Building The EZE-RV

(Last Update December 14, 1999)

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This page under construction


On completing the EZE-2, I had just enough aluminum bar stock left for one more engine, so I decided to complete the family of induction types by making a -1 with a reed valve induction system in place of the rear rotary. The design chosen was stolen direct from Cox: Babe-Bee for the reed and TeeDee for the venturi/spray bar/needle design. Photo #2 shows the reed and retainer clip fitted to the backplate. Photo #1 shows an EZE-2/3 backplate being modified on its interior face to take the reed and clip.


Photo #1
Backplate machining
.

Photo #2
Cox reed fitted
.

Photo #3
Cox TeeDee style venturi
Machining Flats

Photo #4
Cox TeeDee style venturi
Finishing inlet

The venturi design is a direct replacement for that used by Cox on their TeeDee 051. The thread is 1/4"-32TPI (ie, glow plug size). In retrospect, 3/16"-40TPI would have been a better choice as it would then be common to the other EZE venturis permitting interchangability for experimentation. Photo #3 shows the part after all external turning has been completed and the chuck transferred to the rotary table on the mill to cross drill the peripheral fuel spray holes with a #77 drill and machine the spannar flats with a 1/8" end mill. The Cox part measures 0.280" across the flats (AF). A quick guide to the diameter needed to contain a regular hexagon is:

Dia = AF distance * 1.15

For the 0.280" AF hex, this means a circular section 0.322" in diameter. The amount to mill off on each of the six faces will be half the difference between this diameter and the required AF measurement, or 0.021". Photos #3 and 4 show the resultant hex section. In Photo #4 the tricky workholding problem for finishing the venturi inlet has been solved by using the backplate as a fixture. The bell mouth was machined using a long, thin tool made from a broken tap. The compound slide was set over at various angles to eye-ball an approximation of the shape. Finally, the almost imperceptable corners are blended with fine wet and dry glass paper backed up by a wooden former.

After all this work was complete, a light taper expanding from the fuel holes to the reed seat was put in using a "000" taper pin reamer. This reamer tapers from about 3/32" at the tip to about 1/8" at the end of the flutes. Squinting up the Babe-Bee inlet shows a more extreme taper and a much narrower minimum diameter. If I've gone too large here, the engine's ability to draw fuel through venturi action will be compromised. Time will tell.


Photo #5
Spraybar machining
.

Photo #6
Spraybar and Venturi
.

Photo #7
Spraybar Installed
(left)

Photo #8
Spraybar Installed
(right)

Photos #5..8 show the Cox TeeDee style spray bar. Was it worth the effort? A resounding no, but a good thing to do, once! The design is relatively straight forward. The 051 needle has a very fine thread. I'd call it 4-80, if there is such a thing. That's a tap and die size very few modellers will have, so I went with 7BA. Result is slight major diameter reduction (0.110" to 0.089") and a thread of about 56 TPI. The hard part is the hole that feeds fuel from the cavity around the needle seat to the anular groove containing the fuel spray holes. Close inspection (after some sage advice from other Motor Boys) shows this hole is drilled at an angle permitting the drill to clear the opposite side of the venturi hole, but still hit the middle of the needle cavity. The hole is about #70 and with no way to center drill first, the tip wanders like crazy against the inclined surface. I guess Cox used a jig that aligns the part and guides the drill bit all in one operation. If I ever do another, I'll make something like that. Ayou can see in photo #6, I missed the middle badly. It will still feed, but is not optimum. If performance is poor, this will be a good place to start looking.

The needle valve itself is also modelled on the TeeDee part. It shows well in Photo #15 and the exploded view (#13). Turned from steel, it has been "blued" by holding in a flame (applied to the thickest portion) until the end reached a nice blue, then water quenching. A little oil brings up the shine. Also visible in photo #13 is the needle ratchet made from 0.010" brass shim. Drilling large diameter holes in this brass is no fun. It can be done by sandwiching the brass between other, thicker materials, but even this gives tense moments. If you are a real serious model engineer with a budget to blow on really usefull tools, get yourself a "Whitney Jr" hand punch. This tool exerts a ton of pressure and comes with an assortment of nibs and dies from 1/16" to over 1/4". It is most used in the aircraft industry. Takes all the drama out of making holes in brass, too.


Photo #9
Cylinder Head
Squaring for fins

Photo #10
Cylinder Head
Cutting Fins

Photo #11
Cylinder Head
1/4-32 mandrel

Photo #12
Final assembly
ultrasonic cleaning

Photo #13
Exploded View
.

Photos #9..11 show the cosmetic cylinder head fins being cut with a slitting saw. Prior to this, the head attach holes have been drilled and counter bored. The glow plug hole was drilled, counterbored and tapped from the top surface to ensure that the seat and hole would be normal to each other. To cut the fins, I've mounted the head on a mandrel threaded 1/4" 32TPI (the standard glow plug thread). This mandrel was made long ago and is a very handy thing to have. The other end is threaded 1/4" 28TPI - which is a "standard" crankshaft thread.

Before final assembly, all parts are cleaned. This is especially important for parts that have been lapped and may have particles of abrasive still on them. Photo #12 shows a little ultrasonic cleaning bath (sourced from a jewelry repair tool shop) cleaning the aluminum bits. Steel parts are cleaned with a different solution. Finally, photo #13 shows all the parts before final assembly. Note the head attach bolts have not been drilled yet, as this requires the liner to be pressed into the crankcase (an operation that can be undone, but requires a tool that grips the rim of the liner which I've not so far had need to make!)


Photo #14
EZE-RV
Front Right.

Photo #15
EZE-RV
Side view.

Photo #16
EZE-RV
Rear Left.

And here is the assembled engine. How well does it run? So far, poorly. Choking draws fuel readily, but fuel draw is poor when running on the prime. Guess the TeeDee 051 sized venturi bore is too large for the pumping action available thru the Babe-Bee reed. That engine has a real tiny minimum venturi diameter- obviously for a good reason. I'll have to make a smaller one. If I'd made the thread common to the EZE-1 and 3, I could have swapped the assembly and continued testing (*sigh*). However, even running on the prime, with 25% nitro fuel, the RV sounds about as happy as the other glow version, which is to say, not very.

Having taken some care to provide a degree of interchangability, the head and contra piston were removed from the EZE-2 and replaced with the RV's glow head. The EZE-2 was chosen as it was deemed the best of the bunch, so far. Result? No better than the RV. Pops, bursts, but no starts, whereas in the diesel configuration, the -2 is a delightfull little engine. Carefull measurement with a digital vernier shows the gap between the piston at TDC and the bottom of the head was 0.025". The plans call for 0.031" (1/32"). A 0.005" gasket was fitted to bring the gap to very near specification. Result? No difference.

The next experiment will be to convert the RV to diesel.

TO BE CONTINUED...

The measured EZE-RV specs are:

  • Bore 0.408" (13/32" with a spot of lapping)
  • Stroke 0.375"
  • Capacity: 0.049 cu in (0.80 cc)
  • Weight, including spinner, excluding prop: 76 gm.
  • RPM: Not Yet Available.

 

Ruler

 



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