Hello everyone new member here question i have a fox 35that has never been started do i have to take it apart to clean it before i start it? also does it take a whole gallon of fuel to break it in? thanks for any advise.
Hi Wayne;
Ty is correct on the basics of the Fox .35 and other old engines of this type. The simple way to look at it is, that the engine parts are iron, more or less and need the castor oil for lubrication and it also carries out excess heat with the exhaust. The pistons are made from an iron powder that is put into a mold, then fired in an oven, where the powder melts and forms the part. The process makes the parts pretty porous. The cylinder sleeve is machined steel. The length of time it takes to break in an engine depends on how closely the parts fit together when the engine is assembled. It can vary for several reasons and be anywhere from just loose enough to go together to hardly enough compression to run!! Check out the back side of the engine as Ty suggested, and if all is well, and you need a new gasket, just make one from a heavy piece of card stock from some junk mail. Many of us use old playing cards. Cut out a blank a little bigger than what you need, poke a hole with a hobby knife in one corner and run a screw into the hole. then repeat with the other two screw holes. You may have to put a few washers on the screw so it will snug down tight. Take a hobby knife with a new blade and run it around the inside of the opening to cut out the center hole, making it as neat as you can. Take all the screws out, place the back cover back on, tighten down the screws, and you can now trim the outside. If you have any doubts about whether this will leak or not, just put a thin layer of any kind of gasket sealer on it. You now have made a gasket and are ready to run it in. Use fuel with all castor oil or a mix of synthetic with it. It must be the 25 to 29% total oil that Ty mentions. Modern fuel will have to have oil added in the area of 8 ounces to a gallon or so. Check back with us when you get fuel and we can help you with that because it can vary from brand to brand. You want to use a 9-4 or 9-5 prop for the break in. That keeps the load on the engine more manageable so it doesn't get too hot. Set up your test stand with a 4 ounce tank and some tools like a glow plug wrench, hemostats or needle nose pliers and such. Mount the engine and tank. Make sure the bottom of the tank is at least as high as the engine mounts. YOU DO NOT WANT THE MUFFLER ON THE ENGINE AT THIS POINT! Hook up some fuel line with a filter in line, install the prop and you are ready to go. Open the needle at least 7 or 8 turns. It does need to be out that far is it has an original needle valve on it. Choke the engine with your finger over the venturi for two of three flips, then attach the igniter battery and give the prop a smart flip. When it starts, leave the igniter battery on for a while until you get the needle set at the correct setting for a rich, 4 stroke sound. Don't let it run too slow, or too fast. When the tank runs out, let it cool like Ty said, then repeat. You might find that the engine will back fire or kick back, and that will loosen the prop nut, so check the prop nut from time to time. Run the next two tanks like that, and hold a piece of light colored card board in the exhaust flow carefully for a second or so while it's running, to catch some exhaust. While breaking in these old engines, parts will rub together and wear microscopic bits of metal off, and this will appear as dark streaks or even a solid black color coming out of the exhaust in the oil. This is something that you are going to watch for. After 6 runs or so you can lean it out just a bit, and now and them while running, pinch the fuel line for a fraction of a second so it will lean out into a 2 stroke, and then come back to the setting it had. If it stay at the higher RPM and comes bac slowly, it still needs more running. Check the exhaust for metal as you go along, and listen to the engine as you pinch the line and such. The old Fox needles leak air around the needle threads so We put a length of fuel line over it to seal them off against the venturi and the knurled wheel. cut it just a bit longer than what you are seeing at this point. count the turns as you take the needle out, slip the fuel line over the needle, and turn it back in the same number of turns. By the time you get a dozen runs on the engine, you should feel some difference in how it flips over and it should feel a bit more loose. The fuel line pinch test will get better. The number of runs to get to this pint can vary depending on how tight it was to start with. If the exhaust is starting to get more clear, toy can mount it in a model and fly it at a easy needle setting and see how it reacts to climbing and diving. You will be the best judge here for when to start flying stunts with it at this point. Continue to check the exhaust as you clean up the airplane. Take the plug out and soak it in some acetone or brake cleaner to clean it and check the coil. the coil should be nice and round shape. I don't normally do this, but with the price of plugs these days, it's worth the effort to get get every flight out of one that you can!! And a little cleaning now and then might help. Check back here with any questions.
Type at you later,
Dan McEntee