Is it time to make the change?

   For God's sake, YES, it was time to change 40 years ago. And it hasn't been a mainstream competitive stunt engine for about *50* years. It was never a very good sport flying engine compared to many far easier-to-deal with alternatives.

   People used it for sport flying because it was a pretty good competition engine for a brief period in the 50's and then (just like now, to a degree) people wanted to be able to brag about it even if it didn't make any difference for what they were trying to do. It's the same phenomenon that drives every sport flier and casual competitor into buying a "Joe Blow 40LA" instead of a stocker - it has nothing to do with the performance (which is usually much worse than stock), it has to do with wanting to tell their pals they have a "Joe Blow 40LA".   This is the result of a second problem, where many competition aspirants can't grasp a similar situation, where ST46/60s and the like ALSO aren't mainstream competitive stunt engines, not for about *30* years.

    At this point, we have people out there in the field torturing themselves for hours trying to get it to work, burp-quit-crash or shaking the airplane to bits in 3 flights, and then claiming how great the engine is.
   
   These endless problems were potentially worth putting up with because when you got it working right, it was the best you could do in the mid-50's, and about even compared to most of your competitors through most of the 60s unless you were going to take on McFarland/Gialdini etc. Geiseke managed to hold on through most of the 70's but it eventually became too much even for him to overcome. A lot of the alternatives were not tremendously better in terms of performance but you don't have to be a lot better, just a little.

And don't move on to "McCoy/Enya/ST" because they are hardly any better for the most part. Enya now occasionally makes a modern-quality products on a very limited basis, ST makes more-or-less nothing too useful, and McCoy has been out of business far longer than Fox. OS is still in business but doesn't make CL engines, and if you convert a OS-35AX to CL, it has 5x the power you need to fly a Shoestring. Get a few year old 25LA or 20/25FP, convert it to CL with factory parts.

   Note also that the same problem infests budding stunt competitors, still trying to hold on to the 80's to avoid anything "complicated" like a 40VF - which is ironically the EASIEST of all the recent generation to deal with. You bolt it together and go fly it, you need to know very little compared to the old days, it just goes and goes.

      Expect my two cyber-stalkers to descend upon this thread to "correct" me and to claim they have advanced knowledge and that I am un-American, but I am trying to break you into the reality of the year 2017 instead of desperately hang on to 1956. Get a used 25LA from an RC guy, put in a stock venturi and a APC 9-4, and move on with your life.

     Brett
     

In reference to shaking the lines : it shouldn't vibrate that much. Maybe check the con-rod and crank pin fit?
As far as upgrading, I don't know. I like them on a bi-slob. They sound cool!

even the best fox will shake rattle and....you know.
One thing you might try is to find an out of balance prop and put the heavy side in line with the counterweight of the crank shaft. Other than trying to rebalance the engine, I'd get an LA .25

I'm not aware of any balancing "fix" for Fox motors.  If that were so, then a booming cottage industry would have developed to tame them.  I think Fox motors enjoyed some followers in the '50s primarily for their light weight, low cost, and availability.  No other good reason exists.

    There are multiple approaches with some pros and cons. Adding tungsten slugs to the counterbalance is probably the oldest but is definitely a mixed bag. It's probably a good idea for a profile because it can greatly reduce the vibration in the weak direction (while increasing it in the strong direction). For upright or inverted, I would say the results are ambiguous/dubious. The problem is the relatively heavy piston, which leads to...

   ABC cylinder/piston assy - this addresses the vibration better than the counterbalance modification, or in addition to it, because it reduces the reciprocating mass overall.

   The "High Zoot" crank addresses the possibility that the factory crank is not straight or eccentric, in addition to having more counterbalance.  People who really know what they are doing tell me this has much more effect than you would first imagine because most of the factory cranks are not quite right in the first place. It also addressed the crank breakage issue

   Brett

My 2 Foxes vibrate too much, but start easily and fly with the minor burp. I like my LA .25 much better, but for what I do with them, the Foxes are "OK." I do have a hefty tripler on the nose to keep structure intact over the long run and to prevent fuel from bubbling. That has been successful. The one thing I have never encountered is vibrations sensed through the lines. I don't think that should be expected, even from a Fox. inserting a wooden stick into the transfer is said to alleviate the "burping" problem in the Fox, but I haven't tried that.

The OS FP's and LA's are much easier on the planes. They don't "burp" either.

A Shoestring'd probly be a bit nose heavy with a Chev 409 in it .

7.5 mm intake and a Tornado 10 x 6 worn down to 9 1/2 ,floppy. Or the Black 9x6 & 9x4 work well on the Magnum 25 / TT FSR Clones , Gerald.
Thou the leaky Taipan Spray Bar is a intregal part of the ' burble ' . Seal the N V and it wont .

Spraybar above the case - at the outside tank edge laterally , sidemounted . And it richens low , leans off high , 4-2' s and other wonderous things.

My 2 Foxes vibrate too much, but start easily and fly with the minor burp. I like my LA .25 much better, but for what I do with them, the Foxes are "OK." I do have a hefty tripler on the nose to keep structure intact over the long run and to prevent fuel from bubbling. That has been successful. The one thing I have never encountered is vibrations sensed through the lines. I don't think that should be expected, even from a Fox. inserting a wooden stick into the transfer is said to alleviate the "burping" problem in the Fox, but I haven't tried that.

The OS FP's and LA's are much easier on the planes. They don't "burp" either.

Could be the plane. Or plane/engine combination. Run the engine on a test stand. If it runs ok there, the plane/engine is setting up a bad resonance. Different ways to handle that.

QUOTE: "At this point, we have people out there in the field torturing themselves for hours trying to get it to work, burp-quit-crash or shaking the airplane to bits in 3 flights, and then claiming how great the engine is." 
Really? You saw a plane shake itself to bits in three flight? Must have been built by some incompetent jackass.   

Are you trying to set a record for some of the most stupid posts on Stunthanger? 

  Not only is this completely gratuitous  - since this is months old and unchanged since I posted essentially the same thing 20 years ago and many times since- I can only presume that you are taking this opportunity to ream me because you think you can get away with it while I am dealing with a fatal family problem. Quite a hero.

    Take your own advice and just ignore things you don't like. I haven't said a word about your "contributions", such as they are.

    Brett

I have no idea what you're writing about. I

     I am writing about calling my comments that you quoted  an "insidious crock of sh*t" and accusing me of being "stupid"  - while I am trying to deal with a family issue that will end in the death of my father in as little as hours. It doesn't surprise me that much, it's consistent with what I have come to expect, but still, seems a little over-the-top to me.

       Brett

   

     

If your Fox flew fine one day and changed the next then it’s probably not an internal/external engine balance issue of any sort. Yes they vibrate. Check to see if the doublers /fuse have cracked and ensure the mount screws are TIGHT. If you are 100% sure that the nose is solid then try putting thin aluminum strips between the engine and the hardwood bearers. Check to see if the wing joint is secure as well. A flapping nose will give you shakey lines

You could always run it on a test stand and see if the problem follows, but I suspect something went awry with the mounting or airframe.

Nothing wrong with a Fox .35 on a Shoestring. It’s been a good combo just shy of forever.

How many Champions and Championships were won with the Fox .35?  How many designs were built for the Fox .35?
I rest my case.

By the way, Frank, I recently was lucky enough to find a new, never run Fox .59 Stunt motor.  I just ran it today for the first time on the bench.  Runs great.  Not sure when it was made, but it has a ringed piston.
It falls into the category of old Fox CL engines.

Here is what you need:

Very nice! Beautiful sound too.

But the 59's got a INTAKE RESTRICTOR in it , when are you going to take it out . 



This must be about 50 years ahead of its time . a Larry Scarinzi Trabant . Er Yatsenko . Um Little Thing with Big Injun .

Yes Indeed .

 

Thinking Last Night on the Pig Skin Glove , from the building center . Good race pitman glove .
Bind the two fingers with blue 3M tape to avoid cutting the leather .

The Fox is fairly tame but reasonably ferocious .

Now a Big Combat Wing , with the Intake out , should be good for the Ton , easy enough .
Id half saw the bolts at bearer top level , tear a lug loose & its like having the intake out , with the crack under it you cant see.
Had the Peacemaker in the other post at the ton , like that . Crack under left lug .