chuck100charles

I just bought a Fox 2.5 schneurle ball bearing engine with the intent of converting it to diesel with a Davis conversion head. Anybody done this, andhow did it work out?Godd, bad, or maybe just OK idea?

AMB

If it not preform well Davis would not make a head for it he is pretty fussy martin

earlwb

They perform really well as a diesel. DDD makes a head for them. DDD happens to be planning to sell a bunch of Fox .15 diesels real soon too.
Now depending on what you are doing with the engine, the engine works fine as is, but some guys have been known to plug the main transfer port with a piece wood shaped to fit in order to improve its efficiency with fuel and so on. I think there is a free flight event they were competing in that made this an advantageous mod.

franchi

Hi:

I converted a Fox .15 BB two years ago. It seems to be very powerful and starts easily while on the bench.

This weekend, I hope to fly it on a C/L stunt airplane to see how well it performs.

I will post results when I get the information.

Stay well.

Franchi

fiery

My Feedback: (2)

I have received one of these from Bob Davis. It's the first Fox I have personally handled other than the venerable .35 stunt engine.

Bob is supplying the engine complete with his diesel conversion head. It looks really solid. I will upload some more photographs shortly.

Mr Cox

The front end is a very odd design on the Fox. It has a removable prop axis which can be a nice safety feature but they drilled it straight through (!), giving a very odd entry into the crank and a potential leakage...

Here's what it looks like, then take a look at a high performance engine for a comparison...

earlwb

I once thought that it would be a problem with the stud drilled and tapped all the way through, but it hasn't caused any problems on any of my Fox .15 engines. I think the tiny gap in the threads inside get filled in with oil and stops it from being a problem. Also more likely is the prop and nut on the front would seal that off as well. But for performance one could do things like use some machinist's epoxy oe JB Weld epoxy and fill in the extra gap there and smooth it out more too. But if you are doing that, you probably really want one of the high performance .15's for racing or competition instead. Plus the engine oozes oil out past the front bearing anyway so it can lube the front bearingh, so that gap between the crankshaft and crankcase probably would have more potential as a airleak.

AMB

EarlWB do not think Jand B weld a good idea in event of a "hard landing" you would want to remove and replace if bent martin

Recycled Flyer

Nah, that is just part of the comp screw mechanism for the lower crankcase.

Take it as a bonus mate!

earlwb

You can still unscrew the crankshaft stud if you lightly oiled it before filling in the front with JB weld epoxy and smoothing and shaping it.
But then recycled_flyer has a good point too.


But since the engine isn't really designed for pylon racing, speed, etc, it probsably isn't really worth it to do the performance tricks to get more speed or power out of it.

controlliner

One thing to note is the prop stud has a 10X32 "rolled thread" it is a few thou bigger in the major dia than a "cut thread". It fits quite snug in the crank shaft. I have Two of these, a BB and a Bushing version and the stud is in there snug.

Mr Cox

I've already done the JB weld mod on mine, it gave about 500rpm extra on the top end (on a 8x4 prop) and a better handling over all.

earlwb

That is most interesting. I wouldn't have thought it had that much of a effect on the performance.

aspeed

It would depend how much it leaks.  I have made a few fillets and noticed no measureable difference on my tach. A leak is bad though.  A rolformed thread should measure the same as a cut thread.  They are a bit stronger and preferred.  I always liked the prop stud better as well as a rotateable cyl. and head to change from a rear exhaust to side exhaust.  

Recycled Flyer

Honestly, if you really wanted to improve that stud to crank shaft joint I would take a very short length of tight fitting alloy rod, bevel one face of it and insert the other perpendicular edge hard up against the joint and maybe loctiting that in place.

That way you would have easier removal of the stud if ever needed and a gas flow improvement all in one - and you would not need to remove the stud in the first place!

Hobbsy

My Feedback: (102)

If there were a problem with the thread fit fuel would leak out around the stud, I've never seen that on my .15 as a glow nor as a conversion. I keep JB Weld and WD40 miles from anything of mine.

Recycled Flyer

Could this be simply the effect of running the engine in though?

Mr Cox

I didn't remove the stud, I just filled in the large unwanted void in the front part of the crank. This reduces the crankcase volume ( which gives an increase in the crankcase pressure) and also improves the flow by directing it towards the rear. I have done this mod on other engines too, but the Fox .15 is the worse case I've ever seen. The mod helps especially in high rev applications, and high performance engines usually has this machined properly from the start.

aspeed

I usually do the fillet on most of my motors to get a better idle, and hopefully more revs, but never bother unless the crank is out for some other reason.  I always use solder for the fillet so it doesn't come off.  I grind the area with a dremel to clean it and use acid flux, hold the crank in a position that the puddle gives a nice fillet and heat just enough to flow the solder.  The Fox may not be a good candidate because the stud could get stuck forever.  It looks like it is drilled way too deep and something should be done.  I can see being too deep, as it would make machining it easier/faster.  I always hate tapping a blind hole. It usually means clearing the chips and retapping again by hand to get down to the bottom.

earlwb

I think it was just a manufacturing process for helping to simplify the machining process. Since the engines ran Ok that way, Fox never changed it.
But yeah it would reduce the crankcase volume some and if you smooth and angle the intake passage in the crankshaft, it helps the air/fuel flow better too.  One merely has to clean off the oil good from the crank and very lightly oil the threaded stud and that should prevent the stud from becoming glued in when one adds in the epoxy to it.

My .15's ran good as is, so I never bothered with filling in the cavity in the crankshaft. But I might do it if I ever need to replace the bearings on one of the engines.

Mr Cox

I only got about 14400 rpm on an APC 8x4 prop, which I think is rather weak for a .15 engine. After the mod is gives close to 15000rpm which is more on pair with other .15 engines.

The Norvel .15 BB RC is both lighter and more powerful though...

Recycled Flyer

This would worry me for two reasons -
1. Placing a blow torch onto a crank shaft (and I can't see how else you would get enoug heat into the shaft and stud area other wise) may change the temper of the shaft somewhat by bringing the hardness down.
2. And weight, in this case its quite a lump of lead and tin going in there.

But hey, if it works without drama ........

aspeed

The metal never went past the straw colour, and lead isn't a lot heavier than steel. The crankpin is important to not change the temper. The rest of the crank isn't as important for hardness. The front thread can be cut off and drilled and tapped for a stud by annealing the front of the crank too without ill effect. I have done it on a truggy motor to convert to an airplane motor. You can't go crazy with the torch though. Hey, no worries!

AMB

Fiery get a chance to run it yet?? martin

fiery

My Feedback: (2)

Hi Martin

I ran it in last week-end using it's "as supplied" ignition method.

It ran well. No issues at all. It wore a Bolly Clubman 8.5 x 4 propeller. I put six 5 minute runs on it.

The muffler attachment screws are "canted", presumeably to deter loosening in use. Nice touch, although it is a bit fiddly to get the muffler on. No different from an OS FSR or Irvine .40 Mk II really.

Next step is to run it with the DDD conversion head. I will use a broad blade 9 x6 prop on it. Bob Davis suggests a 9 x7. If I can find one that size in my collection I will use it.

The Fox .15BB has no branding or size indication on it whatsoever. However, by looking at it, it can only be a FOX.

The true twin needle carb is excellent. Great idle to full speed transition on my nil nitro fuel. The tensioner springs are like ENYA - one on each side.

Cheers