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Engine basics => Engine set up tips => Topic started by: bill marvel on September 07, 2006, 07:23:29 PM
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What is the current thinking on breaking in a Fox 35?
I sent my very old, crash-damaged Fox 35 to Fort Smith for a new crankcase. Fox told me immediately that it would cost more to "overhaul" than it was worth. They offered to accept my 35 as a trade-in for a brand new 35 for half price ($49).
I have not broken in a Fox in many, many a moon! How much fuel should I run through it on the bench? What prop? When will I know I can bolt the engine onto a plane?
Any information will help. Thanks.
Bill Marvel
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Bill:
I am back into the game after many a moon away as well. But I do run Fox 35's on my Flight Streak and Ringmaster. Break in is pretty straight forward. I use the Fox fuel 5% w/29% oil and 10/6 prop. On the bench, run a tank (3 oz) at slightly rich(kind of a 4 cycle rumble, Fox 35's do shake and rattle a bit.) Then I run another tank just get it into the 2 cycle mode.
Then I take it out and fly. I use the Fox 5/29 for flight also.
Since the Fox 35 does vibrate a bit, always good to check engine mounting bolts before and after every flight.
I am sure there are plenty of fellows on line that would have more detailed and supportive information. Maybe they will jump in here.
Hope this helps.
Jim
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There is in somebody's file, I'll see if I can find it, a copy of Larry Foster's
break-in in instructions. Basically use a smaller propeller, like a 9x4, Fox
Super fuel mix, 5%,x 28%, and do a series of fairly fast 3-5min rich runs. Foxes take awhile to break-in but last a long time. Different people
have different methods but this has always worked well for me.
Walter
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Walter has it right. PowerMAster GMA 5-29 All-Castor is just as good as Fox Superfuel. Don't skimp on the Castor! Do use a 9-4 prop, and wood, if you really like your fingers as they are; APCs are guillotines!
It's not really a matter of how much bench time, but the quality of that bench time. I remember folks saying they'd hook up a quart of fuel to a Fox .35, start it and go do something else for an hour. That doesn't work! What you need is repeated "heat cycling". You'll accomplish more in 30 minutes of 2-minute runs with a full cool-down after each (say another 3 minutes) than you will with the aforementioned quart of fuel and an hour.
You'll be able to tell the engine is ready to put in a plane by the way it "breaks". Most of the break-in should be a series of 2-minute runs at a fast 4-cycle; blubbery rich only pounds out the main bearing. As you near the 2-minute mark, pinch off (and hold) the fuel line to kill the engine; this will give you a 10-second burst of lean running.
After about 5 of these runs, when the engine is warmed up, pinch the fuel line for 1 second. The engine should break into a 2-cycle for 5 - 15 seconds and then drop back into a 4-cycle. IF it tends to stay in the 2-cycle mode, it's not ready. When it reliably breaks lean and then settles back to a 4-stroke run, it's ready to fly, but don't chance a lean run for at least another hour of flying.
FWIW, Larry Foster recommends 10% (minimun) Nitro in his engines. More power at a cooler operating temperature.
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Walter and Ralph have it down.
I have found that about 1 hour of 2-3 min runs insures a long lasting Fox 35. Big Art, GMA, and Larrt Foster recommend using a less pitch prop for break in. This allows a little more rpm with out loading the engine too much. Big Art recommends a 10-3 1/2 Top Flite, which I keep around in a nylon version. Never have flown a plane with it, but use it to break in all my old iron piston engines.
After 4 or 5 tanks, I set it in a "cackle" and pinch the line every so often to hit a 2 cycle. This has always lead to an engine that lasts for years when properly run.
Bill <><
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Using the hard rubber 1/4" dia. Dremel bit, running round the inside edges of all the ports, and the top and bottom edges of the piston, works wonders in eliminating all those little scratchy burrs that give the traditional tramline scratches up the side of the piston. Combined with the other advice in this topic, will lead to a good long life.
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I followed the general advice and had very good luck. I ran the Fox .35 about 55 minutes in 3-4 minute sessions with 5-10 minute cooling periods. At first, I was sorry I didn't bring my starter. That Fox was so tight and so incredibly stiff. I thought I might lose a finger after all these years starting engines.
After three or four tank fulls, I could already feel the difference. After a half dozen runs, she began to start on the first or second flip. I kept the needle at a wet 2 stroke most of the time, pinching it off occasionally. I know she needs more time but it is far enough along that I don't think I have to worry about it leaning out and self-destructing! I spent a little over two hours running her in. I was at the flying field, by myself, sipping a soft drink and reading the latest Stunt News, in between runs. It was a nice way to spend an afternoon.
Thanks for all the help.
bill