Space Bug Jr question?

Ken Cook Sat Oct 31, 2015 1:09 pm

I just took this engine apart. Unfortunately, I have a broken ear on the plastic backplate. I intend to use this for a old model called the "Lil Monster". It seems as if there are 2 reeds under the cover. It appears to be a thick one and a very thin one with the thinner facing the engine side. Does this sound correct? I was fortunate to have a gasket and screw set so I'm giving it the work over. The plane should be a real good flyer. It puzzles me to see such an advanced design for 1957. A constant chord wing which is nearing 25" wingspan and a fairly thick airfoil for 1/2A. This seems quite large for the period. The wing seems to be very similar to the Brodak ARF Baby Clown. Having a true PDQ Baby Clown, I can tell you the two planes are completely different with the PDQ version having a shorter wingspan. I had the kit laser cut to expedite the building. I feel the Space Bug would compliment the nose of this plane quite well and should have plenty of power for this model. Any help with the reed configuration would be most helpful. Ken

batjac Sat Oct 31, 2015 2:28 pm

Ken, I too was wondering about the reason for using two reeds in these engines. Earlier this month over on Stunthangar I asked Larry Renger why they used two reeds instead of one, but he said that was before his time there at Cox. Ah, well. The mysteries of Cox.

The Inquisitive Mark

Ken Cook Sat Oct 31, 2015 3:46 pm

I never dabbled into the older Cox items until my recent exposure. I have had a growing affection towards them in the past few years. I recently acquired some engines from a deceased speed flyer. Amongst the items were 3 older Cox engines this being one of them. I made a note though, I think speed flyers favorite tool was the grinder. I was told that the engine will run fine on one, but it was mentioned to me that doubling them controlled fluttering. I can't comment as I haven't run the engine either way. Currently, it's apart awaiting to go back together. Neat little engine though. Ken

gcb Sat Oct 31, 2015 4:24 pm

For those wondering what the discussion is about, here is the reed setup on one of my Space Bugs:

George

Ken Cook Sat Oct 31, 2015 4:37 pm

George, does it matter which reed is installed first? I see one is obviously thicker by almost twice the thickness in my example. Ken

gcb Sat Oct 31, 2015 5:34 pm

Ken Cook wrote: George, does it matter which reed is installed first? I see one is obviously thicker by almost twice the thickness in my example. Ken

It has been quite a while since I had it apart. I put it back the way it came apart. I THINK the thin one goes next to the tank.

It might be good to try it both ways to see which is better.

One thing I remember reading in a review of the SB Junior is that it is easy to start and has excellent fuel draw.

George

Mudhen Sat Oct 31, 2015 6:00 pm

batjac Sat Oct 31, 2015 6:41 pm

Mudhen wrote:The idea behind two reeds was that one sealed against the tank and the second was a spring return. Later it was discovered that only one was required.
To remember which goes where, “Thin in, fat out.” The thin reed goes on first, then the thicker reed, the retainer, and finally the housing.

Hmmm. Good explanation. I was guessing that the thinner inner reed would be to help eliminate reed float.

The Incorrect Mark

getback Sun Nov 01, 2015 5:51 am

Ken does your SBJ have the older smaller dia. glow head with the 3 piece piston, or the later ? If you haven't ran this engine you will like the way it is so easy to start and the steady run it gives I have been wanting to get one on a plane of the error myself . Eric Babe Bee

Ken Cook Sun Nov 01, 2015 5:59 am

Indeed it's the 3 piece piston and older glow plug. I have two other engines both are Thermal Hoppers. One is entirely clapped out and the other is very frozen and in need of some TLC. Ken

crankbndr Mon Nov 02, 2015 6:28 am

Kinda like Cox didn't want you messing with the reed at all on the Space Bug Jr, the retainer is hard to remove and the parts list only shows the whole assembly.

getback Mon Nov 02, 2015 8:30 am

I have not seen one of these 312j tank/reed assy. before with all the looking I 've done ? I really like the engine and its characteristics , I think I have 10 now and have taken a few apart to clean , the reed cap is not too bad if you take your time I put a flat on the tank surface to use a screw driver and pry a little at a time around till it pops off. This keeps from denting the plastic . Ken I hope you have as good success as I have . Eric Small Cox Logo

Mark Boesen Mon Nov 02, 2015 3:55 pm

The reed assembly was made to be quick and easy to manufacture and assemble, not repair. It makes you appreciate the clever engineering of the Babe Bee that much more.

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