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"RC Speed Boat Power Drive TD .020"

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Post  944_Jim Tue Dec 19, 2023 7:15 pm

Hi all,

This one is pretty silly. I can get awfully close drilling mounting holes for the horseshoe backplate (and the Sure-Start). That is, if drilling in thinner material.

But trying to get the holes just right for really deep material or for the Sure-Start gets a bit tougher. By the time I include stand offs for the snorkel I'm way off! I even trashed a backplate using it as a template.

Does anyone have a ready-to-print full size PDF template? I'd love to print them and stick them to the material before passing it beneath a drillpress.

I've searched the forum, the internet, read the PDFs here and at the MH AeroTools site to no avail.

I hope to be able to drill an aluminum plate with enough accuracy to be able to thread it and use it as a backing plate behind a plywood firewall.

Any help would be appreciated.

Thanks!
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Post  GallopingGhostler Tue Dec 19, 2023 7:42 pm

You should be able to make your own template.

I've marked the locations before by removing a ball pen ink cartridge, once the engine was located where I wanted it lightly trace its outline on the ply bulkhead with a sharp pencil tip or mechanical pencil. This helped me maintain and remaintain alignment while locating bulkhead mount holes.

Then insert a removed ink ball pen cartridge, rotate it inside the hole so you can locate the optimal drill point for the center of the sheet metal screw location. Recheck your work before drilling the engine mount screw holes.

Thus, it eliminated the off center drill problem. Did this also with the tanked Bees too.
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Post  duaneh Tue Dec 19, 2023 10:28 pm

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.
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Post  944_Jim Tue Dec 19, 2023 10:41 pm

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.
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Post  Ken Cook Wed Dec 20, 2023 3:08 am

Take the snorkel off.
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Post  balogh Wed Dec 20, 2023 5:54 am

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
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Post  GallopingGhostler Wed Dec 20, 2023 12:22 pm

Ken and András are correct, both are solutions. As Ken mentioned, if you temporarily (or permanently) remove the "snorkle" (choke tube) Very Happy 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.
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Post  944_Jim Wed Dec 20, 2023 5:16 pm

Wait for it...the polyurethane needs to dry.
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Post  Yabby Fri Dec 22, 2023 5:11 am

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.
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Post  GallopingGhostler Fri Dec 22, 2023 8:09 am

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. Rudolph  Santa

A little patience and care during this operation pays great dividends. Very Happy Christmas Tree
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Post  944_Jim Fri Dec 22, 2023 5:36 pm

Thanks guys,

The engine is mounted and it runs!
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Post  roddie Fri Dec 22, 2023 7:14 pm

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

Horseshoe backplate mounting template  Choke-11

Horseshoe backplate mounting template  Choke-10

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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.
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Post  roddie Fri Dec 22, 2023 8:37 pm

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

Horseshoe backplate mounting template  Stand-10

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

Horseshoe backplate mounting template  Stand-11

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.
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Post  944_Jim Sat Dec 23, 2023 1:22 pm

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

The needle is two turns from close
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Post  GallopingGhostler Sat Dec 23, 2023 4:17 pm

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. Wink
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Post  944_Jim Sat Dec 23, 2023 6:17 pm

George,
That's a Dubro Kwik Clip for .020-.074 engines. But essentially, yes, un-insulated.
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Post  duaneh Sat Dec 23, 2023 10:38 pm

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.
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Post  Ken Cook Mon Dec 25, 2023 7:44 am

I've had several of the Sure Start backplates crack where the needle passes through. This causes very unreliable erratic runs. Fortunately, these are inexpensive and once it happens, you can quickly recognize the problem. Sometimes, you can't visually see this as it's on the inside behind the spraybar. I also prefer to open the venturi up a bit on the backplate. The older horseshoe backplates are a bit more flexible and I've never experienced the cracking issue. I cut the needles down on the Sure Starts, they don't fit well and vibrations make them wander. Cutting them down and soldering a blind nut onto them stops the resonating but the POS black seals are terrible. These are usually useless in a few runs. I wrap a rubber band around the entire engine hooking it to the needle valve and back around to itself. Stupid looking but effective. 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.
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Post  roddie Tue Dec 26, 2023 9:50 am

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.

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Post  1/2A Nut Tue Dec 26, 2023 10:42 am

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.




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Post  944_Jim Tue Dec 26, 2023 4:02 pm

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.
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Post  roddie Tue Dec 26, 2023 7:40 pm

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.

Horseshoe backplate mounting template  20231228

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.

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Horseshoe backplate mounting template  Dsc05317

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... Laughing (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.
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