<p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;">Yo. This is the first engine I've converted myself. I have a new milling machine and lathe and way more optimism than is warranted by my skills. I had a few questions about the carb I chose here .<span style=""> </span>Thanks everyone for the responses. Flipping the existing throttle arm over gives it the perfect geometry - just screwed on a servo arm.<o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;"><o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;">Anyway, my three main questions are:<o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;"><o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;"><span style=""> </span>1. Is the prop adapter too long for this engine?<o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;"><span style=""> </span>2. WIll it stay on with no key and/or set-screw? <o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;"><span style=""> </span>3. What's the best way to attach an ignition pickup (RCExl)?<o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;"><o></o></span><span style="font-size: 10pt; font-family: Arial;"><o>
</o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;">I understand that this is basically a BME 50 classic, (never seen a complete one in person - this is part of the problem). The tapered shaft sticks out 30mm from the seal. My adapter is 58mm long (from back to face). I think I have a near-perfect taper fit and it tightens down real snug. I haven't finished putting a waist on it yet because I was thinking of shortening it by 8-10mm and re-doing the inside taper. The advantages of leaving it this long are twofold: 1. I will only have to space the engine forward about 1 cm from the firewall (going on a BME Edge Mk I), thus the fins won't stick out as far outside the cowling, and 2. I will not risk ruining a part that has about 4 hours of work in it. My concern is that the extra distance will result in too much lateral force on the front part of the crank. I<span style=""> </span>plan to turn the main shaft diameter down to around 25mm (1 inch). Opinions please.<o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;"><o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;">BTW, The reason the shaft key is filed down is that I couldn't get the stupid thing out.<o></o></span></p><p class="MsoNormal" style=""><span style="font-size: 10pt; font-family: Arial;"><o></o></span></p><span style="font-size: 10pt; font-family: Arial;">For the Hall sensor, I was thinking of bending it in an L-shape and epoxying it into a small-diameter tube, like the RCExl instructions say, then mount the tube perpendicular to the shaft at 28 deg BTDC. There's not a ton of room on the housing around the shaft to attach a mount. I threaded the hole that BME uses for their sensor mount (I think) but I'm scratching my head as to how to make the mount adjustable. I figure the easiest would be an L-bracket with a slot in the mounting hole, but here again I'm open to suggestions (with pictures!!). I'm a big fan of mounting things so they can't move.

Iwould be happy to provide exact dimensions and my process for those who are interested in the rest of the conversion.

Thanks in advance.</span>

Extra length multiplies inaccuracies and stress

I think you can see how BME made theirs adjustable with a slotted bracket

Thanks w8ye.

Is that a two-piece prop adapter?It looks like the rear flange has a set-screw in it. I'm assuming the magnet faces the rear?

Imust admit I never considered putting the sensor behind like that.

It is two piece and the magnet is in the rear facing the engine

I do not own this engine but my neighbor does. Might take me a couple days but I could examine it or ask him any more questions about the hub on the phone? The first 4 images are from the RCU Marketplace

W8YE, is that part on/around the prop hub movable by undoing the set screw? If so that is a good way to set timing....right? Thanks Capt,n

I have done a bunch of these. I would try to keep the prop hub to about 2 inches or so for the reasons given. No key needed, I use a high strength Loctite on the threads. The rotation of the motor will want to tighten the hub. The key is only there as a method to attach the flywheel for timing for the product that is being made. Simple for the manufacturer that way. The BME 50 engines have a one piece hub with a seperate timing ring, the ring is held on with one set screw. Works great. The sensor is attached to the case bottom, there is a boss there that is threaded IIRC so it is a simple process. I do all my hubs this way because it is simple and works perfectly. Do a search on my user ID and you will see different hubs and rings I have done.

The adapter from BME is 40mm back to face and comes with the timing ring and magnet. The adapter from Brillellicustoms.com is about 50mm back to face and also comes with a timing ring and magnet. They also sell a very nice set up for twisting and installing your carb. On their site under conversion parts page two. Also on the sensor bracket, it does not need to be adjustable since the timing ring rotates 360* you are able to mount it anywhere convenient and set your timing anywhere you wish.

Just a quick note here, I hope when you do your final installation on your engine mounts, you have more thread protrusion than the pics shown in post #1. BTW did you purchase a short block or did you find a used saw?

Thanks

Mike Morgan

Thanks for all the advice! I started from scratch and re-machined the adapter with a timing ring. It's about 7mm shorter.I'm just waiting for some parts for my milling machine before I finish the front. I also made a hall sensor mount out of aluminum. I'll post some pictures later this week when it's done (post-office willing).

I'm with you on the mounting screws. I just finger-tightened the nuts for the photos. Iactually filed the rail slots a litle bigger to accept 5mm capscrews and mounting will be solid...

I bought the short block new at Farmer's Exchange. Model 1055 I believe.
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OK so I did my best, but I must be missing something. I think it has to do with the internal threads not pulling the hub down straight onto the taper. I am getting 3 thousandths runout mid-hub, 7 thou at the end of the hub (ack!) and 3 thou on the face. Interestingly I have a CF spinner backplate that is so uneven the prop tracks perfectly

I re-indicated the hub and all the parts are concentric to within 1 thou, so the thing is simply sitting cock-eyed on the crankshaft, I think.

I would really like some advice on how a real machinist makes threaded parts that align properly when screwed together. I lathe-threaded the prop shaft and bored the corresponding hole before tapping it (using an aligned tailstock and a good chuck). I used a Four-jaw chuck, indicated everything fanatically before each step, etc and when I screwed the stainless shaft into the hub it had so much wobble it was almost funny. I ended up threading a new piece of hex stock, screwed it into the hub and machined the other end with the shaft in the hub. I thought I was such a genius for carefully facing the mating surface and leaving a gap between the threads and the surface etc...

This my first attempt at machining anything, and I have learned a lot, but to say that I am discouraged is an understatement. I have a new appreciation for how complex a simple-looking item can be. My father-in-law thinks I'm being too picky and that if the prop is tracking OK it's alright, but I don't agree. I think I'll give BME a call tomorrow and see if they'll sell me one of their adapters. Ineed to get on with my life.

Suggestions welcome.

KD

HI KD,

You machine work looks good.I would try it and see how much vibration you get. I guess you are going with CH ignition or some other EI?

Ya Ihave an RCExl Ignition module. Imade a hall sensor mount and a timing ring with a magnet that mounts in the back. That part was easy at least.

When I was doing wood working I coined a phrase, which later I heard it was already thought of.

"Designer Firewood". Perhaps I could loan you the term, "Designer Paper Weights".

Actually your run out is only half of the total reading. The .003 reading is really .0015.

It's only .0015 off from center. That's doable.

KD,

I think the best way to get all of your parts true is to make a mandrel that has the same taper as the crank.Then mount the hub and true it on the mandrel.Or you can disassemble the engine and use the crank as the mandrel and true it all together.This is how I do mine.

KD,

I was wondering what method did you use to machine the taper in the hub?

Thanks Charlie - I thought about using the crank as a mandrel, and if I had the time and energy to repeat the process I would definitely do that.

To machine the inside taper I mounted the crank in the lathe (actually the whole engine, before I cut off the rear part of the crank), dialed it in and then set my compound to the same angle as the taper with a test indicator. I center-drilled the hub and then drilled a hole to the depth of the threaded shaft, using the appropriate size for an 8mm tap (Ican't remember the size). I bored the taper to the diameter and depth of the crankshaft taper using the compound, leaving a 1.5mm shoulder and checked VERY carefully towards the end. I threaded the deeper part of the hole with a bottoming tap held in a drill chuck in the tailstock. Now I'm thinking that it might have been smarter to tap the hole first and then bore the taper. I machined the outside of the rear part of the hub to size before I parted it off from the bar stock.

Ihave a Chinese 10 x 18" lathe similar to the Grizzly Tools model. Actually the company is owned by a relative of the Grizzly Tools folks - Busy Bee Tools in Canada. Ialigned the tailstock using the razor-blade-between-centers technique. Never did a test bar.

Now that I think of it, drilling the threaded hole rather than boring or reaming it might have been a mistake.

KD

Thanks Ralph. Imade two paperweights before this one. Broke off a tap in the first one and machined a big ole gouge in the face of the second one (wasn't paying attention to the bottom of the cutting tool)

And I didn't realize that runout was only half of the indicator reading, just like I didn't realize I was reducing the diameter of my workpiece by twice as much as the amount on the crossfeed dial. What a newb!

Not all lathes do this. some lathes when you take a .010 cut that is what is removed not .020 The cross feed threads account for this. and and as I said not all lathes do this. I test any new lathe with a dial indicator to see what is being removed....but now you know.

I had fits with getting my hubs to be straight with the crank.

The thing is the drill bit you initially used to make the hole proabably wandered. You can correct this by boaring. If you don't have one get a set of quick change tool holders. Using an Armstrong tool holder for this kind of work is an uphill battle. Use an allen wrench with a cutter ground on it to get the hole dead parallel with the lathe bed. Then cut your taper. Then make a relief at the small end of the cone then cut the threads for the crank by boaring. Then cut the threads for the prop shaft by tap. Support the tap in the tailstack. It wil be awfly close a that point. JB it to the crank. At that point I put the tail end of the crank in the 4-jaw and dialed it in. Tape the tie rod so it is not flopping all over the place. The bearing for the front end of the crank went in the steady. I put a center in the prop nut shaft to get the hub real close. At the point I turned the hub to be dead straight. I then cut the radial knurling by broaching withe the cross feed. Reassemble the engine.

Or accept that the engine will vibrate some!

Or order an adapter from BME

Seriously though - Thanks for such a detailed description. I'm going to take another crack at it this winter. Ireally have to get this plane out of my shop so my brother can actually fly it this year. Next time it will be machined on the crank and bored instead of drilled. I haven't tried turning inside threads yet so I'll have to practice that first anyway.

I'll post some pictures when I actually get the prop spinning

@lewdfinger:
What i do to taper the hub is i take a 3/8ths drill bit,or what is close to the crank diameter.
Then i hold it at an angle against my grinder and put a taper on the bit that matches the crank taper.
Then i chuck the hub stock in my 3 jaw chuck.Use the tail stock with the drill chuck attachment.
Use slow speed and drill this out.
Just to about the depth i need.
then i thread it.
Then i use an old crank ive made up as a mandrill,then i turn my hub down.
Most of my hubs come out at .0015 and less.One i had only had 1/2 of .001.

Can any of you guys give me the dimensions of the BME 50? I need to know the length from front of the prop hub to furthest point in rear of engine, and also the maximum width of the engine from outside of carb to outside of either a stock muffler &/or a Pitts muffler. I'm trying to find an engine that will fit under the cowl of an old ARF/ARC called a G-Shark. There is not a lot of room under itscowl; about 6.25 inches from firewall to front of cowl, and about 5.75 inches across.

Thanks.

4-5/8" from back of engine to face of prop adapter

6-5/8" wide, from outside edge of BMEstandard muffler to outside of throttle control arm.