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-   -   .o49 engines by cox (https://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/7210784-o49-engines-cox.html)

bboykin 03-11-2008 06:38 PM

.o49 engines by cox
is the price of .049 right from cox 6.99 hope so have not seen this only on controlines since the 60's is this price right or what do you have to imput

air-madness 03-11-2008 06:42 PM

RE: .o49 engines by cox
Yep, the price is correct. I purchased two of them a couple of months ago. I installed an AP carb on one of them.

longdan 03-11-2008 07:04 PM

RE: .o49 engines by cox
Price is right, but they are out of stock. No one is too sure when they will be available again.

lildiesel 03-11-2008 07:42 PM

RE: .o49 engines by cox
Pictures! I want a Show 'n Tell about this...

ORIGINAL: air-madness
Yep, the price is correct. I purchased two of them a couple of months ago. I installed an AP carb on one of them.

bboykin 03-11-2008 08:01 PM

RE: .o49 engines by cox
thanks for replys would like to know more about this engine what fuel is required and what size planes it will propell. thanks for all infornation received so for

ProBroJoe 03-11-2008 08:16 PM

RE: .o49 engines by cox
Two VERY successful planes for the $7 Sure Start are ptulmer's Das Not Ugly (DNU) and rainedave's Sure Shark. A forum search here will turn up several builds, as well as a few videos. Oh, how could I forget? The Postal Plane Project stickied at the top of the forum page is using a Sure Start as well! [X(] But of course there are many, many more planes that will fly just fine with an .049 reed valve engine, from gliders to trainers, to warbirds and pylon racers... depends on wing area and all up weight of course. For what it's worth, I recently converted a Parkzone J3 Cub to a Cox .049 and at 15 oz, it flew like a scaled cat.

All Cox engines love fuel with medium to high nitro content (15-35%) and a fairly high oil content (20-25%) of which should be mostly castor oil.

Hope some of this helps,


Andrew 03-11-2008 09:19 PM

RE: .o49 engines by cox
I spoke with the folks at COX models today, 3/11 -- they expected a delivery of additional engines by mid-March.

propjobbill 03-11-2008 09:20 PM

RE: .o49 engines by cox
I have purchased more than 40 of them at that price. Just ordered 10 of them this week. They were selling for about $29.00 a little more than a year ago. Cox has stopped making fuel (gas) engines. So these are closeout deals, I called about 2=3 months ago they said they still hade 30,000 left but with everyone selling them on e-bay for $10.00 or more plus some hobby shops also selling them some day they will be all gone.

They are a great sport engine for RC or C/L from the factory they spin a 6x3 prop about 12,000 to 13,000 rpm on average. That means you have about 9 = 11 oz of static thrust. With slight modification you can easy get over 15,000 rpm which is about 14 oz of thrust. anything from 10=20 oz should fly ok with them from 100=250 sqin of wing area. I fly high wing plane at 12 =14 oz and the make good fliers.

These are good little sport engines, and well worth the $7.00 but almost everyone that I have bought needed the piston reset. You can find out about that by doing a search on cox piston reset. They will usually work without a reset, but you add years to their life by doing so, and if you modify them to get more than 18,000 rpm they won't last a long time without a reset of the piston

somegeek 03-11-2008 10:08 PM

RE: .o49 engines by cox

ORIGINAL: lildiesel

Pictures! I want a Show 'n Tell about this...

ORIGINAL: air-madness
Yep, the price is correct. I purchased two of them a couple of months ago. I installed an AP carb on one of them.

I'd like to see this as well!


OzMo 03-12-2008 10:31 PM

RE: .o49 engines by cox
At 6.95 each this is the cheapest way to get a standard cox glow plug and it comes with a free engine!! I bought four and also stashed some 09 stuf and I couldn't pass on a NIB texaco and NIB black widow each for under $50.00 at a little hobby shop.
Replacement heads that use standard glow plugs are nice idea as well cause the plugs for these little motors are getting rarererererer
Hmm may have mispelled something back therererere[>:]:)

KidEpoxy 03-13-2008 12:08 AM

RE: .o49 engines by cox

ORIGINAL: air-madness
Yep, the price is correct. I purchased two of them a couple of months ago. I installed an AP carb on one of them.
I'll get in line to see that too.

longdan 03-13-2008 02:56 AM

RE: .o49 engines by cox
Count me in too! Let's see this thing!

flyinrog 03-13-2008 05:36 AM

RE: .o49 engines by cox

ORIGINAL: air-madness

Yep, the price is correct. I purchased two of them a couple of months ago. I installed an AP carb on one of them.
Thats what Tim W. was doing..puting a carb/venturi on the back,making space bee's or hoppers which ever term it was...maybe rr clones,,anyway its been done..he did make a different back plate for it though....Rog

Honker1 03-14-2008 08:18 PM

RE: .o49 engines by cox


I love these little engines and have bunches of them. Been flying them for years. If you don't mind sharing your secrets, I am dying to know how to get a surestart to rev up to those rpms with a 6x3. I have polished the cranks, smoothed out the inside of the case, enlarged the venturi, used the galbrath head and still don't get near 15K rpm. It is driving me crazy. I placed an order for a Hyper Color engine ( to get a decent reed engine) some months ago but I understand that Tim Wiltse is going through a rough patch, I wish him the best.

Please, I know that many of us would love to here how to get surestart engine up to 18K! If you would be so kind as to share your knowledge.

Thanks in advance,

Pat (also in Ohio)

propjobbill 03-14-2008 10:09 PM

RE: .o49 engines by cox
First of all I can't get 18K with a 6x3 prop. I have been using a 6x2 APC prop for those rpm. I'm not sure how much I can get from a 6x3, but I am thinking maybe 15,000. In a few more weeks I will be able to get back to testing if weather permits. The biggest thing that I do is remove the back plate, remove the spray bar, and reed assembly. I chuck up a 3/16 drill bit into the drill press, and drill very slowly from the reed side to the opening where the spray bar goes through. It is very thin and narrows where the spray bar goes through. If you go to fast it will crack the opening. Apply pressure from the needle side of the spray bar when removing the spray bar. If you try from the other direction it will also crack the tube, (I learned this the hard way). I use pliers and caution, I tried pressing the spray bar out. If you apply pressure to the bar without support for the tube it can snap off. After I clean up all the openings from small plastic shavings the drill leaves I reinstall the spray bar. I then carefully open the chock tub in both directions to 3/16”.

I use about 30% fuel for high rpm, I also reset the piston. That’s the first thing I do. Drilling out these openings give me between 2,000 to 3,000 more rpm., and the 6x2 prop gives at least 1,000 more rpm. I find weather, and humidity also make a difference in my rpm. I have had the engines tach over 19,000 rpm, but so far I have not been able to maintain those rpm. It will run in the 17,000 to 17,500 constantly.
I have a video on utube of a sure start with a chock throttle. It was done inside a garage on a very cold day after dark with a flashlight about ¾ of the way through you can see the tach at over 17,000 rpm. This is not my best running engine. When the weather gets better I plan on making another video outside in good lighting.

I know 17,000 to 18,000 sounds like a lot, but It truly will turn those rpm. With a stock unmodified sure start running a 6x3 prop I get an average rpm of 12,500 = 13,500 rpm. I get a lot more rpm out of APC props than Master Airscrew props. But as I said the biggest thing is drilling the tub and venturi tub out. You don’t have to have a drill press but it helps. I tried it with a hand held drill and broke the venturi tube.

The engine really screams after making this modification. After I do this the engine starts better if you drop 4 = 5 drops of fuel down the chock tube before trying to start it.

In the video the needle turns with the throttle so it doesn't get the best rpm. I am still working on the chock throttle to get it to work better, again this also will be a warm weather job.


propjobbill 03-15-2008 12:08 AM

RE: .o49 engines by cox
I don’t own a 6x3 APC prop I will have to order some to find out what they will turn. I have numbers on about 12 of my cox engines. One of my baby bee engines with an APC 5.7x3 turns 14,300 and another with the same prop turns from 14,500 = 15,000, of course some of them only turn about 12,000 with the same prop. To my knowledge if I did anything to those two engines all I did was to drill out the venturi. But I have no idea what size if i did drill them out.

The APC prop makes a big difference. On every engine I have tried I get more rpm from APC props. I have tried a lot of sizes 5.7" to 11" .049 to .40 engines. and APC always gives more thrust and more rpm. readings. No I don't own or work for APC. I like Master Airscrew props they last much longer for me, and don't break as easy. But for me If it's rpm that I'm after I use APC props.

A couple of years ago combatpigg tested cox BabyBee engines with different props . I have copied His results and will paste them here. You will see the APC prpos make a big difference. I learn a lot by listening to these guys that know what they are doing. In his test APC 5.7x3 worked better than any other prop. I like the 6x2 because the plane flies slower and is more relaxing to fly plus it gives more thrust for climbing.

This is the DYNO report from COMBATPIGGS' extravagant test facility ! I only have a BABY BEE, and it was running an AP head, on 15%. This engine is somewhere in the middle of it's "prime". It is not set up to go into a full scream, it will rev up to a point where it has a slight "cackle", and if you go past that point it will die. In otherwords, a very baseline BABYBEE, that's best hours are behind it. NEEDLEABILITY MEANS 1click is critical, 2clicks is OK, 3clicks or more in a sweet spot is good/great


COX. 5-3 15700 8.0 good needle

GRISH 5-3 16500 7.8 " "

GRISH 5.5-4 12000 7.2 " "

GRISH 4.2-3 16800 5.4 " "

GRISH 4.5-4 15000 8.2 OK "

COX 6-3 11800 9.6 " "

COX 6-4 11800 9.0 critical

7-2 WOOD [custom] 10300 7.8 OK

5.5-2 APC 15800 8.2 good needle

5.7-3 APC 14300 9.2 OK needle

5-3 COX [ depitched ] 17500 7.0 easy to needle

I know that any other hotter reeds would blow these numbers away, and move the smaller props up on output. I don't have any gray props to test, but it's good to know that a 6-3 COX black prop is the champ of the "bench press competition". In actual practice when I'm flying reed combat it works better to cut down to 5.5 to keep the Rs up during manuevers.

Honker1 03-15-2008 06:28 AM

RE: .o49 engines by cox

Thanks for the information on how to get more performance on these engines. I have another question, I have been hearing about Turbo Plugs, what the heck are they? I use Galbreath heads , works OK if it is not to cold out, in the cold I have to switch back to Cox. Might be the fact that the galbreath plug I am using is 10 years old and doesn't hold the heat like a newer one.

Have you ever messed with the re-porting on one of these? I might try to ad the flutes in the ports like what was used in the Killer Bee engine to see if I can pick up some more rpms. Don't know how to do that yet but......



propjobbill 03-15-2008 08:15 AM

RE: .o49 engines by cox
I don’t know much about different plugs or heads. I have read different places that nelson plugs get about 1,000 more rpm. Also all the guys in the know claim that you can get more rpm by changing the number of head gaskets, usually from 1 = 4. Running more head gaskets decreases the compression, and also changes the timing of the engine. If it were possible to change the heat range of the plug this also changes the rpm. Changing the heat range also changes the timing. From what I understand the only way to know which works best is to experiment, and keep a record of the results. Lowering the compression helps as you increase the percentage of nitro, or at least that's what they say.

I am new at making modifications to Cox engines, but when spring gets here I am going to try some of these tricks and see what happens. If I have any success I will share my knowledge. I have no intentions of competing in any way. I simply like the extra power, because it lets me fly a little better.

gcb 03-15-2008 08:52 AM

RE: .o49 engines by cox
A couple of things to consider:

As you increase the venturi size, you decrease the engine's ability to suck fuel. That may be important on some installations. To overcome this you may have to use a pressurized fuel system.
You can also increase suction somewhat by upping the venturi velocity through increasing RPM via a smaller diameter or pitched prop...whichever will work on your plane.

Varying compression (via shims), plug heat range, prop load, and nitro content all contribute to combustion timing. The higher power per cubic inch you get, the more critical these things become to increase performance...until you reach a point of mechanical failure.

With knowledge gained, however, you might know when you need to change prop size or plug for a particular fuel you are using, etc. ...Trial and error also works... ;)


Honker1 03-15-2008 12:55 PM

RE: .o49 engines by cox

Thanks for all of you input. Does anyone know what Tim Wiltse did to get his motors to run so well?

Tee Bee 03-15-2008 10:10 PM

RE: .o49 engines by cox
I don't know his secret tricks but the Stage 3 Skyline engine I bought from him runs awesome. Very smooth and consistent for a reedie once it finally broke in. I know he lightened the piston and modified the venturi shape a bit. Has one of his custom turbo plug heads on it as well. Piston/cylinder fit feels very tight and it has a nice pop to it when you turn it over by hand. I've never disassembled mine and don't feel the need to do so yet since it doesn't have much time on it. He was making neat stuff. Hope he comes back around in time.

Honker1 03-16-2008 06:31 AM

RE: .o49 engines by cox
Thanks Tee Bee,

I ordered a stage 3 last fall and I guess it was a little to late. The pop you are talking about is probably taper in the cylinder. I bought a Kustom Kraftsman Tee Dee back in the eighties and it had that same feel. I wish I new how to do that, that is probably one of the big fixes/mods that make these thing sing. One of these days I will figure it out. I have bought a few dozen Sure Starts so I can afford some learning curve (ruin) modifications. Will work with an old timer in the machine tool busines to see if he can figure it out.

I hope Mr. Wiltse gets back in the game also.



bboykin 03-18-2008 05:22 PM

RE: .o49 engines by cox
just received cox christen eagle ep and also received e-mail that col .o49 engine had shipped today

Bugzidor 04-15-2008 01:35 AM

RE: .o49 engines by cox
1 Attachment(s)
You may like my idea of making a carb. for cox .049 sure start. It looks vary simple, yet effective (pictures will tell the whole story)

Mr Cox 04-15-2008 01:54 AM

RE: .o49 engines by cox
Nice job, but I think there is an inherent problem with a carburator on a reed engine?
The reed only closes due to a higher pressure in the crank and that''s fine at full throttle but near idle the restriction of the carburator gives an underpressure. This would be ok if it stayed constant but as the reed is shut (do to a higher pressure in the crank) the throttle is still "leaking" and the pressure will continue to rise on the wrong side of the reed... [:'(]

I think the TeeDee would be much better suited for a carburator, please feel free to prove me wrong. :)

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