News:


  • March 29, 2024, 02:57:20 AM

Login with username, password and session length

Author Topic: Just had my first experience with runaway(solved)  (Read 7953 times)

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Just had my first experience with runaway(solved)
« on: September 14, 2014, 08:40:38 PM »
Hemi head Fox .35, ST NVA and venturi bored.

So, last week I flew this plane and apart from some plane trim issues it was doing the 4-2 break just fine. This week same setup and no matter how much I messed with the needle the thing would run away after my first loop. It would scream for several laps and then shut off with 1/2 tank of fuel left.

I have been doing some reading here on what to do to correct the problem, but what bothers me is that last week all was well.

The only new development from now till then was a tank pressure test and a new piece of fuel line. I checked the line for pin holes and the tank still has no leaks.

Anybody have any ideas?

Ron
« Last Edit: October 05, 2014, 08:44:10 AM by Ron Cribbs »

Offline john e. holliday

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 22752
Re: Just had my first experience with runaway
« Reply #1 on: September 14, 2014, 09:00:49 PM »
Is this a metal or plastic tank?   You said you checked for pinholes, did you check your filter if you have one.   The silicone tubing is notorious for developing leaks that can't be seen.   Also the filter will some times leak just enough.  I had to one of the screw together types that I had to take the wrench to so it wouldn't leak.   At least the engine started running like it should after I tightened the filter.

By the way the Fox .25 I was having troubles with not running right turned out the needle valve assembly was not sealed good to the body of the venturi.   I had some nylon washers that corrected that problem.
John E. "DOC" Holliday
10421 West 56th Terrace
Shawnee, KANSAS  66203
AMA 23530  Have fun as I have and I am still breaking a record.

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #2 on: September 14, 2014, 09:22:58 PM »
Doc,

It's a metal tank, I can replace the piece of hose again, I forgot to mention that I did re-orient the spray bar to ensure the hole was pointed straight down.

It may be leaking at the venturi. I'll snug it down some more and see if that alleviates the problem. I have attached a picture of my setup

Ron


Offline john e. holliday

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 22752
Re: Just had my first experience with runaway
« Reply #3 on: September 14, 2014, 09:41:49 PM »
That doesn't look like a uni-flow tank.   If it is standard venting, it will lean out as the tank empties.   You might thin of putting a filter in the fuel line between the tank and engine.   All it takes is one small piece of dirt to make things go nasty.
John E. "DOC" Holliday
10421 West 56th Terrace
Shawnee, KANSAS  66203
AMA 23530  Have fun as I have and I am still breaking a record.

Offline RC Storick

  • Forum owner
  • Administrator
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12395
  • The finish starts with the first piece of wood cut
    • Stunt Hangar
Re: Just had my first experience with runaway
« Reply #4 on: September 14, 2014, 09:45:47 PM »
maybe a leaking back plate. Ask Randy Smith.
AMA 12366

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13717
Re: Just had my first experience with runaway
« Reply #5 on: September 14, 2014, 09:50:51 PM »
Doc,

It's a metal tank, I can replace the piece of hose again, I forgot to mention that I did re-orient the spray bar to ensure the hole was pointed straight down.

It may be leaking at the venturi. I'll snug it down some more and see if that alleviates the problem. I have attached a picture of my setup

Ron



   The obvious is dirt or some contamination in the fuel. But you *must* use a fuel filter, it exists to prevent contamination from causing a problem.

    Other possibilities are overheating from incorrect fuel or incorrect mixture, leaky backplate, leaky/loose head. I also don't understand  how much the venturi was "bored". That is very non-standard modification

    Brett

Offline Dennis Moritz

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2464
Re: Just had my first experience with runaway
« Reply #6 on: September 14, 2014, 10:10:07 PM »
Check that mounting bolts are cinched tight. If it's a profile, make sure wing/fues joint didn't loosen up. Back flush spray bar. Pull out needle, inspect passage. It's possible a tiny bit of something is in there. A fleck of plaint, for instance, that does not back flush out. Run a fine wire through needle passage. What kind of needle valve? Old FOX needles had two hole at roughly a 150 degree angle. They both need to be positioned so that they cannot be seen when you look from through the venturi. What kind of muffler? Check muffler bolts. Are they tight. Check muffler for carbon deposits and free flow. Remove any deposits. Are you running muffler pressure? Check pressure tap for blockage. Check pressure tubing. Check tap to make sure there is no leakage around tap. Pressure test tank under water, any bubbles at all, even a very fine stream, means a leak that needs to be sealed. What kind of fuel? If you are running pure castor as many on this forum advise, could be you've varnished up the engine, which means it will need to be stripped and varnish removed. RC fuels usually do not have enough oil. We run Powermaster 50/50 22% oil 5% and 10% nitro in our Foxes. They run well year after year. Some tubing develops pin holes frequently. Pull off tubing, pinch end and blow. Any leaks, discard. Check new tubing before installing.

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #7 on: September 14, 2014, 10:12:40 PM »
Ok, I'll add the filter. The head is tight as is the backplate. Although the backplate on Foxes are known to leak.

At the field I back flushed the NV and it ran the same way after. Fuel used is GMA 10/22 and I am not sure what the venturi is bored to as it was that way when I got it. I imagine it was done to make up for decreased area when the  ST NVA was installed. I'll have to check what size it is sometime. It ran ok last weekend so I assume it's not that.

It's standard vent so yes it does lean as the head pressure drops, but it's going lean way early like after 5 laps or so.

I appreciate the replies.

Ron






Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13717
Re: Just had my first experience with runaway
« Reply #8 on: September 14, 2014, 10:34:31 PM »
Ok, I'll add the filter. The head is tight as is the backplate. Although the backplate on Foxes are known to leak.

At the field I back flushed the NV and it ran the same way after. Fuel used is GMA 10/22 and I am not sure what the venturi is bored to as it was that way when I got it. I imagine it was done to make up for decreased area when the  ST NVA was installed. I'll have to check what size it is sometime. It ran ok last weekend so I assume it's not that.


   If you are only running 22% 50/50 oil, that could easily be the issue. I think it needs 25% bare minimum, and 29 doesn't seem to hurt anything. The difference from week to week could easily be a temperature change or slightly different setting that made it go "over the hill".

      Brett

Offline Dick Pacini

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1628
Re: Just had my first experience with runaway
« Reply #9 on: September 14, 2014, 10:37:49 PM »
Is that a bit of dirt in the middle of the fuel line?
AMA 62221

Once, twice, three times a lady.  Four times and she does it for a living.  "You want me on that wall.  You need me on that wall."

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #10 on: September 14, 2014, 10:57:35 PM »
Is that a bit of dirt in the middle of the fuel line?

Dick,

That is a drop of purple fuel that you are seeing in the picture.

Brett, I have used 10/22 for the past 2 yrs on all my Fox .35 engines without issue. I have also flown at sea level and high altitude conditions in all sorts of weather across the country. The runaway thing is new. I would agree with the fuel being the problem if I just started using it today.

I was turned on to 10/22 by some serious Fox users in Philly and have used it ever since. I used to use 10/29 and when I switched to 10/22 I noticed a much cleaner break from 4-2. The reason I was told is because the 10/29 is like syrup.

Anyway, I know 10/29 or 10/25 is the choice of many and if it works for them that's cool with me. It's just a preference thing.

Something surely changed, I just need to figure out what. You guys have given me plenty of things to look over and I appreciate all your replies!!

Ron






Offline Steve Helmick

  • AMA Member and supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 9920
Re: Just had my first experience with runaway
« Reply #11 on: September 14, 2014, 11:00:07 PM »
Those yellow plastic caps are fine for keeping dirt out of your tank, but they're not trustworthy to seal the overflow or vent tube on a uniflow tank.

Did you happen to notice if the NV 'lever' has stayed put, or maybe could have changed? The lever is what makes them tend to turn, which would be even more likely with a vibrating machine like the Fox. Could solder a nut on as a knob and use a nutdriver to adjust, possibly? Danny Dirt used R/C Car pinion gears for knobs. Expensive, but used ones might be available from somebody you know?  

Also...Fox cranks don't like heavy props. It would be a good idea to change to a good wood prop like an RSM 10-6 (really about 5.5" pitch).   H^^ Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline John Stiles

  • 2014 Supporters
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1928
  • one shot=one kill
Re: Just had my first experience with runaway
« Reply #12 on: September 15, 2014, 05:23:22 AM »
maybe a leaking back plate. Ask Randy Smith.
x-2 check all screws and N/V to make sure they're tight.  H^^
John Stiles             Tulip, Ar.

Offline Dave_Trible

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 6135
Re: Just had my first experience with runaway
« Reply #13 on: September 15, 2014, 07:39:01 AM »
I wouldn't blow off Brett's advice about the oil.  Duke Fox himself told me personally the engine needed the 28% oil he put in the Superfuel.  It was expensive and he wouldn't have put it in if he didn't have to.  Don't know if that is the whole cause or not but when an engine gets too hot it will take off and only recover if the temp drops back enough.  I've had one on the edge that would heat up during a manuever then cool down and drop rpm just before each next manuever.  Be a little careful about advice and go the safer,  wiser choice.

Dave
AMA 20934
FAA Certificate FA3ATY4T94

Offline Ward Van Duzer

  • 2015
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1284
Re: Just had my first experience with runaway
« Reply #14 on: September 15, 2014, 08:15:21 AM »
Note to all:

ALL threaded filters need to be tightened before use. Don't know why, they seem to loosen up during shipping, or what, but you'll always get at least 1/8th to a quarter turn on them! Lots of folks love the Crap Traps, but I've replaced two of them on other peoples planes with successful results. I only use them on fuel cans!

Ward-O
I hate spelling errors, you mess up 2 letters and you are urined!

Don't hesitate to ask dumb questions.
They are easier to handle than dumb mistakes!  Ward-O AMA 6022

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #15 on: September 15, 2014, 08:47:35 AM »
I wouldn't blow off Brett's advice about the oil.  Duke Fox himself told me personally the engine needed the 28% oil he put in the Superfuel.  It was expensive and he wouldn't have put it in if he didn't have to.  Don't know if that is the whole cause or not but when an engine gets too hot it will take off and only recover if the temp drops back enough.  I've had one on the edge that would heat up during a manuever then cool down and drop rpm just before each next manuever.  Be a little careful about advice and go the safer,  wiser choice.

Dave

Dave,

I wasn't blowing of Brett's advice. Far from it actually. I'm checking everything he suggested. It's just from a troubleshooting standpoint it doesn't make sense that an engine runs fine for two years then one day it doesn't like the oil content.

As to the NV, it's a ST so I am able to keep it snug with the lock nut. It's not turning in flight. I made sure of that.

It's not easy to convey emotion in post's but rest assured all your replies are noted and most welcome. I apologize if I offended anyone or made it seem like I was blowing them off. You guys are all great!

Ron



Offline Dave_Trible

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 6135
Re: Just had my first experience with runaway
« Reply #16 on: September 15, 2014, 09:12:12 AM »
Ron I just wouldn't want you to ruin your engine and perhaps not realize what could be a root cause.  You may have been pretty lucky with your other engines and I don't know how much you actually fly them.  This engine could be fit a little tighter (which is good) or due to heat has warped or gouged somewhere building more friction. (Bad). Like Brett I would wonder about the rework to the engine.  Also a tiny piece of loose metal in the engine can reek havoc.  No apology to me needed.  I'm sometimes discouraged when I see folks take some left field advice to a right field problem or question.  It just costs you time, money and more frustration.  Brett and others know there stuff and only wish to pass on the knowledge.  Keep em ' flyin'.

Dave
AMA 20934
FAA Certificate FA3ATY4T94

Offline Motorman

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3243
Re: Just had my first experience with runaway
« Reply #17 on: September 15, 2014, 09:27:36 AM »
I see you have an old perfect tank. Take a propane torch and pop the cap off the end and I think you'll find the tank is full of rust and crud. A filter will not help, this crud is too big to come out into the filter but it clogs the pick up line in the tank. Just had the exact same problem on my flight streak.


MM 

Offline Ward Van Duzer

  • 2015
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1284
Re: Just had my first experience with runaway
« Reply #18 on: September 15, 2014, 09:30:40 AM »
Rather than hacking up a crankcase, this is my solution to a Super Tiger NVA in a Fox...

W.

I hate spelling errors, you mess up 2 letters and you are urined!

Don't hesitate to ask dumb questions.
They are easier to handle than dumb mistakes!  Ward-O AMA 6022

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #19 on: September 15, 2014, 09:52:59 AM »
I see you have an old perfect tank. Take a propane torch and pop the cap off the end and I think you'll find the tank is full of rust and crud. A filter will not help, this crud is too big to come out into the filter but it clogs the pick up line in the tank. Just had the exact same problem on my flight streak.


MM 

That's a Brodak 3.5 oz oval that I bought close to 2 yrs ago. wouldn't hurt to open it up though

Offline Brad Smith

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 287
  • Welcome to the Stunt Hanger.
Re: Just had my first experience with runaway
« Reply #20 on: September 15, 2014, 11:02:28 AM »
if you have more then one fox 35 try another engine with the same set up.
Brad smith AMA780054

Offline Jim Svitko

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 691
Re: Just had my first experience with runaway
« Reply #21 on: September 15, 2014, 12:29:08 PM »
Rather than hacking up a crankcase, this is my solution to a Super Tiger NVA in a Fox...

W.



I have done that as well.  If the venturi is cast as part of the case, then it is easier to neck down the spray bar rather than change something that cannot be restored.  For removable venturis, might be better to modify the venturi as they can be replaced.

When I went to the Super Tiger NVA in a Fox (with ABC kit) the engine would go lean and runaway.  The larger spray bar diameter cut airflow.  Necking down the spray bar solved that problem.

Offline Steve Fitton

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2272
Re: Just had my first experience with runaway
« Reply #22 on: September 15, 2014, 03:05:39 PM »
If you have gone over the engine for loose bolts and cleaned out the NVA, I think I would try another tank.  Unmuffled Foxes like yours run racing events like Foxberg and don't go over the hill lean and quit.  If it worked and now it doesn't, something has failed and it sounds like you have eliminated most but not all of the usual suspects.

I would change the plug as well, albeit that is more voodoo than science.

I think the fuel choice is ok, I have seen the Philly guys in action and I know the Powermaster  22 and 29% oil fuels work fine in a Fox.  I wish I had known that back when I exclusively ran a Fox in my Gieseke Nobler and had to take apart the 40th Anniversary Fox every 110 flights to de gum it from the Fox Superfuel I ran.  It would literally lock up and not start when the castor varnish got bad.  Personally I have run Powermaster and even Sig Champion 20% oil in Foxes in recent years, but not hundreds of flights worth.  Now, having said all that, it still can't hurt to run higher oil, especially when having problems, because it might help protect the engine from burning down during a runaway.  One reason Banjock and the Philly guys can run 10/22 year in and year out is that they really know how to get an engine/tank setup right.
Steve

Offline Dennis Toth

  • 2020 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 4209
Re: Just had my first experience with runaway
« Reply #23 on: September 15, 2014, 03:08:51 PM »
Ron,
The Fox 35 can be frustrating but a couple things seem to give them problems. First thing is to check for leaks around the head. To do this you need to warm (not hot) the engine head with a heat gun then and put some light oil (like 3 in 1) around the head and pull it through compression looking for bubbles. Sometimes even with tight bolts they find a way to leak. If all that is OK then remove the plug and pull though again checking for binding. If you find it binds, loosen the head bolts slowly and keep checking as you go, usually there is one bolt that is the problem and most of the time it is the head of the bolt rubbing against the recess in the head. The quick solution to this is to use the old Fox Philips head bolts (the head is just a few thou less then the socket heads). You mentioned that you were using muffler pressure.

The muffler is the next big issue for a Fox. It holds heat and since the engine has very small fins it can push it over the edge, also it can cause the case to twist as you tighten the muffler and result in binding. To resolve this first make sure there is no binding with the muffler on and plug out. If OK then you need to reduce load (i.e. smaller prop, I use a 9x6 Top Flite) and increase oil to carry heat out (seems any oil will do just needs something that doesn't burn) or lose the muffler.

Last thing is the engine mount, I didn't see if you have hard pads under the mount lugs. The Fox 35 has a slight release angle on the bottom of the mount, you need either wood beam mounts or crush pads (1/32"plywood strips) between the mount and the hard pad (or have them machined flat) to allow a little give. Let us know what you find.

Best,  DennisT

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #24 on: September 15, 2014, 05:16:53 PM »
Hey guys,

This is an older '54 Fox with no provisions for muffler mounting. I don't need a muffler where I fly in OKC. I checked for binding when I installed the head. I find if you cross tighten slowly you negate the binding issue. All appears ok with that.

The venturi was modified before I became the owner so I will have to live with it. I have plenty of info to work off of so I will give a report next time I fly. Thanks everyone!

Ron




Offline George

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1468
  • Love people, Use things.
Re: Just had my first experience with runaway
« Reply #25 on: September 15, 2014, 05:50:12 PM »
Those type Brodak tanks are the old "Perfect" tanks without Perfect stamped on them. John Brodak bought out Perfect tanks years ago.

If it has a brass pickup line, some used to get cracks or holes inside and the symptom was to run good until the hole/crack started sucking air along with fuel. The engine would usually speed-up, then quit. These cracks were sometimes caused by leaving fuel in the tank between flying sessions.

A quick check is to use a different tank and see if it runs better. Good luck - lots of things to check.

George
George Bain
AMA 23454

Offline Dan McEntee

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 6824
Re: Just had my first experience with runaway
« Reply #26 on: September 15, 2014, 05:59:05 PM »
   A quick test before you take things apart, is to back flush the pick up in the tank with fuel. if there is a flake of something in there, it will blow it to another part of tank. Try a flight and see how it goes. If it improves immediately with no there action being taken, change the tank or clean out the old one. Tin tanks will rust as was mentioned. I was dealing with some rust on that yellow airplane I had there Sunday. The engine (OS FP.40) was burping like fuel was being interupted. I went to check the fuel filter, and could se flakes of rust in the fuel line. Tried to blow through it to back flush it and it would hardly pass air! Took the filter apart and it was completely blocked off. I grabbed this tank off my "extra stuff" shelf because I know this particular style works well on profiles. It's a GRW I think. I filled it with some white vinegar and let it soak while I was working on some other part of the airplane. I use white vinegar to clean rust out of vintage dirt bike gas tanks. It disolves the rust but doesn't etch the metal. Model tank is no different, and a model tank will rust due to the residual alcohol in the tank drawing moisture. I guess the vinegar softened up some of the rust but it didn't break loose until engine vibration worked on it a while. I'm popping the back of the tank off tonight to give it a visual inspection and cleaning. One good reason to store models for any extended period of time with the tanks full. Two year is long enough for something like this to happen, even on a model that is flown pretty regularly. Wish I had thought of that while we were there Sunday. This is one reason to use plastic tanks, but you have some pitfalls with them also. Someone asked me recently which I prefer to use and I answered which ever one is closest to reach and fits the model the best!
  See ya later,
   Dan McEntee

   PS To Add: Just read Geprges response and that has a high probablity also, especially if it has brass tubes. Copper tubes last monger but are not immune to failing, or a solder joint coming loose either. An inspection of the innerds is warrented here.
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)

Offline phil c

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2480
Re: Just had my first experience with runaway
« Reply #27 on: September 15, 2014, 06:30:35 PM »
One other "last" thing to check.  The only reliable way to check a tank is with a hand vacuum pump, used in setting up carburetors.  If you can't do that, cap off both vents and pressurize the tank under water at least 5 lb. 

The tank isn't a uniflow, just an open vented tank.  If it is more than 2 in. wide, spanwise, as some fuel is burned the motor can heat up in a maneuver and never cool down until it quits from overheating.  That kind of tank always has to start rich and will gradually lean out through the flight until it quits- which may or may not be when it is empty.
phil Cartier

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #28 on: September 15, 2014, 09:34:58 PM »
Phil,

The tank is right at 2" in span.

I took the tank back off and it looked pretty good inside. No Rust and shiny, all solder joints intact and no split pipes.

Re-sealing was a PITA in my hotel room, but I finally got it. It tested fine while under pressure in a sink full of water.  I capped off the vents and used my filler syringe to pump it up. My mighty vac is at home and I will test further there.

Here is a picture of the tank while open:



I wish there was a way to pressure test the Fox!

Thanks!

Ron






Offline John Rist

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2944
Re: Just had my first experience with runaway
« Reply #29 on: September 15, 2014, 10:29:29 PM »
That's why I went electric.    n~
John Rist
AMA 56277

Offline Steve Fitton

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2272
Re: Just had my first experience with runaway
« Reply #30 on: September 16, 2014, 05:59:03 AM »
Phil,

The tank is right at 2" in span.

I took the tank back off and it looked pretty good inside. No Rust and shiny, all solder joints intact and no split pipes.

Re-sealing was a PITA in my hotel room, but I finally got it. It tested fine while under pressure in a sink full of water.  I capped off the vents and used my filler syringe to pump it up. My mighty vac is at home and I will test further there.

Here is a picture of the tank while open:



I wish there was a way to pressure test the Fox!

Thanks!

Ron


I still wish there was a spare tank you could try.  If those tubes are really brass, and they look that way, there might still be a crack somewhere.

As far as pressure testing the Fox, the good news is old Foxes go on ebay for cheep...!
Steve

Offline John Jordan

  • Balsadust
  • 24 supporter
  • Trade Count: (0)
  • Lieutenant
  • *
  • Posts: 71
Re: Just had my first experience with runaway
« Reply #31 on: September 16, 2014, 06:28:54 AM »
             In one of your posts earler you said you put the spray bar hole pointing straight down the venture. Past experience says rotate to just out of sight from horizontal say 3.30-5-00 oclock or 8.30-7.00 position. Just a thought.   Thanks  John
John Jordan    ama # 5939

Offline Lester Nicholson

  • Trade Count: (0)
  • Lieutenant
  • ***
  • Posts: 114
Re: Just had my first experience with runaway
« Reply #32 on: September 16, 2014, 11:24:45 AM »
Seems to me, and I'm ne expert by any means, but 22% and lean run away runs. Are you sure you haven' cooked that fox?   Nkck

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #33 on: September 16, 2014, 07:18:38 PM »
             In one of your posts earler you said you put the spray bar hole pointing straight down the venture. Past experience says rotate to just out of sight from horizontal say 3.30-5-00 oclock or 8.30-7.00 position. Just a thought.   Thanks  John

John,

Thanks for the info on orientation! You never find info like this when installing one.

Ron

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #34 on: September 16, 2014, 07:28:53 PM »
Seems to me, and I'm ne expert by any means, but 22% and lean run away runs. Are you sure you haven' cooked that fox?   Nkck

Lester,

Funny you should bring this up as it kind of proves the point.  The engine still has gobs of compression. I will say that Fox engines can handle a lean run better than say a McCoy, buy yes they will cook.

I have run a Fox lean for fun just to see how fast I could go and it still has great compression. I wish someone who has more experience and more pull in the CL community than me would be willing to sacrifice a Fox and run it on 10/22 and report back results.

Offline Randy Cuberly

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3674
Re: Just had my first experience with runaway
« Reply #35 on: September 16, 2014, 08:29:10 PM »
Lester,

Funny you should bring this up as it kind of proves the point.  The engine still has gobs of compression. I will say that Fox engines can handle a lean run better than say a McCoy, buy yes they will cook.

I have run a Fox lean for fun just to see how fast I could go and it still has great compression. I wish someone who has more experience and more pull in the CL community than me would be willing to sacrifice a Fox and run it on 10/22 and report back results.


I have run L&J foxes (several of them) on 10-22 half and half and had mixed results.  out of six different ones 4 of them ran fine and two of them overheated until the oil content was brought up to 27%.

A number of years my brouther had two in different airplanes and one ran fine on 10-22 and the other needed 27-28% oil to avoid overheating.

I would also mention that typically it's not the piston and sleeve that get hot first and seize in a Fox it's the crank and front bearing...especially on the older series engines!

I believe that's the real need for all the oil in Fox 35's!

Yeah, I know that a lot of the Fox afficianadoes out there may totally disagree with this but it's fact.  That's why Foxes can seize repeatedly and still have valid compression!  The crank seizes first! No piston sleeve damage!

My opinion is: Dump your desire to run low oil content (low for Foxes), increase the oil content to 28% and the problem will disappear!

Randy Cuberly
Randy Cuberly
Tucson, AZ

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13717
Re: Just had my first experience with runaway
« Reply #36 on: September 16, 2014, 11:05:35 PM »
Lester,

Funny you should bring this up as it kind of proves the point.  The engine still has gobs of compression. I will say that Fox engines can handle a lean run better than say a McCoy, buy yes they will cook.

I have run a Fox lean for fun just to see how fast I could go and it still has great compression. I wish someone who has more experience and more pull in the CL community than me would be willing to sacrifice a Fox and run it on 10/22 and report back results.


  Many people have done stuff like that. That's why we recommend 28.

    Brett

Offline Balsa Butcher

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2357
  • High Desert Flier
Re: Just had my first experience with runaway
« Reply #37 on: September 16, 2014, 11:20:21 PM »
Any ideas...yup, ditch that tank. The old Perfect / Veco wedge style will not give you the reliable 4x2 run you are looking for.  Go with either a Brodak or RSM uniflow. That and Powermster GMA 28% all Castor fuel will give you a chance for success here. My favorite Fox blend though is 25% castor 3% synthetic.  8)
Pete Cunha
Sacramento CA.
AMA 57499

Offline Steve Fitton

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2272
Re: Just had my first experience with runaway
« Reply #38 on: September 17, 2014, 05:48:05 AM »
I have run L&J foxes (several of them) on 10-22 half and half and had mixed results.  out of six different ones 4 of them ran fine and two of them overheated until the oil content was brought up to 27%.

A number of years my brouther had two in different airplanes and one ran fine on 10-22 and the other needed 27-28% oil to avoid overheating.

....
My opinion is: Dump your desire to run low oil content (low for Foxes), increase the oil content to 28% and the problem will disappear!

Randy Cuberly

I had a different "test" as it were: two 40th anniversary Foxes, both bought at the same time from Fox and both run on Fox Superfuel (29% all castor).  One ran so awesome the Philly guys consistently asked what I had done to the engine.  The only bug was stopping to de gunk the castor every 110 flights.  The other engine was consistently *tight*, never really broke in and will quit hot in the square 8 or vertical 8 every time.

My point is that quality control is a *big* issue with Foxes that probably obscures some of the fuel findings.  Fox QC is one of the reasons motors like Aerotigers came to be.
Steve

Offline Jim Svitko

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 691
Re: Just had my first experience with runaway
« Reply #39 on: September 17, 2014, 06:43:15 AM »
Lester,

Funny you should bring this up as it kind of proves the point.  The engine still has gobs of compression. I will say that Fox engines can handle a lean run better than say a McCoy, buy yes they will cook.

I have run a Fox lean for fun just to see how fast I could go and it still has great compression. I wish someone who has more experience and more pull in the CL community than me would be willing to sacrifice a Fox and run it on 10/22 and report back results.


I have run 10/22 (50-50 castor/synthetic) in a Fox but only if it had the ABC kit.  No issues there but I never ran anything but all castor (28%-29%) in any other Fox.

Offline Motorman

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 3243
Re: Just had my first experience with runaway
« Reply #40 on: September 17, 2014, 09:49:40 AM »

Offline RandySmith

  • Administrator
  • Trade Count: (0)
  • Admiral
  • *****
  • Posts: 13747
  • Welcome to the Stunt Hanger.
    • Aero Products
Re: Just had my first experience with runaway
« Reply #41 on: September 17, 2014, 04:30:51 PM »
Hemi head Fox .35, ST NVA and venturi bored.

So, last week I flew this plane and apart from some plane trim issues it was doing the 4-2 break just fine. This week same setup and no matter how much I messed with the needle the thing would run away after my first loop. It would scream for several laps and then shut off with 1/2 tank of fuel left.

I have been doing some reading here on what to do to correct the problem, but what bothers me is that last week all was well.

The only new development from now till then was a tank pressure test and a new piece of fuel line. I checked the line for pin holes and the tank still has no leaks.

Anybody have any ideas?

Ron

You have a lot of good advice:
remember just because the bolts are tight doesn't mean the gasket is good, FOX rear cork gaskets are VERY easy to tear or break
The head shim can be leak with tight screws
I would use at least 25% oil in the FOX
Stay away from pressure unless you have to use it, alway use a good, sealed, clean filter.
Read the engine articles pinned at the top of this engine forum

Randy

Offline Dennis Moritz

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2464
Re: Just had my first experience with runaway
« Reply #42 on: September 17, 2014, 05:58:42 PM »
Another thought. Have you tightened the head bolts. If so, they may be overtightened, or tightened in a way that causes excess friction between piston/cylinder.  Fox cases are on the thin side. Remove plug, rotate prop, loosen head bolts, tighten gradually in sequence, go from one bolt to it's opposite. Easy to distort head, easy to distort case. The aim is to tighten head so that piston rotates smoothly.

Having looked at the picture you supplied of your plane and mounting. (Finally realizing you posted it.) Could be a bad vibe developing on the profile. This happens. Profiles loosen up. Zap the fues/wing joint with CA, or epoxy, if you think that joint has loosened. Do it anyway. Put aluminum pads between engine and fues. Put pads on opposite side of fues so that the bolts and nuts have a firm surface so you can cinch tight. Fuel soaking, vibration of engine, can over time soften nose causing vibration issues. I have flown profiles that needed mounting bolts tightened every few flight. Tightened very tight. If I neglected to this, run, run, run, runaway. I mean tightened, by the way, with heft and crudeness. Not uncommon for the mounting bolts on that plane (hardened, socket, 4-40s) to pop now and then. But the method worked. Dan Banjock hisself has made up steel pads on a few models to distribute vibration stress.

Did you pressure test that tank by sealing up the feed tubes, dunking tank, and running lots of air pressure into tank. I have a dedicated fuel syringe that I push on hard as I can with tank submerged. Even a tiny trail of bubbles can reek havoc.
« Last Edit: September 17, 2014, 07:22:38 PM by Dennis Moritz »

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #43 on: September 17, 2014, 09:26:38 PM »
Thanks,

Not a vibe issue as this is the smoothest running of all the Foxes I run. Not like my '52.

Tank was pressure tested yesterday, and not a binding issue as the engine turns freely. I am leaning towards a leaking backplate at the moment

Ron

Offline Dennis Moritz

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2464
Re: Just had my first experience with runaway
« Reply #44 on: September 17, 2014, 11:01:42 PM »
Could be the back plate. Definitely. Some folks have been successful using silicon seal. A friend machined a new back plate with a groove for an o-ring.

Vibration is not a function of engine smoothness by itself, usually it's a harmonic mix, engine vibration interacting with the airframe. Even on a plane that has made reliable runs, it's possible for the nose to loosen altering the harmonics in a way that upsets engine stability. Profiles are more prone to bad vibes than full bodies. But full bodies are not immune. Some profiles are fine right off the board, requiring a minimum of tinkering. Some, not so lucky. The bad vibe (bad harmonics) can occur with profiles with solidly built front ends. Some profiles with less robust front ends, built like Old Sterling models, can run smooth no fuss no muss.The aluminum or steel pads, cinching bolts tights, have helped to reduce bad vibe issues.

Prop balance. Was that checked?

Do not ask about the inverse Tetra Tank! ;D
« Last Edit: September 17, 2014, 11:30:10 PM by Dennis Moritz »

Offline Ron Cribbs

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 330
Re: Just had my first experience with runaway
« Reply #45 on: September 18, 2014, 11:36:06 AM »
The O-ring is a good idea.

I never fly without a balanced prop.

Usually when I have a bad vibe issue it hurts to touch the needle. I'll re-engage this weekend.

Ron

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13717
Re: Just had my first experience with runaway
« Reply #46 on: September 18, 2014, 12:35:57 PM »
You have a lot of good advice:
remember just because the bolts are tight doesn't mean the gasket is good, FOX rear cork gaskets are VERY easy to tear or break
The head shim can be leak with tight screws
I would use at least 25% oil in the FOX
Stay away from pressure unless you have to use it, alway use a good, sealed, clean filter.
Read the engine articles pinned at the top of this engine forum

  And in that article, it has a potential mechanism for your symptoms - it will run for some time on less than normal oil, until the enough of the varnish has been removed, or damage slowly accumulates, that you lose enough of the hot seal that it won't run properly anymore. Going lean is a classic sign of loss of the piston/liner seal when hot. Not guaranteed but pretty likely.

  As mentioned above, some us have thousands of full-pattern flights using Foxes. I would guess I am in the 3-4000 range myself and that is LOTS of fuel at 4 ounces/flight.  There are a myriad of possible causes not related to oil content. I would have expected that the 22% would work fine for a while, but eventually you will have more-or-less the problem you are seeing.

   Do as you wish, of course.

    Brett

Offline Dennis Moritz

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2464
Re: Just had my first experience with runaway
« Reply #47 on: September 18, 2014, 08:38:36 PM »
Philly Flyers run Foxes year after year. Fly them in competition. I think the fellow asking for advice probably has a vibration issue. Ringmasters are notorious for developing vibration issues after being flown for a while. Almost any Saturday or Sunday you can see Sterling's Ringers dancing around Neshaminy Park (Philly Flyers home field) powered by Fox 35s. We run the fuel specified above. At some point when running pure castor fuel, varnish has to be removed, because a severely varnished engine will run erratically. When the varnish is removed piston seal is often ruined. Engine is worn out. Running a synthetic blend of 50/50 keeps the varnish from forming, the way to go. in our experience Fox 35s live long and work hard on 22% 50/50 oil.
« Last Edit: September 19, 2014, 07:03:00 AM by Dennis Moritz »

Offline Dennis Moritz

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2464
Re: Just had my first experience with runaway
« Reply #48 on: September 19, 2014, 07:16:11 AM »
Brett doesn't think much of Fox 35s, regarding them as an archaic relic of 1950. Always recommending LA25s or something else, when the subject of Foxes comes up. Many Philly Flyers love the fossil. Don't mess with dedicated Harley Riders. Leave Foxes to those who delight in their eccentric charms. If you want to fix a Harley or get a Fox 35 to perform ask (complete the sentence). Pundits are pundits. Even in our little world that goes round and round.

Offline DanielGelinas

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 427
Re: Just had my first experience with runaway
« Reply #49 on: September 19, 2014, 07:28:54 AM »
I can't speak for Philly flyers but I an say in GENERAL TERMS an engine running on all castor oil (this is an 1952 fox, isn't it??) for a long time (probably since 1952), will not benefit from half syn/half castor oil at 22%. The synthetic oil will clean away the old castor buildup and reduce the compression. Again, I'm not saying this is the case for Ron's engine. I'm saying in general.

A new fox running 10/22 will probably not have problems, with the piston and liner, in the short to medium term life span. But what about the rod bushing??

Now, I truly think if all the other things have been checked and are fine, then try adding more castor and see what happens. I believe you will be pleased with the results. You already have the synthetic oil in it to keep it clean, but the added castor will keep in cool.

I run ALL my fox's, from the '52 to the 60th anniversary, on 29% synthetic/castor mix.

Please let us know your finding.

Good luck H^^ H^^
-Dan


Advertise Here
Tags:
 


Advertise Here