How to improve an old Fox .40 Stunt circa 1970-72?

[frank mccune]

      Any Old Timers out there?

      I have one a couple of those old Stunt .40 Fox engines that I dug out of the attic to use.  After a careful break in I am using one in a Magician with an 11-5 wooden prop. ST nva, RC Long plug, and10% fuel with 28% castor oil.

     The 4-2 break is not crisp and clean but seems to be slow breaking into one or the other.  I have been told that an extra head gasket is the answer.  The engine is a dream to start and needle but so far, the perfect 4-2 break alludes me.  I have been informed that this engine was designed for Stunt by George Aldridge so the timing must be correct.  Perhaps a profile is not a good place to search for that good Stunt break.

     Any suggestions?

                                                                                                                                                   Tia,

                                                                                                                                                   Frank

[Bill Little]

Hi Frank,

I have run a few of those, and always had to take a pretty good while to get the tank height correct on a profile.  No problems in a built up fuselage/inverted engine.  From what I remember the last profile I used one on, the tank was set about 3/16th" high.  Had a lot of flame outs inverted until I got that fixed.

BIG Bear
RNMM/AMM

[frank mccune]

     Hi Bill:

     Thanks for the reply.

      This Magician has the tank, a four ounce wedge, inlet into the fuselage so that about 1/2" is projecting on the outside of the body.  I have never seen a profile plane where the tank is installed into the nose.  The tank is on centre line of the engine and is uniflow. I have not had any problems with the engine going inverted.  The engine runs a constant 4 cycle except near the top of a loop etc. when it breaks into a 2 cycle.  Being newer to stunt, I am going to leave the engine as is as it appears to everything that I need from an engine.  I know that I will grow weak and have to add an extra head gasket to satisfy my curiosity. Lol

                                                                                                                                                             

                                                                                                                                        Be well,

                                                                                                                                         Frank

[Bill Johnson]

I might be completely off base, Frank, but Randy Smith's tips at the top of this section suggests you might be a little under propped, based on your description. Maybe try an 11-6 or a wide blade prop to load the engine better and get better 4-2-4 breaks.

[frank mccune]

     Hi Bill:

     Thanks for the tip.  I will make that change.  It is a bit easier to change props than it is to add a head gasket! Lol

     This engine is one of those good Fox products.  I bought it many years ago and broke it in very carefully.  It was in storage for at least three decades and when I put it on the test stand, it started first flip.  It still starts flip.  I am holding my breath hoping that it will not wear out" very quickly.  It is a pleasure when you have a good handling engine! I have a ton of parts to keep this engine running for a long time. As a matter of fact, I bet I have at least one extra engine in the attic.

                                                                                                                                                 Be well my friend,

                                                                                                                                                 Frank

[frank mccune]

     Hello BB:

     You're correct! Why the constant search for perfection.  I should just enjoy what I have!

                                                                                                                                                      Be well,

                                                                                                                                                       Frank

[Brett Buck]

 You're correct! Why the constant search for perfection.  I should just enjoy what I have!

   It should, however, be pretty amenable to *small* tweaks, and if nothing else, if you are careful, you will learn something. The weak/slow break is a classic sign of either not enough oil, or not enough compression ratio. A *very small* (like a .003 thinner head gasket) should have a minor but detectable effect and improve the sharpness of the break. Either that, or add 3% castor to the fuel, and see what happens. Be careful to control the other conditions and observe carefully.

    Brett