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Engine basics => Engine set up tips => Topic started by: Jim Roselle on July 06, 2015, 07:48:41 PM
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Hey all,
I have a new in box Fox 40th anniversary I would like to use for club racing. Any insight on break in for this application would appreciated.
Thank you,
Jim
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I used one of those for Fox racing for a while. It was one of the best Fox vintages. I like the high RPM rich break in with a 9/6 cut down to 8/6. I don't lean it out enough to over rev. Just get it a bit over operating speed.
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Jim,
The best Fox 35's I've run I lapped in. I used 0.007 lapping compound. You can use white DuPont rubbing compound, it just takes a little more time. You have to disassemble the engine. If the cylinder is a little difficult to pull out use a heat gun to warm the case and it should slide out. Remember to watch which port is on the exhaust side.
Put a small amount of whatever compound you choose around the bottom of the cylinder and top section of the piston. This is just a wipe of compound not a lot. Slowly move the piston into the cylinder working it up slowly deeper, twisting it as you push in then out. Once you get to where the piston baffle is within say 1/8", clean off the compound and test fit the piston to have just a little pinch at the top. Some like to go to 1/16" but I go with the 1/8". Once they fit, clean the piston and cylinder with hot water and detergent, dry them, oil with light machine oil or after run oil (make sure you oil the ends of the wrist pin and connecting rod ends). Once the engine is re-assembled you can then mount in the test stand and using low nitro, high oil 25% (50/50). Use the 9x6 cut to 8 and run it rich for a couple tanks then starts pinching the fuel line to up the revs a bit. After about three tanks (assume 4 oz) you can switch to a full 9x6 and start to bring it to a fast 4 cycle for three more tanks. After that remove the plug, slowly turn over it over through top dead center, it should be smooth. If still tight run a few more rich tanks it should be ready to bring up to a rich 2 cycle. A few tanks at rich 2 cycle it should be ready to put in the ship and fly a little rich to make sure you have it set.
Best, DennisT
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Hi Jim:
One quick story about breaking in a Fox .35 Stunt for racing.
Years ago, I took a new Fox .35 cleaned it and mounted it on my test stand. I hooked a 1 gallon can of fuel to it, installed an 8x6 prop. started the engine and allowed it to run in a rich 4 cycle for at least an hour. Mounted it in a CG Shoestring and raced it. If I remember correctly, this engine never lost a race!
That engine would run 7 laps in 22 seconds! My other engines would take 27 seconds for 7 laps on the same airplane.
I do have a nib Fox .35 that I may try this again but alas, Fox racing is dead in this area!
I have other engines that had other beak in methods tried, but non were as fast as this one. What does this mean? Not much as a sample of one does make a valid test.
Good luck,
Frank McCune