Author Topic: Running in a Fox 35 (Read 4136 times)

Timothy Payne · « **on:** October 14, 2012, 05:24:13 AM »

Hello all you plane fanatics from across the pond here on good p
ol' England. Recently aquired three Fox Glow engines (2 35's and a 36X). One of the 35's is new, I've ran it intermitently using 5% glowfuel with added castor oil taking it up to around 28% oil content.

I'm using an old nylon 9*4" prop. - I've mainly used diesels in the past (PAW, DC), and other than an ever-reliable Thunder Tiger .25 I have little knowledge of these older glow engines. (Also any advice on what type of Glow Starter and temperature plug to use would be most helpful. - I've already blown about 12 of the damn things using everything from'D' size dry batteries to a 6 volt lead-acid battery, with a 1 ohm load resistor.)

Many thanks Yanks!

Chuck Feldman · « **Reply #1 on:** October 14, 2012, 07:49:09 AM »

Use a proper 1 1/2 volt igniter. This is the proper voltage. Your using a good prop for run in as you call it. Also your fuel is good. The old Fox 35 takes a lot of time to run in. So run it often and make it run in 4 stroke and then 2 stroke by leaning and richening with the needle valve. I believe running a 1/2 gallon of fuel should do the trick. The standard prop for the Fox 35 is 10/6. Set the needle so that the engine is in a four stroke mode and that it breaks to a 2 stroke. This should happen all by itself. Start it rich and slowly turn the needle in and you will hear it jump into 2 cycle running. If it stays in 2 cycle just back off the needle. Being a diesel man you should master this easily. Good luck mate.

john e. holliday · « **Reply #2 on:** October 14, 2012, 07:50:34 AM »

Measure your voltage to get it down to 1.5 volts at the plug. Of course Fox does make a 2 volt plug which I have used a few times. Remember to not run the old Fox's too lean. In the early days we would run on the bench enough so that it would hold a flying setting with a 10-6 prop without getting hot and slowing down. Most of mine run between 9000 and 10000 rpm. Recent times I do most of the break in with the engine in a plane and small tank. Just have to get to operating temps for some laps. With my tanks, the last 3 or 4 laps the old Fox will go lean. Also remember to have some castor in the fuel. I quit using pure castor blends years ago. Your use of a 9-4 prop seems a little light. Go to a 9-6 for bench running. This is my method.

George · « **Reply #3 on:** October 14, 2012, 09:08:36 AM »

Timothy,

Break-in for iron steel glow engines is similar to breaking in a diesel in that you need heat cycles. Best way for me is to start at the point where it is just going into a two cycle and run for 1-2 minutes. Use a small tank so it runs out of fuel or pull/clamp the fuel line so it stops by running out of fuel. Let it cool naturally. Every other run lean it a couple of clicks. If it sags (slows down) stop it and let it cool, open the needle a couple of clicks and repeat the run. When it holds a full run at peak, it is broken in and ready for a plane.

As mentioned previously, never run an iron/steel glow engine over lean. Running over lean can lead to thermal runaway and damage/ruin the engine. For that reason, most use at least half castor in the lube for protection.

Of course there are as many break-in procedures as there are modelers, so this is only one way...but is fast and effective.

Good luck with your Foxes.

George

Jim Thomerson · « **Reply #4 on:** October 14, 2012, 09:57:22 AM »

What you are doing is fine, except for the glowplug problem. I use Fox 2 volt plugs with a 5 amphr Cyclon lead acid gelcell, and a 5 ft long lead. As said, probably best to get one of the clip on igniters. I lapped the piston and cylinder on my Fox stunt 35s and had a fairly quick break in as a result.

Brett Buck · « **Reply #5 on:** October 14, 2012, 05:37:59 PM »

Quote from: Timothy Payne on October 14, 2012, 05:24:13 AM

Hello all you plane fanatics from across the pond here on good p
ol' England. Recently aquired three Fox Glow engines (2 35's and a 36X). One of the 35's is new, I've ran it intermitently using 5% glowfuel with added castor oil taking it up to around 28% oil content.

I'm using an old nylon 9*4" prop. - I've mainly used diesels in the past (PAW, DC), and other than an ever-reliable Thunder Tiger .25 I have little knowledge of these older glow engines. (Also any advice on what type of Glow Starter and temperature plug to use would be most helpful. - I've already blown about 12 of the damn things using everything from'D' size dry batteries to a 6 volt lead-acid battery, with a 1 ohm load resistor.)

A "D" cell should be fine. The Fox has very low compression and should not blow plugs. I can't recall ever blowing one. I would suspect that the plugs are defective or there is some other issue. What type plug are you using? It is possible that someone tried to change it to run on FAI fuel?

I would also suggest a *wooden* prop. It sometimes controls the vibration to some extent. It's very common to see the old soft nylon types with standing waves in the blades, particularly at the speeds likely with a 9-4.

Brett

Garf · « **Reply #6 on:** October 14, 2012, 06:46:34 PM »

You must be trying to use Fox plugs. Find a K&B 1L, OK G-2, Fireball standard, or any other medium to medium hot plug. If you insist on using Fox, use the "miracle" plug.

Dennis Moritz · « **Reply #7 on:** October 14, 2012, 07:19:51 PM »

Too much voltage will pop a plug. Reason I stopped using rheostat power panels to power plugs plus starter. It took a year a two to realize that there was a sharp voltage drop to the plug when I hit the starter. In order to compensate for this I'd up the voltage to the plug. This started engines reliably but plug life was often short. Sounds like this might be happening to you when using a resistor plus a 6 volt. Fox plugs should last better than your luck. Wire 4 D cells in parallel or get nicad ingniter. In stunt we use a hot plug, which means a plug with more filament, because we're usually 4 stroking or running a rich 2 stroke. In Philly we run 22%(50/50 synthetic/castor) 5% Powermaster fuel. We do not add extra castor. Our Fox engines run year after year after year. Frequently they are run hard. When the engines are broken in, they can be run hard without damage. Fox machining is hit or miss. We have run into Fox 35s that needed their pistons lapped to perform without seizing up. Sometimes crank bushings were over large and sloppy. Sometimes too tight. Watch out for back plate leaks. Use a new fox needle, one without the flat paddle at the tip. Or something better. Adjusting the spaded needle is an intuitive art. If you have the feel, o.k.

Garf · « **Reply #8 on:** October 14, 2012, 07:40:29 PM »

I have a mod for the Fox slash cut NV. Duplicate the slash at 90* from the original cut.

Chris Wilson · « **Reply #9 on:** October 14, 2012, 09:43:58 PM »

Quote from: Brett Buck on October 14, 2012, 05:37:59 PM

It's very common to see the old soft nylon types with standing waves in the blades, particularly at the speeds likely with a 9-4.

Now THAT answers a question that has been puzzling me for years, old nylon props that seem to surge forward with no change in engine speed!

Thanks Brett.

Steve Helmick · « **Reply #10 on:** October 14, 2012, 10:06:57 PM »

I don't trust OLD nylon props at all, since I saw a buddy throw the blade off one on his first whack of a McCoy .19 Redhead. That said, if you opt for a wood prop, pick out one with good straight grain. Bad wood grain can cause the same result.

Steve

Chris Wilson · « **Reply #11 on:** October 14, 2012, 10:41:05 PM »

Quote from: Steve Helmick on October 14, 2012, 10:06:57 PM

I don't trust OLD nylon props at all, since I saw a buddy throw the blade off one on his first whack of a McCoy .19 Redhead. That said, if you opt for a wood prop, pick out one with good straight grain. Bad wood grain can cause the same result. Steve

Hi Steve,
I meant "old" as in I did it years ago not age of the props, I used to run a full circle unbalanced PAW 19 diesel using Kavan nylon props and marveled at the fact that upon warm up the engine could run without misfire, very evenly but the prop would flex alarmingly back and forth - and I am talking what seemed like a good 1/2"!

Always wondered what caused that. Standing waves from an unbalanced engine, makes sense to me.

Brett Buck · « **Reply #12 on:** October 14, 2012, 11:07:12 PM »

Quote from: Garf on October 14, 2012, 07:40:29 PM

I have a mod for the Fox slash cut NV. Duplicate the slash at 90* from the original cut.

I don't think that is a good idea, unless you do something else to it, too. The end of the needle is a close fit ("close" by Fox standards, that is) with the far side of the spraybar. The idea is that the needle is supported approximately halfway around and reduces the tendency to wiggle back and forth in the threads like a tuning fork. Remove material from the end, and now it is just cantilevered from the threads - with predictable results in a very short time, I would guess. If you are going to do this, leave the last 1/16" of the free end untouched. That gets the desirable shape in the area of the spraybar holes without interfering with the support the end of the needle provides.

One thing that people sometimes don't get, and I didn't get for many, MANY flights with the stock parts is that the metering of the needle is fine as it is, and nice and linear. What is wrong with it is that the alignment of the "flat" with the spraybar holes makes a huge difference in the way the engine runs. If the flat happens to line up the right way (and I forget which way is the "right" way, but I think it's with the flat parallel with the axis of the hole) it feeds the fuel out nicely from both holes and is pretty linear right around there for about 3 clicks either way -which is just about all you ever need as long as you never change anything. If it's the other way, more fuel comes out one hole than the other, and one click changes it at almost random. Of course change something (like the fuel, the prop, etc) then the needle has to move and the relationship of the flat to the holes changes. I can't tell you how long it took to figure that one out.

Of course, you have to be a real die-hard, or like me at the time, not know any better, to keep using the God-forsaken thing when you can get an ST51 needle, a PA needle, or even an OS needle, all of which are far superior.

Brett

Brett Buck · « **Reply #13 on:** October 14, 2012, 11:27:01 PM »

Quote from: Steve Helmick on October 14, 2012, 10:06:57 PM

I don't trust OLD nylon props at all, since I saw a buddy throw the blade off one on his first whack of a McCoy .19 Redhead.

Good point! The old TF white nylon types are pretty notorious for that, and particularly when they have been bolted down tight for the last 50 years. I was told at one point that you had to boil them in water periodically to relieve stresses and to get moisture back into them, but as I have grown older and had several decades to think about it, that doesn't really make any sense. Maybe if you boiled them in plasticizer, but I doubt it. Put them on for a static display of "how we flew stunt in 1963" and fly with wood. GRP or carbon props.

For what it is worth the old Top Flite conventional 10-6 sport flier wood prop, just like it shows on the Nobler plans, was the best all-around prop I ever ran on the Fox, generally better than the other options I tried and a much better compromise for all conditions than the Rev-Up 10-6EW or W.

Brett

Geoff Goodworth · « **Reply #14 on:** October 14, 2012, 11:45:09 PM »

Re NVAs, as Brett said, there are others much better than the Fox item.

However, while the ST and PA NVAs fit in neatly the Fox crankcase, the Fox NVA is necked down across the venturi opening. Given the prodigious [/sarc] output of the Fox 35, I would be most reluctant to use an NVA with a larger diameter than standard across the venturi.

That said, Randy Smith sells a version of his ST-type NVA necked down to suit the Fox. It's an excellent device.

Timothy Payne · « **Reply #15 on:** October 15, 2012, 04:54:59 AM »

Thanks guys, I've got an igniter starter on order from ebay with some '8' Fox plugs. - (They might be a bit cold as I'm Duraglow 5% with about 15% castor added; 15 + 15 = 30). The engine isn't converted to FAI, as it was bought NIB (it's an early 70's matt silver finish). Would I need a new crankcase gasket for it since I removed it along with the head for a thorough cleanout in paraffin prior to running. - I just hope I haven't shot myself in the foot and over tightened the backplate, thus creating more filings from the crankpin fouling the plate! - Just need some Classic C/L plans now. - A Stuntmaster maybe (60 foot lines of course, over here we run PAW .09 & .15 Combats in 30 foot, but that would be telling now wouldn't it???!!!!).

Andrew Hathaway · « **Reply #16 on:** October 15, 2012, 09:10:25 AM »

When Fox came out with the fully tapered (round) 35 needle in the early 90's, they gave out samples and said that the earlier flat sided needle could be modified to the new style by grinding or filing. The round needle works considerably better, but it helps to make sure it actually meters the flow through the spraybar. A short piece (1/4-3/8") of fuel line slipped over the threads, so it sits between the end of the spraybar and the first knob helps too.

The first thing I do to any Fox new or used, that's been sitting for a year or two, is pull the backplate and check to see if the connecting rod is free on the wrist pin. It doesn't take long for castor to stick the parts together. Aside from not running right, it can damage the engine in short order if the problem isn't corrected. A heat gun softens the old castor very quickly, then the goop can be cleaned and the parts lubricated. Heat also works for stuck pistons, and sticky crankshafts. Afterwards, either replace the backplate gasket or at least RTV the old gasket to reseal the case. All kinds of weird issues can pop up if that gasket leaks.

I avoid the break in issue altogether. A new Fox 35 takes a lot of time and fuel before it starts to run right. After a few bench runs they usually start easily enough, but they don't really get broke in until they've been run many, many times. The secret is to buy those very obviously well used Fox 35s off Ebay. I look for complete engines, without obvious crash damage, that are a bit dirty but not black with burned castor. That way I get what's usually a very nicely broke in engine, with lots of life left. A little clean up, a new backplate gasket, a tapered needle and they're usually ready to run. The alternative just takes too long.

Timothy Payne · « **Reply #17 on:** October 18, 2012, 08:11:04 AM »

Cheers, just waiting for the plugs and starter now. - Went to Manchester Science Museum yesterday. Saw a later Spitfire and Wellington Bomber there. (My heart goes out to those young men who fought in those planes during WW2; especially when you consider the technology of the time.) Awe inspiring. Still trying to find out the whereabouts of a De Havilland Mosquito, I think theres one in York.

I need to find one as I've got a plan for a very old C/L model. Using a pair of PAW 149s. Watch this space..............

(As a matter of interest, these 'wooden wonders' were built entirely from wood including balsa!)

Jim Thomerson · « **Reply #18 on:** October 18, 2012, 09:23:48 AM »

I couldn't get consistent runs with the Fox needle, back in the 1970s, so installed an ST NVA. Allen Brickhaus told me how to neck it down, but I never got around to it. Particularly after a couple of guys at contests asked me if I was running an ST 46.

Timothy Payne · « **Reply #19 on:** October 24, 2012, 07:02:13 PM »

Ran the Fox 35 (properly) for the first time yesterday. - I used an 1800mah HSP Glow Starter along with a Fox no.8 long-reach plug. Although I was a bit apprehensive at first; with the plug, it soon fired up on 30% fuel and a 10*6" prop. Managed to get about 2 minutes running time from the tank on a 4-stroking cycle. (It did make some rather spectacular flames from the exhaust prior to start up! The tank was originally intended for a PAW 149, so flooding was inevitable with the fuel-lines being unlevel.)

I'll put about half a dozen tanks through it on a rich 4-stroking cycle, occasionally changing to a 2-stroke cycle.

Incidently, I'm gonna try my 36X (recently rebuilt albeit a rather clapped out bottom end) using a 12*6" prop just to see the results. It's still a strong motor, as I freed up the little-end then drilled a 1mm oil hole in the big-end and refitted the conrod back to front after some honing with wet 'n' dry on a drill. - Works a treat except I needed to take a bit of metal of the conrod to prevent it from fouling the bottom of the liner!

Heres the snag though, upon stripping this beast down, I accidently damaged the edge of the gasket/spacer which sits between the top of the liner and the engine block. (There isn't one of these on a 'standard .35.) This meant that when the head was replaced it doesn't sit quite level to the top of the block. I know it isn't really a major problem as this doesn't seem to affect the compression at all, but I know it would probably do the motor more harm than good if I try to remove the liner and chuck the spacer. - The head probably wouldn't seal then anyway, and the exhaust port wouldn't line up either! See I don't think I'd get another spacer.

Oh, and also on a final note anyone rebuilding anything right now, don't do what I did and try and twist the liner out of the engine block twisting the conrod in the process!!! Finally straightened it though after a few attempts, almost resorted to lapping the top of the bore it was binding so bad. The moral of this story is: If at first you don't succeed try, try, try again.

Many thanks to all you US engine experts out there, I must visit America some day!

Brett Buck · « **Reply #20 on:** October 25, 2012, 12:02:10 PM »

Quote from: Andrew Hathaway on October 15, 2012, 09:10:25 AM

When Fox came out with the fully tapered (round) 35 needle in the early 90's, they gave out samples and said that the earlier flat sided needle could be modified to the new style by grinding or filing. The round needle works considerably better, but it helps to make sure it actually meters the flow through the spraybar. A short piece (1/4-3/8") of fuel line slipped over the threads, so it sits between the end of the spraybar and the first knob helps too.

That will reduce the tendency of the threads to self-destruct now that the far end is unsupported, but who know for how long?

The original needle with the flat meters the fuel perfectly well, as far as I could tell, but the flow out the holes and the atomization of the fuel was radically affected by where the flat fell WRT the holes.

Brett