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Engine basics => Engine set up tips => Topic started by: Paul Taylor on May 17, 2006, 10:12:51 AM
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About how much fuel should you run thru a 1978 NIB Fox 35 before you mount it on a plane and fly it.
Thanks
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Paul: according to Larry Foster who is probobly the best Fox man he says:
use a 10-4 prop and do 2oz. 6 times letting it cool between (fast 4 don't let it break)
same prop and do 4oz 5 times letting it cool between (fast 4 don't let it break)
10-6 prop 4oz turn needle out 1 turn 6 times ( strong 4 don't let it break, no sloppy rich)
Change glow plug and fly richer than normal for the first few flights
56 total oz.
He also said the best way to improve the Fox 35 is to install Randy Smith's Hi-Zoot crankshaft.
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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
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Back in the late 70's a discounter had Fox 35's for $12.95. I bought four and started learning the pattern. Second in Beginner , first stunt contest in 1978. I lapped the piston and cylinder of all four engines. The crank fit was OK so I did nothing to it. Ran them 3 or 4 times on the bench in a rich 2-cycle with a 9 x 4 and went flying. Put over 1000 flights each on all four. Sold or gave away two of them. One has a new piston and liner as a result of a number of squeaky lean runs trying to run crankcase pressure. The other one is good as it ever was and is flying a trainer.
I'd say when a Fox 35 will hold a rich 2-cycle without overheating, it is good to go. A bit rich the first three or four flights just to be sure.
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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...
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Yes Andrew you can do that but the big problem is if you get a FOX that goes lean, you have to fly it out , all the time burning down the motor.
I have seen this happen many times.
And there have been many engines destroyed that way
Regards
Randy
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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!!!
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Like I said, I'm no expert. No need to gang up on me. ;D
While I will admit it's possible that a Fox could go lean in the air and burn up with no way to stop it, or that it could quit with unfortunate timing, that is where exercising a little common sense and a little restraint goes a long way. I wouldn't set the needle even remotely close to a 2 cycle, and I wouldn't attempt any stunts beyond a few inside loops or a wingover. It's still possible to get in trouble, but somewhat unlikely.
On the other hand, I know if I run an unmuffled Fox 35 in my driveway or backyard, I'll have at least one police officer, and more likely two or more on my front step in less than an hour.
I personally prefer to fly engines in rather then bench run em. It works better for me personally. As they say, your mileage may vary.
Besides, its my OS's that always run away, my Fox's if anything quit early. **)
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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
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Can you explain the quiet pipe? Maybe a picture or two?
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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!!!! ;-)
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Can you explain the quiet pipe? Maybe a picture or two?
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Hi Russell
I have a cheap metal baffled 60 size quiet pipe, I just used a FP header and mounted it to the FOX 35 then slid the silicone tube coupler onto the pipe.
The pipe is mounted to the back of my test table.
I can use it for almost any motor i have, I have even hooked it up to a muffler stinger before also.
Not at all complicated.
Regards
Randy
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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. :)