|Jan 05, 2013, 11:05 AM|
Joined Jun 2004
Ringed 2 Stroke Break-in
What is the best way to break-in an O.S. 95 AX ringed engine? There seems to be a lot of new information out there.
Also, what would be the best fuel brand to use in this particular engine?
Was looking at some of the synthetic fuels, but don't know if they will work, as well as, castor based fuels.
Thanks in advance,
|Jan 05, 2013, 11:26 AM|
United States, NC, Locust
Joined Jul 2001
I would follow the mfg's suggestion. You could send a note to Bax at Hobbico for more information. I personally like to use a little (5%) or so, castor in glo fuel, as this gives a bit of extra protection to the bearings. Run the engine a few minutes 2 -3 times on the ground to get the needles set, and heat cycle the engine. Don't set it too lean. Check all the screws for tightness, then just fly the plane. No 3D until you get a couple of tanks of fuel thru it.
|Jan 05, 2013, 11:35 AM|
Nothing is new.
Just run it extra rich on the ground for the first tank, then lean it a bit and fly it around for 2-3 more tanks, changing the load as you go (doing vertical figure-eights is recommended).
|Jan 05, 2013, 03:00 PM|
The following link is basically what I was taught 35 + years ago when I was young and decided I wanted to be a mechanic. I've used it over the years and it has worked for me well. This will not work for an ABC engine but any ringed engine it is they way to go. The only caveat for our model engines is like Dar said, run them a bit rich at first. NOT slobbery rich, just rich enough, if you know what I mean. Personally, I run the engine just enough to get a stable idle and a steady but slightly rich top. Put the engine in the plane and go fly. Loading and unloading the engine by doing loops of vertical figure eights is very good. Don't feel you have to fly for ten minutes doing this as it is quite boring. Land an go up again. After three tanks or so still leave the engine a tad rich but don't worry about it, just go fly. After a gallon of fuel set for top power with a 300 RPM or so drop on the rich side and enjoy your engine.
|Jan 05, 2013, 10:44 PM|
Personally I run them in for at least an hour on the test stand with 25% all castor starting with full throttle and as rich as it will stay running without glow power then each successive run of about 5 minutes each I'll gradually lean out until after an hour it's on the verge of 2 stroking where it's good enough to fly but keeping it still just barely 2 stroking for another hour.
My G51 actually kept slowly improving over about a 15 hour period which confirms precisely what Super Tigre used to advertise for their ringed engines . The photo shows the ring in my Enya 60-IIIB after 90 minutes of running. Note how the ridges from the machining process have smoothed out on top but have done it evenly from top to bottom indicating the ring is square against the liner. I'd call this nicely run in.
|Jan 05, 2013, 11:10 PM|
I did mine exactly the way the directions said. Install in Plane. I use cool power (green) 15-20%. Full tank. On the ground. Start. Run very rich for ten seconds then lean out for ten seconds and then rich for ten and so on until you empty the tank. The directions state run rich (four stroke operation) then lean the needle just until it reaches two stroke operation. Don't over lean it. Just until you hear the change. I have had NO issues with mine since and have had it over a year
|Jan 06, 2013, 01:15 AM|
What Lycoming have to say about it...
I guess y'all know who Lycoming is... And for those that don't, it is a large manufacturer of engines, some of them piston engines that reside 'under the hood/bonnet' of most light planes built by American manufacturers.
For all those that think an engine should be idled-through the break-in...
Read this carefully:
A new, rebuilt or overhauled engine should receive the same
start, warm-up and pre-flight checks as any other engine. There
are some aircraft owners and pilots who would prefer to use low
power settings for cruise during the break-in period. This is not
recommended. A good break-in requires that the piston rings
expand sufficiently to seat with the cylinder walls. This seating
of the ring with the cylinder wall will only occur when pressures
inside the cylinder are great enough to cause expansion of the
piston rings. Pressures in the cylinder only become great enough
for a good break-in when power settings above 65% are used.
Full power for takeoff and climb during the break-in period is
not harmful; it is beneficial, although engine temperatures should
be monitored closely to ensure that overheating does not occur.
Cruise power settings above 65%, and preferably in the 70%
to 75% of rated power range, should be used to achieve a good
Remember that if the new or rebuilt engine is normally aspirated (non-turbocharged), it will be necessary to cruise at lower
altitudes to obtain the required cruise power levels. Density
altitudes in excess of 8000 feet (5000 feet is recommended) will
not allow the engine to develop sufficient cruise power for a good
For those who still think that running the engine hard during
break-in falls into the category of cruel and unusual punishment,
there is one more argument for high power settings during engine
break-in. The use of low power settings does not expand the piston
rings enough, and a film of oil is left on the cylinder walls. The
high temperatures in the combustion chamber will oxidize this oil
film so that it creates a condition commonly known as glazing of
the cylinder walls. When this happens, the ring break-in process
stops, and excessive oil consumption frequently occurs. The bad
news is that extensive glazing can only be corrected by removing
the cylinders and re-honing the walls. This is expensive, and it is
an expense that can be avoided by proper break-in procedures.
To summarize, there are just a few items to remember about
1. If a preservative oil has been added by the aircraft manufacturer, drain it no later than the first 25 hours of operation;
2. Follow the engine manufacturer’s recommendation regarding
the oil to be used for break-in and the period between changes;
3. Run the engine at high cruise power levels for best piston
ring/cylinder wall mating;
For the engine, as far as our glow engines go, not to suffer damage from the ring overheating, ends butting and the 'running-in' becoming a 'ruining-in' , the ring end-gap should be checked before beginning.
After that's off the table, just let'r-rip!
|Jan 06, 2013, 03:17 AM|
I know your OS.95AX is not a full-size Lycoming engine...
But the materials are the same (steel cylinder sleeve honed to size and finish, aluminium piston and cast-iron ring(s)), as is the objective of the break-in.
So, I believe the best suggestion is to follow what Lycoming wrote, with the necessary changes.
It is similar to what you've heard here.
|Jan 06, 2013, 08:29 AM|
As for cylinder pressures expanding the ring against the liner (as mentioned in the Lycoming bit)...it does, but the highest combustion pressures the rings ever encounter in our 2 strokes is at the point where they're running at the fastest 4 stroke.
|Jan 06, 2013, 08:49 AM|
That Lycoming thing is a bad analogy, aircraft engines are built very loose, they have more piston slap when new than a Mack 711 has after 500.000 miles. No comparison to a precise model engine.
|Jan 06, 2013, 09:52 AM|
On that I agree with you fully, Brian!
...On the firing cycles only, of course.
I do agree it would be logical for full-size aero engines to be built rather loose.
After all, piston-slap is no more than noise (that develops into nothing); but if a piston seizes in mid-flight, that plane's a goner!
I don't understand; are you afraid the rather tight piston in a precisely built model engine, will over-grow and seize in the sleeve; if the engine is run at over 65% of its maximum torque (we all know RPM will never cause any damage to a new engine)?
I don't think it will happen; at least not if the ringed engine is run at a fast four-cycle, as Brian just mentioned. That, instead of running it very wet and very cold (worthy of a meehanite-steel engine).
|Jan 06, 2013, 10:08 AM|
There have been two schools of thought on how to break in a ringed piston engine for ages now. One group prefers the slow and easy break in method. The other group prefers the hard and fast break in method. But if one watches how the big boys break in their racing engines for racing (such as drag racing for example), then the hard and fast method has a lot to say for it. The main method being to get the piston ring to seat and wear in fast is the main goal.
I sort of aspire to a compromise on both methods. I tend to run the engine rich and slow for a while at first to get it lubricated up good. This is because with a new engine you don;t really know how well it was lubricated to start with and you can't really depend on your own lube when you reassemble a engine either. Then I start working on running it harder and faster. Being a air cooled engine, that expands and contracts a lot more than a liquid cooled engine, I alternate fast full speed runs with periods of cooling off, both with heat cycling and low speed idling periods).
MECOA's ringed engine break in method works quite well which is pretty much about what I do anyway.
|Jan 06, 2013, 03:45 PM|
Escondido, CA USA
Joined Jan 2001
Great link to the Mecoa site. I've been doing break-ins that way for years on my ringed engines with no trouble. I have a Fox Eagle .60 from the mid-Seventies with its original ring/cylinder and compression is still very good as evidenced by the fact it's still in the first airplane I bought it for, back in 1978; I have no idea how many gallons of fuel I've run through it and the performance hasn't deteriorated at all. I've always run name brand fuels (Fox, K&B, Powermaster) and made sure there was at least some castor in the lube package, and don't have the slightest problem adding a little as the need arises. Makes me feel better and smells good, too Can't tell if the engine is grinning or not
As an A&P mechanic for the last 40 years and an IA for 30 of those years, I've always followed what the manufacturer says about breaking-in their engines. I have flown break-in flights with airplanes powered from a Continental A-65 up to their GTSIO-520--from 65 HP up to about 375, and the Lycoming-powered stuff from the O-235 to the TSIO-540 engines (from 100 HP in a PA-12 up to about 385, such as the Beechcraft Duke), including their older, radial products and those engines almost always have successfully completed their recommended service run times. I'll also ask the overhaul shop what they want if the engine in question was not from the factory, as they will be warranteeing that engine, not the factory. The afore-mentioned companies assembled and certificated it, not me. I don't experiment with someone elses expensive engine/s. Too much liability, man.
And yes, it's true: Full-sized airplane air-cooled engines are set up loose, especially when compared to liquid-cooled engines for any other purpose. Temperature variations during normal operations are too great for the tighter clearances you can do for a liquid-cooled engine. Hmm--next time I see him, I'll ask the one who cares for several R/R Merlin engines how closely they are set-up.
|Jan 06, 2013, 05:00 PM|
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