldn't seem to run
backwards at all.

The rotation direction thing is what Ed was referring to -- most model
airplane 2-strokes have intake ports that are timed by the crank, and
that lead the piston by a considerable amount. This makes the engine
prefer to run in just one direction. Cox reed-valve engines are
direction agnostic, as are the really old piston-timed engines.


I'd really like to see the engine the OP is talking about.


Me, too -- Eric, can you post a picture someplace, or a link to the
seller's website?

Chances are
that it's a piston-port engine, as most bike motors have been since the
beginning. My old O&R bike motor is a cross-scavenge, piston-port engine
-- the basic 2-stroke design that powered everything including
lawnmowers and ancient washing machines, and was used in all sorts of
applications where you're after low cost and smooth running, rather than
performance.


Weed-whacker and chainsaw motors are, to my knowledge, piston timed,
with the intake port to the crankshaft opened and closed by the skirt of
the piston rather than by the crank or a rotor attached to the crank.
So, they'll run pretty much the same in either direction, once you get
the spark timing sorted out.


I think that both piston-port and reed-valve intake have both been used
in chainsaws.


I could see that -- chainsaws have a bit more need to be high performance
in a small package than a lot of other 2-stroke applications. I suppose
I wouldn't even be surprised at a crank-timed one (I'm kind of surprised
that crank-timed 2-strokes only seem to be ubiquitous in model airplane
use, and even there the really big ones are piston-timed, either because
they've been repurposed from weed-whacker engines, or because they've
been re-designed from such engines).


I've actually had my hands on only two rotary-valve 2-strokes: my old
McCoy Red Head .35, which had a hollow crank with a window in one side
for a port (very strange), and a Yamaha 175 dirt bike. I put a "Git
Kit" in that bike, which included a new rotary-port disk, with
different timing.

--
Ed Huntress

Either one will allow an engine to run in either
direction, given the ignition timing issue discussed before.

  #14   Report Post  
Old October 23rd 15, 09:54 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Apr 2008
Posts: 1,949
Default Mount a 2 stroke upside down?

On Thu, 22 Oct 2015 09:03:57 -0400, Ed Huntress
wrote:

On Thu, 22 Oct 2015 00:00:13 -0500, Tim Wescott
wrote:

On Thu, 22 Oct 2015 08:53:44 +0700, John B. wrote:

On Wed, 21 Oct 2015 14:01:25 -0700, wrote:

Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a 2
stroke bicycle engine upside down. Maybe upside down and backward. If I
did this the carb would need to be inverted because it is a float bowl
type carb. I suppose I could use a pumper type carb instead but I don't
know if I have one that is suitable as far as fuel and air flow are
concerned. Besides, small engine pumper carbs tend to be kind of on/off
devices in that they idle OK and and run wide open well but don't do so
well in the mid range throttle settings. I suppose I could buy one but
I'm cheap. So, if there is room to invert the carb what else do I need
to worry about? Will the crankcase tend to get too hot since it will now
be above the cylinder? And lets say that the engine is not only inverted
but also turned around. Now the engine will be rotating the wrong way to
drive the bike forward. Since the engine is a two stroke it seems to me
that I will only need to change the ignition timing. I think this can be
done simply by broaching a new keyway in the spinning magnet flywheel.
The ignition is a fully electronic CDI type with no points. I assume the
ignition works by sensing the voltage rise in the magneto primary
winding as there is no other provision for detecting the position of the
flywheel magnet. Have I missed anything?
Thanks,
Eric

Model airplane 2 stroke motors are frequently mounted upside down and
run all right although if you flood one it might be a bit more difficult
to start and chainsaw run all right upside down.

As for running backward, I'm not sure of the efficiency as some modern 2
strokes use some pretty exotic porting that may be rotation directional
in nature. I'm leaning on model engine experience but some glow plug
designs of model engines seemed to run in either direction with no
problems and other, different in design, wouldn't seem to run backwards
at all.


The rotation direction thing is what Ed was referring to -- most model
airplane 2-strokes have intake ports that are timed by the crank, and
that lead the piston by a considerable amount. This makes the engine
prefer to run in just one direction. Cox reed-valve engines are
direction agnostic, as are the really old piston-timed engines.


I'd really like to see the engine the OP is talking about. Chances are
that it's a piston-port engine, as most bike motors have been since
the beginning. My old O&R bike motor is a cross-scavenge, piston-port
engine -- the basic 2-stroke design that powered everything including
lawnmowers and ancient washing machines, and was used in all sorts of
applications where you're after low cost and smooth running, rather
than performance.


Weed-whacker and chainsaw motors are, to my knowledge, piston timed, with
the intake port to the crankshaft opened and closed by the skirt of the
piston rather than by the crank or a rotor attached to the crank. So,
they'll run pretty much the same in either direction, once you get the
spark timing sorted out.


I think that both piston-port and reed-valve intake have both been
used in chainsaws. Either one will allow an engine to run in either
direction, given the ignition timing issue discussed before.

ED-the engine is piston ported. These engines are ubiquitous online. I
know they are not all made in the same factories but they are all
similar. See the link:
www.californiamotorbikes.com
I had, years and years ago, a Yamaha 80 that used the rotarty valve
setup. It was interesting because the carb was inside the engine case
on the right side. I think Kawasaki made a similar engine. Also
interesting was the fact that there was a Honda motorcycle that not
only looked a whole lot like the Yamaha but had some parts that were
interchangeable. Like the front forks. These weren't the telescoping
type forks so to swap forks the whole front end needed to be changed.
Eric
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Old October 24th 15, 12:15 AM posted to rec.crafts.metalworking
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Posts: 12,505
Default Mount a 2 stroke upside down?

On Fri, 23 Oct 2015 12:54:23 -0700, wrote:

On Thu, 22 Oct 2015 09:03:57 -0400, Ed Huntress
wrote:

On Thu, 22 Oct 2015 00:00:13 -0500, Tim Wescott
wrote:

On Thu, 22 Oct 2015 08:53:44 +0700, John B. wrote:

On Wed, 21 Oct 2015 14:01:25 -0700,
wrote:

Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a 2
stroke bicycle engine upside down. Maybe upside down and backward. If I
did this the carb would need to be inverted because it is a float bowl
type carb. I suppose I could use a pumper type carb instead but I don't
know if I have one that is suitable as far as fuel and air flow are
concerned. Besides, small engine pumper carbs tend to be kind of on/off
devices in that they idle OK and and run wide open well but don't do so
well in the mid range throttle settings. I suppose I could buy one but
I'm cheap. So, if there is room to invert the carb what else do I need
to worry about? Will the crankcase tend to get too hot since it will now
be above the cylinder? And lets say that the engine is not only inverted
but also turned around. Now the engine will be rotating the wrong way to
drive the bike forward. Since the engine is a two stroke it seems to me
that I will only need to change the ignition timing. I think this can be
done simply by broaching a new keyway in the spinning magnet flywheel.
The ignition is a fully electronic CDI type with no points. I assume the
ignition works by sensing the voltage rise in the magneto primary
winding as there is no other provision for detecting the position of the
flywheel magnet. Have I missed anything?
Thanks,
Eric

Model airplane 2 stroke motors are frequently mounted upside down and
run all right although if you flood one it might be a bit more difficult
to start and chainsaw run all right upside down.

As for running backward, I'm not sure of the efficiency as some modern 2
strokes use some pretty exotic porting that may be rotation directional
in nature. I'm leaning on model engine experience but some glow plug
designs of model engines seemed to run in either direction with no
problems and other, different in design, wouldn't seem to run backwards
at all.

The rotation direction thing is what Ed was referring to -- most model
airplane 2-strokes have intake ports that are timed by the crank, and
that lead the piston by a considerable amount. This makes the engine
prefer to run in just one direction. Cox reed-valve engines are
direction agnostic, as are the really old piston-timed engines.


I'd really like to see the engine the OP is talking about. Chances are
that it's a piston-port engine, as most bike motors have been since
the beginning. My old O&R bike motor is a cross-scavenge, piston-port
engine -- the basic 2-stroke design that powered everything including
lawnmowers and ancient washing machines, and was used in all sorts of
applications where you're after low cost and smooth running, rather
than performance.


Weed-whacker and chainsaw motors are, to my knowledge, piston timed, with
the intake port to the crankshaft opened and closed by the skirt of the
piston rather than by the crank or a rotor attached to the crank. So,
they'll run pretty much the same in either direction, once you get the
spark timing sorted out.


I think that both piston-port and reed-valve intake have both been
used in chainsaws. Either one will allow an engine to run in either
direction, given the ignition timing issue discussed before.

ED-the engine is piston ported. These engines are ubiquitous online. I
know they are not all made in the same factories but they are all
similar. See the link:
www.californiamotorbikes.com


Aha. Yes, your basic piston-port 2-stroke.

I had, years and years ago, a Yamaha 80 that used the rotarty valve
setup. It was interesting because the carb was inside the engine case
on the right side. I think Kawasaki made a similar engine. Also
interesting was the fact that there was a Honda motorcycle that not
only looked a whole lot like the Yamaha but had some parts that were
interchangeable. Like the front forks. These weren't the telescoping
type forks so to swap forks the whole front end needed to be changed.
Eric


There sure were a lot of oddities in those early Japanese bikes. They
were pretty clever.

--
Ed Huntress


  #16   Report Post  
Old October 24th 15, 10:23 AM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Sep 2015
Posts: 194
Default Mount a 2 stroke upside down?

On Fri, 23 Oct 2015 16:50:45 +0000 (UTC), Cydrome Leader
wrote:

John B. wrote:
On Thu, 22 Oct 2015 15:58:43 +0000 (UTC), Cydrome Leader
wrote:

wrote:
Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a
2 stroke bicycle engine upside down. Maybe upside down and backward.
If I did this the carb would need to be inverted because it is a float
bowl type carb. I suppose I could use a pumper type carb instead but I
don't know if I have one that is suitable as far as fuel and air flow
are concerned. Besides, small engine pumper carbs tend to be kind of
on/off devices in that they idle OK and and run wide open well but
don't do so well in the mid range throttle settings. I suppose I could
buy one but I'm cheap. So, if there is room to invert the carb what
else do I need to worry about? Will the crankcase tend to get too hot
since it will now be above the cylinder? And lets say that the engine
is not only inverted but also turned around. Now the engine will be
rotating the wrong way to drive the bike forward. Since the engine is
a two stroke it seems to me that I will only need to change the
ignition timing. I think this can be done simply by broaching a new
keyway in the spinning magnet flywheel. The ignition is a fully
electronic CDI type with no points. I assume the ignition works by
sensing the voltage rise in the magneto primary winding as there is no
other provision for detecting the position of the flywheel magnet.
Have I missed anything?

Is rebuilding an engine really the easier option here? I just can't
imagine that it is.

I have a bike with an engine strapped on. It's a decade old Golden Eagle
kit with the drive ring and belt and a 25cc Redmax weed wacker engine. The
only engine problems have been gas tank leaks from that ethanol **** in
the gas. It starts in negative temps, or with old gas. Very solid little
engine.

It sounds like you're going for the engine mounted inside the triangle of
the frame and not something strapped over the rear wheel though. The fake
motorcycle style is all I see these days. Never come across another belt
drive bike like I have yet.


The "Whizzer" motor bicycle, and motor kits for bicycles, was made
from around 1939 until about 2009 and there are some NOS still
available.


That's the style of kit I see in Chicago. I still prefer the leafblower
type as you just put a plastic bag over it and nobody knows it's a bike
with an engine.


Don't your "plastic bag" make a funny noise when you are driving?
--
cheers,

John B.

  #17   Report Post  
Old October 26th 15, 05:03 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Jul 2006
Posts: 1,829
Default Mount a 2 stroke upside down?

John B. wrote:
On Fri, 23 Oct 2015 16:50:45 +0000 (UTC), Cydrome Leader
wrote:

John B. wrote:
On Thu, 22 Oct 2015 15:58:43 +0000 (UTC), Cydrome Leader
wrote:

wrote:
Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a
2 stroke bicycle engine upside down. Maybe upside down and backward.
If I did this the carb would need to be inverted because it is a float
bowl type carb. I suppose I could use a pumper type carb instead but I
don't know if I have one that is suitable as far as fuel and air flow
are concerned. Besides, small engine pumper carbs tend to be kind of
on/off devices in that they idle OK and and run wide open well but
don't do so well in the mid range throttle settings. I suppose I could
buy one but I'm cheap. So, if there is room to invert the carb what
else do I need to worry about? Will the crankcase tend to get too hot
since it will now be above the cylinder? And lets say that the engine
is not only inverted but also turned around. Now the engine will be
rotating the wrong way to drive the bike forward. Since the engine is
a two stroke it seems to me that I will only need to change the
ignition timing. I think this can be done simply by broaching a new
keyway in the spinning magnet flywheel. The ignition is a fully
electronic CDI type with no points. I assume the ignition works by
sensing the voltage rise in the magneto primary winding as there is no
other provision for detecting the position of the flywheel magnet.
Have I missed anything?

Is rebuilding an engine really the easier option here? I just can't
imagine that it is.

I have a bike with an engine strapped on. It's a decade old Golden Eagle
kit with the drive ring and belt and a 25cc Redmax weed wacker engine. The
only engine problems have been gas tank leaks from that ethanol **** in
the gas. It starts in negative temps, or with old gas. Very solid little
engine.

It sounds like you're going for the engine mounted inside the triangle of
the frame and not something strapped over the rear wheel though. The fake
motorcycle style is all I see these days. Never come across another belt
drive bike like I have yet.


The "Whizzer" motor bicycle, and motor kits for bicycles, was made
from around 1939 until about 2009 and there are some NOS still
available.


That's the style of kit I see in Chicago. I still prefer the leafblower
type as you just put a plastic bag over it and nobody knows it's a bike
with an engine.


Don't your "plastic bag" make a funny noise when you are driving?


The bag is for bringing it inside buildings where bikes are ok but not
other "vehicles".


  #18   Report Post  
Old October 26th 15, 10:06 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Apr 2008
Posts: 1,949
Default Mount a 2 stroke upside down?

On Sun, 25 Oct 2015 07:38:24 +0000, Charlie+ wrote:

On Wed, 21 Oct 2015 14:01:25 -0700, wrote as underneath
:

Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a
2 stroke bicycle engine upside down. Maybe upside down and backward.
If I did this the carb would need to be inverted because it is a float
bowl type carb. I suppose I could use a pumper type carb instead but I
don't know if I have one that is suitable as far as fuel and air flow
are concerned. Besides, small engine pumper carbs tend to be kind of
on/off devices in that they idle OK and and run wide open well but
don't do so well in the mid range throttle settings. I suppose I could
buy one but I'm cheap. So, if there is room to invert the carb what
else do I need to worry about? Will the crankcase tend to get too hot
since it will now be above the cylinder? And lets say that the engine
is not only inverted but also turned around. Now the engine will be
rotating the wrong way to drive the bike forward. Since the engine is
a two stroke it seems to me that I will only need to change the
ignition timing. I think this can be done simply by broaching a new
keyway in the spinning magnet flywheel. The ignition is a fully
electronic CDI type with no points. I assume the ignition works by
sensing the voltage rise in the magneto primary winding as there is no
other provision for detecting the position of the flywheel magnet.
Have I missed anything?
Thanks,
Eric


I just wonder if the ignition in a point-less system will work so well
if the flywheel rotation is reversed? With the points type magneto it
makes no difference but with the pointless type the system is optimised
with a mapped timed firing by potted electronic components built into
the coil assembly (hence the modern easy start 2-stroke systems) and the
coil can be much smaller and cheaper as the UHV is generated by
electronic circuitry rather than directly by the magneto. So- maybe the
mapping will not make the corrections in the right direction etc.? I
would anyway try running it in reverse with an electric drill etc. to
see how the ignition might work if you do this?! Just a thaught - I
havnt tried so absolutely no actual experience with running this type of
ignition in reverse, someone else here might have?! C+

Thanks for the reply Charlie. It would be a good idea to see when the
spark occurs. If, for example, it happens at 12 degrees before TDC
then I need to make sure it happens on the other side of TDC since the
crankshaft will be spinning the other way. Using a drill to spin the
engine so I can watch the spark timing is a good idea. The electronics
for the ignition are located away from the engine, it appears that the
magneto coil is only a coil and has no device for sensing crankshaft
position, so all the timing is done in the black box that is mounted
away from the engine. But I still need to see what the timing is to
make sure I get it right when reversing the engine.
Eric
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Old October 26th 15, 10:18 PM posted to rec.crafts.metalworking
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Posts: 12,505
Default Mount a 2 stroke upside down?

On Mon, 26 Oct 2015 14:06:48 -0700, wrote:

On Sun, 25 Oct 2015 07:38:24 +0000, Charlie+ wrote:

On Wed, 21 Oct 2015 14:01:25 -0700,
wrote as underneath
:

Because of the size and the way my bicycle frame is shaped it may be
more convenient, strictly from a mechanical point of view, to mount a
2 stroke bicycle engine upside down. Maybe upside down and backward.
If I did this the carb would need to be inverted because it is a float
bowl type carb. I suppose I could use a pumper type carb instead but I
don't know if I have one that is suitable as far as fuel and air flow
are concerned. Besides, small engine pumper carbs tend to be kind of
on/off devices in that they idle OK and and run wide open well but
don't do so well in the mid range throttle settings. I suppose I could
buy one but I'm cheap. So, if there is room to invert the carb what
else do I need to worry about? Will the crankcase tend to get too hot
since it will now be above the cylinder? And lets say that the engine
is not only inverted but also turned around. Now the engine will be
rotating the wrong way to drive the bike forward. Since the engine is
a two stroke it seems to me that I will only need to change the
ignition timing. I think this can be done simply by broaching a new
keyway in the spinning magnet flywheel. The ignition is a fully
electronic CDI type with no points. I assume the ignition works by
sensing the voltage rise in the magneto primary winding as there is no
other provision for detecting the position of the flywheel magnet.
Have I missed anything?
Thanks,
Eric


I just wonder if the ignition in a point-less system will work so well
if the flywheel rotation is reversed? With the points type magneto it
makes no difference but with the pointless type the system is optimised
with a mapped timed firing by potted electronic components built into
the coil assembly (hence the modern easy start 2-stroke systems) and the
coil can be much smaller and cheaper as the UHV is generated by
electronic circuitry rather than directly by the magneto. So- maybe the
mapping will not make the corrections in the right direction etc.? I
would anyway try running it in reverse with an electric drill etc. to
see how the ignition might work if you do this?! Just a thaught - I
havnt tried so absolutely no actual experience with running this type of
ignition in reverse, someone else here might have?! C+

Thanks for the reply Charlie. It would be a good idea to see when the
spark occurs. If, for example, it happens at 12 degrees before TDC
then I need to make sure it happens on the other side of TDC since the
crankshaft will be spinning the other way. Using a drill to spin the
engine so I can watch the spark timing is a good idea. The electronics
for the ignition are located away from the engine, it appears that the
magneto coil is only a coil and has no device for sensing crankshaft
position, so all the timing is done in the black box that is mounted
away from the engine. But I still need to see what the timing is to
make sure I get it right when reversing the engine.
Eric


Many of the very simple old 2-strokes just relied on the magnet
*leaving* the field to time the spark. Sort of time, that is. g As
the motor speeds up, the spark timing actually can advance a few
degrees that way.

You may be able to tell from the relative position of the magnet in
the flywheel, to the magneto coil, where the timing is. In any case,
it will give you guidance about setting it on the opposite side of TDC
if you want to run the motor in reverse.

--
Ed Huntress
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Old October 26th 15, 11:58 PM posted to rec.crafts.metalworking
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Default Mount a 2 stroke upside down?



Many of the very simple old 2-strokes just relied on the magnet
*leaving* the field to time the spark. Sort of time, that is. g As
the motor speeds up, the spark timing actually can advance a few
degrees that way.

You may be able to tell from the relative position of the magnet in
the flywheel, to the magneto coil, where the timing is. In any case,
it will give you guidance about setting it on the opposite side of TDC
if you want to run the motor in reverse.

I have worked on a lot of old two stroke motors, motors with cast iron
pistons, completely unbalanced cranks, and grease cups to lubricate
and seal the crankshaft where it exits the crankcase. And I have never
seen an ignition like that. The oldest magnetos I have seen had points
of some type. I can't see how leaving the magnetic field would cause a
spark. Can you explain it?
Eric


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