Also included in this column:
• Making your own gaskets
• Joe builds a “PAWllson”
Alternatives to chroming for enhanced compression
The Engine Shop Joe Wagner | [email protected]
Not much “tooling” is needed to make replacement gaskets for engines such as this
K&B Green Head .29. (The freebie CD-ROM makes a great cutting base!)
RCV engines provide good proof that snappy “cold compression” isn’t a necessity for a
fine-performing model engine.
IRV ST. GEORGE (Selah WA) wrote to
me about a problem with a SuperTigre .40
he owns. According to him, “It runs good,
and I like it. But it has very low
compression.” Irv went on to mention his
idea of having the SuperTigre’s piston
chrome plated to improve the engine’s
compression.
I replied that chrome-plating a sportflying
model engine piston merely to boost
“cold compression” isn’t likely to be worth
the time, cost, or trouble it takes to achieve
the proper-running fit. Chromium plating
for “engineering purposes” is far more
involved and costly than applying
decorative chrome.
I wrote to him that true, snappy cold
compression makes an engine feel potent
when you flip its propeller, but that
doesn’t necessarily have much beneficial
effect on the running engine. (It does help
in hand-starting.)
Decades ago, one of my favorite CL
Precision Aerobatics (Stunt) models was
powered by a well-used McCoy .19. Its
piston was so worn that a vigorous flip
could spin the propeller through two or
even three complete revolutions.
To start that engine I’d squirt a shot of
3-In-One oil into the exhaust just before
hooking up the glow plug. Then once I got
the engine going, it ran fine and delivered
ample power. My friend and champion
Stunt flier Bob Palmer had a Mac .19 that
was as worn as mine was. He’s the one
who taught me the trick of how to start it.
More recently I acquired three varioussized
RCV engines. These are fourstrokers
with an unusual valveless design,
in which the cylinder rotates as the engine
runs. Most of the moving parts are
lubricated by oil that is forced through the
clearance between the rotating cylinder
and its housing.
Because of that clearance, none of my
three RCVs has much cold compression.
Yet all of them start easily and run
extremely well at any speed, from idling to
maximum rpm.
106 MODEL AVIATION
April 2006 107
The vintage Ohlsson .60 on the left shows how well a PAW RC .19 diesel can be
disguised to look like an antique spark-ignition power plant.
The PAW .19 is bolted to a standard molded plastic mount. The dummy O&R .60 is
too, via an internal screw that is accessed by the spark-plug hole.
Another faked model engine. This adds authentic looks to an
electric-powered miniature version of the Good brothers’
famous 1938 RC Big Guff.
Irv didn’t indicate what fuel he was
using. I assume it’s one of the commercial
brands. Try adding a 4-ounce bottle of
drugstore castor oil to a quart of glow fuel.
That should improve the SuperTigre’s cold
compression—and it will require no
additional break-in time (as a chromed
piston would). It will probably add a
couple hundred to the top-end rpm too.
I regularly receive inquiries from readers
about where to obtain gaskets, and I
regularly reply that I don’t know. That’s
because for more than 30 years I’ve been
making my own replacement gaskets for
model engines. It’s neither difficult nor
expensive, but the work does require
patience.
The main tool I use is a modified
draftsman’s compass—not the friction-set
type, but the rigid, screw-adjusting style.
(They are available inexpensively from
Office Depot and Office Max.) I replace
the 2mm pencil lead with a short piece of
3/32-inch music wire sharpened to a 45°
knife edge. Of course, the lead-holding
clamp of the compass needs to be drilled
out with a 3/32-inch drill bit—do that by
hand—to accept the wire.
Sharpening the music wire calls for
care and patience to avoid overheating the
hard steel and destroying its temper. I do
most of my own knife-edge shaping on a
fine-grit grinding wheel—but not the usual
way.
I dampen the wheel surface with a
sponge, and then I turn on the engine just
long enough to get the wheel spinning at
roughly half its normal speed. Then I turn
it off and let it coast.
The slow-spinning, moist grinding
surface removes metal slowly and doesn’t
build up heat. When I eventually get the
knife-edge shape I want, I finish the
sharpening job by hand on an oilstone until
the cutting point is keen enough to slice
tissue paper.
Gasket material can be any of several
types. I’ve even used drop-out reply cards
from magazines for crankcase gaskets. But automotive Vellumoid
or the like (available at auto-parts dealers) works better, especially
for sealing as-cast surfaces such as the case covers for 1950-era
K&B Torpedos. Never use Vellumoid for head gaskets; it will
char and burn.
(Vellumoid comes in roll form. It’s stiff and wants to remain
curved, but it can easily be flattened by soaking it in hot water and
then ironing it dry with a MonoKote iron.)
Cutting the gaskets takes persistence. Many light passes are
needed. Pressing too hard will only distort the material and can
cause the cutting edge to dig in and go off its path.
Something that helps greatly is a firm undersurface upon which
to do the gasket cutting. And here, at long last, is a use for the
free-offer CD-ROMs that keep coming in our mail! The plastic in
those disks is hard enough to provide firm support under the
cutting edge, and it won’t let the center point of the compass bury
itself the way a wooden cutting support will invariably do.
This method also works with thin aluminum. I’ve cut many
head gaskets from pop-can bottoms. With the compass positioned
in the center of the can bottom, the resulting ring gasket has a
“Belleville Washer” cross-section that ensures leakproof sealing.
With care, thin, flat sheet aluminum (such as the pull-off tops
favorite models are the prewar “cabin”
types that look much like the Rearwin
Cloudsters and Stinson Detroiters of that
period. And one of those designs that has
appealed to me for a long time is
Berkeley’s 1940 Buccaneer C Special.
(Copies of the original plans for it are
available from AMA.)
The C Special version of the Buccaneer
was powered by the then-new Ohlsson .60.
I’ll build my own RC Assist model as
close to the original Berkeley design as I
can—with my “PAWllson .1960” in its
nose for maximum authenticity.
There are more ways of enjoying
working (and playing) with model engines
than the usual. My PAWllson isn’t the first
time I’ve used a dummy engine to disguise
the real power provider either.
Awhile back I wanted to build an
electric-powered miniature replica of the
Good brothers’ famous pioneer RC
airplane: the 8-foot-wingspan Big Guff.
The original 1938 version was powered by
a Brown engine.
Therefore, I made a Scale model of the
Brown for the prop shaft of my geared
HiLine micro motor to pass through. The
same kind of thing could be done, and
probably has been, with bigger motors
disguised with the exterior parts of gas
engines.
In the December column I mentioned
working up a flight-prediction computer
program to help modelers determine, with
minimal trial and error, the best propellers
and engines to use for their RC projects. I
received a tremendous response to that,
with many offers of help and even more
requests for copies of the software.
However, my progress on completing
that project was slowed considerably by the
severe illness and recent death of my wife.
By the time you read this a greatly enhanced
and upgraded-to-Windows version of my
original ENGPOWER.BAS program should
be available on a CD-ROM. E-mail me for
further information. MA
Edition: Model Aviation - 2006/04
Page Numbers: 106,107,108
Edition: Model Aviation - 2006/04
Page Numbers: 106,107,108
Also included in this column:
• Making your own gaskets
• Joe builds a “PAWllson”
Alternatives to chroming for enhanced compression
The Engine Shop Joe Wagner | [email protected]
Not much “tooling” is needed to make replacement gaskets for engines such as this
K&B Green Head .29. (The freebie CD-ROM makes a great cutting base!)
RCV engines provide good proof that snappy “cold compression” isn’t a necessity for a
fine-performing model engine.
IRV ST. GEORGE (Selah WA) wrote to
me about a problem with a SuperTigre .40
he owns. According to him, “It runs good,
and I like it. But it has very low
compression.” Irv went on to mention his
idea of having the SuperTigre’s piston
chrome plated to improve the engine’s
compression.
I replied that chrome-plating a sportflying
model engine piston merely to boost
“cold compression” isn’t likely to be worth
the time, cost, or trouble it takes to achieve
the proper-running fit. Chromium plating
for “engineering purposes” is far more
involved and costly than applying
decorative chrome.
I wrote to him that true, snappy cold
compression makes an engine feel potent
when you flip its propeller, but that
doesn’t necessarily have much beneficial
effect on the running engine. (It does help
in hand-starting.)
Decades ago, one of my favorite CL
Precision Aerobatics (Stunt) models was
powered by a well-used McCoy .19. Its
piston was so worn that a vigorous flip
could spin the propeller through two or
even three complete revolutions.
To start that engine I’d squirt a shot of
3-In-One oil into the exhaust just before
hooking up the glow plug. Then once I got
the engine going, it ran fine and delivered
ample power. My friend and champion
Stunt flier Bob Palmer had a Mac .19 that
was as worn as mine was. He’s the one
who taught me the trick of how to start it.
More recently I acquired three varioussized
RCV engines. These are fourstrokers
with an unusual valveless design,
in which the cylinder rotates as the engine
runs. Most of the moving parts are
lubricated by oil that is forced through the
clearance between the rotating cylinder
and its housing.
Because of that clearance, none of my
three RCVs has much cold compression.
Yet all of them start easily and run
extremely well at any speed, from idling to
maximum rpm.
106 MODEL AVIATION
April 2006 107
The vintage Ohlsson .60 on the left shows how well a PAW RC .19 diesel can be
disguised to look like an antique spark-ignition power plant.
The PAW .19 is bolted to a standard molded plastic mount. The dummy O&R .60 is
too, via an internal screw that is accessed by the spark-plug hole.
Another faked model engine. This adds authentic looks to an
electric-powered miniature version of the Good brothers’
famous 1938 RC Big Guff.
Irv didn’t indicate what fuel he was
using. I assume it’s one of the commercial
brands. Try adding a 4-ounce bottle of
drugstore castor oil to a quart of glow fuel.
That should improve the SuperTigre’s cold
compression—and it will require no
additional break-in time (as a chromed
piston would). It will probably add a
couple hundred to the top-end rpm too.
I regularly receive inquiries from readers
about where to obtain gaskets, and I
regularly reply that I don’t know. That’s
because for more than 30 years I’ve been
making my own replacement gaskets for
model engines. It’s neither difficult nor
expensive, but the work does require
patience.
The main tool I use is a modified
draftsman’s compass—not the friction-set
type, but the rigid, screw-adjusting style.
(They are available inexpensively from
Office Depot and Office Max.) I replace
the 2mm pencil lead with a short piece of
3/32-inch music wire sharpened to a 45°
knife edge. Of course, the lead-holding
clamp of the compass needs to be drilled
out with a 3/32-inch drill bit—do that by
hand—to accept the wire.
Sharpening the music wire calls for
care and patience to avoid overheating the
hard steel and destroying its temper. I do
most of my own knife-edge shaping on a
fine-grit grinding wheel—but not the usual
way.
I dampen the wheel surface with a
sponge, and then I turn on the engine just
long enough to get the wheel spinning at
roughly half its normal speed. Then I turn
it off and let it coast.
The slow-spinning, moist grinding
surface removes metal slowly and doesn’t
build up heat. When I eventually get the
knife-edge shape I want, I finish the
sharpening job by hand on an oilstone until
the cutting point is keen enough to slice
tissue paper.
Gasket material can be any of several
types. I’ve even used drop-out reply cards
from magazines for crankcase gaskets. But automotive Vellumoid
or the like (available at auto-parts dealers) works better, especially
for sealing as-cast surfaces such as the case covers for 1950-era
K&B Torpedos. Never use Vellumoid for head gaskets; it will
char and burn.
(Vellumoid comes in roll form. It’s stiff and wants to remain
curved, but it can easily be flattened by soaking it in hot water and
then ironing it dry with a MonoKote iron.)
Cutting the gaskets takes persistence. Many light passes are
needed. Pressing too hard will only distort the material and can
cause the cutting edge to dig in and go off its path.
Something that helps greatly is a firm undersurface upon which
to do the gasket cutting. And here, at long last, is a use for the
free-offer CD-ROMs that keep coming in our mail! The plastic in
those disks is hard enough to provide firm support under the
cutting edge, and it won’t let the center point of the compass bury
itself the way a wooden cutting support will invariably do.
This method also works with thin aluminum. I’ve cut many
head gaskets from pop-can bottoms. With the compass positioned
in the center of the can bottom, the resulting ring gasket has a
“Belleville Washer” cross-section that ensures leakproof sealing.
With care, thin, flat sheet aluminum (such as the pull-off tops
favorite models are the prewar “cabin”
types that look much like the Rearwin
Cloudsters and Stinson Detroiters of that
period. And one of those designs that has
appealed to me for a long time is
Berkeley’s 1940 Buccaneer C Special.
(Copies of the original plans for it are
available from AMA.)
The C Special version of the Buccaneer
was powered by the then-new Ohlsson .60.
I’ll build my own RC Assist model as
close to the original Berkeley design as I
can—with my “PAWllson .1960” in its
nose for maximum authenticity.
There are more ways of enjoying
working (and playing) with model engines
than the usual. My PAWllson isn’t the first
time I’ve used a dummy engine to disguise
the real power provider either.
Awhile back I wanted to build an
electric-powered miniature replica of the
Good brothers’ famous pioneer RC
airplane: the 8-foot-wingspan Big Guff.
The original 1938 version was powered by
a Brown engine.
Therefore, I made a Scale model of the
Brown for the prop shaft of my geared
HiLine micro motor to pass through. The
same kind of thing could be done, and
probably has been, with bigger motors
disguised with the exterior parts of gas
engines.
In the December column I mentioned
working up a flight-prediction computer
program to help modelers determine, with
minimal trial and error, the best propellers
and engines to use for their RC projects. I
received a tremendous response to that,
with many offers of help and even more
requests for copies of the software.
However, my progress on completing
that project was slowed considerably by the
severe illness and recent death of my wife.
By the time you read this a greatly enhanced
and upgraded-to-Windows version of my
original ENGPOWER.BAS program should
be available on a CD-ROM. E-mail me for
further information. MA
Edition: Model Aviation - 2006/04
Page Numbers: 106,107,108
Also included in this column:
• Making your own gaskets
• Joe builds a “PAWllson”
Alternatives to chroming for enhanced compression
The Engine Shop Joe Wagner | [email protected]
Not much “tooling” is needed to make replacement gaskets for engines such as this
K&B Green Head .29. (The freebie CD-ROM makes a great cutting base!)
RCV engines provide good proof that snappy “cold compression” isn’t a necessity for a
fine-performing model engine.
IRV ST. GEORGE (Selah WA) wrote to
me about a problem with a SuperTigre .40
he owns. According to him, “It runs good,
and I like it. But it has very low
compression.” Irv went on to mention his
idea of having the SuperTigre’s piston
chrome plated to improve the engine’s
compression.
I replied that chrome-plating a sportflying
model engine piston merely to boost
“cold compression” isn’t likely to be worth
the time, cost, or trouble it takes to achieve
the proper-running fit. Chromium plating
for “engineering purposes” is far more
involved and costly than applying
decorative chrome.
I wrote to him that true, snappy cold
compression makes an engine feel potent
when you flip its propeller, but that
doesn’t necessarily have much beneficial
effect on the running engine. (It does help
in hand-starting.)
Decades ago, one of my favorite CL
Precision Aerobatics (Stunt) models was
powered by a well-used McCoy .19. Its
piston was so worn that a vigorous flip
could spin the propeller through two or
even three complete revolutions.
To start that engine I’d squirt a shot of
3-In-One oil into the exhaust just before
hooking up the glow plug. Then once I got
the engine going, it ran fine and delivered
ample power. My friend and champion
Stunt flier Bob Palmer had a Mac .19 that
was as worn as mine was. He’s the one
who taught me the trick of how to start it.
More recently I acquired three varioussized
RCV engines. These are fourstrokers
with an unusual valveless design,
in which the cylinder rotates as the engine
runs. Most of the moving parts are
lubricated by oil that is forced through the
clearance between the rotating cylinder
and its housing.
Because of that clearance, none of my
three RCVs has much cold compression.
Yet all of them start easily and run
extremely well at any speed, from idling to
maximum rpm.
106 MODEL AVIATION
April 2006 107
The vintage Ohlsson .60 on the left shows how well a PAW RC .19 diesel can be
disguised to look like an antique spark-ignition power plant.
The PAW .19 is bolted to a standard molded plastic mount. The dummy O&R .60 is
too, via an internal screw that is accessed by the spark-plug hole.
Another faked model engine. This adds authentic looks to an
electric-powered miniature version of the Good brothers’
famous 1938 RC Big Guff.
Irv didn’t indicate what fuel he was
using. I assume it’s one of the commercial
brands. Try adding a 4-ounce bottle of
drugstore castor oil to a quart of glow fuel.
That should improve the SuperTigre’s cold
compression—and it will require no
additional break-in time (as a chromed
piston would). It will probably add a
couple hundred to the top-end rpm too.
I regularly receive inquiries from readers
about where to obtain gaskets, and I
regularly reply that I don’t know. That’s
because for more than 30 years I’ve been
making my own replacement gaskets for
model engines. It’s neither difficult nor
expensive, but the work does require
patience.
The main tool I use is a modified
draftsman’s compass—not the friction-set
type, but the rigid, screw-adjusting style.
(They are available inexpensively from
Office Depot and Office Max.) I replace
the 2mm pencil lead with a short piece of
3/32-inch music wire sharpened to a 45°
knife edge. Of course, the lead-holding
clamp of the compass needs to be drilled
out with a 3/32-inch drill bit—do that by
hand—to accept the wire.
Sharpening the music wire calls for
care and patience to avoid overheating the
hard steel and destroying its temper. I do
most of my own knife-edge shaping on a
fine-grit grinding wheel—but not the usual
way.
I dampen the wheel surface with a
sponge, and then I turn on the engine just
long enough to get the wheel spinning at
roughly half its normal speed. Then I turn
it off and let it coast.
The slow-spinning, moist grinding
surface removes metal slowly and doesn’t
build up heat. When I eventually get the
knife-edge shape I want, I finish the
sharpening job by hand on an oilstone until
the cutting point is keen enough to slice
tissue paper.
Gasket material can be any of several
types. I’ve even used drop-out reply cards
from magazines for crankcase gaskets. But automotive Vellumoid
or the like (available at auto-parts dealers) works better, especially
for sealing as-cast surfaces such as the case covers for 1950-era
K&B Torpedos. Never use Vellumoid for head gaskets; it will
char and burn.
(Vellumoid comes in roll form. It’s stiff and wants to remain
curved, but it can easily be flattened by soaking it in hot water and
then ironing it dry with a MonoKote iron.)
Cutting the gaskets takes persistence. Many light passes are
needed. Pressing too hard will only distort the material and can
cause the cutting edge to dig in and go off its path.
Something that helps greatly is a firm undersurface upon which
to do the gasket cutting. And here, at long last, is a use for the
free-offer CD-ROMs that keep coming in our mail! The plastic in
those disks is hard enough to provide firm support under the
cutting edge, and it won’t let the center point of the compass bury
itself the way a wooden cutting support will invariably do.
This method also works with thin aluminum. I’ve cut many
head gaskets from pop-can bottoms. With the compass positioned
in the center of the can bottom, the resulting ring gasket has a
“Belleville Washer” cross-section that ensures leakproof sealing.
With care, thin, flat sheet aluminum (such as the pull-off tops
favorite models are the prewar “cabin”
types that look much like the Rearwin
Cloudsters and Stinson Detroiters of that
period. And one of those designs that has
appealed to me for a long time is
Berkeley’s 1940 Buccaneer C Special.
(Copies of the original plans for it are
available from AMA.)
The C Special version of the Buccaneer
was powered by the then-new Ohlsson .60.
I’ll build my own RC Assist model as
close to the original Berkeley design as I
can—with my “PAWllson .1960” in its
nose for maximum authenticity.
There are more ways of enjoying
working (and playing) with model engines
than the usual. My PAWllson isn’t the first
time I’ve used a dummy engine to disguise
the real power provider either.
Awhile back I wanted to build an
electric-powered miniature replica of the
Good brothers’ famous pioneer RC
airplane: the 8-foot-wingspan Big Guff.
The original 1938 version was powered by
a Brown engine.
Therefore, I made a Scale model of the
Brown for the prop shaft of my geared
HiLine micro motor to pass through. The
same kind of thing could be done, and
probably has been, with bigger motors
disguised with the exterior parts of gas
engines.
In the December column I mentioned
working up a flight-prediction computer
program to help modelers determine, with
minimal trial and error, the best propellers
and engines to use for their RC projects. I
received a tremendous response to that,
with many offers of help and even more
requests for copies of the software.
However, my progress on completing
that project was slowed considerably by the
severe illness and recent death of my wife.
By the time you read this a greatly enhanced
and upgraded-to-Windows version of my
original ENGPOWER.BAS program should
be available on a CD-ROM. E-mail me for
further information. MA