Horseshoe backplate mounting template

The instruction manual for the Killer Bee, available here, has the mounting hole pattern dimensions for the horseshoe backplate.

I usually lay out the location of the first hole, and drill. Then attach the backplate using that hole. A 1/8" drill is the largest that will fit through the holes in the backplate, so I use that to spot the remaining 3 hole locations. Then drill for #2 screws. By using #2 mounting screws in the provided 1/8" clearance holes, plenty of tolerance for mis-located holes is assured.
Of course, a drill press makes all this much easier. If making deep holes for standoffs, it would be a necessity.

I came around the mis-alignment by slotting the plywood mount for the snorkel, and using my micro-rattail file to "move" the off hole. Polyurethane tomorrow...something worth publishing in a couple of days. I'm fitting this in-between work and Christmas.

Expect pictures and video...we'll have 60 degree weather through next week.

Oh, and Duane...thanks. I don't know how I missed the manual. I'll have the pattern in a moment.

Bernie and Matt used to sell adaptors that mounted on the horseshoe backplate, encasing the Sure Start snorkel, making the mounting of snorkeled engines on plain firewalls possible...Bernie still has it on stock:
https://coxengines.ca/cox--049-engine-firewall-helicopter-mount.html

Ken and András are correct, both are solutions. As Ken mentioned, if you temporarily (or permanently) remove the "snorkle" (choke tube) then it is easier to mark the mount holes for drilling.

https://www.coxengineforum.com/t9381p50-recent-engine-acquisitions#126692 is an alternative to András' suggestion, if you want to retain the choke tube. I bought those stand offs at Lowes home improvement center.

Wait for it...the polyurethane needs to dry.

the black helicopter mounts work very well with the grey horseshoe backplates. but drilling to mount them is just as tricky or so as for the grey horseshoe without the snorkle. I drill one hole. bolt it in place then drill the others. seems to work ok.

Yabby, I've done that too, drill 1st hole and temporarily mount 1st screw to hold whilst drilling the others. Helps especially with Pee Wee's. They are particularly intolerant of off-drilled holes, also over-tightening.  

A little patience and care during this operation pays great dividends.

Thanks guys,

The engine is mounted and it runs!

This is good Jim! It nudged me to update my photo archives for Cox accessories to add a choke tube and mount folder.









I generally trace the four holes of a bare carb.. using a mechanical-pencil.. and then I center-punch those four marks with a small "awl".. which serves as a pilot for a 1/16" drill. A drill-press is great.. and I have one, but if I'm careful.. I can get the holes close enough to effectively meet the requirements of most fastening-jobs.

George posted of some Nylon(?) stand-offs that are 9.54mm (.375") length.



I have a bagful (1000's) of aluminum tubes (not seamless though..) that measure .190" (nominal OD) X .312" length.



The snorkel/tube's protrusion rearward is approx. .340"... making mine a bit too short to use alone; as a stand-off for that application.. but if any of you want a lightweight option for moving your engine forward by 5/16"; I'm your guy. PM me.

Close up. Now it is boxed. I missed Christmas by 35 minutes.

The needle is two turns from close

Good run, Jim. Looks like you have uninsulated pigtail connectors, OK for low voltage automotive but not for house. I got the exact same but nylon insulated plated copper and UL rated. Also got a set for binding the uninsulated ground wire in household electrical boxes, a little heavider duty and good for larger engine use. But, the aluminum is lighter in weight, which would be advantageous where you need to lighten the fuselage on the engine side.

My nylon offsets are stout enough, would do good for control line use. Best solution is one that works, goes to show how we all approach similar problems, never a dull day.

George,
That's a Dubro Kwik Clip for .020-.074 engines. But essentially, yes, un-insulated.

Woo-Hoo!
I saw 16,900 on the tach once. That's a good one. With a zero-drag starter spring, It would go over 17,000.

Ken Cook wrote: One thing I do dislike in regards to the horseshoe backplate is that it doesn't allow the needle valve straight up and the cylinder over on it's side like most conventional profiles do with a integral tanked bee. However, you can rotate the entire assembly having the needle inboard and the fuel nipple outboard with the cylinder on it's side.

You "could" mount the case with cylinder 90 degrees to the NVA.. by removing the cylinder to mount/dismount the engine to the model (for accessing that 4th mounting-hole that's blocked with the cylinder in place..) A little bit of a PIA.. but it can be done.

Using socket-head screws with a ball-end driver would greatly simplify it.

I like this configuration with the needle off to the side with no downward loop in the fuel feed.
Good running with no pressure tap.

Chapter one is finished. The rig is on the way to PA today. Hopefully we get to see chapter two in the new setting!

I need to thank DuaneH and CStatman for their assist.

Thank you both. I owe you and will get back with both of you shortly.

Here's something else Jim... If you have some thin 1/16" (1.5mm) preferably or less plywood; you can pre-cut some some panels, mark your 4 holes.. then "spot them" with an awl or wire-brad. When it's time to build your firewall; just epoxy the thin panel on... in the desired orientation and drill your 4 screw-holes.

I make them.. and keep extras ready for the next firewall-build.



The "light-tone" wood-panels are 1.25" X 1.375" and are marked T,B,I,O (Top, Bottom, Inboard, Outboard) for orienting the Horseshoe backplate with the NVA horizontal with the fuel nipple facing outboard.. for a conventional U-control model airplane. That's my preferred Horseshoe carb mounting-orientation on most of my profile-fuse designs.













There's a straight-line back and easy access to a fuel-filter and fuel-cell/tank/bladder/balloon or what have you.. mounted to the outboard-side of the model's nose.. or over/under the wing-saddle. Provides for visual confirmation of fuel-flow.. as well as easy spotting of fuel leaks in the system. Having an inboard needle adj. position is less likely to sustain damage in a crash.

The light-tone panels also have the tank-mount's pattern if I so choose.

Onion crates (and the like...) can be a source of thin wood to make some panels. You can find them behind a restaurant/diner before (or after.. ) they're thrown in the refuse... (modelling isn't always pretty folks...)

Leftover ply-scrap from an old boat model kit box can be another source for cutting some thin panels. The thinner.. the better.. so as not to add excess length to an aircraft's nose.