About how much fuel should you run thru a 1978 NIB Fox 35 before you mount it on a plane and fly it.

Thanks

About how much fuel should you run thru a 1978 NIB Fox 35 before you mount it on a plane and fly it.

Thanks

Hi Paul

The answer is you should run enough fuel thru it untill it will hold in a 2 cycle without getting overly hot.
And  will also  snap back into a  4 stroke very rapidly.
If you pinch  the fuel tube to make the motor go into a  2 cycle  and  it  doesn't  come  instantly back to a 4 stroke, It is  still building  too much heat and  needs  more  breakin.

There is  NO magic  number of ounces, but I have used  from a half gallon  to over a  gallon of fuel to breakin a  FOX 35.  Some  take more  some  take  less.

Many of these motors  come from the  FOX plant  with a  very tight  P\S  fit, and  many have  a  loose  P\S  fit

Regards
Randy

Bench break in is fine if you don't have neighbors or you've got an acoustically sealed place to run engines. 
On the other hand, as long as you don't get carried away you can run in a Fox 35 on a plane without a problem.  It might get a little tedious the first few times since it won't start easily, but its not going to hurt anything.
The instructions even suggest doing the break in on a plane in the air.  Also when flying the engine in you don't have to worry about heat cycling so much. 

I've got 20-some Fox 35's and I've only ever broken in one on the bench, and only then because it wouldn't hardly turn over and I was bored.  Only one has had a serious problem and that was because the wrist pin retainers came loose and ate the cylinder.

Besides that, a Fox will typically continue to run better as it wears until it finally wears out.  Most of the time it takes nearly a full busy season of flying before one comes into its own.  If you do it all on the bench you'll be wasting a lot of time that you could be spent flying, not to mention fuel.

Another thing to keep in mind is this, if the engine is new and has never been run and is that old... It's likely the internals will be goo'd up.  It would be advisable to at least pull the backplate and check to be sure the connecting rod is not frozen to the wrist pin.  The easiest way to check is to use the short end of a allen key slipped under the connecting rod between the rod and the crank and pull it back while watching the wrist pin end.  If it is frozen it could push the keepers out of the piston when it's run which will destroy the liner.  The cork backplate gasket might also have developed a set and may need to be replaced after pulling the cover, but at least its cheaper then a liner.

Here's a scan of the instructions for a 1978 Fox 35, the instructions for 1980, 1989, and 1992, all say the same thing.  I'm no expert, but it works for me.

Edit: added scan of instructions dated 1978 for reference, and notes...

Bench break in is fine if you don't have neighbors or you've got an acoustically sealed place to run engines. 
On the other hand, as long as you don't get carried away you can run in a Fox 35 on a plane without a problem.  It might get a little tedious the first few times since it won't start easily, but its not going to hurt anything.

   I would have to respectfully disagree with that. While you may get away with it, sometimes, it's definitely NOT without risk. One missed needle,  or air leak and resulting lean run (with no way to stop it)  will kill that piston/cylinder fit for all eternity. If that happens on the bench, you just stop it - in the air, you are in for 8-9 minutes of burn-down.  Not to mention the fairly high likelyhood of the engine quitting unexpectedly in the middle of a flight, which is not so good for the airplane if it happens at the wrong time.

    I agree that if it doesn't burn down, quit, or sieze it probably does provide a slightly quicker break-in. I have noticed that no matter how long you run the engines on the ground, it still takes a fair bit of time to really settle in. That's not just with Foxes, it's just about anything.

    But it needs to run on the ground at least long enough to get over the initial seize-up, "way too tight to run reliably" problem before you attempt to run it on an airplane. I've seen PLENTY that were far too tight to run for more than a few 10's of seconds without seizing up, and that can easily be disastrous  if the airplane happens to be in a bad spot at the time.

   Brett

p.s. Randy and I DO NOT have a open line on which to confer on a second-to-second basis!!!

Hi Andrew

Not to worry  no one  is  ganging up on you, Just using a bit of caution because the FOX 35 is very notorious  for  seizing up  when  new. I have personally  had  and  seen  many of them do it.
So its  better to err on the  caution side.
By the  way you don't need to run the FOX without a muffler on breakin, and  some  people  use  a  much quieter  OS  FP  or  LA  muffler  on the  FOX  when breaking them in.
I personally  hook them up to a  quiet  pipe  when I bench run them,

Thanks  for  your  input

Regards
Randy

Like I said, I'm no expert.  No need to gang up on me. 

   Heh! I think that was strictly a coincidence!

     It's just a slight word of caution. I've seen so many Foxes seize early on (usually, from bad fuel, but not always) that I would hate to see a lot of people running out and trying it. If it's any consolation, I responded essentially the same way about 10 years ago when GMA himself suggested breaking the engine in in the air. Maybe if you are George Aldrich, it's not to0 risky - but most of us are not George Aldrich.

   I have a box, with handles, and a bit of formica-covered particle board on top, for my engine test stand. Just rig it all up the night before, then go out to the flying field and run it there. If they don't care about the airplane they don' care about the engine.

     I would suggest AS A BARE MINIMUM about 20-30 minutes in a fast 4 to at least take the edge off the chance of quitting in the air. Larry Foster's break-in procedure, as posted above, it highly recommended, and there's not many people who have more experience with the Fox than he does.

     Brett


p.s. - GEEZ Randy, cut that out now! He really WILL think we are ganging up on him!!!! ;-)

Just rig it all up the night before, then go out to the flying field and run it there. If they don't care about the airplane they don' care about the engine.

Hmm... 'flying field'  oh to dream... 
I've got three locations to choose from when I go fly.  The first is a soccer field, second is a football field that is on a flood plain that is typically a swamp if it has rained recently, the third is a large open field with spotty grass and nothing anywhere nearby to slow the wind or dampen noise.   At any of the locations I face the likelyhood that I won't be able to fly if someone else is using the area.  Even if no one is using the ground, there's still no guarentee a police officer won't show up and tell me to go home.

There was a dedicated site here for C/L with two paved circles and at least one grass circle.  One of the circles was demolished, and the other had a chain link fence put across it a few years before we moved here in 1995. 

I'm not saying that breaking in an engine on a plane is necessarily ideal, it is however an alternative and honestly it's about the only option I have available.  It has worked for me, and I'm sure it has worked for others. 

And I was just kidding about the ganging up part.  I knew my opinion was controversial before I ever posted to this thread.