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Best piston/liner fit Baby Bee Empty Best piston/liner fit Baby Bee

Post  Roland Mon Dec 28, 2020 12:06 pm

Hello,
I am Roland Dieterle, located in the southwestern part of Germany. 59 years ago, my first engine was a Cox Pee Wee.
It gave my lots of fun and was a perfect match in the free flight Topsy built from a Graupner kit. Unfortunately, in a crash, the mounting lugs broke and I traded the engine for a Baby Bee plus 5 DM, which was about 5 months pocket money. This engine I still have today. During the years, don't know how it came, all of a sudden, I find 7 Baby Bee's and some Tee Dee's in the engine cabinet. And, how this comes, I even also don't know, there is a little Biplane luring around, no engine, no RC, but everytime I am in the workshop, this thing is wheeping and begging for getting in the air. Zaunkönig, some call it unflyable, some call it Adrenalin. As, in my age, even after some years FAI pylon racing, I thought, this PeeWee would be a perfect match. I managed to get this thing into the air. Not too fast, but ok for leisure flying. But, bad luck during a stupid throw by me, it hit the frozen ground. Crankshaft broke. Too bad, too bad. Lucky me, I found the last bottom end at coxengines.ca and its on the way. I have another PeeWee, but do not want to risk it. Decision made, go for a Baby Bee. I grabbed one from the drawer, put it in the plane, voila, tzzzz, the Baby Bee turned a 5x3 12700rpm. It was not enough to get the plane reliably into the air. Then I decided to start some educational test runs. I dismantled and cleaned all of the remaining Bee's. Checked the piston/liner fit of all of them. some are pretty good, some a more sloppy. Today I tested their performance using a COX 5x3, which I think is a not too heavy prop. So far only three, fingers are getting too cold quickly.

Fuel 20% Castor 30% Nitro, 50% Methanol

Bee #1   14300,    TD head 15100   two slit exhaust slot,  two transfer ports, no boosters
Bee #2  14400,    TD head  14650   old style exhaust slot, 1 transfer port, cylinder marked "2"
Bee #3  13000,    TD head, it was getting too dark for the tach,  two slit exhaust slot, 2 transfer ports, no boosters

Big surprise, the #3 Bee has the "best" piston/liner fit, #2 is on the loose side,  and '1 is also feeling good.

Question, should the piston/liner fit be more on the easy side or do the engine suffer in a too tight eg, good plopp?
#3, there is no sticking, a good plopp. All 2 liners are not "perfect located" for the transfer ports on the crankcase. Does this makes a big difference?

I always used the same Tank to eliminate a maybe tired reed valve.
Has one some rpm figures for the Bee's with a 5x3?
Is the 5x3 ok to use or a better advise?

regards and thank you for your help
Roland

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Post  706jim Mon Dec 28, 2020 12:48 pm

Ok Roland, your query inspires me to relate an old story regarding the Pee Wee 0.020 an engine I find simply adorable. When my first Pee Wee crashed, the crankshaft broke right at the splined connection. Engine otherwise runable but seemingly dead. I disassembled the engine, shortened the crankcase with a file, crudely ground a taper on the end of the broken crankshaft and created an inside taper on the drive washer using a countersink. I put the engine back together and to my amazement it ran! So I installed it onto a simple profile free flight called a Berkeley "Baby Yank" and set off to fly it. Normally I would use 0.4cc of fuel to get a 30-40 second engine run, but this time I filled the tank, started the engine and launched the plane. The engine was running poorly and I figured it would quit. No such luck! The little gem cleared it's throat and sailed off into the sky. By now, the wind had picked up and the last I saw of it it was headed off to Valhalla. I searched through the farmer's pastures for the longest time but the airplane is still out there somewhere with my phone number penciled into the fuselage. That event was in 1971!

So you might try my "repair" and save your good Pee Wee for a more controlled environment.
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Post  emanuel Mon Dec 28, 2020 2:25 pm

Hi Roland,
Greatings from Bavaria.
PeeWee and Topsy metoo 😁

I would use a TD or at least one Venome ll for the Zaunkönig.

Like thouse Guys...
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Post  balogh Mon Dec 28, 2020 3:56 pm

Hello Roland

Welcome to CEF! In my humble opinion as long as the piston to cylinder fit is not so sloppy as to cause difficult starting, your compression is OK..some folks here say sometimes the sloppier the fit the more terrific runner the engine!
I - having experienced the hiatus of COX engines during my childhood and owning only maybe 3 COX engines before I found a wealth of them later on ebay etc - have always preferred longevity = perfect fit to short-lived performance i.e. loose fit/low internal friction.

There is probably a performance  break-even between good fit/higher internal friction and loose fit but poor compression.

Hope to have helped you, András from Budapest, Hungary

Enjoy the forum.
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Post  Roland Mon Dec 28, 2020 4:14 pm

Hello Jim,

thank you for your reply. I checked it, but unfortunately, there are only about 3 windings left to get the screw in. This is maybe not enough. The crankshaft broke just about at the end of the prop screw. But worth a try. I will do more checking tomorrow.

regards
Roland
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Post  Roland Mon Dec 28, 2020 4:30 pm

Hello Balogh,

this is what I am wondering too!! I don't understand why people argueing about the bad starting habbits of the little Cox engines. 2-3 drops into the cylinder, and whopeeee....

Emanuel,

thank you for the welcome, I am living near Stuttgart. No need for a Venom, or TeeDee in my little Zaunkönig. I first want to fly this little plane in a more controlled manner. :-) But who knows?

Question to all, what about my rpm figures for the Cox 5x3 prop?
Is this the right choice for a Baby Bee???

regards
Roland

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Post  GallopingGhostler Tue Dec 29, 2020 2:55 am

Roland, welcome to the forum. RPM figures you had for the Babe Bees seem typical, are you using a lower level of nitro in your fuel, like 10%? For optimal, I use at least 15% but prefer 25% for the Bees.

Regarding props, the Babe Bee is a torquey little bugger, 6x3 prop was considered optimal. You can read up a little on the magazine engine test articles at http://sceptreflight.com/Model%20Engine%20Tests/Index.html .

The .020 Pee Wee was my first engine also. 1965, I received as a birthday present that and a Walt Musiciano's Scientific 18 inch wingspan stand off scale Grumman F6F Hellcat for control line. My first RC in 1973 used a new Pee Wee, the Ken Willard's Top Fight 27" wingspan Schoolboy rudder only.

Regarding props, I'd suggest having a couple sizes and trying them. You'll find one that works best with the Babe Bee in your biplane. When I lived at sea level, 5x4 and 5.25x4 props worked well for me along with the 6x3. At higher elevations where I live, 4,300 feet above sea level, larger diameter, 6x3 works best. Smaller diameter 5x4 showed a definite reduction in power compared to a 6x3.
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Post  Roland Thu Dec 31, 2020 9:28 am

Hello,

finally today I got it to scream. I was testing some piston/liner combinations and, one was outstanding.
About +1000rpm than before, with low compresion head, 5x3 Cox prop same fuel. But, I would say, not the very best "plop" . More on the loose fit side.


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Post  Mark Boesen Thu Dec 31, 2020 3:54 pm

Find the mouse engine article posted, lots of tips.
Snug ball socket, somewhat loose piston, properly shimmed cylinder for starters.
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