IN THE LAST column I wrote about lapping to free the needle
valve for smooth operation. The nonimbedding compound I
mentioned in that column is useful for other items in engine
rework.
I started flying Speed by competing in the Formula 40 event.
When I started I used a K&B 6.5 .40 engine. These are still
competitive in Formula 40, and they can often be purchased new
for roughly $70 on eBay.
The engine would fly my airplane in the 130-135 range right
out of the box. I took the engine apart to examine it and found that
I had to use a piece
of wood to pry the
liner out of the case.
After the liner
moved
approximately 3/8
inch, it came out
easily. The liner was
measured from just
How to lap in a case for proper liner fit
[Speedtimes@chartermi.net]
Control Line Speed Dave Mark
Also included in this column:
• Speed Times newsletter
archive CDs are available
from Chris Sackett
Go to http://community.webshots.com/user/clspeed to view more
than 500 pictures of CL Speed models and fliers.
A 22-year collection of Speed Times is available on CD from Tom
Wilk. The column contains additional information.
The backplate with the large pie-shaped opening Dave made
added a small amount to engine output, but not nearly as much as
correcting the internal fits in the case and shaft bearings.
below the top lip to the end and found to be straight within a few
ten thousandths of an inch.
I held the case up and looked inside and noticed that the liner
diameter had a good finish down to the area where the exhaust
opening in the case intersected the cylinder bore. From this point
down the finish was rough, and this was the area the liner was
sticking in.
The interrupted cut caused by the ports had caused the boring
tool to create a rough finish. It was still usable, but I felt that this
bind was probably getting worse when the engine was running.
To correct this I made a lap and used the TimeSaver Lapping
Compound to clean the rough area. I like to apply toolmaker layout
fluid to the area above the rough zone so I have a way to see when I
have gone far enough with the lapping.
The lap is uncomplicated. It is just a piece of cold-rolled 1018
steel that is turned a few thousandths smaller than the liner. The
end is threaded approximately 1/2-inch deep with a 3/8-inch tap.
Using a band saw or hacksaw, cut from the end roughly an inch
deep. Screw a short setscrew into the end until it just snugs up. Put
the lap back in the lathe and take a skim cut to bring the expanded
area back to size.
Mix the lapping compound with some light oil, and put the lap
into the case and drip the lapping compound onto the lap through
the exhaust port. Turn the lap by hand; you should feel some drag
on the lap as you turn it. Move the lap up and down so you are
lapping the full zone in the case that was tight. Stop. Clean the case
and look in the hole.
If you have not hit the blued area yet, tighten the setscrew a bit
and repeat the process. As you lap the bore in the case you will
probably find that six small, tight areas will show up at the top of
the case. They will be in line with the screw holes for the head. Lap
the bore until these clean up. Stop again and clean the bore.
Use acetone to remove the bluing and try the liner in the case. It
should go right to the lip on the liner in one smooth movement. If
the liner gets tighter at all as you install it, lap the case some more.
The liner must go in freely. This change alone caused a jump in
speed to the mid-140s.
Many people feel that to win in the Speed events they must have
a full machine shop to make exotic parts. This is seldom the case;
attention to small details will pay off many times.
The same year this case rework was tried, then-MA Speed
columnist Glenn Lee had a column published in the May 1996 issue
about lapping a cylinder to improve
performance. I strongly recommend that
anyone who is interested in tuning engines
download this from the AMA Web site.
After reading Glenn’s good information I
took my K&B apart and inspected the cylinder
liner. When I held the liner up to a bright light
I could not help but notice the shiny, highly
polished area around the transfer and exhaust
ports on the inside of the liner. The cause was
the piston’s rubbing tightly against this area as
the engine ran. This was not what I wanted in
a Speed engine.
I made a lap as described in Glenn’s
column and lapped the area with diamond dust
I obtained from a local supplier. Don’t let the
name fool you; diamond dust is inexpensive.
If you try this, use care; do not get carried
away.
Lap this area until the high shine
disappears, clean the parts, and fly the engine
to see if speeds improve. Fly it a few times,
and then take it apart and check it again for
shiny areas in the liner. If they show up, lap a
bit more.
These few changes produced an engine
that exceeded the 150 mark. I have not
replaced any of the basic engine parts; I just
cleaned up the engine fits to allow it to do its
job. I tried many other modifications, such as
new backplates with large pie-shaped
openings, different exhaust stub adapters, and
many heads. All of those made slight
improvements, but none produced the speed
increases the processes I have described in this
column did.
In the last column I mentioned the Speed
Times Technical Issue but did not do a good
job of describing how to obtain it. You can
purchase this publication by sending a check
for $10, made payable to the North American
Speed Society (NASS), to NASS at Box 371,
Fenton MI 48430.
NASS has also completed a project that
should be of great interest to anyone who is
interested in tuning engines or getting started
in Speed. Past issues of the Speed Times
newsletter—from the first issue Chris Sackett
put out in April 1982 to the December 2002
issue—will be available
Edition: Model Aviation - 2006/04
Page Numbers: 142,143
Edition: Model Aviation - 2006/04
Page Numbers: 142,143
IN THE LAST column I wrote about lapping to free the needle
valve for smooth operation. The nonimbedding compound I
mentioned in that column is useful for other items in engine
rework.
I started flying Speed by competing in the Formula 40 event.
When I started I used a K&B 6.5 .40 engine. These are still
competitive in Formula 40, and they can often be purchased new
for roughly $70 on eBay.
The engine would fly my airplane in the 130-135 range right
out of the box. I took the engine apart to examine it and found that
I had to use a piece
of wood to pry the
liner out of the case.
After the liner
moved
approximately 3/8
inch, it came out
easily. The liner was
measured from just
How to lap in a case for proper liner fit
[Speedtimes@chartermi.net]
Control Line Speed Dave Mark
Also included in this column:
• Speed Times newsletter
archive CDs are available
from Chris Sackett
Go to http://community.webshots.com/user/clspeed to view more
than 500 pictures of CL Speed models and fliers.
A 22-year collection of Speed Times is available on CD from Tom
Wilk. The column contains additional information.
The backplate with the large pie-shaped opening Dave made
added a small amount to engine output, but not nearly as much as
correcting the internal fits in the case and shaft bearings.
below the top lip to the end and found to be straight within a few
ten thousandths of an inch.
I held the case up and looked inside and noticed that the liner
diameter had a good finish down to the area where the exhaust
opening in the case intersected the cylinder bore. From this point
down the finish was rough, and this was the area the liner was
sticking in.
The interrupted cut caused by the ports had caused the boring
tool to create a rough finish. It was still usable, but I felt that this
bind was probably getting worse when the engine was running.
To correct this I made a lap and used the TimeSaver Lapping
Compound to clean the rough area. I like to apply toolmaker layout
fluid to the area above the rough zone so I have a way to see when I
have gone far enough with the lapping.
The lap is uncomplicated. It is just a piece of cold-rolled 1018
steel that is turned a few thousandths smaller than the liner. The
end is threaded approximately 1/2-inch deep with a 3/8-inch tap.
Using a band saw or hacksaw, cut from the end roughly an inch
deep. Screw a short setscrew into the end until it just snugs up. Put
the lap back in the lathe and take a skim cut to bring the expanded
area back to size.
Mix the lapping compound with some light oil, and put the lap
into the case and drip the lapping compound onto the lap through
the exhaust port. Turn the lap by hand; you should feel some drag
on the lap as you turn it. Move the lap up and down so you are
lapping the full zone in the case that was tight. Stop. Clean the case
and look in the hole.
If you have not hit the blued area yet, tighten the setscrew a bit
and repeat the process. As you lap the bore in the case you will
probably find that six small, tight areas will show up at the top of
the case. They will be in line with the screw holes for the head. Lap
the bore until these clean up. Stop again and clean the bore.
Use acetone to remove the bluing and try the liner in the case. It
should go right to the lip on the liner in one smooth movement. If
the liner gets tighter at all as you install it, lap the case some more.
The liner must go in freely. This change alone caused a jump in
speed to the mid-140s.
Many people feel that to win in the Speed events they must have
a full machine shop to make exotic parts. This is seldom the case;
attention to small details will pay off many times.
The same year this case rework was tried, then-MA Speed
columnist Glenn Lee had a column published in the May 1996 issue
about lapping a cylinder to improve
performance. I strongly recommend that
anyone who is interested in tuning engines
download this from the AMA Web site.
After reading Glenn’s good information I
took my K&B apart and inspected the cylinder
liner. When I held the liner up to a bright light
I could not help but notice the shiny, highly
polished area around the transfer and exhaust
ports on the inside of the liner. The cause was
the piston’s rubbing tightly against this area as
the engine ran. This was not what I wanted in
a Speed engine.
I made a lap as described in Glenn’s
column and lapped the area with diamond dust
I obtained from a local supplier. Don’t let the
name fool you; diamond dust is inexpensive.
If you try this, use care; do not get carried
away.
Lap this area until the high shine
disappears, clean the parts, and fly the engine
to see if speeds improve. Fly it a few times,
and then take it apart and check it again for
shiny areas in the liner. If they show up, lap a
bit more.
These few changes produced an engine
that exceeded the 150 mark. I have not
replaced any of the basic engine parts; I just
cleaned up the engine fits to allow it to do its
job. I tried many other modifications, such as
new backplates with large pie-shaped
openings, different exhaust stub adapters, and
many heads. All of those made slight
improvements, but none produced the speed
increases the processes I have described in this
column did.
In the last column I mentioned the Speed
Times Technical Issue but did not do a good
job of describing how to obtain it. You can
purchase this publication by sending a check
for $10, made payable to the North American
Speed Society (NASS), to NASS at Box 371,
Fenton MI 48430.
NASS has also completed a project that
should be of great interest to anyone who is
interested in tuning engines or getting started
in Speed. Past issues of the Speed Times
newsletter—from the first issue Chris Sackett
put out in April 1982 to the December 2002
issue—will be available