wierd problem with glow engine
 

Hello,,
I am breaking in an OS46ax and have a problem I have never seen before..
I can start the engine very easily, It will start and idle, go to about 1/2 throttle and then start burbling and die. BUT if I take the pressure hose off the muffler, and leave it off, the engine starts easily, runs and will go to full throttle no problem, put the hose back on the muffler and it will die. Its like the pressure is flooding the engine,, I have never seen this before,, what to do,, Run the plane with the tank vented, and not go to muffler,, or is there some kind of restrictor to put in line,, The engine is totally stock,, I have the needles set correctly, just rich on the high side because I am breaking it in.

ANY IDEAS FELLAS??

It is just set too rich on the needles for the set-up with pressure from the muffler. Just turn in the needles a little.

There are no "correct" factory setting, the recommendations from them are extra rich to make sure that the engine will not run too lean straight away...

+1

An overly rich engine runs poorly, an overly lean engine doesn't run (long) at all.

As already pointed out, the "factory"settings are very rich as a precaution against lean runs.

When breaking in an engine and starting at idle, it is often not possible to bring it up to full throttle with a very rich mixture. You either need to lean it down then richen it when it gets up to speed, or start the engine with the throttle at or near full throttle. The latter is a bit more dangerous, but when I flew control line we always started them at full throttle.

YEP there are ideas. As basically stated above, a glow engine does not give a tinker's darn about what some directions may state. It runs when the mixture is right, when the glow plug is proper, when the fuel is OK and several other items. It may or may not behave just like one of its own family.
One of the big items especially with NEW engines, especially if the engine is of a higher than normal compression ratio, such as Nelson, Dub Jet, Dykes Ring, and high nitro is that the engine will be close to a freeze-up because the ABC/ABN piston top and the chromed sleeve most likely will need some wearing in.A smaller prop is needed and high speed break-in is also welcome. One never knows exactly what the Needle setting is going to be from any new engine. It will change as the engine loosens up. Typical ringed engine will not act as finicky but can also be the same problem.
Your main problem seems to be your use of "...needles set correctly." In addition you might try a couple glo plug changes. The GP can be a not-so-good even if new.
Toy airplanes are NOT a scientific item. :confused: :o

Thanks fellas

I would not be running a ABN/ABC very rich for break in. It will not reach proper operating temperature. It is not a ringed engine that may require excessive fuel when new to set the ring. ABN/ABC engines need to get up to operating temperature so that the expansion in the cylinder grows to the proper dimensions for optimum operation or peak performance. That is why it is often advised to set the new engine slightly rich, richer than normal (not blubbery rich as in a four cycle run) and go fly it. It does not require a long bench run in like a ringed engine. So you may be just wasting fuel and flying time.

Actually if you go by the OS instructions it will be broken in very rich, sometimes even four stroking. With the low amount of taper in the OS engines (for quick break in) I see no harm in a very rich mixture. The low taper ABC cylinders are also used in control line stunt and will run in four stroke mode all day long, and still have a good seal when they break in to a two stroke.

I would never have a nickle plated OS engine, the ringed engines are good though.

After reading the OS instructions, it's broken in like most other abc/abn engines. You start the engine at the initial settings (as a starting point) and go to full throttle right away. There is a typo that states if the engine cannot run after removing the glow driver "to open the needle valve further". You need to close the needle valve and lean the mixture to keep the engine running. For the first tank, run the engine WOT rich in 4cycle operation for one minute then lean the needle just to 2cycle operation for 10 seconds and repeat this for the first tank of fuel. Then make your first 3-4 flights rich where it just enters 2cycle operation at WOT and avoid nose up operation (lean runs). That's it.

Its spelled out on page 2.

http://manuals.hobbico.com/osm/46ax2-manual.pdf

Actually most other ABC/ABN engines are not broken in at a four cycle, but I accept that OS does not have as much taper as some others and may break in well with inital 4 cycle rich runs.

OS are broken in while riding in the box to your door. No need to do much of a break-in as they're already pretty much ready to go as-is. Most nickel liners have little taper so there isn't much accomplished with a big break-in. TT engines are very similar in this respect. If the piston gets stuck towards TDC without the plug in then it needs a fast hot break-in. IMHO ABN engines are setup a lot similar to a lapped engine. I would not group them with ABC or AAC engines as these are usually pretty tight and thus need more heat to run-in. So fast rpm and a small prop is used on those to generate the needed heat while still being rich.

Check to make sure that the connector to the muffler tap is not plugged. If it is, it will usually start fine if needle valves are set close to correct but will soon die as you quickly create a vacuum in the tank when the engine starts running if the line to the muffler is stopped up.

raron:

Start the engine, leave the igniter on and bring the engine to idle.

Let it warm up a bit.

Then run it up and back to idle.

Wait for a second or two and remove the igniter.

ANY drop in RPM's indicates the low speed needle is too rich.

Replace the igniter. If possible adjust the needles while the engine is running, or if not possible shut off and re-adjust until there is no difference in RPM's at idle with the igniter on or off.

Once you reach that point, adjust the HS needle again and do the same check again for the LS needle.

Finally, richen the LS one or two CLICKS no more, remove the igniter and go fly.

Hard to go wrong when following the instructions. Not much of a break in is required on these. As was said before, the reason to go WOT after start is to heat up the engine rapidly to minimize friction between piston & cylinder. I've heard from others that damage can occure to the connecting rod if it's run slobberingly rich during break in.

I would agree to heating up a non ringed engine quickly to loosen the pinch, but not with a ringed engine.

Let's hope so, he is breaking it in and is intending to break it in rich. So rich it may not start well at idle.

Not on OS and most modern nickle plated engines. They are not tapered as much as the chrome plated engines. If they were they probably would peal the liner before bending a rod.

Yes, this is very true. Most sport engines are not tight enough for the pinch to be any problem. With a glow plug installed they can easily be hand flipped over TDC, and will certainly not be any colder once fired up, no matter how rich they are set.

On dedicated racing engines, i.e. true ABC, one sometimes have to preheat an engine to get it started the first few times. But even there I don't think that I've ever had an engine running so cold that it would start to squeak at TDC again, during running...

What I read was that the connecting rod ends have elongated or simply broke from a break in that was performed too rich on an abc engine. Not sure if it was due to the taper, high amounts of fuel/oil or both.

This is not an ABC engine, the taper is what causes the pinch and grabs the piston at TDC. If there is a lot of taper and the engine is not brought up to running temp then it is grabbing the piston on every stroke and that would elongate or even break the rod.

While not really an ABC engine it is close in design, not many true ABC engines out there these days. IMO the reason that the older ABC engines had so much pinch is that was the best the machining processes of the day could do. Now that most work is done on CNC machines the manufacturers can get closer to optimal fits. In other works 30 years ago we would have to break in an engine to get optimal parts fit, now they can be machined much closer.

For break in of this particular engine, bolt on a 10X6, fuel it up with 10%-15% fuel with minimum of 18% oil, OS#8 plug. Set the high speed needle just a few clicks leaner after it gets into a 2 stroke and idle so that you just notice a slight drop off in RPM after the heat is removed and go fly it. After a 1/2 gallon of fuel lean both down just a smidgen. Avoid extended runs on the ground.

There has been no significant improvements in dimensional quality in the past 30 years or so. That is they could manufacture to the same tolerances back then as now. CNC does little to improve that, it mostly improves repeatablility over large runs and speed. A good machist back then can machine these to tolerances much closer than required for a good taper.

I and others have mentioned the reasons the taper is less for these engines. Some people with more experiance with this than I agreed. This is not "I think", this is "I know".

Sport, read what you just typed. CNC improves repeatability.............in other words some liners would be different then others, same as pistons. Some manufacturers back in the day would have to match pistons and liners.

Abc/abn pistons & liners still come in matched sets.