FOX GOLD ANNV. EDITION REFUSES TO RUN

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FOX GOLD ANNV. EDITION REFUSES TO RUN

Postby Doctor House MD » Sat Jun 13, 2009 7:31 am

HI GUYS, I KNOW SOMEONE OUT THERE HAS THE ANSWER I
NEED. GEORGE CAME TO MY RESCUE WITH THE NEEDLE VALVE SPRAYBAR DEAL. IT STILL REFUSES TO RUN. I USE WILDCAT 15%
NITRO (fresh). THE PLUGS A K&B AND IT GLOWS BRITE. I CLEANED
THE NEEDLE VALVE AND SPRAYBAR, FUEL LINE AND TANK ARE
CLEAR AS ARE THE VENT LINES. I HAVENT CHECKED THE MUFFLER
TAP OR THE BACKPLATE SCREWS. IT DOES RUN OUT THE PRIME
EVERYTIME. I USE TO THINK THE NEEDLE VALVE WAS AT 2.5 TO
3 TURNS TO RUN BUT THERE SEEMS TO BE NO NEEDLE VALVE
SETTING THAT WORKS. HEAD SCREWS ARE TIGHT TOO. IM
THINKING I MAY HAVE TO TEAR IT DOWN I JUST HATE THINKING
ABOUT FINDING A GASKET SET....ID ALMOST BET THE BACKPLATE
GASKETS BAD. OH WELL NOTHING IS EVER EASY IS IT. PLEASE HELP
I DO APPRECIATE IT. :?:
Doctor House MD
 
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Location: Lakeland Fl.

Postby stunter » Sat Jun 13, 2009 1:26 pm

It sounds like you don't have the needle out far enough. Turn the needle valve out to 4 turns and try it there.
Also that motor likes about 28 percent oil mostly castor. I think the fuel your useing
is about 18 percent oil. Roughly for every 4 oz of oil added to a gal.of fuel
raises the oil content 3 percent. Brodak or Sigs has castor.
Fox Manufacturing should have any part you need for that engine.
George
stunter
 
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Postby Doctor House MD » Sun Jun 14, 2009 4:34 am

:lol:
Hi George,
Thanks for the help, I'll try your suggestion this
afternoon. By the way, my better half is from
Columbus, Ohio. Her brother lives in Klamouth Falls,
outside of Columbus. I'm not looking forward to
removing this engine from the plane and tearing it
down. It does sound fuel starved doesn't it ?
THANKS AGAIN !!!!!! :lol:
Doctor House MD
 
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Location: Lakeland Fl.

FOX GOLD ANNV. EDITION REFUSES TO RUN

Postby Ken McClenahan » Sun Jun 14, 2009 3:04 pm

I assume that it is an iron piston Fox 35. If so, they are still in production so parts are available. Search for Fox Manufacturing on the internet.

The ideal fuel has 5% nitro and at least 25% castor oil. This engine likes lots of oil. I have never tried using synthetic oil in mine (I have four) but if I did I would add Klotz to bring the total oil up to at least 25%. You can buy Klotz at Harley-Davidson motorcycle stores.

Do not try to use fuel with more than 10% nitro because the engine is not mechanically built for high nitro fuels and something (like the wrist pin) will probably bend or break. I am using SIG 10% with 25% castor oil because that is all that I can get where I live. This works OK because I am flying at 5000 feet altitude.

The normal needle valve setting for these engines is usually with the needle opened about six turns.

There is a chronic manufacturing problem with the needle valve assembilies on these engines. Read the folowing (sorry the table format does not copy):

From: Ken McClenahan [mailto:klmcclen@comcast.net]
Sent: Sunday, December 21, 2003 10:40 PM
To: 'Foxmotors@aol.com'
Subject: Fox 35 Stunt Needle Valves

Sometimes it takes a very long time to figure out the cause of a problem.

I have recently been breaking in a Fox 35 stunt that I bought circa 1983 (it was a spare that I had bought for backup but never needed). It was generally running okay (but not perfectly) as long as the weather was warm. When the weather turned cold, it died as soon as I put the nose of the airplane up. Someone suggested that the problem was a sloppy needle valve thread fit. Since fuel and air was coming out around the needle valve threads when I blew out the tank, I checked the outer diameter of the thread on the needle and it was 0.004” undersize. I put some castor oil on the threads and it ran better. Then I had an afterthought and checked the size of the threads of the needle valve body by dropping drills in until I got to a drill that would not go in. The thread checked out as a 66% thread. After thinking about this for a few days it occurred to me that I have had similar problems with engines many times in the past so I checked all of the Fox stunt needle valve bodies that I have. The results follow listed by quantity needle valve bodies and the size of the largest drill that will go through the thread in the body along with the corresponding percent thread size.

Number
Drill Size No
Thread in %

4
47
75

5
46
66

3
45
62

1
42
20

1
41
10

Four of the bodies came out of previously unopened packages that I bought as spares in the early 80s. The part number on the packages is 13510. Three measured #46 drill and one measured #47 drill.

Even worse, the needle setting is typically at about ten turns out so there are only three or four threads engaged. After a lot of thought on how to do it, I used my Unimat to grind the flat back on the needle for the engine that was the subject of the second paragraph above*. It should now run at about two turns out.

If I were making my own needle valve bodies (and I may have to do so), then I would use the smallest tap drill that I could make work. I can’t claim that I could run a tap through a #50 drill size hole to get a 100% thread but I am sure that I could tap through a #49 drill size hole.

As a matter of practical experience, I have one engine that I used for about 500 flights without any problems and the needle valve body has a #47 hole, but I put castor oil on the threads and never adjusted the needle valve after the first couple of flights.

Looking back on many years of flying (6-bolt head Fox stunt 35s from 1953 but excluding from 1989 through 2000 when I did not have a place to fly), I am sure that I lost two Noblers and some other airplanes due to this problem.

Have a Merry Christmas and a Happy New Year.

Ken McClenahan
AMA 1973
Lone Tree, CO

* A better solution that I now use is to drill the step in the body back about 3 mm or 1/8" using a lathe and a number 48 drill.
Ken McClenahan
 
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Postby loucrane » Sun Jun 14, 2009 3:28 pm

Doc,

Any idea of the oil content in that Wildcat 15%? Fox 35's like a lot of castor, not just any kind of oil. For a new engine, think 25% castor minimum. I'd heard a while back that Wildcat blends fuels by weight; specific gravities of castor and synthetic oils we use are heavier than methanol's (Nitro is 'heavier', too.)

What that might mean is that, say, 18% oil by weight at SG of ~0.95 is less volume than 18% of methanol at SG ~0.8. Most of us think of fuel ingredients by volume, where 25% by volume of castor is a lot more than you get from 25% by weight.

For Fox 35s, this may make a big difference.

BTW, Fox Mfg responds very quickly for parts or any other order, and prices for a gasket set are not outrageous. Might launch your order if you call them... The Fox website has a parts catalog - kinda clunky, last I looked, but you can find your way through it. The factory gaskets for all Fox 35s since after the first 4-bolt head/2-bolt backplate version are the same spec.

With the NVA "sealed" a bit better you should be able to draw fuel by choking - cover the intake with a finger, turn the prop through a few times. With silicone tubing, you can see the fuel drawn up to the spraybar. When it gets there, turn the prop a few more choked turns to get some prime into the crankcase. If it won't draw fuel, open the needle until it does.

I'll trust the sleeve isn't in backwards - often happens if someone with little experience has opened an engine. Check that the port visible in the exhaust stack it higher than the one opposite it...

Sounds like you've checked the plumbing properly. The stock Fox needle valve often leaks air between the inner "wheel' and the face where the needle screws in. A short piece of fuel tubing, say 1/8" or so, slipped over the needle threads can sorta "caulk" around where the needle goes into the spraybar, and put some 'tension' on the threads - which also helps seal.

I see Ken McClenahan posted while I'm writing this. (Hi, Ken!) Good info!

The fuel tube 'spacer' may help make up for the "generous" clearances, and move your start/run setting in a few turns. If you're interested in less fussy use of this engine, I'd suggest replacing the stack Fox NVA with an OS or ENYA NVA - just make sure the fuel jet is about centered in the intake width, and pointed at the shaft a bit past where it is visible. It doesn't have to be straight st the shaft! Just past visible is actually better airflow to draw fuel. These NVAs are much more steadily progressive...

Incidentally, if you weren't aware of it, Fox 35s like a bit more break-in than newer ABC types. Soft, rich running for at least 15-20 minutes, in one or two minute short runs, cooled right down between them, is a minimum for an un-run Fox 35 to get longer and better life from it. Then, fairly gentle flying settings for a dozen flights or so.

They don't last very long run flat-out screaming, but you get most of their power at around 10,000 RPM. No need to run much more than that, in other words.
loucrane
 
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Postby Doctor House MD » Mon Jun 15, 2009 3:37 am

To; Lou, Ken, And George,
Thanks so much for lending your help and wealth of knowledge,
in my pursuit of solving this problem. I know it sounds like a
fuel starvation problem. The other side of the coin is that a
crankcase leak can cause the same or nearly same symptoms.
As for the fuel, I do have the level of castor oil @ 25 to28 %.
However here in the Florida heat and sun, its easy to lose 5%
of your nitro content in a day or two of flying. Even if you are
diligent about replacing the cap.
Once again guys THANKS for your kind help. I'll let you know
how ti all turns out. May the wind be at your back and your circles
round !!! Doc 8) 8)
Doctor House MD
 
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Location: Lakeland Fl.

Postby Doctor House MD » Sun Jul 19, 2009 12:20 pm

TO Ken, George and all ; I got the Fox to fire up at last. What Ken made
light of about the thread slop with Fox needle valves was the problem....
I used to in a past life maintain photographic package printers. Many of them had pneumatic sub systems. I always found teflon thread sealer
handy when changing out fittings or actuators. So I tried this on the threads of the needle valve. No more slop and she fired right up on the second flip of the prop. What a sweet sound too. THANKS GUYS !!!!!! :lol: [/i][/b]
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Re: FOX GOLD >> lost Noblers

Postby TuffsNotEnuff » Sun Oct 03, 2010 6:39 am

Ken McClenahan wrote:......I am sure that I lost two Noblers... due to this problem.

Ken McClenahan


Weeping...................... and remembering a deep blue Nobler kissing a parking lot goodbye.

That's a lot of good build time and doing your own mods and the cockpits and all the stuff for prettiness. Sounds like Fox ran a sloppy shop. Helluva fix, btw.

And, of course, back in the day.... we didn't have teflon.
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