Technical Information

Replacement screws for Cox engines

Sometimes it can be difficult to obtain genuine Cox replacement parts. The following table lists some of the screws used on Cox engines.

Note: please check with your engine before you buy: - I will not take any responsibility for errors in the list. If you have additions or corrections I will be happy to add them to this page.

The thread dimensions are the usual US designation of the form "drill# - threads per inch". This means a #2-56 corresponds to a #2 drill and has 56 threads per inch. All screws are of the NC/UNC type.

ENGINE MODEL

ENGINE
SIZE

GLOW
HEAD

CYLINDER
NECK

BACK
PLATE

VENTURI

FUEL
TANK

PROP
SCREW

OLYMPIC DRUM VALVE

.15

¾-32

¾-32

13/16-32

3/8-32

 N/A

#8-32 X 1.5

OLYMPIC

.15

¾-32

¾-32

13/16-32

3/8-32

 N/A

#8-32 X 1.5

SPORTSMAN

.15

¾-32

¾-32

13/16-32

3/8-32

 N/A

#8-32 X 1.5
QUEEN BEE .074 .074 11/16-40 11/16-40 N/A N/A   #5-40 X 1.0

MEDALLION

.15

¾-32

13/16-32

13/16-32

N-A

 N/A

#8-32 X 1.5
MEDALLION .09 11/16-40 11/16-40 11/16-40 N/A N/A #6-32 X 1.25
MEDALLION .049 17/32-40 17/32-40   N/A N/A  

TD .09 R/C

.09

11/16-40

11/16-40

11/16-40

5/16-32

 N/A

#6-32 X 1.25

TD .09

.09

11/16-40

11/16-40

11/16-40

5/16-32

 N/A

#6-32 X 1.25

TD .050 R/C

.050

 

 

 

1/4-32

 N/A

#5-40 X 1.0
SPECIAL MARK II .15 ¾-32   13/16-32 3/8-32 N/A #8-32 X 1.5
TD SPECIAL MARK I .15 ¾-32   13/16-32 3/8-32 N/A #8-32 X 1.5
TD .15 .15 ¾-32 ¾-32 13/16-32 3/8-32 N/A #8-32 X 1.5

TD .051

.051

17/32-40

 

 

1/4-32

 N/A

#5-40 X 1.0

TD .049

.049

17/32-40

17/32-40

 

1/4-32

 N/A

#5-40 X 1.0

TD .020

.020

25/64-48

25/64-48

#2-56 X 1/4

 

 #2-56 X 1/4

#3-48 X 3/4

TD .010

.010

 

 

 

 

  

#2-56 X 5/8

DRAGONFLY

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40 X 1.0

RC BEE

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40 X 1.0

VENOM

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40

KILLER BEE

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40

KILLER BEE

.051

17/32-40

17/32-40

N/A

N/A

  

#5-40

RR 1

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40 X 1.0

TEXACO JR

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40 X 1.0

TEXACO

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40 X 1.0

BLACK WIDOW

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40 X 1.0

GOLDEN BEE

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40 X 1.0

QRC

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40

QZ

.049

17/32-40

17/32-40

N/A

N/A

  

#5-40

BABY BEE

.049

17/32-40

17/32-40

N/A

N/A

 #2-56 X 15/16

#5-40 X 1/2

PEE WEE

.020

25/64-48

 25/64-48

N/A

N/A

 #2-56 X 1/2

#3-48 X 1/2

SPACE HOPPER

.049

17/32-40

17/32-40

N/A

 

 N/A

#5-40

STRATO BUG

.049

17/32-40

 

N/A

N/A

  

#5-40

THERMAL HOPPER

.049

17/32-40

17/32-40

N/A

 

  

#5-40

SPACE BUG JR

.049

17/32-40

 

N/A

N/A

  

#5-40
SPACE BUG .049 17/32-40   N/A N/A   #5-40

SPACE BUG EARLY

.049

 

 

N/A

N/A

  

#5-40

 

Gas transfer systems in Cox .049 engines

The cylinders of these Cox engines came with three different porting systems. These differ in the arrangement and number of transfer channels. Initially these transfer channels were milled with a single milling operation, resulting in a single, wide transfer flute; cylinders could have a single or a pair of two opposing flutes.

With the development of the Tee Dee and Medallion series it was discovered that the addition of one or two narrow secondary flutes would increase performance notably. Therefore these engines were equipped with either a single boost flute (the Medallion family) or two boost flutes at each edge of the basic transfer flute. Only some of the Bee family engines were equipped with such cylinders, most noticeable the Venom engine.

An additional feature built into the cylinder is the height of the lower edge of the exhaust window. This edge can be machined low enough for the piston skirt to open a slot below the piston when the piston is at top dead center. This is called sub-piston induction because the engine can suck in an additional amount of air directly into the crankcase, thus bypassing the carburetor. This works only well as long as no muffler is used. A muffler would lead to the induction of exhaust gas instead of fresh air.

 

Cylinder  #

# of bypass
ports

# of boost flutes
per port

sub piston
induction

tapered
bore

used on

#1

2

0

YES

NO

290

#2

1

0

YES

NO

Golden Bee

#3

1

0

later: YES

NO

Mercedes car

#3

2

0

later: YES

NO

  

#4

2

2

YES

YES

Tee Dee .049

#5

2

2

YES

YES

Tee Dee .051

#6

2

0

NO

NO

  

#7

1

0

YES

NO

  

#8

1

0

NO

NO

cars

#9

?

?

?

?

?

#0

2

0

NO

NO

  

n.a.

2

1

YES

YES

Venom

Cylinders for Cox .15 engines

Last modification of this page: 21.05.18

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