My Cox .049 Marine inboard engine

F4D Phantom II Thu May 02, 2024 8:35 pm

I made this engine many years back using a Black widow crancase cylinder and piston. I made a Flywheel,water jacket,reed valve backplate and motor mounts. Since this engine has an SPI P/L I didn`t try to make a muffler. I don,t know if it will vibrate too much since I have not tried to run it yet. I made some hefty motor mounts to mount it solidly. Lately I decided to get back working on it and tried to buy a carburator. I got lucky 944_jim gifted me a carb for my project, Im very greatful for his gesture. I will need to make a new backplate reed valve unit to mount the carburator. Here are some pics of what I have done.
Juan

My Cox .049 Marine inboard engine Img_7312

My Cox .049 Marine inboard engine Img_7313

My Cox .049 Marine inboard engine Img_7314

1/2A Nut Thu May 02, 2024 8:55 pm

Very nice Juan!

Do you recall the weight of the aluminum flywheel?
You can mount it to some wood and run it up with a
bottle of water with a feed line to cool the engine.

Small Cox Logo

Here is a bench test with one of mine,

Jul 28, 2018
Cox TD .049 RC Boat engine break in / vibration test up to 13.96k
Ran very smooth kept it rich to avoid over heating 3 progressive
runs turning in the needle a bit more each time. Idle was good at
around 8.8k rpm. Pressure tap off the muffler helped to keep a steady low idle.

F4D Phantom II Thu May 02, 2024 9:44 pm

Hello 1/2a nut
The Flywheel weights 14 grams. I don`t know if it will be too light so I bought some brass in case I might want to increase the weight of the flywheel. The plan is to build a runabout boat that might look like a Chris Craft. The flywheel is centered on the crankshaft by a brass collet and it runs true. I will be cheking the flywheel balance as I want to make sure I have as minimum vibration as possible.
Where do you get your octura propellers? What size are you using on your .049?
Juan

My Cox .049 Marine inboard engine Img_7316

My Cox .049 Marine inboard engine Img_7315

MauricioB Fri May 03, 2024 12:55 am

Hello Juan, You have done an impeccable and professional job. The bench is something extraordinary, a bench with an adjustment system. Congratulations Hand Shake

P.D.1 you should put it in next month's engine photo selection! Eyebrows

P.D.2 Hey Brad, you are a teacher to me! Thumbs Up

1/2A Nut Fri May 03, 2024 2:41 am

14g is enough add in the brass collet, coupler and drive line mass will be plenty.
I use 16g steel small dia. to keep the sheer loads down.

Dumas 1"x1 for submerged prop can still be source for 1/8th hub.

These work with reed engines left and right hand prop your choice.
24.5 mm Prop Dia. - Fits 2mm drive shaft:

https://www.ebay.com/itm/284996331060

Can just google source Octura props be prepared to buy anywhere as needed.
1/8 hub the 0930 is good for submerged drive will need to cut down to 27mm
with the power of a reed engine.

https://www.offshoreelectrics.com/proddetail.php?prod=oct-0930

Cut down for 1/2A

My Cox .049 Marine inboard engine Imag4315

Picco P0 .05ci / .8cc / 43 mph cut down Octura 1427 to 1.4" x 26mm / stock sharp X427 - 39 mph

My Cox .049 Marine inboard engine Imag4316

My Cox .049 Marine inboard engine Imag8126

davidll1984 Sat May 04, 2024 8:07 am

I too should get to work if I want to be able to use my boat for the moment I don't have much free time with the preparation in order to put my yath in the water and I have to buy equipment to make som of the parts for the shrimp boat project and other projects F4D Phantom the little engine you made is very cool I imagine that the water jacket fits in a press fit way?

F4D Phantom II Sun May 05, 2024 12:24 pm

MauricioB wrote:Hello Juan, You have done an impeccable and professional job. The bench is something extraordinary, a bench with an adjustment system. Congratulations

P.D.1 you should put it in next month's engine photo selection!

P.D.2 Hey Brad, you are a teacher to me!

Hello Mauricio
Your kind comments mean a lot.Thanks I really appreciate them.
Juan

F4D Phantom II Sun May 05, 2024 12:27 pm

1/2A Nut wrote:14g is enough add in the brass collet, coupler and drive line mass will be plenty.
I use 16g steel small dia. to keep the sheer loads down.

Dumas 1"x1 for submerged prop can still be source for 1/8th hub.

These work with reed engines left and right hand prop your choice.
24.5 mm Prop Dia. - Fits 2mm drive shaft:

https://www.ebay.com/itm/284996331060

Can just google source Octura props be prepared to buy anywhere as needed.
1/8 hub the 0930 is good for submerged drive will need to cut down to 27mm
with the power of a reed engine.

Hello 1/2A nut
Thanks for the information on propellers and the tips given. I know you have a lot of experience with the little engines.
Juan

https://www.offshoreelectrics.com/proddetail.php?prod=oct-0930

Cut down for 1/2A

Picco P0 .05ci / .8cc / 43 mph cut down Octura 1427 to 1.4" x 26mm / stock sharp X427 - 39 mph

F4D Phantom II Sun May 05, 2024 12:45 pm

davidll1984 wrote:I too should get to work if I want to be able to use my boat for the moment I don't have much free time with the preparation in order to put my yath in the water and I have to buy equipment to make som of the parts for the shrimp boat project and other projects F4D Phantom the little engine you made is very cool I imagine that the water jacket fits in a press fit way?

Hello davidll1984.
I did not pressfit the water jacket on the engine. Press fitting something on the cylinder might cause a tight spot on that area for the piston. I used a pair of "O" rings to seal the jacket to the cylinder. I left the bottom fin on the cylinder and shaved the other ones and part of the top of the cylinder. I also shaved some of the fins on the glowhead to provide for a seat for the top "O" ring. The good thing is that you can add shims to the glowhead and still have a seal for the jacket also that makes the water jacket removable to be used with another cylinder if you have to. Here are some pics.
Juan

My Cox .049 Marine inboard engine Img_7318

My Cox .049 Marine inboard engine Img_7319

roddie Sun May 05, 2024 9:07 pm

Hi Juan, That's a very interesting engine that you've modified there! You, David, Brad and I all have interest lately with marine applications for the Cox glow engines. I love the old Chris Craft runabouts.. and I'm hoping to see your engine powering an example!

F4D Phantom II Mon May 06, 2024 8:33 pm

roddie wrote:Hi Juan, That's a very interesting engine that you've modified there! You, David, Brad and I all have interest lately with marine applications for the Cox glow engines. I love the old Chris Craft runabouts.. and I'm hoping to see your engine powering an example!

Hello Roddie
I have had interest on building something similar to a chris craft runabout and I did the engine many years back but I haven`t gotten around to do one. I have too many projects going on. I have some Triumph motorcycles and an old 1951 Ford project too. I want to see if I can make a drawing of the boat I want and build from that. I will be asking questions. 1/2A nut already helped me with prop information.

Juan

My doctor said that as long as I have projects to make I would live a long time so I have projects to do until I`m 110 years old.

MauricioB Tue May 07, 2024 4:50 am

F4D Phantom II wrote:

Juan, beautiful dismantling of your engine. The venturi along with the flap valve seat, did you make it yourself or did you modify one from Cox? Thank you.

rsv1cox Tue May 07, 2024 7:41 am

A beautiful blend of color, detail, and craftsmanship Juan.

My Cox .049 Marine inboard engine Juan_e10

F4D Phantom II Tue May 07, 2024 1:39 pm

MauricioB"
beautiful dismantling of your engine. The venturi along with the flap valve seat, did you make it yourself or did you modify one from Cox? Thank you.[/quote]

Hello Mauricio
I made the intake using a baby bee tank to which I added a venturi. but in other occassions I have made the intake portion and reed section. Like in the Cox tether car engine I made.
Juan

My Cox .049 Marine inboard engine Img_0417

My Cox .049 Marine inboard engine Hpim1113

F4D Phantom II Tue May 07, 2024 1:41 pm

rsv1cox wrote:A beautiful blend of color, detail, and craftsmanship Juan.

Hello rsv1cox
Thanks. I appreciate your comment.
Juan

F4D Phantom II Tue May 07, 2024 1:53 pm

Hello
Well guys how big of a boat should I build for the .049 marine engine? I don`t want it to be too big but since I will be installing a radio I thought 15" to 18" please give me some guidance on size.All help appreciated.
Juan

roddie Tue May 07, 2024 2:48 pm

F4D Phantom II wrote: Hello
Well guys how big of a boat should I build for the .049 marine engine? I don`t want it to be too big but since I will be installing a radio I thought 15" to 18" please give me some guidance on size.All help appreciated.
Juan

Yes; 15-18 inches length/5-6 inch beam would be good. The Dumas model boat kits that are offered for the .049 engines are pretty much "all" 18 inches length. Incidentally; Dumas offers a nice little kit called the "Half Pint" Cabin Cruiser. It's all wood with mahogany veneers that would emulate the Chris Craft/Century vintage runabout look. You could of course; customize it to your liking.

weblink to the kit

F4D Phantom II Tue May 07, 2024 9:33 pm

Hello roddie
I have looked at the half pint and I`m thinking about it.thanks for the link and advice.

I went to my local hobby shop and they had a flex shaft with a propeller the type that is used on a Rage R/C Black marlin will it work for my project? I also sent for an Octura 0930 prop. here is a pic of the flex shaft and prop. I bought it with the proviso that if I could not use I would return it.
Juan

PS.I ordered the Half pint from Dumas as you suggested and the hardware kit.

My Cox .049 Marine inboard engine Img_7322

1/2A Nut Wed May 08, 2024 2:42 pm

What is the mm dia. of the prop?

Can always sculpt it down to a suitable dia. for the .049. Key is to file back in a sharp edge.

My Cox .049 Marine inboard engine S-l16y10

You can see how small the Cox engine looks with a 18" boat made back in the day for 4 AA batteries large RX and servo.
Today's light weight gear will really help get it moving. Must bag up the RX to keep water out or get a marine RX.
There is a spray you can use to waterproof the circuit boards or seal the case and always elevate the RX and Servo
off the bottom of the hull so they are not subject to sitting in water if it gets in the hull..

My Cox .049 Marine inboard engine Sk_dad10

My Cox .049 Marine inboard engine Imag8018

F4D Phantom II Wed May 08, 2024 8:05 pm

Hello 1/2a nut
The prop is 1.125 inch. I will be making a comparison with the one I get with the boat kit hardware. I will try mods after finishing and running the boat,also have the octura 0930 on the way. Thanks for the input I`m saving all information.

Juan

1/2A Nut Wed May 08, 2024 11:41 pm

The black surface drive prop in stock form good for TD .09 / QB .074 with a Kamtechnik turbo plug adapter.
Since the black prop is nylon can modify sculpted down to run well with a .049 and keep the engine running.

The white nylon Dumas prop you will see in your drive kit is sized well for submerged drive.
Prop in the Dumas kit is a 1"D x 1.1"P

Originally they only sold metal props.

My Cox .049 Marine inboard engine Dumas_14

Sharpened, balanced and shined up.

My Cox .049 Marine inboard engine Imag8127

Small, low weight RC gear should allow this .051 - 10.5" mono, est. 7oz / 2ch sprints in pools and ponds.
Much lower weight / drag, can prop down to where the engine stays running at half throttle and still be fast.

My Cox .049 Marine inboard engine Td_05114

gkamysz Fri May 10, 2024 4:41 pm

Great project! I have a Dumas flywheel (I think anyway, looks just like it, second hand) which weighs in at 37g. I have no experience with boats to say whether it really needs to be this heavy.

1/2A Nut Sat May 11, 2024 2:52 am

Circa 1974 filmed with a Super 8mm movie camera

Mark Nickells 389 views
Vintage RC Dumas boats,

1st boat filmed is the Dumas Miss Thriftway 1/2A unlimited hydro.
Running a single channel "Digit Midget" radio, non throttled Cox Golden Bee .049
Dumas white nylon prop submerged prop drive with standard 1/2A hardware.
Mark said he ran it for about a year, was going to upgrade to a Black Widow for
more rpm but flipped it and sank the boat due to no internal foam floatation.

Heavy vintage "Digit Midget" weighed down the back of the boat quite a bit.

My Cox .049 Marine inboard engine Single10

Lower weight all balsa DYI hydro with a bit more modern RC gear.

By Seewolf1972 / German translated
8,327 views Jan 5, 2009
This is my Cox speedboat Cox Black Widow 0.49 Engine, Since the motor cannot be throttled,
the crate can also take corners at over 30 km/h (measured). 18.6 mph
The boat is extremely robust and unsinkable.

Of course all the Dumas gear for the 1/2A engines likely derived from what was learned with
tether boats prior to RC and the ole skewl trick of setting the rudder for the craft to run in circles.
The right prop back then vs loaded RC craft today really requires testing and can be done at home
with a tether line and small 6ft pool simple enough to try pitches / diameters and flywheel masses.

This vid shows the early days with non Cox engines -less power.
Note the prop was small enough to keep the engine running under static load.

1956-57 film clip
.8 cc engine which is the displacement of an .049 is powering
Jim Walker's Miss Thriftway tether boat.

Small Cox Logo

roddie Sun May 12, 2024 1:48 am

Those vids are all awesome Brad. I loved them! We just don't see too much about 1/2A Marine glow-power. The vid of the Cox Rennboot is one I'd aspire to.. I'm hoping for speeds of at least 15 mph. for my rigger design. The latest RC gear alone; weighs much less than it did when that vid was published.

1/2A Nut Sun May 12, 2024 9:52 pm

1/2A boat projects can excel in 2024, look forward to seeing modern water running vids.

My Cox .049 Marine inboard engine Resize33

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