Fox .35 Engine?

Jim, if I understand your question, your looking for the proper hole spacing for a Fox .35? This isn't that easy. No two are identical and hole spacing can be off. They can be very close but some versions aren't exactly identical. Seeing that this is your first "Big Plane" I would suggest that you don't use Allen cap screws. If you hit the ground with those screws in the fuse, your going to break the case. If you use softer steel slotted head screws, the screws will either shear or bend. I would also recommend that you glue a piece of 1/8" plywood to the face of your fuel tank. Ensure that the ply covers the entire end cap. In the event of a ground strike the tank makes contact with the backplate due to sliding forward. This instantly damages the tank and the ply prevents this.

Thanks Chancy,
I saw that one before. The problem is it didn't print at the right scale. It did get me the ratio from side to length. Enough so that once I had my real length, I got the width pretty darn close! At least this time I read the article in detail, so I have a really good handle on fuel requirements, and potential props. I won't be so unprepared on flight day now.

Yes, Ken,
I understand your points...I think it is funny that Ole LM Cox was able to consistently replicate his little engines millions of times with more accuracy! This engine does have reasonably close measurements, but even one of the holes was double-drilled at the factory...as in two side-by-side holes. That "hole" has a look of a Venn diagram with a lot of common area! After reading your post, I'm thinking I may be over-engineering/over-thinking this thing (not that this would be the first time).
Now you have me double-guessing if I will be able to honor Rusty by hanging the Golden Fox on the intended airframe (relax, breath deep...see above).

This engine is going on my UKIE, and I intend on mounting the plastic three-line 4 ounce slant tank inboard opposite the engine. There isn't a lot of room between the backplate and wing root. I got that idea from StuntHanger several weeks ago.
It is funny you mentioned the screws. I really started sweating over what to use, and caught that fillister screws may be best for this engine from SH. So I ran all over town looking for them to no avail. Then I started looking for socket head screws...also a bust. I was starting to think mild steel panhead screws were the only available option, but was still concerned about strength. Your comment regarding them makes me feel better.
Mild steel screws are already on hand for all bits, and I printed the "Competition Notes" for this plane posted on SH for final setup. So this plane may maiden shortly.

The plane has a name already, but I won't disclose it until the maiden flight. I'll just say I hope a guy in Texas will enjoy the name! The town sounds something like Llamas Passing.

I appreciate both of your responses, Guys.

Jim it should be close enough. Don't you currently have a Fox .35? If anything, one of the holes my need a bit of reaming. In addition, you have a foam wing. If you need to mount a larger tank, the solution is to notch out the foam where the tank butts up to it. The leading edge is not the strength of the wing the spar is so you can make a cut into it if needed as this was standard practice. Chicken hopper tanks are a good solution for the Ukie.

Cox engines used extrusions and not castings. Therefore, much of the machining was automated through the use of the screw machines they were produced on. Apples to oranges in reality.  When using cast molds, they wear out not too mention the material distorts when cooling. Duke was monumental above anyone else at the time. While some of the engines had it's shortcomings, Duke provided engines lighter than any engine on the market. In addition, the MK series when introduced in the 70's was very ground breaking as it was one piece from the backplate to the nose. He used many different draft angles to allow this case to be removed from the mold which no other manufacturer was doing at the time.