Hi, Dave - I've done cold break-in on quite a few engines -  Foxes, Saitos, some FP 40s and 35s.
Sometimes the temperature was in the single digits.
Occasionally, I would use lighter fluid to get them going.
Never had a problem. Once they're running, the temperature doesn't seem to have any negative effects.

Bob Z.

Dave Mo,

I would not try to "break in" that engine by simply spinning it.

The engine is made with different metals that have different coefficients of thermal expansion. The parts will grow when the engine runs. They will not grow--except from the heat of friction--if you just spin it. And they will not all grow the same, which is why you need to simulate the heating during any wear-in effort.

When the engine runs at proper temperature, the heat distribution is not even. The head is hotter than the bottom of the case, for example. Another issue is front-to-back cylinder case temperature. If the cowling cools the front of the cylinder really well thru a vertical slot intake, but the back is sitting in stagnant air, the cylinder will actually lean forwards with increasing engine temps. So you want the engine to run at temperature to establish the clearances it will see in normal use.

The parts are also made of metals which have been produced and processed in different ways. Some castings, some wrought stock. I have lots of stories about how a part "moved during machining." What that means is that there were internal stresses, and removing part of the material allowed the part to relax to a new, temporarily stable state.  So the parts in an engine need heat cycles to stabilize them and get them to stop moving around from internal stresses from the manufacturing processes. That is why you need to get the engine up to temperature repeatedly, and then let it cool down.

An engine that is newly broken in on a stand running on 10% nitro, and installed in a tight cowl may need more break-in because the heat distribution when cowled may be sufficiently different to make the fits too tight again. A similar statement may be made about upping the nitro content a lot. More power out means more heat losses. And so on.

An engine that has really loose internal fits may be insensitive to changes in cooling, nitro, etc. An engine with a ring will be less sensitive to the piston fits. The ring has to be tight, but is designed as a spring to take up tolerances and bore taper. So some engines can be tough to get the perfect fit and others it is so easy that you don't even think much about it.

Some may say that a particular engine, based on newer materials, newer processes, better heat treating and so on does not require as much break-in, or as many heat cycles. I would agree. I don't think an older Enya is in that category.

A really unique example are the F2C engines. They are diesel and are run as hard as they can go. Diesels inherently run hotter. And to go fast, you have to absolutely minimize the cooling drag, which on an airplane is a really big deal. (This is a really fun topic, so if you are interested, there is a ton of good stuff to think about.)

I'd always welcome comparing notes with Randy on this topic. He may have other points that are important. And he certainly has a lot of practical experience with the different makes and metallurgies.

Divot McSlow



* There is an old racing story that old school bus engine blocks were prized by sprint car guys (I think it was sprint cars) because they were so stable that they could set them up pretty tight, and get a tad more power. Old lore which may have a nugget of truth in it somewhere....

How nifty is that?  A precision bath heater for your engine? The website didn't provide any description. What is it supposed to do? (In the context of this thread, I'm afraid you are going to tell me that it is a way to "break in" an engine....  But the label on the machine might really be more accurate; you are breaking down your oil by heat cycling it. But do R/C car guys use crankcase oil anywhere? In their gearboxes, maybe?)
 
Divot McSlow

PS--If I was going to buy a nifty machine, I'd get a high quality ultrasonic cleaner. That would let me get engine parts clean, and maintain other hardware more easily. After that, I would get a really good TIG welder, to fix the engines that hit the pavement---after I cleaned them in my nifty ultrasonic, of course.

Bob:

Good to hear. So you are starting and running the motors outside in those chilly temperatures? When trying to hand start my motors, I only manage to fill the crankcase with unburnt fuel whenever temperatures are below 50F. Perhaps I could use a few pointers on cold starting.

Questions: Is the shot of lighter fluid in the venturi in addition to the regular prime or by itself? Have you warmed up the fuel and tank and engine before trying to fire them outdoors?  Does the heat range of the plug make any difference? Nitro content of the fuel? Are you using an electric starter? Any other techniques?

Thanks.

Dave Mo...

Hi, Dave
No, I don't do anything special.
Choke it a bit - DON'T FLOOD IT!
A few drops of lighter fluid in the venture or exhaust and start flipping.
No, I don't use an electric starter nor do I warm the fuel.
If you're going to use a Ni-Cad type battery, make sure it's fully charged and keep it warm in your pocket.
I use my Little Red Box. As shown, it has four "D" cells and puts out a hearty 1.5 volts, even when somewhat cold.
The Ni-Cads put out 1.2 volts as I recall.

Bob Z.

Well, that was interesting! Thanks for locating the video, Pat. They did quite a few things that seem non-ideal to me. But if it is working for car guys....

1. When you spin at such a low rpm, you do not get anything like the inertial forces acting on any of the moving parts that you would during actual running. For example, running at 10,000 rpm would increase the force on the rod by a factor over 100. The wear pattern will be different due to dynamic distortions that are likely. So the break-in isn't really done, but it may be started. It seems that the entire focus is on the pinch at the top of the stroke. That makes perfect sense.

2. Running without the backplate seems pretty questionable. In the mode they are operating, there won't be much load on the piston, so the effect is reduced, but the big end of the rod could start walking south with gravity, tending to wear the lower bush at the edges.

3. The temperature they are achieving seems a bit of a mystery. They didn't talk about whether the engine was fully immersed, but if it is (and you avoid stalling the motor from hydrolock) then with the very high heat transfer rate possible with liquid contact, the whole engine will track the bath temp.

4. I wonder if the change in the noise at just below 900 rpm is when the engine is now going fast enough that the oil will not significantly re-enter the cylinder between cycles. If so, I can see why they would not want to run it just below this speed, as the loads and forces might be fairly high as you try to pump oil instead of a vapor bubble, again assuming the engine is fully immersed.

5. The only thing that seems sure about this method is that your engine won't suffer from a paucity of lubrication at any time. By the way, flooding ball bearings during operation actually raises the temperature of them higher than they would see if they had a normal lubrication level. Since we assume the bearings are highly coupled to a controlled bath temp, that's not an issue with this setup. But it is a reminder to guys that think that running sealed bearings heavily loaded with grease "for long life" may not get you what you are looking for.

6. Having an exposed wing nut style knob on the top of the unit is a safety issue in my mind. But the interlock switch is thoughtful. However, the switch actuator should have been recessed so that no one can easily put their finger over it to defeat the system just like he did in the video. Yeah, I've been around the tree a few times with the product liability lawyers...with little to show for it but a few more dead brain cells that they passed on to me.

7. I'd throw a samarium cobalt magnet in the bottom of the tank to scavenge any steel swarf and wear particles. If I owned one of these.

The approach is obviously a creative answer to a perceived problem. If it is working for them, then it's all good. I am a bit puzzled though, because I have run a few car engines on racing planes and never seemed to have any break-in issues. These were mostly OS engines, if that makes a difference to guys that know cars and truggies, although I did run a few others.

I think this process would actually help an Enya .09 more than an OS car engine, for what that's worth....

Divot McSlow

Dave the lighter fluid should be mixed with a small amount of atf then used as a prime in place of glow fuel. It evaporates at a lower temp than glow fuel so it will fire your engine in the cold. Don't get it near silicon tubing.

I don't think you'll need allot of break in on that engine if you just want to wait. Ground hog says early spring.

      I don't know, I got a brand new Enya 09 from the late, great Jim Thomerson, and it took an amazing amount of running before it was right, at least a couple of hours. Fortunately it doesn't use much fuel.

     Brett

Gents:

I just couldn't wait until Spring on this, so I gave it another try in the cold basement this AM (much to the chagrin of the smoke alarm).

All the advice gleaned from above paid off. When Bob said not to flood it, I now understand what he meant. Only one drop in the exhaust would lead it to fire. Two drops? A no go.

I can now bring it up to two stroke with the needle, but still need to keep glow heat on. With some confidence in my cold weather starting technique, will now relocate the running to the garage. So happy to have it behaving predictably during this heat cycling! Sweet little mill.

Many thanks again to all here.

Dave Mo...

Hmmm, Fred.  I think that my workshop has all of those items laying around.  So, good to know this.  I'm hoping that I escaped the worst consequences of my ineptitude by just a few, short runs. Cold starting skills will eliminate recidivism on the part of this ol' boy!

So, quite OK and thanks for the pointer.

Dave...