HI, GANG! Last time we got together, in
the December issue, I described what
happened after the well-worn, and
somewhat corroded, crankshaft bearing let
go in the YS61 engine that powered my
Tiger 60. It’s a dandy airplane, and I love to
shoot tankfuls of touch-and-gos with it.
When a few bits of rust flaked off of the
bearing and scratched the piston and
cylinder liner, the first thing that went away
was—no, not the horsepower—the reliable
idle. A loss of idle reliability is often the
first sign that something is wrong with an
engine.
The rebuild will require new crankshaft
bearings to go along with the new piston/
liner I obtained from YS Parts and
Service.
Let’s do a how-to about changing
crankshaft bearings. If you are smart (as I
wasn’t), you’ll heed the warning signs that
the crankshaft bearings are in the beginning
stages of failure and replace them before
they damage other, more expensive engine
parts.
Those signs are:
1. A rumbly or gravelly feel and sound
as you turn the propeller back and forth.
2. A turbinelike whine.
3. A loss of idle reliability (which
happens for several reasons).
4. Visible rust when you remove the
crankcase backplate.
The rear bearing typically fails first,
although it is good practice to replace both
of them at the same time. The front bearing
rarely rusts like the rear one does, as a
result of being exposed to fuel. I prefer to
replace the OEM (original equipment
manufacturer) rear bearings with stainless
steel, because corrosion is the biggest
enemy.
To begin, disassemble the engine. Take
care to remove all gaskets, O-rings, and
plastic parts from the crankcase, because
the process of bearing removal involves
heat that can destroy them.
At this point, I prefer to clean the entire
engine using denatured alcohol. Not only is
it helpful when taking apart the power
plant, but the heat used in the bearingremoval
process will bake any crud onto the
engine’s innards, and that can complicate
the reassembly.
Removing the piston and connecting rod
from most engines requires that the cylinder
liner be lifted up out of the crankcase after
the cylinder head is removed. With the
piston at Top Dead Center, there is room to
slide the connecting rod aft and slide it off
of the crankpin.
There is usually
wiggling involved,
and gummed-up oil
and rust under the
piston can make this
difficult. Fourstrokes
require a bit
of extra care and
attention because of
the camshaft. Take
note of any timing
marks on the
camshaft with the
power plant at Top
Dead Center. If in
doubt, consult the
instructions that
came with the
engine or the
Internet!
It’s time to
remove the bearings.
You need special
tools. Make one
from a piece of 1/2-
inch-diameter wooden dowel, similar to the one in the pictures.
Taper it so that it fits snugly into the central passage on the
crankshaft, like a lollipop.
Remove the crankshaft from the engine. If it requires a bit of
persuasion, remove the drive washer and collet or keyway, and put
the prop nut back on the shaft so it protects the last thread.
Gently smack the engine head-on into the edge of your wooden
building tabletop (no hammers, please!) and be prepared to catch
the crank. Next, make sure that the back end of that wooden dowel
is the right size for pushing the front bearing out of the crankcase
later. Now we are ready.
With the engine thoroughly cleaned, grab it with a pair of visegrip
pliers by the mounting lug. Light your propane torch and
gently warm the bottom of the case, all around, for roughly one
minute. Hold the case nose-up and never park the flame on one
spot, because a lot of heat should not be necessary.
Sometimes the rear bearing will fall out on its own, but a sharp
rap against the tabletop, or wooden cutting block, will do the trick.
Quickly (before the aluminum cools) push the front bearing out with
the dowel and let everything cool completely before touching it!
Some of us prefer to use the oven for heating the crankcase, but
care must be taken not to set it higher than 300°. Temperatures near
350° can distort the case and ruin it. Place the engine nose-up on an
old cookie sheet and listen for the “tink” as the rear bearing drops.
Reclean the crankcase with alcohol and an old toothbrush, paying
special attention to the bearing seats.
Assemble the lollipop as shown, with the rear bearing firmly in
place against the crank disk. Have the front bearing ready, as well as
the deep socket wrench that you will use to press the front bearing
into place.
Warm the case with the torch, taking care to warm the front end
as much as the rest and, moving quickly, push the lollipop home and
place the front bearing onto the shaft. Push the whole mess together
using the socket against the outer race of the front bearing. Your
goal is to get both fully seated. Replace
the drive washer and any washers or
keys associated with it, and tighten a
propeller onto the engine so it is snug but
not tight.
The power plant might start to bind as
it cools; do not panic. Turn a hammer the
wrong way around; using the wooden
part, “ring” the crankcase like a bell. The
bearings will move a tiny fraction of a
thousandth of an inch and all will free
up. Retighten the propeller and repeat
until the engine is cool, the propeller is
tight, and everything rotates freely.
Some engines use sealed greased
bearings. For those without seals (not
metal shields), I like to wash the grease
out of them with mineral spirits, so that
the crankshaft binding test, described in
the preceding, is nice and sensitive.
Afterward I relube the bearings with
Mobil 1 synthetic oil and replace the
rubber seals, if any. The oil in the fuel
will replace it under running conditions.
All that remains is to reassemble the
engine. Take care to correctly orient the
piston and connecting rod. If there is any
question, the hole in the connecting rod
normally has a bigger chamfer on the
front edge. If the piston has a ring, take
care to orient it so that the ring collapses
properly into its groove, and carefully
slide the bottom edge of the cylinder
liner over it.
When reassembling, take extra care to
make sure that the carburetor is fully
seated and that all gaskets and screws are
properly tightened. Nothing ruins the
way a two-stroke runs as does an air leak
to the crankcase. For those of you with
four-strokes, take the time to check the
camshaft alignment twice before you put
on the cover.
Maybe someday I will go into more
detail about the innards of our engines,
but until then, have fun and do take care
of yourself. MA
Sources:
YS Parts and Service
(775) 267-9252
www.yspartsandservice.com
Edition: Model Aviation - 2010/02
Page Numbers: 77,78,80
Edition: Model Aviation - 2010/02
Page Numbers: 77,78,80
HI, GANG! Last time we got together, in
the December issue, I described what
happened after the well-worn, and
somewhat corroded, crankshaft bearing let
go in the YS61 engine that powered my
Tiger 60. It’s a dandy airplane, and I love to
shoot tankfuls of touch-and-gos with it.
When a few bits of rust flaked off of the
bearing and scratched the piston and
cylinder liner, the first thing that went away
was—no, not the horsepower—the reliable
idle. A loss of idle reliability is often the
first sign that something is wrong with an
engine.
The rebuild will require new crankshaft
bearings to go along with the new piston/
liner I obtained from YS Parts and
Service.
Let’s do a how-to about changing
crankshaft bearings. If you are smart (as I
wasn’t), you’ll heed the warning signs that
the crankshaft bearings are in the beginning
stages of failure and replace them before
they damage other, more expensive engine
parts.
Those signs are:
1. A rumbly or gravelly feel and sound
as you turn the propeller back and forth.
2. A turbinelike whine.
3. A loss of idle reliability (which
happens for several reasons).
4. Visible rust when you remove the
crankcase backplate.
The rear bearing typically fails first,
although it is good practice to replace both
of them at the same time. The front bearing
rarely rusts like the rear one does, as a
result of being exposed to fuel. I prefer to
replace the OEM (original equipment
manufacturer) rear bearings with stainless
steel, because corrosion is the biggest
enemy.
To begin, disassemble the engine. Take
care to remove all gaskets, O-rings, and
plastic parts from the crankcase, because
the process of bearing removal involves
heat that can destroy them.
At this point, I prefer to clean the entire
engine using denatured alcohol. Not only is
it helpful when taking apart the power
plant, but the heat used in the bearingremoval
process will bake any crud onto the
engine’s innards, and that can complicate
the reassembly.
Removing the piston and connecting rod
from most engines requires that the cylinder
liner be lifted up out of the crankcase after
the cylinder head is removed. With the
piston at Top Dead Center, there is room to
slide the connecting rod aft and slide it off
of the crankpin.
There is usually
wiggling involved,
and gummed-up oil
and rust under the
piston can make this
difficult. Fourstrokes
require a bit
of extra care and
attention because of
the camshaft. Take
note of any timing
marks on the
camshaft with the
power plant at Top
Dead Center. If in
doubt, consult the
instructions that
came with the
engine or the
Internet!
It’s time to
remove the bearings.
You need special
tools. Make one
from a piece of 1/2-
inch-diameter wooden dowel, similar to the one in the pictures.
Taper it so that it fits snugly into the central passage on the
crankshaft, like a lollipop.
Remove the crankshaft from the engine. If it requires a bit of
persuasion, remove the drive washer and collet or keyway, and put
the prop nut back on the shaft so it protects the last thread.
Gently smack the engine head-on into the edge of your wooden
building tabletop (no hammers, please!) and be prepared to catch
the crank. Next, make sure that the back end of that wooden dowel
is the right size for pushing the front bearing out of the crankcase
later. Now we are ready.
With the engine thoroughly cleaned, grab it with a pair of visegrip
pliers by the mounting lug. Light your propane torch and
gently warm the bottom of the case, all around, for roughly one
minute. Hold the case nose-up and never park the flame on one
spot, because a lot of heat should not be necessary.
Sometimes the rear bearing will fall out on its own, but a sharp
rap against the tabletop, or wooden cutting block, will do the trick.
Quickly (before the aluminum cools) push the front bearing out with
the dowel and let everything cool completely before touching it!
Some of us prefer to use the oven for heating the crankcase, but
care must be taken not to set it higher than 300°. Temperatures near
350° can distort the case and ruin it. Place the engine nose-up on an
old cookie sheet and listen for the “tink” as the rear bearing drops.
Reclean the crankcase with alcohol and an old toothbrush, paying
special attention to the bearing seats.
Assemble the lollipop as shown, with the rear bearing firmly in
place against the crank disk. Have the front bearing ready, as well as
the deep socket wrench that you will use to press the front bearing
into place.
Warm the case with the torch, taking care to warm the front end
as much as the rest and, moving quickly, push the lollipop home and
place the front bearing onto the shaft. Push the whole mess together
using the socket against the outer race of the front bearing. Your
goal is to get both fully seated. Replace
the drive washer and any washers or
keys associated with it, and tighten a
propeller onto the engine so it is snug but
not tight.
The power plant might start to bind as
it cools; do not panic. Turn a hammer the
wrong way around; using the wooden
part, “ring” the crankcase like a bell. The
bearings will move a tiny fraction of a
thousandth of an inch and all will free
up. Retighten the propeller and repeat
until the engine is cool, the propeller is
tight, and everything rotates freely.
Some engines use sealed greased
bearings. For those without seals (not
metal shields), I like to wash the grease
out of them with mineral spirits, so that
the crankshaft binding test, described in
the preceding, is nice and sensitive.
Afterward I relube the bearings with
Mobil 1 synthetic oil and replace the
rubber seals, if any. The oil in the fuel
will replace it under running conditions.
All that remains is to reassemble the
engine. Take care to correctly orient the
piston and connecting rod. If there is any
question, the hole in the connecting rod
normally has a bigger chamfer on the
front edge. If the piston has a ring, take
care to orient it so that the ring collapses
properly into its groove, and carefully
slide the bottom edge of the cylinder
liner over it.
When reassembling, take extra care to
make sure that the carburetor is fully
seated and that all gaskets and screws are
properly tightened. Nothing ruins the
way a two-stroke runs as does an air leak
to the crankcase. For those of you with
four-strokes, take the time to check the
camshaft alignment twice before you put
on the cover.
Maybe someday I will go into more
detail about the innards of our engines,
but until then, have fun and do take care
of yourself. MA
Sources:
YS Parts and Service
(775) 267-9252
www.yspartsandservice.com
Edition: Model Aviation - 2010/02
Page Numbers: 77,78,80
HI, GANG! Last time we got together, in
the December issue, I described what
happened after the well-worn, and
somewhat corroded, crankshaft bearing let
go in the YS61 engine that powered my
Tiger 60. It’s a dandy airplane, and I love to
shoot tankfuls of touch-and-gos with it.
When a few bits of rust flaked off of the
bearing and scratched the piston and
cylinder liner, the first thing that went away
was—no, not the horsepower—the reliable
idle. A loss of idle reliability is often the
first sign that something is wrong with an
engine.
The rebuild will require new crankshaft
bearings to go along with the new piston/
liner I obtained from YS Parts and
Service.
Let’s do a how-to about changing
crankshaft bearings. If you are smart (as I
wasn’t), you’ll heed the warning signs that
the crankshaft bearings are in the beginning
stages of failure and replace them before
they damage other, more expensive engine
parts.
Those signs are:
1. A rumbly or gravelly feel and sound
as you turn the propeller back and forth.
2. A turbinelike whine.
3. A loss of idle reliability (which
happens for several reasons).
4. Visible rust when you remove the
crankcase backplate.
The rear bearing typically fails first,
although it is good practice to replace both
of them at the same time. The front bearing
rarely rusts like the rear one does, as a
result of being exposed to fuel. I prefer to
replace the OEM (original equipment
manufacturer) rear bearings with stainless
steel, because corrosion is the biggest
enemy.
To begin, disassemble the engine. Take
care to remove all gaskets, O-rings, and
plastic parts from the crankcase, because
the process of bearing removal involves
heat that can destroy them.
At this point, I prefer to clean the entire
engine using denatured alcohol. Not only is
it helpful when taking apart the power
plant, but the heat used in the bearingremoval
process will bake any crud onto the
engine’s innards, and that can complicate
the reassembly.
Removing the piston and connecting rod
from most engines requires that the cylinder
liner be lifted up out of the crankcase after
the cylinder head is removed. With the
piston at Top Dead Center, there is room to
slide the connecting rod aft and slide it off
of the crankpin.
There is usually
wiggling involved,
and gummed-up oil
and rust under the
piston can make this
difficult. Fourstrokes
require a bit
of extra care and
attention because of
the camshaft. Take
note of any timing
marks on the
camshaft with the
power plant at Top
Dead Center. If in
doubt, consult the
instructions that
came with the
engine or the
Internet!
It’s time to
remove the bearings.
You need special
tools. Make one
from a piece of 1/2-
inch-diameter wooden dowel, similar to the one in the pictures.
Taper it so that it fits snugly into the central passage on the
crankshaft, like a lollipop.
Remove the crankshaft from the engine. If it requires a bit of
persuasion, remove the drive washer and collet or keyway, and put
the prop nut back on the shaft so it protects the last thread.
Gently smack the engine head-on into the edge of your wooden
building tabletop (no hammers, please!) and be prepared to catch
the crank. Next, make sure that the back end of that wooden dowel
is the right size for pushing the front bearing out of the crankcase
later. Now we are ready.
With the engine thoroughly cleaned, grab it with a pair of visegrip
pliers by the mounting lug. Light your propane torch and
gently warm the bottom of the case, all around, for roughly one
minute. Hold the case nose-up and never park the flame on one
spot, because a lot of heat should not be necessary.
Sometimes the rear bearing will fall out on its own, but a sharp
rap against the tabletop, or wooden cutting block, will do the trick.
Quickly (before the aluminum cools) push the front bearing out with
the dowel and let everything cool completely before touching it!
Some of us prefer to use the oven for heating the crankcase, but
care must be taken not to set it higher than 300°. Temperatures near
350° can distort the case and ruin it. Place the engine nose-up on an
old cookie sheet and listen for the “tink” as the rear bearing drops.
Reclean the crankcase with alcohol and an old toothbrush, paying
special attention to the bearing seats.
Assemble the lollipop as shown, with the rear bearing firmly in
place against the crank disk. Have the front bearing ready, as well as
the deep socket wrench that you will use to press the front bearing
into place.
Warm the case with the torch, taking care to warm the front end
as much as the rest and, moving quickly, push the lollipop home and
place the front bearing onto the shaft. Push the whole mess together
using the socket against the outer race of the front bearing. Your
goal is to get both fully seated. Replace
the drive washer and any washers or
keys associated with it, and tighten a
propeller onto the engine so it is snug but
not tight.
The power plant might start to bind as
it cools; do not panic. Turn a hammer the
wrong way around; using the wooden
part, “ring” the crankcase like a bell. The
bearings will move a tiny fraction of a
thousandth of an inch and all will free
up. Retighten the propeller and repeat
until the engine is cool, the propeller is
tight, and everything rotates freely.
Some engines use sealed greased
bearings. For those without seals (not
metal shields), I like to wash the grease
out of them with mineral spirits, so that
the crankshaft binding test, described in
the preceding, is nice and sensitive.
Afterward I relube the bearings with
Mobil 1 synthetic oil and replace the
rubber seals, if any. The oil in the fuel
will replace it under running conditions.
All that remains is to reassemble the
engine. Take care to correctly orient the
piston and connecting rod. If there is any
question, the hole in the connecting rod
normally has a bigger chamfer on the
front edge. If the piston has a ring, take
care to orient it so that the ring collapses
properly into its groove, and carefully
slide the bottom edge of the cylinder
liner over it.
When reassembling, take extra care to
make sure that the carburetor is fully
seated and that all gaskets and screws are
properly tightened. Nothing ruins the
way a two-stroke runs as does an air leak
to the crankcase. For those of you with
four-strokes, take the time to check the
camshaft alignment twice before you put
on the cover.
Maybe someday I will go into more
detail about the innards of our engines,
but until then, have fun and do take care
of yourself. MA
Sources:
YS Parts and Service
(775) 267-9252
www.yspartsandservice.com
