Stalker Engine Update

     Below are some points I have gained from flying (and selling) Stalker engines from .40 to .76 for about 2 1/2 years now.  You may benefit from these: 

Tank Height/NVA Position - If the engine, and standard 1 inch thick tank, both sit flat on the motor mount beams, the engine will run richer inverted. (Standard cylinder towards landing gear installation).  A quick, easy ’fix’ is to remove the needle valve assembly and drill a second hole for the fuel outlet directly across from the original hole.  Use a #55 or #56 drill bit, drill through the original hole, and out the other side.  Be sure to remove all metal chips!  Re-install the spray bar with the holes pointed fore and aft in the venturi.  Doing this raises the place where the fuel meets the atmosphere by approximately 75 thousandths of an inch…it’s the same as shimming the engine off
the mounts that much.
     Of course, if you are building a new plane, put 3/32 inch (.093 “) aluminum pads between the engine and the wooden beams.  If using a plastic tank, the center of the tank still needs to be about .075” to .080” below fuel exit hole(s) in the spray bar.  On profile models, the center of the tank needs to be about 5/16 of an inch above the centerline of the engine (side exhaust, outboard mounted cylinder).  Side mounted, side exhaust Stalkers will often give a “Fox burp” on outside turns (wingovers, outside squares) but will always keep running.

Nitro and Head Shim Spacing - If running nitro fuel, Stalker engines will require somewhere between 20 and 50 thousandths additional cylinder head spacing.  Start with .030”, and add a shim if the 2 cycle break is too harsh or too long.  If the power is soft above 45 degrees, take a shim out. In hot weather or high altitude, more nitro, or less head spacing may be needed.  The opposite is true at sea level, or cold weather.  Stalker provides about 40 thousandths worth of .008” shims with each engine. 0.010” shims are also available from me or Jim Lee.  In my engines, I have usually run .030” of shims and use 5% nitro Sig Champion fuel.
     However, with the recent problems with Sig fuel availability, I am going to re-tune everything for zero nitro fuel.  Preliminary ‘backyard’ test running showed no difference in starting on 0% nitro fuel.  I have mixed my own 0% nitro, 18% synthetic oil fuel with methanol purchased at a local go-kart/motorcycle racing shop.  A 5 gallon container of VP brand straight methanol was about $35.00 including the can.  The oil is Klotz from Sig...next time I will probably get the oil from the place that sells the methanol.  They may have the nitro too, but I want to fly without dependence on nitro.  Fortunately, Stalker and Discovery Retro engines were designed from the beginning to use no nitro fuel.  No nitro fuel is easier on finish materials too.


Props – I generally prefer wood props for cost and availability reasons.  However, Steve Wilk (Eliminator Props, (763) 257-3588, cell, Swilk117@yahoo.com) is a USA manufactured source for carbon fiber props.  Many are copies of Rev-Up stunt size two blade props.  He also has 3 blade props aimed more at the tuned pipe engines, but I am sure they could be pitched up if needed.  Steve’s website is Eliminatorprops.com.

Retro-fitting – Stalker engines are a bit longer, mounting holes to prop driver, than similar engines.  However, with a little work, they can be installed in the place of existing engines.  The mounts in the plane need to be re-drilled, then fitted with threaded inserts (available from Sig, DuBro, Brodak’s, etc.).  You only need to drill far enough, approximately 3/8 of an inch, so the inserts will be flush with the top of the motor mounts.  A piece of masking tape wrapped around the drill bit helps as a guide to drill “just to the tape”.  Fill the old mounting holes with dowels and epoxy unless you want to switch engines back and forth.
     The threaded inserts actually have an advantage, as the engine cannot compress the wood beams; it can only tighten down as far as the inserts.  Naturally, you will need to modify the NVA and exhaust outlets, etc. too.

                                                                                                                         Tom Dixon
                                                                                                                         April 2018