(Last Update November 17, 1999)
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The EZE-1 and EZE-3 were made in about a week of evenings apiece. If I can maintain the rage, the -2 should go together the same way.Then I can really get back to work on the Weavers. This page will be just photos and any truly salient comments (as if I can keep my mouth shut). For a more detailed construction write-up, visit the EZE-3 page.
About the only part for this engine I've not made before (for the -1, or the -3) is the front bearing and induction housing. Would you guess it? There's a dimension missing. Now I've done enough CAD to know this happens. I've also done enough CAD to know the cure is to have other people check your work. 'Taint happinin' here, folks! The omission is minor, but indicative. It relates to the size of the intake protrusion.
The location of the center line of inlet hole is given as 11/32" from the thrust face of the housing. I'd have chosen the rear face of the mounting flange as the datum. This would make measurement easier (3/16" from a flat face), if nothing else. What's missing is any indication of the distance from the hole center line to the front face of the venturi protrusion. No big deal. The hole is 5/32" dia, so it needs to be half that, plus some. I added on 1/16", making the distance from the face that mates with the crankcase 0.328", or 21/64".
I may as well describe the machining sequence I chose to produce this part, but I stress one more time: I am not a trained, professional machinist and my way is neither the only way to do it, nor probably the best way. But it worked for me and it may work for you.
If you look very closely at photo #7 you'll see two tiny pyramids I've missed. I figured these would be flattened during drilling and spotfacing, so I didn't bother (and yes, they were). You may've seen some CAD/CAM maching centers that produce extremely complex 3D shapes doing contour milling with ball-end mills, direct from three view drawings. Amazing!
The drawings show sharp intersections around the venturi. I've radiused everything. It increases the amount of work and requires spot-facing the spray-bar faces as described and the mounting holes as well (see photo #4). I think the result was worth it, but the design as drawn would be perfectly satisfactory and easier to make.
Day 3The only defference between the crankshaft for the -2 and the -3 is the the need to drill the intake port in the EZE-2. Photo #9 shows how I decided to setup to do this. The crankshaft has been set in a small "V" block with the pin in the TDC location. This was done with the help of a DTI reading against the pin (tune for maximum smoke, as we used to say in amateur radio). The V block is then set at the correct angle in the machine vice with a small protractor - 28 degrees in this case. Double check everything three times before drilling - remember, the hole needs to reach TDC before the crankpin when the engine is rotating counter-clockwise, viewed from the front. Finally, center drill the follow with #33 and #31 drills, taking care as the drill breaks through into the central transfer passage (photo #10).
In the EXE-2 article, I kinda glossed over the prop driver knurling operation. With a little practice, it's easy to get quite good results. Here are a few tips:
That's all there is to it (plus practice). On these drivers, I've used a one half of a "diamond" knurl set on center height. The resulting pattern will grip a prop well for driving, but in retrospect, it would probably be better if they faced the other way so they bite into the prop during back-fires, thus preventing it from unscrewing. I'll remember next time; maybe.
As per schedule, this session produced the cylinder, piston and several contrapistons! It also uncovered yet another drawing mystery. The -2 uses the cylinder liner from the -1 which has a flange on top. This flange is called out as 1/16" thick and 0.688" in diameter (11/16"). By contrast, the diameter of the flange on the -3 is reduced to 5/8" (0.625"). The cylinder head of the -2 has a 1/32" deep recess on its underside intended to register on the liner flange, but this is dimensioned 5/8" which will fit the -3 (that had not been published when the -2 head appeared), but not the -1 liner that it was intended to mate up with.
Now none of these things are any big deal, however they serve to illustrate a point highlighted by one reader in the "Letters to the Editor" column. Namely, when preparing a CAD drawing, the value and importance of a General Arrangement. This is especially relevent with plans targetted at trusting, first-time builders. CAD GA's are simply produced by taking the parts already drawn and fitting them together, cross sectioning where appropriate. Because this is a cut 'n paste operation, if the drawn bits don't go together, neither will the parts made from those drawings. Enough said.
Photo #15 shows the completed cylinder liner and piston, viewed from the transfer port perspective. Note the use of a milled baffle on the side of the piston which uncovers the cylinder transfer port shortly after the exhaust port opens. The baffle causes the new fuel/air charge to be deflected upwards, minimising loss through the open exhaust, while forcing out residual burnt gasses remaining in the top of the cylinder. The transfer process is refered to as scavenging and engines such as this that use a piston baffle are sometimes called "Loop Scavenged" designs.
Photo #16 shows the crankcase interior, viewed through the open backplate, with the piston at Bottom Dead Center (BDC). Note here how the piston skirt contouring just clears the crankshaft web. The last photos show the complete engine, both assembled and exploded. I've made the needle valve and spray bar to conventional practice, which took a lot longer than the far simpler approach presented with the EZE-1 plan.
Another minor design departure is the spigot left in the middle of the backplate cavity. This is blind drilled and tapped to carry a bolt, or stud, that will secure a small plastic tank. A trial fit of the tank is shown in photo #18. These tanks are injection molded from some type of poly-somethene material and are available currently from Owen Delta Engines in Australia, or from Barton Model Products in the UK (ie, the editor of MEW himself). If you want to make your own exactly like this, buy Dave Gingery's book "Secrets of Building a Plastic Injection Moulding Machine" available from Lindsay Publications. Even if you don't build it, this is an interesting book. Hmmm. Wonder if my tank was once a plastic milk container?
The measured EZE-2 specs are: