Ball Hopper Monitor - Casting Project

[Jasonb]

Having done quite a lot of boring on the lathe with a between ctrs bar and the work moving I would say you need a more rigid setup than holding at one end only.

Does your lathe have a decent tee slotted cross slide as that makes mounting work a lot easier than those that just have a small area for the top slide to mount to.

Also bear in mind in all those that you have seen the hole was being bored for a liner. The more critical bore that the piston fits was machined into a separate easily held liner. You are looking to cut the cylinder bore direct into your casting so a more critical setup. The liners also only make contact top and bottom often two slightly different diameters to aid insertion so far less critical of the need for those two bore to be totally parallel unlike the actual cylinder bore.

 

[GreenTwin]

If the hole in the bottom of the crankcase was machined exactly the same size as the boring bar, then the boring bar could support the end of the crankcase, and the live center could support the end of the boring bar.

I think this is basically what Myfordboy did, although he used a bushing in the end of the crankcase for some reason.

Edit:
So how to machine the hole in the bottom of the crankcase precisely?

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[Jasonb]

Myfordboy also had easy cutting aluminium not cast iron

And not just the accurate hole in the bottom, you would also need to have machined the head perpendicular to your intended bore and set the hole pCD to the ctr of the yet to be cut bore if you are hoping to use that as your mounting surface.

If you have the head room on your mill it would be possible to do the feet, then the top and you could bolt a guide plate to the feet, the bottom hole simply being clearance.

 

[GreenTwin]

Lets talk about ignition systems.

I have an electronic iginition system, but I prefer the old school points, condenser, and coil, since I can troubleshoot it, and make it work no matter what.

The problem with all electronics is that one day, for no particular reason, they just stop working, and generally you cannot repair them.
Don't get me started on my dislike of electronics, which I have to deal with every day at work.

I purchases some small spark plugs, but I have never built an IC engine, and am unfortunately ignorant about them in many respects.

I have NGK's "CM-6" plugs.
What exactly do I have ?
Is this a metric thread or what ?
The reach on this plug seems a bit short.

Can someone give me the 10 cent tour on all things sparkplugs for model engines ?

What is a good source for small ignition coils, points and condensers ?

There was a post recently about small spark plugs, and I posted some links, but I forgot where that was.

Seems like there was a 1/4" thread on the smallest plug.

I don't want to make my own plugs.
I have bigger fish to fry.

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[GreenTwin]

Here is a model engine sparkplug site.

The problem is I have no idea what I am looking at or what I need.

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https://miniaturesparkplugs.com/

 

[GreenTwin]

Here is another site for model engine sparkplugs and ignition systems.

https://www.model-engine-ignition.com/model-engine-ignition/spark-plugs-wire-more

 

[GreenTwin]

I found this book by Bob Shores.

https://ia601005.us.archive.org/8/i...ion_Coils_and_Magnetos_by_Bob_Shores_text.pdf

 

[GreenTwin]

I found this info.
Looks like I may have to purchase a metric tap.
I am not a metric person, and don't want to be a metric person (call me old-school or whatever).

NGK-CM6 Spark Plug​

NGK traditional plugs are constructed for longer life and optimum performance. Corrugated ribs prevent flashover. NGK uses only the purest alumina silicate in its ceramic insulator which give all NGK plugs greater strength and better heat transfer. Copper cored and triple sealed to further aid in heat removal and prevent interior leakage.
10mm Thread, 8.6mm (.339") Reach, 9/16" (14.3mm) Hex Size, Gasket Seat, Non-Resistor, Solid Terminal, .016" (0.4mm) Gap, Heat Range 6

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[GreenTwin]

And I seem to recall my dad having sparkplugs that had pipe threads on them, I guess for an old Ford Model "T" engine ?

I think all modern sparkplugs use straight threads (no taper) ?

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[GreenTwin]

I recall finding a formula for balancing a single-cylinder engine, but I forget exactly where I put that.

I remember that a single cylinder engine cannot simply be balanced by adding counterweights that match the weight of the crank webs, crank pin, connecting rod, piston, and piston pin, since the counterweight is also swinging side-to-side.

Some sort of compromise was made in the equation to spread the vibration equally between vertical and horizontal.

I need to go find that equation.

For the Ball Hopper Monitor, there are curved slots in the rims of the flywheels, and I notice that the slots in the scale model BHM engines don't match the slots in the analogous full sized engines (2hp or 4hp).

I have noticed that some of the scale BHM engines seem to run with little vibration, so obviously some folks are getting the balance correct.

There are other things to consider for balance, such as the governor weight that is attached to the flywheel, and the pinch bolt in the flywheel hubs.
I consider those weights to be static from the standpoint that they only rotate, and don't move side-to-side, and so should be easy to balance.

Edit:

I found the forumula that I was using on a steam engine to calculate the counterweights on the crankshaft.


Equation for minimizing engine vibration:

W1 = [K*(W2+W3)*r] / X

where:

W1=weight of counterweight (lbs.)

W2=weight of crank, outside of hub around main shaft (lbs.)

W3=weight of reciprocating parts (piston, piston rod, crosshead, one half weight of connecting rod) (lbs.)

X=distance of center of gravity of counterweight from center of shaft

K=constant (use 0.67 for minimum vibration at right angles to centerline of engine)

(use 0.75 for minimum vibration at crank dead center)

r=distance from center of shaft to center of crank pin

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Solidworks automatically calculates the mass of any given part, and that is very helpful when considering balancing things.
Someone also mentioned years ago that SW could be used I think in a dynamic motion study to look at the movement of the center of mass, and that could be used to equalized and minimize the vibration in an engine.

I guess a simple starting point would be to find a static balance point by comparing the flywheel rim recesses with the items connected to the crank throw, and the crank throw.
We know that the static balance point is what I would call "overbalanced", and so we need less of the flywheel recess cuts.

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[GreenTwin]

And as someone mentioned in another thread discussing model engine compression ratios, should I adhere to the scaled engine compression ratio, or do I need to adjust, ie: the compression ratio does not scale down linearly ?

I seem to recall that model engines run well at low compression ratios, but what are the pros and cons of raising the compression ratio to something like 7.5:1 or slightly higher ?

I guess I would want to keep the compression ratio as high as possible, since I may actually connect this engine to something that requires a significant amount of power (fractional hp).

What sort of horsepower could this engine produce ?

Does the rpm scale down, or does this engine run at say 400 rpm ?

So many questions; so little time.

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Edit:
I remember a really good post about scaling model engines, and how that worked out from a physics standpoint, such as mass, volume, velocity, acceleration, strength of materials, etc., and while I recall saving that post, I can't seem to find it now.

I have noticed that some large engine cranshafts, when scaled down, become so small in diameter that the don't have sufficient strength to function as part of a running engine.

 

[GreenTwin]

Equation for minimizing engine vibration:

W1 = [K*(W2+W3)*r] / X

where:

W1=weight of counterweight (lbs.)

W2=weight of crank, outside of hub around main shaft (lbs.)

W3=weight of reciprocating parts (piston, piston rod, crosshead, one half weight of connecting rod) (lbs.)

X=distance of center of gravity of counterweight from center of shaft

K=constant (use 0.67 for minimum vibration at right angles to centerline of engine)

(use 0.75 for minimum vibration at crank dead center)

r=distance from center of shaft to center of crank pin


This equation was used for a steam engine, so in our case there is no crosshead.

The Galloway 7 hp engine that I have worked on has counterweights added on the opposite side of the crank pin, and this is additional weight cast into the inside of the flywheel rim, as was typically done on steam locomotive wheels.

The Ball Hopper Monitor subtracts weight from the flywheel rim via a machined slot, and that slot is on the same side as the crank pin.
The Monitor flywheel would have some weaknesses in it around the slot, and I have seen more than one flywheel that has cracked.

I think the Galloway design makes for a more robust and stronger flywheel design, but we will adhere to the Monitor flywheel design, as flawed as it is.
For a low speed, low power engine, I would say flywheel failure due to the slot would be minimal.

For the Ball Hopper Monitor, the equation would be as follows:

W1 = weight of the two slots (one slot in each flywheel rim) (lbs.)

W2 = weight of the crank webs and crank pin outside of the flywheel hub (lbs.)

W3 = weight of the reciprocating parts (piston, rings, wrist pin, 1/2 the weight of the connecting rod) (lbs.)

X = distance from the center of gravity of counterweights (slots in our case) from the centerline of the crankshaft (inches ?)

K=constant (we will use a generic 0.71 )

r=distance from center of crankshaft to center of crank pin

W1 = [K*(W2+W3)*r] / X

So the mass of each slot would be 1/2 W1, I assume.

I will do some calcs in Solidworks, and see if the scaled slot masses falls within the range of the equation above.

The other method, as someone mentioned to me, is to plot the center of mass as the engine is running in simulation in Solidworks, and see if that plot is a circle, an ellipse, or what.
I don't know how to plot the center of mass in a SW simulation, but supposedly it works.

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Edit:

The equation is basically mass times distance = mass times distance, times a constant which is less than one.

 

[GreenTwin]

I did a quick calculation with the equation above, and compared it to what I think would be the mass of scaled slots in the flywheels, and I am of almost by a factor of 2.

I have seen some folks on ytube use a handheld vibration meter to check various small 4-stroke engines for vibration.

I suppose the Ball Hopper engine could be assembled without the head, and then rotated with an electric drill, and then lead strip weights added to the slots in the flywheel, one strip at a time, while either feeling for vibration, or using a vibration meter.

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[Jasonb]

CM-6 has an M10 x 1 metric form thread where the Major diameter is 10mm and the pitch 1mm if you don't want to go metric then look out for a 3/8 x 24 "V" plug

https://sparkplugs.morrisonandmarvin.com/v.php.
I don't see a CM-6 as being too short in the thread even if you mount it on the tank side of the valve block. It is also nice and short on the exposed end which you will need, no chance of getting that longer plug you show to fit.

Stick with scale compression ratio

As for putting points onto what is supposed to look like a scale model I certainly would not. Either go electronic (non hall sensor) or buy/make a buzz coil both just needs simple contacts like the original engine had.

 

[GreenTwin]

Looking at various photos of ball hopper monitor model engines on the net, I think it is safe to say that many don't know how many slots there are in the flywheels, and don't know their position relative to the crank throw and the governor weight.

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[Jasonb]

Try this link for the V plugs as that one I posted earlier seems not to work

https://sparkplugs.morrisonandmarvin.com/

 

[GreenTwin]

The CM-6 is about 1/3 the cost of a 1/4 plug, so if the CM-6 is the right scale, I will use it.

This engine is large enough that I don't think I will be forced to use a 1/4" plug.

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[Jasonb]

That is mass production for you and also the higher cost of US making over far eastern.

Don't forget to factor in the cost of a tap and 9mm drill bit whereas you may have a 3/8 x 24 imperial one

The V is also shorter bodied than the CM-6 which may help with fitting it between the tank

 

[Oldiron]

I use Ford coil over plug (COP) ignition coils and have had good luck with them. Some of the external ears and shields can be removed to get them down to a reasonable size. They work well at 6 volts or less. If you go up to 12v you will get a hellacious spark that will arc out all over the place. Just make sure that the engine doesn't stop with points closed and leave the power on. A most impressive smoke show will result I can insure you. Bob

 

[joeprindle]

And I seem to recall my dad having sparkplugs that had pipe threads on them, I guess for an old Ford Model "T" engine ?

I think all modern sparkplugs use straight threads (no taper) ?

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The Monitor used a buzz coil and a 1/2npt spark plug. Some of the later pump jack engines and the HJ horizontals could be ordered with a magneto.
As far as compression ratio goes 3.5 or 4 to 1 is good, anything higher and they hit too hard. You don’t want the engine to jump every time it fires, do you?
What made you settle on the 4 horse engine? I always thought that 1/2 scale of the 2 hp would be nice or 1/3 scale of the 6/7 horsepower would be interesting, the 6 (later treated to 7) has a mechanically operated intake valve, which is unique.