9 Cylinder Radial Build using Cox Sure Start 049's - RC Groups
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Dec 30, 2010, 01:05 AM
Double Naught Spy
iamplanecrazy2's Avatar
Build Log

9 Cylinder Radial Build using Cox Sure Start 049's

Early last week I started working on an engine project that I wasn't sure
I would be able to pull off. Well after a few sessions in the shop with it I
think I might actually get the thing built. Whether it will run or not is a whole
'nother story! It is a 9 cylinder radial built with parts from Cox Sure Start 049
engines. I got the idea from similar engines I have seen selling on eBay. I did
some research and found a neat article on the web about an engine that my
design is based on. Here is a link to give an idea of what my goal is.
John V Thompson "Trantula 9 Cylinder Radial"

I'm going to detail this well enough that should someone want to give it a
try they can follow along. If it gets boring let me know and I'll just go over
the highlights.

I started out by making a manifold out of a Cox 8cc Bee type fuel tank.
I thought it would be neat to use as many original Cox parts as possible
throughout the build. I built a jig to hold the tank as the holes are very
close together and tolerances must be close for it to work. Notice the paper
between the tank and the jig. It has lines marked at 40 degree angles. Nine
holes were needed. A circle is 360 degrees, divide that by 9 you get 40. So,
centering the holes at 40 degree intervals spaces them out just right. Jig
works by lining the bit up on the line and drilling the hole. Loosen the nut,
rotate the tank to the next line and drill again, and so on and so on.
Here are photos of this step. I have a good bit more work done but will have
to post more later.
By the way, I drilled the holes in 3 steps using gradually larger bits until I
reached the final size of 5/16". Holes are about 1/16" apart!
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Dec 30, 2010, 01:44 AM
Double Naught Spy
iamplanecrazy2's Avatar
How is that for some shade tree machine work! I meant to add that
I do not have a machine shop. I'm doing all of the work using what I
have, a drill press, band saw, stationary belt sander, ect. Pretty much
the tools you would find in an average to serious modelers shop.
Later I'll show how to turn your hand drill into a lathe! Yeeee Haaaaaa!

Anyway, onward with the build.

Next I modified the Sure Start back plates and choke tubes. The back plates
need to be cut down & the venturi tubes shortened. With the use of a jig this is easy to do on the
band saw. I mounted a Babe Bee case to a piece of plywood as a means of
holding the back plate so it could be rotated against the saw. A stop on the
fence controls the depth of the cut. A modified 5/16" socket and nut driver
do the rotating as this is so close to the saw blade. All I did to the socket is
cut a notch in it so it would go around the spray bar. this really worked out
well. Check out the photos and you will see just how easy this was.

The choke tubes will be used as fuel passages from the manifold. It is they
that the 8cc tank was drilled to accept. The choke tubes have been a bit of
a job to modify and I am not done with them yet. To start with I used the
bench grinder to get the bulk of unwanted material off of the tubes. Then,
I chucked up a piece of wood dowel in a drill and pressed the choke tube
over it. I clamped the drill in my bench vice and with a nice sharp chisel as a
cutting tool and a piece of 2X4 set on the bench as a tool rest I turned the
tubes down until each fit a hole in the manifold nice and snug. As work has
progressed I have found that the tubes will need to be turned so they can
slide farther into the manifold. They will then have to be shortened flush
with the inside of the manifold. But for now you should have the general
idea on how I modified them. Still need photos of my shade tree lathe!
Last edited by iamplanecrazy2; Dec 30, 2010 at 03:21 AM.
Dec 30, 2010, 01:54 AM
Double Naught Spy
iamplanecrazy2's Avatar
I decided to us a back plate off of a 3 1/2" aluminum spinner as a plate on
which to mount all of the Sure Starts. After some measuring I found that the
spinner itself will work as a nice shroud to cover all of the gearing and engine
cases. Just as prop blades would only the cylinders will protrude from the spinner. Can't wait to get that far along with this!

Anyway, here is a view of what the rear of the engine will look like. Keep in
mind that the choke tubes still need to be shortened a good bit.
Dec 30, 2010, 02:10 AM
Double Naught Spy
iamplanecrazy2's Avatar
Next I drilled the spinner back plate full of holes for attaching the Sure Start cases and
for the venturi tube passages. Another jig was necessary for this. Again I used a paper guide
marked with lines at 40 degree angles. As a drill guide I sacrificed a Babe Bee case by
drilling the bottom 2 mounting holes all the way through to the front with a 3/32" bit.
I then CA'ed the case to a piece of aircraft ply cut at a 40 degree angle and with a pivot
at the center. I bushed the opening in the spinner back plate so a 6-32 bolt fit snuggly
and attached the drill guide to it. On the drill press I drilled the 2 small holes first. Drilled
2 holes rotated to the next space and drilled 2 more and so on until all 9
sections were drilled. I then drilled the larger venturi passage holes. I drilled through
the Babe Bee case crank shaft opening with a 7/32" bit. I then removed the drill guide and
enlarged the 7/32" holes to 5/16".
The jig worked great! All the holes are where they need to be.
I hope to have the Sure Start case mods done in a day or so.
It will be nice seeing all 9 cases mounted up.
Will be posting that next.
Last edited by iamplanecrazy2; Dec 30, 2010 at 03:27 AM.
Dec 30, 2010, 04:54 AM
Suspended Account
this is looking very cool keep it up!!
Dec 30, 2010, 06:52 AM
Registered User
kerwin50's Avatar
Some years ago I seen either a 7 or 9 cyl cox that some one was making and selling.
Dec 30, 2010, 08:50 AM
Registered User
earlwb's Avatar
Fantastic job. Please keep us apprised of your progress. I can't wait to see it all done.
Dec 31, 2010, 02:07 AM
Double Naught Spy
iamplanecrazy2's Avatar
Thanks fellas! I'll definitely keep posting as I go along.
Did some head scratching today over what to use for a prop shaft. Came
upon what I think will turn out to be a good solution. I thought of how an
O&R (Ohlsson & Rice) engine has a thrust bearing that the crank web rides
against and happened to have a partial O&R 23 so gave the crank a look and
came up with the idea of modifying a crank from some engine to use as a
prop shaft. The O&R crank is to short and its prop driver set up won't do but
I hope that I can find a crank of suitable length and diameter with a
stout prop drive set up that I can make work. The plan is to grind the crank
pin side of the crank flat and grind the crank web down leaving only a flat
for a thrust bearing to ride on.
It is tough to explain but if you look at the drawing of John V Thompson's
"Trantula 9 Cylinder Radial" on this page: http://modelenginenews.org/cardfile/tarantula.html
by looking at how the crank is set up you will get the idea.
I'm also posting some photos that should help explain.

The problem with my idea is that the modified end of the crank will be inside the
intake manifold where there can't be any air leaking in and the thickness of
the modified web (especially with the thrust bearing and
washer under it) will be an issue as it will interfere with the venturi tubes
that fit into the manifold. The air leak can be stopped with a cap and the thickness
can be solved by cutting a recess for the bearing and washer. Problem for me
is a lack of real machine tools for doing it. I might have to go to a friend for
help with this part. I'll get a photo posted that will help show what I'm getting
at. I'll use the O&R crank and another spinner back plate for examples. I'm
thinking an OS 40 FP crank might work but will have to take one I have
apart to find out. Anyway here is a photo and sorry for being so long winded!

Oh, I added a photo showing how the cases will be modified. Notice the bottom
screw lugs have been ground off. This allows the cases to be mounted further
towards the center of the plate. This reduced the overall diameter of the engine
by about 5/8". It also reduces the weight. In place of the 2 screws I'll add one
screw at the center of the case about where the red dot is in the photo. That will
total 9 screws that will pull a plate down to rest on the lip at the middle of the case.
This plate will house the front prop shaft bearing as well as hold down the bottom
of each case. Does this make sense? I hope so. Photos should help and this part
of the build is coming up next so should be very clear in a couple of days.

Happy New Year to All!!

Last edited by iamplanecrazy2; Dec 31, 2010 at 02:17 AM.
Dec 31, 2010, 02:40 AM
Grumpa Tom
Kmot's Avatar
This is awesome! Definitely going to follow this!
Dec 31, 2010, 02:38 PM
Double Naught Spy
iamplanecrazy2's Avatar
After spending some time measuring several different crank shafts it appears
that the idea isn't going to work. The prop shaft is definitely going to be the
toughest part of the project. Will probably result in the need of a real machinist.
I do have a 6" Craftsman (Atlas) lathe. I have never used it as it is missing some
parts. I have often searched eBay for parts and they are readily available but
they aren't cheap. This might just be what it will take for me to get the lathe up
and running. I guess having never used a lathe I have been a bit intimidated by
it. I'll just have to get it going and give it a shot. Have not finished the case mods
but am working on them!
Dec 31, 2010, 09:11 PM
Registered User
Originally Posted by iamplanecrazy2
After spending some time measuring several different crank shafts it appears
that the idea isn't going to work. The prop shaft is definitely going to be the
toughest part of the project. Will probably result in the need of a real machinist.
I do have a 6" Craftsman (Atlas) lathe. I have never used it as it is missing some
parts. I have often searched eBay for parts and they are readily available but
they aren't cheap. This might just be what it will take for me to get the lathe up
and running. I guess having never used a lathe I have been a bit intimidated by
it. I'll just have to get it going and give it a shot. Have not finished the case mods
but am working on them!
Nice work on the Cox Radial... I haven't seen this done before!

I have a old Craftsman 109.21270 lathe I've done a little work on. There is a great message forum for the 109 lathes that might help get you some tips to get it in order. The guys on there are very helpful and respond quickly.

Jan 02, 2011, 05:08 PM
Registered User
i-fly-any-and-'s Avatar
let us know if you need anything turned on a "real lathe or done on a bridgeport vertical milll". LOL I'm a machinist so I'm interested in watching your progress. remember tolerance is the key to success. keep tolerance to 2 to 3 thousandths of an inch (+ or - .002, .003).
Jan 03, 2011, 01:36 PM
T.L.A.R. eng
I love seeing these kinds of builds, shows what some thought and determination can accomplish.
However if some suggestions could be offered?

Unless all nine cylinders intake at the same time and the engine runs at 274.3 gazzilion rpms, your carb area is way too big for the .049 cylinder. You will probably have to sleeve the venturi down to a more reasonable size.

A distribution fan inside the intake housing would certainly help with the mixture distribution problems that are common with radial engines.

I don't want to rain on anyone project, but I know from experience what works and what won't. I much rather see a successfull running project.

Don't stop, it is great way to learn and have FUN doing it.
Jan 03, 2011, 07:37 PM
Suspended Account
Yep , got my attention , and I hope there will be Video of the finished product running !
Jan 04, 2011, 03:33 PM
Double Naught Spy
iamplanecrazy2's Avatar
Thanks for the interest everyone. I have not been in the shop for a few days. Hope to
get some time in today.

GEARHEAD, thanks for the link. That will be a very helpful site for sure. I have been
spending a good bit of time watching videos on YouTube. Came upon this man whose
videos are going to be a lot of help getting familiar with the lathe:
http://www.youtube.com/user/mrpete222 This guy casts his own parts and machines them. Really
amazing. Check out his 10 part series on building a model steam engine:
BUILDING A MODEL STEAM ENGINE part 1 tubalcain (9 min 7 sec)

i-fly-any-and-, a big thanks for your offer of machining help! I'll definitely let you know.

T.L.A.R., thanks for the input. I have had doubts about the venturi diameter and the
volume of the manifold. Figured that issue would be solved during the test runs. There
is also the issue of the size of the air/fuel passage in the back plates. Cutting off the
portion that housed the spray bar has enlarged the passage a great deal. I believe I
have that solved and will post some photos.

init4fun I sure plan on finishing this project and sure will be posting a video of the
test runs. It is bound to at least make some noise burning off primes!

My biggest concern has become the aquisition of the gears. I found what I need and
wouldn't you know it, there is going to be a 6 to 8 week wait on them as they are
out of stock and on back order.

Anybody know who can cut spur gears?

I know a man in Australia that made some gears for a Nylint Real McCoy tether
car conversion I did. I'll have to give him a try on these.

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