Red Wing Engine Project 10/17/12

 Posted on October 17, 2012:

       Hello again folks! The next step in getting the Red Wing engine running is to mount the magneto on the engine. Before I can do that I will need to decide where the magneto will fit on the engine and how will it be driven by the crankshaft. The answer to the first part of that question really depends on the answer to the second part so I must first decide on how I will drive the magneto.
       Traditionally a magneto is driven off of the timing gears so that the magneto pulses (sparks) are synchronous with the piston reaching top dead center on the firing stroke. The rotational relationship between the crank and the magneto must be consistent for this to happen. My mini magneto will also need to be synchronous with the crankshaft so I must drive it with either a roller chain and sprockets or a set of timing gears to keep it in-time with the crankshaft (1:1).
       The roller chain method mentioned above has been used successfully by many Falcon magneto builders. This type of system uses a sprocket on both the magneto and crankshaft of which the two are connected with a miniature timing chain. The only drawback to this system is that the timing chain would have to mount on the non-governor side of the crankshaft which would be in plain sight. This would not lend well to the scale look of the Red Wing engine.
       I want a drive system that will be somewhat hidden so the basic look of the engine is not altered. This is why I have opted to use an additional set of timing gears to connect to the existing timing gears under the cam follower assembly of the engine. This setup will somewhat hide the drive gears behind the flywheel and allow me to mount the magneto inside the base of the engine as to not ruin the scale look of the engine.
       I do, however, have a concern about using a timing gear system. I am not quite sure how noisy the gears will be considering the magneto is a bit “notchey” when it turns. By this I mean the magneto will surely cause backlash in the gears as the magnets on the rotor swap poles over the core of the coil. This means the gears will chatter as the rotor pushes and pulls (twice) every time the crankshaft turns over.
       I am not sure how noisy this chatter will be and won’t know until I have a prototype system developed. I guess I will find out shortly ;0)

       The timing gear assembly I will use will consist of two gears that are identical to the ones used on the Red Wing engine. The larger 48 tooth gear (below - middle) will ride against the existing timing gear (below - left) and be used as an idler gear to drive the smaller 24 tooth gear (below - right) on the magneto. This will give the magneto a 1:1 ratio with the crankshaft.
       Note: Both of these gears were acquired from
PM Research from their spare parts inventory.

       To mount the idler gear to the engine I must install a new gear shaft below the existing timing gear shaft. This will require a little machining so I mounted the engine frame and base on my angle bracket as seen below.

       Next I set the angle bracket on my milling table and squared the bracket to the table as well as leveled the engine on the bracket.

       I now used the wiggler tool to find the center of the timing gear shaft hole (seen below). Once the hole was centered under the spindle I zeroed out the “X” axis hand wheel and locked down the “Y” axis so the table couldn’t move accidentally move.

       The next step is to drill and tap the hole for the idler gear shaft on the side of the engine frame. I moved the table 1.990” to the left (X = +1.990”) and then used a 9/16” end mill to spot face where the gear shaft will mount.
       Note: The 1.990” measurement between the two gear shafts is slightly closer than the recommended pitch diameter of the 48 tooth gears I am using. I am placing the gears .010” closer to each other to minimize backlash.

       Next I used a #2 center drill to spot the new gear shaft hole.

       Now I used an “I” drill (.2720”) to drill a hole straight through the side of the engine frame. Note: The gear shaft will eventually seal this obvious hole in the side of the gas tank ;0)

       A 5/16-24 hand tap was now used to finish off the hole...

       The next step is to drill out the hole for the magneto shaft. I moved the table an additional 1.490” to the left for a total of 3.480” from the center of the timing gear hole (X = +3.480”). This should be the ideal location for the 24 tooth gear that will mount on the magneto shaft.

         Next I spotted the hole with a #2 center drill as seen below...

       I followed the CD with a 1/2” drill straight through the side of the engine base.

       The next step is to move the table to the left again to 4.108” (X = +4.108”). This is where I will drill one of the two mounting holes for the magneto. I used a 3/8” end mill to spot face the casting just deep enough to clean up the surface.

       Next I used a #2 center drill to spot the hole followed by a #11 drill bit...

       I now moved the table once again right to 2.852” (X = +2.852”) to drill out the second mounting hole for the magneto just as before.

       The next step is to remove the base from the engine frame so that the inside face of the base can be machined flat for the magneto to mount to...

       I mounted the base on the milling table and then squared it to the travel of the table with a dial indicator (not shown). I then mounted up a 3/4” end mill into a collet for the next few steps.

       I located the center of the magneto shaft hole and aligned the spindle over the hole (0°). I then used the end mill to plunge cut a vertical notch right over the center of the hole. I then moved the table to the left in .100” increments and repeated the process 10 times to mill out the right side of the hole as seen below. You can see that I left a small strip of untouched cast iron at the top of the cuts. This will be smoothed off later on with a horizontal pass of the mill...

       I now repositioned the spindle over the center (0°) and worked my way to the left of the hole for a total width of 2”.

       Now that a majority of the metal was removed from the base I could flatten out the side with some horizontal passes from the end mill. I removed just enough material to remove the ripples which ended up leaving the top edge at a thickness of .260”.

       To get the magneto in and out of the base I needed to cut a beveled edge on the inside top of the magneto hole. I used my Dremel tool to carve the bevel as seen below. This bevel cannot be seen from the outside of the base...

       The magneto now freely slides into the engine base without disassembly.

       The next step is to drill and tap the holes needed to mount the magneto to the engine base. I used the wiggler tool to find the center of the rotor shaft and then zeroed out the “Y” axis of the table.

       I moved the table up .628” for the first hole and spotted it with a #2 center drill.

       Next I drilled a #21 hole to a depth of .475”...

       I now used a 10-32 tap to thread the hole as seen below.

       Next I moved the table down .628” (from the zero reference) and repeated the process for the other hole.

       To mount the magneto to the engine’s base I will be using a set of 10-32 stainless hex cap screws and #10 lock washers that I got from McMaster-Carr (Cat# 91720A855 - 92146A550).

       At this point I cut down the 1.5” long hex screws to a length of .550” so they won’t bottom out in the magneto. Note: It is common for me to order hardware longer than I need it so that it can be cut to length as needed.

       The magneto fits perfectly!!!

       The next step is to machine an idler gear shaft out of some 1/2” W1 tool steel rod. I laid out two cut lines at .900” and 1.130” from the end of the rod as seen below.
       Note: The 1.130” measurement dictates the thickness of the base of the gear shaft (.230” in this example). The base thickness will in turn effect the alignment of the idler gear with the engine’s timing gear. It is a good idea to double check your gear alignment before machining this part so you won’t have to alter the shaft later on.

       Next I cut down the OD of the shaft to a diameter of .312” up to the first cut line.

       I lightly sanded the shaft with some 600 grit sandpaper (not shown) and then laid out one more cut line at .250” from the end (.650” from the shoulder cut).

       I now used my .058” wide HSS parting tool to cut a thread relief at the right edge of the cut line to a depth of .056” (.200” dia.). I also trimmed down the OD of the end to a diameter of .245” for threading.

       Next I used my custom ground parting bit to thread a 1/4-20 thread on the end of the shaft.

       The next step is to cut the shaft free from the rod stock at a total length of 1.405” long. I then flipped the shaft around in the chuck and cut down the OD of the end to .310” up to the 1.130” cut line (about .275” wide). Note: make sure the shaft is correctly aligned in the chuck before cutting this end...

       Next I cut a thread relief with the .058” wide HSS parting tool to a depth of about .020” (.270” dia.).

       I now used my custom threading bit to make some 5/16-24 threads on the end of the shaft as seen below.

       The next step is to cut some flats on the base of the shaft so that it can be tightened into the engine’s frame. I mounted the shaft in a 5/16-24 steel nut and then used my rotary table’s chuck to secure the shaft on the milling table as seen below.

       I now set the rotary table to 0° and cut a small flat on the top side of the shaft as seen below. The flat spot was made to a depth of .030” and .070” in from the edge so as a 7/16” open end wrench can be used on the shaft later on.

       Next I rotated the table to 180° for the next cut at the same depth...

       I deburred the sharp edges and the shaft was complete.

       I tested the fit of the shaft at this point and I am quite pleased at how it looks. The shaft will eventually be sealed into place with some aircraft gas tank sealant so it will not effect the tank’s operation. Should my magneto system be a bust I can always cut off the shaft and call this a fuel tank drain plug :0}

       I am excited yet nervous to see if all this effort will result in a running engine. There are only a few more steps before I test run the engine so please check back for the continuation of the Red Wing engine project!!!

Till Then stay inquisitive my friends ;0)

Don R. Giandomenico


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