New Fox .15

I don't know if it matters, but when I'm breaking in an engine I always let it cool with the piston at BDC. It just seems like a good idea. I don't remember if i was ever told to do this or not. I used 0% nitro to break in my MP Jet but I primed it with nitro to start it.

RknRusty wrote:I don't know if it matters, but when I'm breaking in an engine I always let it cool with the piston at BDC. It just seems like a good idea. I don't remember if i was ever told to do this or not. I used 0% nitro to break in my MP Jet but I primed it with nitro to start it.

For an ABC or ABN engine construction the plated brass liner expands a little faster than the aluminum piston head. However break-in is different from lapped steel/iron in that you get them hot and keep them hot.

source: 2-Stroke Glow Engines, David Gierke, 1994

Based on that I agree letting a new ABC or ABN engine cool at TDC is a bad idea, but probably will not cause it to seize. Cooling at BDC is probably safer for all engines.

Oh yea. The Fox needs to be run really rich so it is 4-cycling for the first few ounces of fuel through it. The first few runs should only be about an ounce of fuel each. Shut down by pinching off the fuel line, or only using a small amount of fuel, never with a rag.

Phil

Does the engine look like this? I think all Fox engines break in the same. If I remember to bring the manual to work, I'll scan them and I can then email them to you. I have all the paperwork with this one. I bought it about a year ago and haven't used it yet. I just bought another Akromaster to put it in. They recommend Dukes fuel of course or Missle Mist. I believe Fox fuel was 10% nitro with 22% oil. I use Powermaster 10/22, which is castor and synthetic 50/50. Hope this helps. if you need more yell. It's a cool plane and the last one I had was powered by an old Fox steel fin .15. It was great fun.

I believe ALL Fox .15's run best on either 8-4 or a 7x6 props for general applications. The newer ones just turn those props faster.

George

The only Fox .15 that's being currently made is the coffin back schneurle ported ball bearing engine. I personally wouldn't run this engine rich and I wouldn't use a 8x4 to break it in. I would lighten the pitch and go with a 7x4 myself and probably a narrower bladed 7x4 like the Master Airscrew. Keep the load light and run the engine where it's just breaking into a two stroke settling back into a four. These engines don't want to run rich. The piston sleeve fit is too tight out of the box (also my opinion). Fox doesn't recommend lapping in the fit as they claim it will ruin the engine. I quickly disregarded that tidbit of info and proceed to my usual Fox procedures doing what they should've done from the start. I feel that running an engine rich as stated does more harm than good due to the conrod and the wrist pin taking a lot of shock. I've seen many wristpins egg out the hole in the piston before the engine even gets broken in.
I certainly would check to see if there's any bind in the engine prior to running. This is accomplished with the engine totally free of lubrication and glow plug removed. We use these engines in clown racing. I have a few to compare my results with. If not satisfied, I go back and due further inspection. Out of the box they will run fine, I just go for all out performance. This doesn't mean I'm tearing up equipment and piston liners etc. I'm just in search of fast reliable starts and consistency.

This is the only engine that I know of currently produced that uses the short glow plug with no idle bar. I would certainly have a few on hand as this engine probably and most likely will take out the plug in the first few runs. Do not install a std long plug as it will hit the piston. I like Duke Johnson, use the same fuel but that's me. Others will tell you what it needs as do the instructions. For me, I never have seen a failure in ANY engine that I've run Powermaster GMA 10-22 in. I don't run high castor fuels in my engines. This one in particular due to it being a ball bearing supported crank in my opinion doesn't need all that castor. For break in high castor fuel will help, but I would certainly break it in without the muffler. As George claims, the 7x6 is ideal on the Fox .15 after break in.

Make sure the screws are tight on the venturi after a few runs as these can be problematic at first so check for tightness. Also watch for ground impacts as the venturi can be snapped off at the case. Usually the venturi ears break and not the case which is good. Ken

Ken Cook wrote: This is the only engine that I know of currently produced that uses the short glow plug with no idle bar. I would certainly have a few on hand as this engine probably and most likely will take out the plug in the first few runs. Do not install a std long plug as it will hit the piston.

I don't agree, and I've actually had a closer look at just that before. A long reach plug will not hit the piston but it is a little too long for an ideal combustion chamber shape. The short plugs on the other hand are too short, while a medium reach (OS or Enya) have the correct length. Here are two pictures, first one with and short plug (Fox) and the second picture one with a medium reach plug (OS);

And I disagree as well but I'm not inviting a arguement. Here is my Fox .15 with a std long and it clearly sticks out beyond the bottom of the head button. A idle bar would certainly protrude even further. Not all plugs are the same length and if this one had an idle bar the engine wouldn't turn over. Os plugs are typically different than a Fox and this difference has been a major contributing factor in differences of engine runs in stunt on the LA series engines as plug lengths can definitively change timing. I clearly stated my findings and here is the picture of what I have. From the bottom of head button up to the mating rim of the head button measure .134". The piston at top dead from deck to the top of the liner is .145 leaving a .010 margin give or take due to conrod and wristpins play which is close but adding a idle bar could present a problem. I typically use Thunderbolt r/c longs in my Fox's which I have none currently on hand. The Sig R/C longs with idle bar( not pictured) is also protruding beyond the bottom a few thousandth's and is visibly noticeable. Certain plugs just may work as stated, I'm just saying before someone goes and throws in any old plug, it certainly is worth a check . Also, running a new engine usually blows the plug which is why I said keep a few on hand. The engine is really shaking around a bit and is prone to flooding which takes out the plug equally as well. It's a bit difficult to see but it's clear that my std plugs are far greater in length than yours pictured. Either were using way different plugs or my deck height is completely different than the version you have. This engine was made in a plain bearing and also a ball bearing and knowing Fox anything could be different.I've made Nelson head buttons for my engine and no longer use the stock setup. The last two pictures is the Nelson head configuration in which I made the hemi chamber slightly deeper as the initial tests were blowing plugs. Ken

I see the picture didn't work on my las post. But here's a try at the Fox instructions. After I break in the .15's I run a 8 x 4 or a 8 x 5, I think some planes like different props. My Akromaster seemed to like the 8x4.

Ken Cook wrote:And I disagree as well but I'm not inviting a arguement.

What's wrong with a discussion?
It looks like you have a four-stroke plug in the picture? That's the longest one available and it is longer than a "long reach plug". So, yes, don't put a four-stroke plug in your two-stroke engines.

I'm not a Fox plug user Kris. In fact I hate them. They're pretty much about useless other than breaking in an engine. If the rpm's don't immediately fall off when removing the plug, the post is blowing out of the top or the insulator pops out. You are indeed correct as I went downstairs and pulled out a brand new r/c long. However, the r/c long due to the idle bar does reach beyond the bottom of the landing. I believe in my initial posting, I might have stated std long, I should've stated r/c long with idle bar. I truly believe with the few thousandth's I have left, that this was Fox's intention as well for using the short plug. Ken

I've never had problems with Fox plugs...but the newest ones I have are over 20 years old, some brand spanking new still.

Well, other than the 2 new RC short idle bar ones I just got for my 20 year old Fox 15 BB that hasn't been flown yet.

Phil

Duke, I'm curious as to how you balanced the Akromaster. Seeing the Akromaster was designed for a older non muffled .15, it may have even been designed for the .15 steel fin. The slant plug .15 and the steel fin weighing in or around 4 oz's. I believe the coffin back is almost 1.5 oz's heavier. I had issues with an Enya .15 as once the power cut it was causing ground shattering earthquakes when it tumbled. This was some of the reasoning I suggested to others in regards to increasing the wingspan. I had 1 oz in the tail to make the Enya flyable. If done again, I would certainly try to move the wing forward slightly. The nose of the Akro doesn't have much room in the nose, so using up real estate by moving the wing forward needs to be considered. Ken

Ken
Well, the last Akromasters we had were powered with a steel fin Fox without the muffler and the other with a muffled OS .15 LA. They both flew great. The plans do show a Fox .15 steel fin, you are correct. If I remember right, there's room to move the engine back towards the LE which would help tons (i think). And of course you would have to cut back the nose to make room for the prop. I don't know for sure, I'll have to look at it before I start that project. Maybe I'll have to put an OS .15 LA in it. I already planned to put the steel fin Fox in the Akromaster that my daughter is building now.

There is one poor design thing with the Fox 15. The crank shaft has been completely drilled out in the front and the prop axis is just stuck in there until its threads ends. This give a poor inner volume of the crank and a potential missalignment of the prop axis. I've stuff one crank with JB weld and gained about 500rpm on an 8x4 prop.