Engine basics > Engine set up tips
Fox 35 Break-in
bill marvel:
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
Jim Treace:
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
wmiii:
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
Ralph Wenzel (d):
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.
Bill Little:
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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