OK Cub .049

Just to note, these engines were never the power houses that Cox easily outdid and changed history forever.

FYI in theory, the venturi tube was to align the incoming airstream to smooth airflow turbulence to align the air around the spraybar for better fuel draw and atomization for air-fuel mixing. The late Joe Wagner, model designer and engine guru had an engine article some time ago, that described how this work and how it improved efficiency on some engines.

Unfortunately, there aren't many technical articles on the OK engines. One I found on Scepter Flight, https://sceptreflight.com/Model%20Engine%20Tests/OK%20Cub%20.049X.html Sept. 1953 Model Aircraft Engine Tests No. 15, The OK Cub .049X gave it 0.0533 BHP at 14,400 RPM on 30% nitro. OK introduced it as the racing version. This is basically Babe Bee power.

Leroy Cox's Thermal Hopper bested it 2 years later with his Thermal Hopper on 25% nitro at 0.066 BHP at 17,200 RPM.

https://sceptreflight.com/Model%20Engine%20Tests/Cox%20Thermal-Hopper%20%282%29.html Model Aircraft Engine Tests No. 76 - The Cox Thimbledrome .049 c.c. (Thermal Hopper)

Powerhouses they are not, but Walt Musciano used a lot of them as examples for Scientific half-A C/L planes.

Thanks for the information guys. I have a lot of experience with free flight rubber models and some experience with free fight gas. But I have no experience with control line models. Even though I am 65 years old I have never built or flown a control line model. So, I would probable just use it with an eyedropper.

I'm a control line flyer and for the better part of 50 years I always stayed away from OK engines. A few years ago one of my senior club members who's now passed on gave my son a OK Cub .049. He said this was a engine he bought and used it on a Dakota. We built the Dakota and I made it with a inverted engine. I had the eyedropper and I have to say, I never had so much enjoyment out of a combination like that. In fact it worked so well we lost the plane. I changed the prop to a more modern prop over the old woodie Rev-Up I was using because I didn't want to break it. Well it turned out to be pretty efficient and it took the model to about 250 feet in a left spiral. This plane always leveled off when the power cut and immediately turned into a right hand downward spiral. This time 6 of us watched it fly out into the sunset.

I've since built another Dakota and currently use a OK .074 in it. It's dead reliable. What great little engines they can be when you acquire a good one.

         The problems I'm faced with using the stock OK needle and the eyedropper is this. If the engine doesn't immediately start, the needle isn't sufficient enough to stop the siphoning into the crankcase and it will flood. I've had to change the height of the eyedropper by lowering it. Now the problem is that at the end of the eyedropper the run leans up too much and pitches the nose high. I've changed the height and somewhat split the difference and went in between. However, the Cox 128 tpi needle solved these issues immensely.

Can the snorkel be removed for more power?

I just came across a paper copy made from tracings of an All American 21" Trainer recently sold on eBay.

Don't ask me why (I don't know), but the plane appeals to me. I don't want to make a rocket, so I think one of these beam-mounted may be just the ticket. I really don't want to waste a Medallion on it.

I personally never found the venturi tube to do anything but restrict power. It's also something else to catch your finger on when flipping. The early case OK engines from 1948 utilized a large venturi opening and essentially no venturi at all. These have always been my strongest runners. One thing I've found with OK engines, don't be afraid to put the nitro to them. I also have found they tolerate 4 pitch props slightly better than a Cox engine. I use all of mine for schoolyard freeflight and I just use 3 pitch props and less. What I never realized is that some are even dual bypass . There were literally many many different versions of these engines in all types of configurations. One thing these will benefit from is a good crank polishing. You want no drag on the crank. I chuck it up in a drill press and wrap 400 grit paper and oil and work it up to 2000 grit. When the prop is clocked horizontal, I want the weight of itself to fall on it's own smoothly.

I've become quite a collector of these engines and I'm not a collector. They've just become such a unique thing to play with. I also own the OK Super.60 ignition which is also a very reliable engine. As they say, they were hardly OK and they were never super.

Thanks, Ken,
Can the snorkel be removed?

I just took a cruise through eBay and Sceptreflight. The Trstors McCoy (T/M) engine also fits my desired specs. That is, an older beam mount engine that isn't a medallion/Tee-Dee.

The T/M appears to be much the same as the Cub.Do you know if the T/M can take a Cox glowhead?

Regarding removal of the "snorkel", I don't think you will find any performance gain.

Take a look at the tank .049 Bee's. The passage from needle valve - spray bar cross sectional area is not that large. Herkeimer put it there for a reason, again goes back to obtaining laminar air flow to the spray bar.

These are not high revving performance engines.

I’m leaving the “snorkel “ on mine just because it came that way from the factory…. I kinda like its power output where it’s at…. Sorta between a Bee and a PeeWee…. Might be just right for some particular air frame….

It’s too bad though on the poor quality needles…. Mine isn’t as bad as @bsadonkill’s but will not stop fuel completely when closed….. Plus it’s touchy when running…It can be worked around somewhat but still a potential to flood the engine in certain conditions

The spray bar in another Cub I have got loose in the case and would spin so I replaced it with a Cox assembly as Ken mentioned…. Works great!

Robert, appears that you have the "higher performance" version, the Cub .049-X.

Also, it appears that the needle you have is not the OEM, perhaps a Cox? I plan to do as Ken has done, replace my odd OK OEM NVA with a Cox one.

The odd split threaded collar over the needle, does not allow one to effectively seal it with a small section of silicon fuel line, leaks, very touchy to adjust.

Yes, my observations too from running them, between a Pee Wee and Babe Bee.

As Ken has pointed out, they make excellent free flight engines. No doubt with our lighter R/C gear of today, works fine as schoolyard scale engine, too.

It is just the weak needle arrangement that affects reliable runs. I guess back in the day, manufacturers were doing various things to avoid patent and copyright problems.

Also, perhaps the prototypes had tighter tolerances than the production models. Perhaps the better tweaked engines were sent to reviewers like Peter Chinn and H.R. Warring?

Perfect made replacement needle valves for various 1/2A engines and I've used a lot of them. This stuff was on a rotating display on the counter at the hobby shop I used to attend. There was hundreds of items on that display. I don't think anything on that display was more than $1. I never purchased the stuff and now I really regret it. I recently acquired some of the flexible versions for my OK engines and they work light years ahead of the stock OK needle. Some have said they experienced quite the opposite. I however have never experienced this. The fit is usually better not too mention the needles actually have a taper.

Not all of the venturi tubes have the same ID, some are so small it's a wonder the engine even runs. So yes, removing these will increase performance. As George states, these aren't burn burners. They're just fun engines which Walt Musciano also discovered, you can really enjoy them. Walt wanted to provide models for those abandoned engines as I recall him saying. He would sometimes provide a list of engines suitable for the model he presented. I always though that was pretty cool. In addition, the OK engines are extremely light which was a huge benefit to some of the models he made. If Cox engines were used on some of his models, it would create tremors when the power cut and the model hit the ground.

The X version is a very neat engine. I own one new in the box and one I keep for a runner. It's very close in bolt pattern to a Wasp almost identical. I'm also a fan of the reed valve versions. I have a practically new .059 and .049 in these versions and they run terrific. One thing I will say is that the reeds don't seem to get stuck as in the Cox engines do. The reed system is a bit more complicated in these and I don't make a habit of taking them apart.

Hi fellas, The engine in my last photo may be a bit of an odd duck, I think it looks like an
“X” but it’s an .039…..And you’re right Ken about being near to Wasp bolt pattern…. In fact the Wasp back plate will fit this engine if I use 2-56 screws instead of 3-48’s for just a bit more wiggle room in the bolt holes…..I thought it may be a good option if I didn’t want to use the tank/mount….. However the engine doesn’t run well this way…. The tank mount “stuffs” the crankcase much more than the Wasp backplate does and I think there’s a good bit of case compression lost there…

I found something I’ve been watching for, for a while, A parts engine for my .039…. Specifically for the backplate that would allow for the use of a remote tank…. Nice to have the option for either…. As a bonus it came with a nice needle valve assembly…Perfect I’m guessing?….. My .039 has already been converted to a Cox needle but the new needle might find its way to my .049A if it tests out OK…. The crank is free in the donor but piston is locked…. Time for a Rem Oil soak  

That needle valve looks like a OS unit to me and not a Perfect needle. In addition, don't ever try and remove a cylinder on these OK engines without freeing the piston first. It instantly twists the rod and ruins it. Unlike a Cox engine, no ball socket which doesn't allow for rotation.

The Enya needle valves usually are concave in the center of the knob not convex and are larger .

Good advice on the cylinder removal Ken, Much appreciated ….. Here’s a little better photo of the needle assembly….I’m glad the parts engine just happened to have it….Regardless, whoever had the engine before understood the virtues of having a better needle in a Cub….

rsv1cox wrote:......... but I have never seen an Enya needle with a double ratchet.  

Strange.  I'm pretty sure all my Enyas have a double ratchet.  Certainly the ones in your photos do!

I decided to go ahead and try and run the “parts “ engine after cleanup…. Really all that was missing was the head and plug so I borrowed it from the other engine….I helped it initially with a pulley and string…. I think it will hand start fine after a few tank full’s….About 8 K on a Cox 6-3… Which is too much for it really…..It did hold it steady though….Will play props some more….The needle works great!!… The other one may be the parts engine now LOL!!!

I think Ken nailed it…. I found this on an OS .15 on the net….

rsv1cox wrote:

Oldenginerod wrote:

rsv1cox wrote:......... but I have never seen an Enya needle with a double ratchet.  

Strange.  I'm pretty sure all my Enyas have a double ratchet.  Certainly the ones in your photos do!

Hi Rod, are you seeing the same thing that I'm seeing?




Maybe it's a Perfect universal NVA?

I see the problem Bob.  When you say double ratchet, you mean two rows of knurling.  I was looking at the side spring tabs that engage in the knurling.  Example is a McCoy with only one side tab.