........good one, Brian....

Yes, it's hard to teach an old dog new tricks. Back in the 70's I had a dear friend
that was flying "carrier" c/l competition with his son at the handle...."Jim" tweaked
the engines (Super tigers)....looked me straight in the eye, and told me that "engines
will idle a lot better with a non idle-bar plug".

This of course went against everything I had "thought I knew" about the aero-model
engines. He explained...."why block the fire from the fuel ?" It made sense to me, I
tried it....and he was right. The regular plugs....having perfect exposure to the fuel
charge....does in fact work better. Try telling that to some died-in the wool idle
bar users, and watch the expression on their faces. They might even call you a liar.

Same thing with engines, like this ring thing. You get these "Internet Jockey's" that
never had a day of formal mechanical training, never worked in a shop for a day
in the lives.....probably never physically held a piston ring in their hand....

....and they want to argue and nitpick about how rings seal on a cylinder wall.

WHEW !!

FBD.

FBD, you be careful.

You'll be getting off the fence one of these days...!

Flyboy Dave,
You seem to think that because you cannot see the out of round ring, even when you put the ring in the bore and cannot see light that it is perfectly round. Well it's not. Let me through one more bit of information not previously discussed. In fact when most engines run, especially air cooled engines, the cylinder is definitely not round, no mater how close to perfect it was before. It will be hotter on one side than the other, which makes it a bit wider on the hot side. That is one reason it is important to bring the engine up to temp during break in.

While I do not have the engine building experience you do. I am a licensed engineer who has some considerable experience doing thermodynamic, heat loss, and thermal expansion analysis. As an engineer I learned long ago that the ring is sprung with a gap because the dimensions of the cylinder is constantly changing from heat and wear.

The breakin of an engine is determined by its materials, its type, and how precisely it's made.

Years ago, model engines tended to be more sloppy in fit, and needed considerable running until they worked well and developed the power they should. Lapped engines, with the steel alloy piston running in a steel liner could require considerable running time until they would be able to maintain running near their intended peak.

Ringed engines, with the "springyness" of the ring never required the running time of a lapped engine, but they still need some time to allow the part to fit together better. The tighter the production tolerances of the parts, the less time needed. However, model engines are usually not made with the precision of some of the automotive racing engines. You're also not paying "racing engine" prices.

Some breakin is good because you want all of the parts to start fitting together. During this process, a bit of extra oil helps to carry away any eroded metal products and helps a tad in the cooling. As the parts wear together, the engine will be able to accept running closer and closer to its peak RPM. I've seen engines that would take over an hour's worth of running until they'd accept being leaned enough that the engine could develop enough power to fly. Other engines do well right out of the box.

Another good reason for spending some time running the engine, in effect breaking it in, is to get thoroughly familiar with it. As it's being run, you become familiar with how it's supposed to be set and how it reacts. Starting rich and "sneaking up" on the peak RPM setting is the best way to go because the engine will never be deprived of lubrication. Too lean is always a no-no, regardless of the type.

During the first few hours of running, the parts will come together and polish themselves to a good fit. That's why some engines actually deliver better performance after a bit of running time. SuperTigre engines have been a good example of this for several decades. The big 'Tigres tend to improve in performance over the first few gallons' worth of running, and then will deliver reliable power for a long time, barring accident or abuse.

There are many reasons an engine should be run for a bit before it's put into service. Your engine manufacturer should mention this in their operating instructions. They don't go by traditions or hearsay, but by sound experience with their products.

Since we all seem to be climbing on the bandwagon, can I join in?

I have a PhD in Advanced power systems (fuel cells) and used to lecture in thermodynamics to Ford and Jaguar MSc racing engineers at Loughborough University.

I also think I know a bit about engines, but my knowledge pales in comparison with the experience of some of you guys with respect to model engines.

The truth is, both FBD and and Sport Pilot are absolutely correct, as we all know. The cylinder will indeed be subject to thermal differentials due to its assymetric heat loadings and will expand unevenly.

The ring, however, is flexible enough to easily accomodate these small out of circular distortions so the running-in process will not be unduly affected by this. It is my understanding that a four stroke ring will bed in rapidly and evenly since the function of a ring is to seal under normal cylinder bore expansion irregularities. The surface metallurgies will adapt more rapidly on a ring than an ABC engine because the contact areas are reduced and the pressures will be higher. And everybody thought the ABC engine runs in quicker...? Of course we still have the piston skirt and the crankpin/bottom end to consider - the skirt is lightly loaded and is not significant. The bottom end IS significant, but will bed in rapidly assuming sufficient lubrication (rich).

From my understanding of the issues I would recommend running a ringed engine very rich for a tank to help ALL surfaces settle a little. Then I would say fly it: start off with enough WOT power to fly (but rich) then lean gradually by the flight.

The most favourable running-in conditions are in the air. The loading on the engine is constantly changing; there is (should be) plenty of cooling and the engine revs cannot settle into a resonating patch where harmonics can apply stress loadings to the rod, shaft, pins etc.

It is however, a truism that if you ask 100 people how to run in an engine you will get 150 answers.

Just get it in the air quickly, but run it a bit rich. Okay?

Job done.

If all the experts on this subject were laid end to end they would never reach a conclusion.

jess

PS: I know the answer, but to avoid controversy it shall never be revealed

Just as an addendum on the running-in issue:

A ringed engine will run in fairly rapidly and will then improve slightly in performance for a few hours. The performance will then stabilise for the life of the engine until it begins to wear beyond its tolerances. The end will then be in sight and the engine performance will deteriorate quite rapidly.

In contrast, an ABC/Nickasil/whatever layout is either running in or wearing out. There is a point where this engine layout will reach its optimum fit - and performance - and after that will deteriorate. Of course, this is so gradual that no one would notice until the performance has faded to the extent that the engine is losing power.

In practice little difference, but it does highlight the difference between these two engine layouts.

Hi Dave,
This Cognitive Dissonance is so true. I would never had known what you would call it but it is something you will see in life thats for sure. I have seen this in the hobby before as well. It always amazes me how passionate people get about their hobbies. Even to the extreme's of terrible arguments that will end friendships over things as trivial as how you break in an engine or what blend of fuel you run. I am fairly new to the hobby (going on 4 years now) and have only owned a handful of "new" engines. I am currently involved in another thread hear regarding my OS FL70. One reply to my question there was regarding whether I had broken it in properly. I did the same as I've done with my other new engines and this is the only one I've had problems with. I am always looking for a new technique or a bit of info that I had'nt had before. Thanks Jeff

Clarence Lee always said if a ringed engine can maintain its rpm when leaned to peak then it can be considered run in. If the rpm drops after its peaked out then it needs more time. Older foxes and Supertigres seem to improve a lot with time. All my "older" OS's could be leaned to peak after a couple of tanks. I have never ran a model engine for more than the few minutes it takes to set the carb before it was in the air and they all run great and last years. I do think it odd when someone makes a big deal about fuel and breakin procedure, then flies from a dirt runway.

"...."Jim" tweaked the engines (Super tigers)....looked me straight in the eye, and told me that "engines
will idle a lot better with a non idle-bar plug". "

sure.... in most Super Tigre's (variation of Curtis Porting) or Schneurle ported engine it's probably true.... Idle Bar plugs were developed to cure fire-dousing when trying to get a baffled-piston cross flow scavenged engine to idle..... the baffle atop the piston directs the incoming flow directly at the plug.... in the Super Tigre's and Schneurle ported engines, the flow from the bypasses is swirled upwards by intersecting flows and doesn't impinge 100% on the plug....


[:-]

I recall an article by one of the early greats, Dunn perhaps?, in which he stated that his tests showed improved performance if the idle bar was oriented parallel to the baffle. This was accomplished by using gaskets of varying thickness.

jess

For what it's worth, here is one more tidbit.

I just bought a new ringed Enya 50SS 2-stroke. The instructions that came with it say simply to run it rich for the first hour and after that lean it out to a normal (slightly rich) setting. The instructions say the engine may take 2~3 hours to reach its peak performance.

Interestingly, the instructions that come with the ringed OS 50SX say to run it 4-storking at full throttle for the first minute then lean it to 2-stroke for 10 seconds then back 4-stroke and repeat until the first tank is empy. OS doesn't distinguish between ringed and non-ringed breakin. The instructions for the FX engines are the same.

Jess....that's another old Wives tale....a K&B .61 which is loop scavenged cross
flow, with a baffled piston will run better and idle better with a K&B 1L plug,
rather than a Fox long idle bar plug. Of course now, this is only my finding, and
I've only been on this experiment since 1972, so I'm sure the next poster will
say his K&B's run better with the Fox plugs, and don't idle at all with the K&B plugs.

BTW....keep this under your hat....Cast iron (rings) and steel (cylinders) expand
at the same rate. Also, when cylinders are bored and honed in the manufacturing
process....they are indeed perfectly round. The rings are made as round as is
humanly possible, and the slight (negligable) imperfections (high spots) wear
quickly into the bore. This is how single ringed two stroke engines run quite well.

And remember this....an Engineer is a guy that says...."that won't work"....

....and a Mechanic is a guy that says...."O yeah, watch this".

FBD.

FlyboyDave,
Cast iron and steel have slightly different coefficients of expansion. That means there is at least some difference. Also when a cylinder and piston of the same material are heated up, the cylinder will have a slightly larger internal diameter than the piston's outside diameter. Unless there was an interference fit.

I think Bax hit the nail on the head, you and other machinists, racers, etc. Build engines to very exact tolerances, in fact I mentioned the AA dragster trick of actually honing (maybe it was lapping?) their rings because the only break in was a short idle period after rebuilding between runs. Manufactured engines cannot afford this precision.

Phew !!!

There is no such thing in our discussion of rings wherein a cylinder and piston
are made of the same material. Secondly, there is no such thing as an
interference fit between a piston and a cylinder.

An "interference fit" is used when two cylindrical parts are assembled by
shrink-fitting or press-fitting one part upon another. A shrink fit is made....in
the case of our crankcase/liners by heating the cylinder to temporarily expand
its inside diameter and by cooling the liner to temporarily reduce its outside
diameter. The heated and cooled parts can then be slipped together. When the
assembly returns to room temperature, the subsequent cooling of the
crankcase/block) shrinks down onto the liner, which is expanding (heating up)
and tightening into the case. This creates the required interference for frictional
contact and locks the parts into position.

There is no such thing as an interference fit between the two as you stated.
Further, cast iron and steel do in fact expand at the same rate. There is no
difference between the two at rest, or in operating temperature....that is to
say, the ring gap stays the same, relative to one another as a % always.

You might want to think about hitting those books again, instead of your
never ending nit-picking of everything I say.

FBD.

Excited Flyboy,

My discussion was hypothetical. I did not mean to imply that cylinders and rings were made of the same material, though I am sure it has been done at some time in the past.

I know about fitting parts with interference fits, however there are other purposes, such as the interference fit at the top of an ABC piston and sleeve.

As far as the thermal coefficients of cast iron and steel, I suggest that you look at the linked chart, they are indeed different. Not only that they absorb heat at a different rate.

http://www.engineeringtoolbox.com/th...ls-24_859.html

I could not care less about theoretical or hypothetical issues. My job is to repair
engines....not dream up problems with them.

FBD.

Time for me to move on....I've unsubscribed to this thread.

FBD.

One thing in favour of a bench breakin of a ringed engine is that the idle responce will improve during the break in. Fewer dead sticks.

One myth seen on this thread. "You can't hurt an ABC running it in 4 stroking." []

Well that might be true if this keeps the piston and liner at their designed operating temperature but as this is not likely you will wear out the engine in a few runs.

The speed/pylon merchants often use a cylinder head temp sensor on ABC or ABN engines when running in to keep in the right temp band.

Mythbusting....
http://www.rcuniverse.com/forum/New_...2875125/tm.htm
It's just information, not a recommendation.

All of O.S.'s instructions sfor breakin are the same I believe.. I know this rubbed off on alot of guyhs in my club and they do their break in in 5 minutes then fly! Then on top of that they wander why i the world their engine dies on them all the time for the first gallon or two!

Teh manual for my ST 51 says to keep the engine slightly rich for the first tank then lean it to peak and back if off to a slightly rich setting by the end of the second tank and into the 3rd.. Say in 1/2 hour this can be done.. Still not anywhere near a 5 minute break-in.. It is apparently true that the initial break in can be done fairly quickly but I think as you put gallons through your engine it WILL get stronger...

M 2300 on the other hand started right up and transitioned great but wouldn't Idle.. And was not making max power and would not accept being leaned.
It took 3-4 gallons of fuel to get her to peak RPM and it will now idle several minutes without loading up! Its getting stronger and stronger..

My SAITO 4-stroke manual says that either bench runnning or running in on the model is acceptable. It give a recomended top speed setting for a VERY RICH setting... It unlike the ST manual say not to exceed 4,000 RPM's for the first 10 minutes of running! It also says around 40 minutes to break in the engine just enough to fly it.. It does not say this completes the break in..

So while it's true some engines may do their INITIAL break-in under an Hour... After this the engine may still be breaking in.. And SHOULD run better, Idle better, rev better, pull larger props etc etc..

downunder I had a look at the thread. Two divergent views and I certainly have not carried out your experiment but I compete in disciplines where engine performane is critical and easily compared. I run in my ABC?ABN hot, fast and lightly loaded. My engines are usually quick.

Running in slow. cool and rich has resulted in a slow engine in several cases. Engine tacho readings bear this out.

A piston ring made for a particular cylinder bore, when in a "True" position as reached by using the piston to locate it, will have no gap between the outer surface of the ring and the cylinder wall at any point. If there as a gap either the ring is not properly machined, or the cylinder bore is out of round. No exceptions, this is the way it is.

If the cylinder bore is true and you have an air gap then most likely the ring manufacturer has used a single base stock for his rings and gapped it differently for the over bored cylinder. Sad to say, but some of the less expensive (and lower quality) makers do this.

And to the gentleman who mentioned short ring life in the ambulances, it's more probably due to over cooling than the extended idling itself. tell the head wrench at the shop to put the thermostats back in, use clutch fans, or both, his problem will most likely go away.

Finally, the ring will seat in the first few seconds or minutes of running, and a high initial load helps this a lot. Full break-in can still take several hours of running, but the ring seating is almost immediate.

Bill.

HI Bill,
The comments I made regarding engines in the ambulances was in reference to a previous question made regarding running an engine to rich or slow. I could believe the damage was caused by running to cool. I had a 94 Dodge with a Cummins diesel in it, when you idled, the engine temp would stay at the bottom of the guage. There was very little heat generated while it idled. It would even go from a running temp to a cold guage reading if you pulled in and let the engine idle for more than 20 minutes. That was with the entirely stock package under the hood. My point in reference was only that running under conditions that the engines werent exactly designed for can lead to other problems. Run them the way they were intended and under appropriate loads and conditions and you will have a long lived engine. Happy flying, Jeff

What are you guys calling initial seating? Because I have had engines apart that had run for a half hour or so and the ring ridge's were still visible, though you could see some wear. Also I did not or should not have said that there is a gap, at least not a visible gap between the ring and cylinder. Rather it is usually uneven pressure until broken in. Still with manufacturing tolerances there may be a lot of model engines that actually have a very small gap. Of course we are not talking about ring end gap.