I bought a Hobbico NexSTAR Select. It comes with the O.S. Max FXi 46 engine. Supposely, I thought, the engine was broken in at the factory. It has a limiter on the high speed needle that was set at the factory. However, the NexSTAR manual references running it rich while breaking in the engine. The manual does not cover the break-in procedure.
I have the engine manual that comes with the RTF kit. It says to open the needle valve to the advised starting setting and start the engine, then adjust so the engine doesn't stop. Run for one minute with throttle fully open but with the needle valve adjusted for rich, slow "four cycle" operation. Then close needle valve until engine sppeds up to "two-cycle" operation and allow it to run for about 10 seconds, then reopen the needle valve to bring the engine back to "four cycle" operation and run for another 10 seconds. Repeat this procedure until the fuel tank is empty.
This being said, with the needle valve limiter installed, full counterclockwise is "rich" and full clockwise is "lean." What do they mean by "two cycle" and "four cycle" operation? How do I tell the difference between the two? I read somewhere on this forum that you can tell by the sound of the engine.

In four cycle operation, a typical two stroke engine will run rough and "burble". That's the best I can describe the sound. It makes a sorta low "burble". It spits a lot of unburned fuel and oil in the exhaust and will probably not transition well. It may miss a lot. DO NOT break in an ABC/N engine in this mode, you'll ruin it. The two cycle operation will sound smooth and accelerate fairly well. It will have that smooth whine you're used to hearing from other engines.

ABC/N engines need to be broken in at only a SLIGHTY rich two cycle. The reason is this. In ABC/N engines, the cylinder is ground with a slightly smaller diameter taper at the top. When the engine gets up to proper operating temperature, this taper expands and allows for the proper fit of the piston. If it doesn't get hot enough (and it won't in four stroke operation) the taper won't expand. The piston constantly pushes against the taper, and will quickly wear out the cylinder and piston.

Start your engine and adjust the needle valve until it just begins to run smoothly, at full throttle, with that high pitched whine. Let ut run about half a tank, maybe 4-6 ounces. Shut it off and let it cool. Repeat this several times. How do you know when it's broken in? When it will hold an idle for about 30 seconds and still accelerate smoothly, it's ready to fly. The remainder of the break in is done in the air. After this, you may adjust the needle for full power. How can you properly do this? Easy. At full throttle, briefly pinch the fuel supply line. If the engine sags immediately and dies, it's too lean. If it picks up speed and runs a while, it's too rich. If it picks up speed and then starts to die, it's right.

Dr.1

I don't mean to be ignorant but I'm new to this....what's an ABC/N engine?

Aluminum piston and Brass cylinder liner with a Chrome or Nickle coating. These are designed to have a very tight piston to liner fit at the top of the compression stroke. The other regularly used type of engine construction uses a piston with a ring.

First of all, the engines are not broken in but they are "pre-set" at the factory which requires very little running.

ABC & ABN refers to the metalurgy of the engine

Base of Aluminum
Then Brass plating followed up with either Nickle or Chrome plating.

Piper Chuck told you right. There are also a few ringed engines with chrome cylinders out there. There is also a iron cylinder with a ring (not seen much any more), and a lapped cylnider/piston where the liner is iron and the piston is iron or aluminum and there's no ring. This isn't seen much amy more, either.

For all practical purposes, any engine made recently that does not have a ring is a ABC/N. Your OS FX is that type of engine.

Not right, Bruce. It's an Aluminum piston with a Brass cylinder plated with Chrome or Nickle.

Dr.1

the OS engine that comes with your plane will run fine without any of the break in running needed for a new out of the box engine,when the manual says run it rich they are referencing the high speed needle as long as smoke and a little fuel is coming out the pipe when you fly the plane and you get idle to full throttle transition your fine.

the engine has been run once and pre-broke in before installation in the plane and you should not have to go through the break in procedure described in the engine manual just run the engine slightly rich for a few flights.the manual is included because you have a new engine and need to learn what each part does and proper maint. for good running the planes inst. states you do not need to do a break in run.

OS engines have a simple break in procedure to follow when you buy a new one, your plane"s engine has been done for you make sure you have a knowledgable helper to make sure your plane checks out radio and engine runs idle to full speed and have some fun.

Unless you have a ringed Super Tigre, ringed OS, ringed Magnum, ringed Webra, ringed.......
All of these use an aluminium piston with a ring and need a long and careful breakin.

No engine ever made has had an iron liner and a plain aluminium piston. Engines like the Enya 40 still use a cast iron piston and also need a special break in similar to a ringed engine.

The 2 cycle sound is what you normally hear at any RC field with that smooth high pitched sound. If the needle is opened to richen the mixture then as the revs drop the engine will begin to give what sounds like an intermittent misfire (because it is ). A little richer and a few less revs and that misfire becomes continuous and the pitch of the exhaust drops to more like a rumble. This is what's called 4 stroking and it's literally true because the engine then misfires every other stroke. With most engines this will begin at about 2-3000 below peak revs and continues down to less than half peak revs if the mixture is richened even more until it's so rich it can't keep running because the plug gets too cool.

Contrary to popular belief you won't harm an ABC type by running them just into a 4 stroke because there's very little difference in temperature compared to a rich 2 stroke.

Unless you have a ringed Super Tigre, ringed OS, ringed Magnum, ringed Webra, ringed

I'll bet they aren't plain iron cylinders.

Dr.1