Cylinder Identification

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Cylinder Identification

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May-2023
sosam117's

"Pre-1956 Thermal Hopper -- cleaned and completely rebuilt."

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Choosing a cylinder for an engine is not always that easy that is if you are looking for performance.
Here is a chart of Cox cylinders and their numbers.
(These are all .049/.051 cylinders)

Number	Description
1	Used on early Black Widow and 290-291 series engines. 2 bypass, sub-piston induction, some cylinders had milled top fins and some older ones didn't.
2	Used on Golden Bee and older Babe Bee engines. Single bypass, sub-piston induction, top fin not milled.
3	This number was used on lots of different cylinders. The Venom used a #3 (or 4, see below) cylinder that was 2 bypass, 1 booster, sub-piston induction, tapered, top fin milled.
4	Used on T.D. .049 engines. 2 bypass, 2 booster on each bypass, each with 3 separate milling cuts, sub-piston induction, top fin milled, has tapered grind. Sometime in the 1980s, TD cylinders were no longer tapered. This number has also been seen on the Venom .049 which is a 2 bypass, 1 booster, sub-piston induction, tapered, top fin milled.
5	Used on T.D. .051 engine. 2 bypass, 2 booster on each bypass, each with 3 separate milling cuts, sub-piston induction, top fin milled, has tapered grind.
6	Used on QZ and QRC and seen on some Sure Start engines. 2 bypass, no sub-piston induction, top fin milled. NOTE: The Sure Start cylinder had a twin slit exhaust, 1 booster on each bypass and no SPI
7	Used on many engines: product engines, car engines, Sure Start engines, Single bypass, sub-piston induction, top fin milled. (Sure Start had 1 boost port on each bypass)
8	Product engines and car engines. single bypass, narrow exhaust, no sub-piston induction, top fin not milled.
9	Very rare, not much known, seen on some product engines
0	Used on product engines, 2 bypass, no sub-piston induction, top fin milled.

P-40	Used on the "Super Bee" .049 engine, came on the ready-to-fly P-40 planes 1959 through 1961. 2 bypass, sub-piston induction, top fin not milled.

Slit Cylinders	Description (note: some engines such as Black Widow, QRC, Medallion... had slit cylinders on later models)
Sure Start	2 bypass ports, 1 boost port on each bypass, top fin milled, no SPI
Babe Bee	2 bypass ports, top fin milled, no SPI
Texaco	2 bypass, 1 boost port on each bypass, top fin milled , no SPI
Killer Bee ('92-'01)	(.049/.051) 2 bypass, 1 boost port on each bypass, top fin milled, has SPI, has tapered grind.
Killer Bee (post '02)	2 bypass, 1 boost port on each bypass, top fin milled, has NO SPI, no tapered grind.
Medallion	2 bypass, 1 boost port on each bypass, top fin milled. no SPI (RC version ground for use with throttle ring)
NFFS Medallion .051	.051, 2 bypass, 1 boost port on each bypass, top fin milled, no SPI
Dragonfly	2 bypass, 1 boost port on each bypass, top fin milled no SPI
RC Bee	2 bypass ports, top fin milled, no SPI (ground for use with throttle muffler)
QRC	2 bypass, top fin milled, no SPI
Cast Crank Sure Start	2 bypass, 1 boost port on each bypass, top fin milled, no SPI
Black Widow	2 bypass, 1 boost port on each bypass, top fin milled, no SPI

Early Engine Cylinders (No Number)	Description
Space Bug	2 bypass, open exhaust, has SPI, top fin not milled
Space Bug Jr.	1 bypass, open exhaust, has SPI, top fin not milled
Thermal Hopper	2 bypass, open exhaust, has SPI, top fin not milled
Strato Bug	2 bypass, open exhaust, has SPI, top fin not milled
Space Hopper	2 bypass, open exhaust, has SPI, top fin not milled
Babe Bee ('56,'57)	1 bypass, open exhaust, has SPI (may appear to have very little to no SPI depending on piston type), top fin not milled
Golden Bee ('57)	1 bypass, open exhaust, no SPI (may appear to have very little SPI if the piston and con rod connection is loose), top fin not milled
RR-1 ('57)	2 bypass, open exhaust, has SPI, top fin not milled

Porting Examples

Cylinder Style Examples

From top to bottom, left to right.
[SureStart slit cylinder], [#7 open exhaust cylinder, ground for use with muffler, throttle muffler or throttle ring], [Black Widow open exhaust cylinder],
[step cylinder and throttle ring, cylinder ground for better fit of throttle ring]

Thinner style cylinders can be found on engines made before the 1970s. They can run much cooler due to their thin walls. But can be damaged more easily when removing/replacing or in a crash.

They are both #2 cylinders, the one on the left (the average one) is off a 1978 Babe Bee and the one on the right (the thin one) is off a 1962 Babe Bee.

Non .049/.051 Cylinders
(coming soon)

Tee Dee .010
Tee Dee .020
Pee Wee .020	2 bypass ports, open exhaust, top fin may or may not be milled depending on age, may or may not have SPI
Tee Dee R/C .050
Queen Bee .074
Tee Dee .09
Tee Dee .15	2 bypass, 2 booster on each bypass, each with 3 separate milling cuts sub-piston induction
Special .15
Special MkII .15

In Feb of 1956, Cox switched over from the small diameter cylinder/head threads to the current size.

If you spot any issues at all on this list, PLEASE let me know! It would really help!