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OS .55AX problem

Old 05-08-2007, 09:56 AM
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Default OS .55AX problem

Bought a new .55AX recently and have not been satisfied at all. I'm experiencing dead sticks on each flight at mid to high throttle settings. I have removed carburator and cleaned thoroughly. First - the low end settings recomended in manual are wrong. Instead of 1.5 turns on the low end needle you need about 2.25 turns out. After doing that transition is good and mid range is good. High end I'm getting about 12,500 rpm. I ran the engine with an APC 11-7 prop at 9,000 rpm. Running the engine at these settings the cylinder head temperature was hitting 315 degrees F and after about 2 minutes of running just abruptly stopped. I then richened the low end needle and obtained a richer setting at this same rpm and the head temp was better, but still hitting 265 degrees (seems high). But again engine abrutly stopped after 2 minutes of running. There are no air bubbles in the fuel line in each of the tests on the ground. I have also installed 3 new plugs - 2 - #8's and 1 - A3.
I have a friend who has one also and he removed it from his plane due to overheating but that plane was a pusher so we thought maybe not enough air. I'm going to install in my plane and try just to eliminate tank, plane, etc.
The first engine I had in this plane was an OS .46FX - not quite as much power as the .55AX, but I'm certainly not getting the 15% increase they advertise.
Any ideas???
Old 05-09-2007, 10:09 AM
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Default RE: OS .55AX problem

Well, we'd tend to prop the engine so that it will turn mid-12,000's when leaned to just rich of peak RPM on the ground. If the engine has less than a gallon of fuel run through it, it may not be fully-broken in. We usually run an engine 45-60 minutes on a test stand before flying. ABL engines, like the .55AX get run as rich as possible without letting them go into "4-cycle" mode. We then gradually lean them towards peak RPM.

We ignore engine temps, and don't measure them. We go by how the engine sounds and handles. That's a better indication of how the engine's running. We've found that too much reliance on engine temps tends to cause short engine life...it's that unreliable as a tuning checkpoint.

Needle settings advised in the instructions are only starting points. You must adjust them as needed from there. Engines that use methanol-based fuels cannot be adjusted to a "book" setting because the actual setting will change from day-to-day as the air temperature, pressure, and humidity changes. No such thing as "set and forget" with methanol (glow) engines.

We'd strongly suggest that your fuel contain castor oil if it does not. We like the oil to be closer to 50/50 castor/synthetic, but even 5%-10% of the oil mix being castor helps. Non-ringed engines benefit from castor.

If the engine's quitting in mid-flight, it's overheating, which means bad cooling, low-oil fuel, bad tuning, bad fuel delivery, and so on. Some detective work is needed. The high temps just tell you it's hot, but don't tell you why.
Old 06-25-2007, 08:28 AM
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Default RE: OS .55AX problem

Longson
Yep, I have a similar problem. My 55 AX can be tuned fine at idle and top end at 12000rpm. However it will hesitate when accelerating through the 50 to 60% range and if run in that range for any more than 30 or 40 seconds it will quit. Its not hot. I have tried different fuel blends with varied success. No nitro = more reliable although less power. Overall I am very dissapointed it is not a patch on my old 46FX as far as usability is concerned. I startedwith a 12* 8 and got 11000rpm and then changed to an APC 11*7. this gives around 12000rpm on 10% nitro and 18% full synth. On reading these forums a carb problem may be present in some engines and could indicate a quality issue. All other areas this engine is fine but if it dont run right it aint right.
Old 09-03-2007, 06:56 AM
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Default RE: OS .55AX problem

I have an OS 55 and still having problems with overheating and quitting in mid-flight. Has anyone come up with a solution to the problem over overheating? I have tried props 12X4 to 13X6 APC and Zingers to slow the rpms down. I have cleaned the engined many times, cleaned the carb, and even shimed the engine to get more gas in the head, but it seems like nothing works. I am at he end of my rope with this engine...HELP!!

Henry
Old 09-04-2007, 10:35 AM
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Default RE: OS .55AX problem

Overheating is caused by a too-lean setting, not enough airflow through the engine's fins, too little oil in the fuel, and too much load.

From what your post shows, you have too much propeller. To keep down RPM, you should use the throttle, not the propeller.

If you use a propeller that will allow the engine to turn 12,000 to 12,500 RPM at full throttle when leaned to just rich of peak RPM, then you can use the throttle for lower RPM, and the engine should not overheat from overload.
Old 10-23-2007, 07:47 PM
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Default RE: OS .55AX problem

Hey Longson, I'm in the same boat as you so to speak... I didn't see your post so I just made one on the same subject. I've tried everything I can possibly think of too but it still dies in the air. Can't get it to do it on the ground though...

Let us know how you go, and I will too. Surely this engine is good if we can work out the problem.

Jon

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