Typical Runtime

I recently got the bug to fire up the old Cox 049 engines I flew back in the 70's. I drug out the little guys and cleaned them up.

The Babe Bee has a #1 piston and a low compression head, the old style copper star reed.
The Golden Bee has a #2 piston (thin wall with single bypass, a high compession head; 3 washers), old style reed.

I hadn't started them since the early 80's but had tried to keep the engines limber by putting some light machine oil on them periodically over the years and turning them gently, so the engines weren't frozen.

At first inspection:
The tank backs had grown some sort of corrosion, as had all unprotected metal in the old flight box; wrenches, old control horns, metal flight cable, screws, etc. Don't know what that was. The cylinders, heads, and aluminum parts seemed immune.

I cleaned the engines by soaking in alcohol for a couple of hours, and took them apart. Scrubbed them with a tooth brush in alcohol. Most of the corrosion on the tank backs seemed to come off. Both of the fuel pick-ups had gone all hard and one even had broken inside the tank. Otherwise they seemed to be OK. The reeds looked like they had little circular grooves on them where they should seat against the tank. These engines were run hard when I was a kid. The needle on the Golden was a little bent at the external part of the tank.

I ordered some replacement fuel lines and tune up kits from EX engines, what great service. Replaced the fuel lines, both tank gaskets and reeds. I didn't replace the head gaskets as they seemed OK. I put a little light oil in them after cleaning as I had no fuel. I took a good bit of time trying to make sure they were clean and refurbished as best I could.

When I put the engines back together the Babe had good action, like I remember. When you rotate the prop with your finger when you reached Top Dead Center the prop would kick over and slap the back of your finger. There was a little bit of a compression pop as the exhaust port opened. When you stopped the rotation at TDC the compression would slowly leak out over 10-15 seconds.

The Golden had virtually no compression. You could rotate the prop and, unless you did it very fast, there was no kick-back. There was no compression when stopped at top TDC This was always the best running engine I had. Anyway, I checked the head for leaks by filling the cylinder with alcohol and slowly rotating the prop. There was no leak around the glow head, but there was all sorts of fluid leaking around the piston and out the exhaust ports. Even with the cylinder filled with liquid, there was very little resistance to rotating the prop; not a good sign.

Oh well, what did I remember? Maybe cleaning the shellac off the piston screwed up the compression. I put the guy aside and went on a hunt for fuel. After scouring all the local hobby shops, I finally got some air fuel: 15% nitro, 17% oil (50/50 castor/syn). I figured this was OK to fire the little guys, at least for a test run, especially if I kept the mixture rich.

I started with the Golden, as this was the one that I worried about most. Well, it fired up pretty fast, even with the low compression, but only ran for a minute or so. Then it wouldn't run anymore. The prime would burn, but nothing else. I pulled the engine apart and found that there was some sort of gunk that had broken free and plugged the fuel intake on the tank back, not in the hose but inside the nipple. I cleaned this with a soft piece of wire until I could run fuel through the tank-back pathways in all directions using my fueling bulb.

I could fire up the Golden OK and, when I could get it to run a full tank, it seemed to run for such a short time. I know I was purposefully running it rich because I wasn't sure of the fuel, but the run time was way short. Maybe only a 1:45 or, at best, 2 min. This seems like about half the time it used to run when I was a kid.

It was also a little cranky about maintaining a constant RPM. I would tune it to best speed, then back off to run it rich. The engine wouldn't hold the RPM, it would go rich or lean after a little time and quit. Most of the time I had to start it two or three times to run a full tank. Getting it to run a full tank was an interesting problem. I could only get it to run a full tank with constant fiddling with the needle. I remember setting this engine where it just wanted to break to best RPM and then it going best RPM during flight, screaming around the circle, combatting with my buddy.

I was thinking that better compression might fix the issue, so I ordered a new "Black Widow" type cylinder (Modified Sure Start with the exhaust ports opened, dual induction and SPI and bypass) and a piston tightening tool. This cylinder had great compression. You couldn't even rotate the prop if you filled the cylinder with fuel; no leaks around the head or past the piston. I also got some other parts just to have them, like replacement needles, glow heads, and cranks.

Anyway, I tried another run session after I got the new parts. It didn't seem to help when I tightened the push-rod, replaced the head gaskets, added or subtracted head gaskets, polished the glow seat, changed glow heads, changed the needle valve, or even when I put in the new cylinder/piston. (The new piston had really good compression and I checked it for leaks.) The engine was hard to maintain RPM and the run time, when I could get it to run a full tank, was always under 2min.

I'm beginning to think that (best scenario) there is something wrong with the fuel, or (worst case) I have damaged the tank back. If it's the fuel, I don't want to run the other engine until I correct it. If I have damaged the tank back, I'm going to be a little mad since I don't like the plastic replacements you can get now.

Anyway, what is the typical run time of an engine with an 8cc tank? Do I need new fuel, what type, and where to get it? Sig doesn't have 20% nitro and 20 pure castor and niether does Ritchesbrew. Should I try the tank back from the Babe just for test runs to see if that is any better?

Any suggestions to getting the little guy rehabilitated or is the little Golden beauty ready for its final resting place?

Thanks,

Jaye

Jaye,

Did you replace the reed? I assume so if you installed an overhaul kit.

Try this:

Close the NV and plug the overflow with your finger. Take a syringe with a piece of fuel tube attached and pump the tank up with air through the fill tube. If you see any bubbles coming from the tank to crankcase gasket, backplate screws, tank to backplate seal or the venturi hole then you have an airleak which could result in a unsteady run.

Also remove the NV spring and use a small piece of fuel tubing in place of it and see if that helps as air can be drawn in around a loose needle.

If all seems good you may have some old crud in there somewhere. Compressed air will help eliminate that issue.

One last thing, make sure the reed clip is installed correctly. The tang should point away from the tank and the reed should be able to rotate 360 degrees when clipped in place.

Ron