Greetings,

Ijust purchased a n.i.b. OS.61 SF ring engine that has never been run (ran?) Ihave always had ABC engines and this is my first ringed engine. The engine turns over fine, is in great shape, etc. Idisassembled to verify the "no runtime", and oiled it to make sure everything turns over smoothly. It is obvious this has never run, including break-in. What Ido notice when I install the glow plug is there seems to be very little, almost no compression. Is this normal on a ringed engine? Perhaps the ring needs to seat with a run-in? I did not remove the piston/liner assembly as this is obviously new with the rest of the engine. Before Ifire this up, I wanted to check on this. My ABC version of the .61 SF is an awesome and reliable engine with plenty of compression.

Appreciate any feedback.

You'll be amazed at what a difference even 5 minutes of slow, rich running will make. In about an hour it should hold compression like an ABC engine does only it will still hold it long after the ABC engine has start to show signs of wear.

Great! I was hoping this would be the case. Thanks!

Break it in slobbering rich for a while, just the opposite of an ABC engine.

Ernie Misner

Thanks Ernie, will do. I guess this is normal not to have a lot of compression (hardly any) on a new ringed engine. Does the ring expand, or simply conform to the cylinder wall?

Yes as mentioned already the ringed engines need some run in time to get the ring seated in order to provide the best performance.

One thing to mention is that some engines use a Dykes ring on the piston. This type of ring is located right at the top of the piston. The Dykes ring has low resistance as the piston moved up and down, and when on the combustion cycle the ring is forced outward to seal the cylinder as the piston is heading down. So engines with Dykes rings feel like they have no compression. But usually when you give them a quick strong prop flip, you can feel the ring engaging and the compression increases enough to let the engine fire up and run.
The Dykes ring ism a evolutionary development that allowed a piston ring engine to turn higher RPMs than a conventional ringed engine. But even the Dykes ring has a RPM limit too. Then the lapped piston engines with no rings could rev a little higher than a ringed engine as there is no ring to flutter and cause a power loss when the engine reaches a certain peak RPM. Later the tapered cylinders with ABC, ABL, AAC came about, no rings too, and they allow a engine to turn much higher RPMs, up to the engine design limits.

That pretty much covers it

Wait, there's more! Some ringed engines will appear to have compression when you turn them over in one direction and none or little in the other direction. That's usually the non-pinned rings like in a 4-stroke though and if the gap winds up facing, say to the left, there will be more or less pressure on that side of the piston depending on which direction you are turning the engine over. No kidding!

Ernie Misner

Hook it up to a gallon jug of fuel and let it run nice and rich for a good long time.

I would rather suggest that after maybe 15 minutes on the ground for initial breakin then fly the plane moderately to get the airflow over the engine cylinder for cooling. Only short bursts at wot increasing until the engine has probably another 5 or 6 flights of 10-12 min each. This has become my practice for the last several years.

While not totally broken in till well after a gallon of fuel is run, I would think two tanks or so would be enough before flying. Set it on the rich side, and be prepared for the compression to be up and down for a gallon of fuel or two.

You only need to run a few tanks, two or three maybe, sometimes more to iron out the kinks and get it adjusted reasonably well.
You really need to heat cycle the engine as that helps it run in much faster than simply hooking it up to a gallon of fuel and letting it run non-stop.
You want the engine to heat up and cool off. Also at first you want to run the engine for short period of times at a rich full throttle and then back it off to a high idle letting it cool off, then repeat. As the engine gets run in more, the full throttle intervals get longer and longer.

Heat cycling is where you run the engine for a few minutes and stop it, let it cool off, then repeat.  Some engines, such as the vintage free flight ignition engines from many years ago, only run a small fuel tank for maybe a minute or less and then you let the cool off and repeat the engine run, and so on. You couldn't run these engines very long, especially at first when new.

Now with the ABC engines, they basically run them near their top speeds as you need them to heat up and expand the cylinder out straight so the piston doesn't get shrunk down with the swaging effect from the tight taper or pinch in the cylinder. But you still need to run them on the rich side some at first though.

In order for the ring to seat properly the engine needs to get up to operating temperature.

Running motors blubbering rich is old school. Modern engines are built to very close tollerences and need very little break in. Too much fuel and it wont create enough friction in the sleeve to properly seat the ring.

Run it a little rich for a few flights. Raw fuel pouring out the exhaust does nothing but waste fuel and prolong the break in.

Not for ringed engines, though built to higher tolerances they still have a lot of friction when new. Running rich enough to four cycle ensures that they will not overheat and wash's out the initill wear. Also heat cycling does nothing but take up your time. Unless overheated the engines ge nowhere near the temperatures to heat treat or temper the metals. Just run a tank at a strong four cycle, and another starting out at a rich two stroke and lean it out a click or two every so often. Then adjust the mixture and install the engine. Fly and have fun. Don't mind the 101 ways to break in an engine, you will just get confused over something that has no value.

I would respectfully disagree, though they need to be somewhat rich, pouring raw fuel does nothing.

I've broken in a pile of nitro helicopter engines.

Start out a little rich and it will run richer/cooler as the ring starts to seat. You lean it a little as a time until the motor no longer requires tweaking (3-5 tanks depending on oil content of the fuel), then you let it rip. I'm talking engines without a prop blowing on them running at 16-18K so they are operating in a lot harsher environment as an airplane engine.

You should run new Saitos as blubbering rich as the manual recommends.

I'm with Earl with heating up non ringed engines quickly.

But only for the first 10 minutes on the Saito. I don't run ringed two strokes sloppy wet, just where they break into fourstroke. Then when you fly it, it fourstrokes part time on the level, two strokes in a climb and fourstrokes full time in a dive. I don't break in any engine at the point you need glow power after starting.

I run 2 strokes hard after the first minute or two.....depending on how they sound, etc. i use the same rpms like you for each tank on new Saitos, but they get a lot of wide open run time after the first 10 minutes.

RTFM - that is the best advice to heed. I have owned and run many OS engines both ringed and ABC, though I am down to just two these days, both ringed, due to thinning out my collection.

Generally speaking, a person who invests in an OS engine does so because they want an engine that will give good service for a long time. That long relationship starts with with the all-important break-in period so getting it right counts for a lot. Ignore the impatient jokers who advocate running too lean too early - if they want to torture their engines to a premature death then that's up to them - that stuff is for cheap 'throw away' ABC engines and people with money to burn.

Manuals for most engines can be found online if you didn't get one with the engine.

Not since they quite selling the SF engines. OS is not known for longevity. They are known for ease of use, and quick break in. The quick break in is part of the reason for the ease of use, and part of the reason for their short life.

For longevity try a Enya, Fox, or the older SuperTigre's (not sure about the Chinese versions).

For bfreak in just be sure it is very rich, a 4 cycle run is not mandatory but helpfull to prevent overheating. Also read your manufactures instructions as not all engines are the same.

You can also consider an engine to be a 'throw away' if the parts are too expensive.

I think (ok I'm sure) that if you RTFM from OS it will say they require very little break in.

Wow - I had no idea that OS had done a kamikazi raid on their justification for their high prices - guess I won't be buying another one any time soon!!!

The oldest engine I have still in use is an Enya 45 6001 that has two rings - it will probably out-last me!

I love my Super Tigres, but have never owned a Fox engine that I can remember...

Ringed is the way to go if you want an engine that will last - run it in right

Would that be the manual for the ringed .61 in question?

That would be an excerpt from a ringed heli engine, they don't vary greatly though.