Engine basics > Engine set up tips
Fox 35 stunt stuck piston
Greg Nelson:
Ok here it is. I just picked up a new in the box fox 35 stunt for a price I couldn’t pass up. The only problem is the piston seems to be stuck. The guy I purchased it from said it was never ran and it appears to be true there is no evidence of old fuel residue anywhere and the needles are still perfectly in the box. So what is the best way to try to free it up without damaging it anymore than it is? And what is the best way to brake it in once I get it free? And dose anyone know what year this motor might be from?
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john e. holliday:
Pull the glow plug, remove backplate care fully so hopefully you won't ruin the gasket. Douse it real good with fuel. Let it soak for a bit. Mount a 9-6 prop and after soaking see if it will move. Some say use a heat gun, but I don't like that. Brand new Fox 35 Stunt are usually very stiff at the start. Do not use an electric starter on it. Get a heavy glove to use once it starts to move. also make sure the wrist pin in the piston gets plenty of lubricant. If you are lucky it may not take much to get it moving. Of all the Fox's I have each one has been different. Just don't get too forceful with it.
Now the experts can tll you how to really do it. D>K
john e. holliday:
By the way did you get the muffler with it? If so, don't mount the muffler until you get some runs on it. D>K
Dan McEntee:
All Fox engines were supposedly test run at the factory before sale, and this one is of the vintage where I believe that they really did that. It was just a short run of a minute or two just to make sure things percolated, then wiped down and boxed for sale and shipment. It is just stuck from congealed castor oil. If you have a monkote heat gun, put a prop on it and just heat it until you see some of the oil starting to smoke a bit, or gets too hot to hold. Keep the heat gun moving around the engine to make sure you heat it evenly. When you think it's hot enough, try turning the prop, and as Doc mentioned, don't force it too much. It will probably move hard at first and then get more free. At this point, I like to use PB-Blaster penetrating oil and give it a shot where ever you can to lubricate things, or use some automatic transmission fluid. both have some detergent and cleaning properties to them. Pretty soon it will loosen up quite nicely. If you have a plug in it, see what the compression is like and if it will go "flipity flipity" for you. This same process can be done after heat soaking the engine in the oven at 125 to 150 degrees or so. When cool, you can take it apart and clean things if you wish. I just flush with some fuel, put a good, hot plug in it and test run on a bench stand or in a model. For a really stuck, crusty used engine, the crock pot routine works well and has been covered numerous time and a search wil get you the info for that, but I don't think you will need it for this engine.
Good luck with it,
Dan McEntee
Dan McEntee:
I forgot the break in part. That can be found with a search of the forum also, but the short version is to mount a 9-4 or 9-5 prop, put it in a test stand, run some 28 % total oil fuel in it, and run it in a high four stroke like this for a few tanks of fuel. As Doc also pointed out, leave the muffler off. Check how clean or dirty the exhaust is and monitor how easy or hard it is to restart after cooling. When the exhaust starts to come out clean or light brown from the castor oil in the fuel, and you can pinch the fuel line for a fraction of a second to get it in a two stroke and it settles down quickly to original RPM, and it starts easily each time at that needle setting, you are ready to mount it in a model and finish the job in the air. Some run all castor fuel, but I have learned to like having a bit of Klotz in my Fox fuel now to help keep things clean.
Type at you later,
Dan McEntee
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