Ball Hopper Monitor - Casting Project

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Well-Known Member
Staff member
HMEM Supporting Member
Global Moderator
Jul 2, 2021
Reaction score
MidSouth, USA
I have seen others build ball hopper monitor kits, and I had a kit from Lone Star, which I sold a few years ago.

I wanted a larger ball hopper monitor than the kit, which had 9" diameter flywheels.

I have been working on the 3D models for a Ball Hopper Monitor, and have made a little progress (no progress in recent years).

With the advent of the new Prusa XL, with its 14" square footprint, I am rethinking the size of the monitor I want to build.

I don't want to get outrageously large in size, but a 12" diameter flywheel is not out of the question, nor is a 14" diameter flywheel.

The bhm kits that I have seen seem to have a bore that is in the 1.5" diameter range.

For a bhm with 12" flywheels, I would use a 2" piston.
For a bhm with 14" flywheels, I would use a 2.5" piston.

Assuming the flywheel pattern was printed 14" diameter, the after-machined diameter would probably be 13.5".

I have been developing my 3D models from photos of existing Ball Hopper Monitor Engines, and I would like to get as close to an original engine as possible.

I have never seen photos of an actual bhm engine that has been disassembled, so if anyone has any of those, I would like to negotiate getting a copy.

This is as far as I got on the 3D models for the Ball Hopper Monitor.
Red engine is not my photo, and I don't know the source of it.

I am working on the logo, but I really need to figure out how to 3D print this item.

This logo was cut from a block of linoleum.

Not quite as good as I would like it to be as a pattern, but perhaps I can improve it.

It is flexible, and so it can be bent around the round fuel tank.

I think this is where CNC would come in handy, using a very fine bit.

Here is a guy I ran across on ytube, and it looks like he has gotten ahead of me on the bhm casting game.

That is an impressive first atttempt for sure.
I could tell him exactly what to do in order to get a successful casting, but I don't have his contact, and by this time he may have it all figured out.

I have looked all over for photos of a disassembled Ball Hopper Monitor, but I don't see any on the net.

These engines seem exceptionally rare.

There are a few videos of full sized BHMs on ytube, but no rebuild photos anywhere that I can find for a full sized engine.

I am wondering how they cored the water jacket around the cylinder.
I guess the models have a pressed-in sleeve, but the full sized engines would almost certainly have cast-in water passages, and no sleeve.

I am attempting to contact the gentleman in the video above, but not sure if I will be able to connect with him.
He may have photos of a BHM rebuild.

I suspect the clamps are due to a cracked casting. Someone may have left some water in the lower cylinder jacket and the engine froze causing the casting to crack. The crack has been patched with a clamp on band.

Jacket would have been cored, core supported by the slots in the top of the cylinder that allow the water to flow between jacket and hopper. Probably also made use of teh drain hole to support the lower end of the core. The one I built used a sleeve to form the water space so just one large cmplex core for the whole internal cavity but easily supported on seberal places..

The 1/3rd scale one that wa smarketed by Pacific Model Design had the original patterns built by the owner of a 4HP engine so he had one to measure and then whan Bob Bromps bought the patterns from him he was given access to the disassembled engine of Dale Petty so the parts are quite accurate to original design yet the model is practical to cast and make with it's separate liner.

You are going to need a good length bed on your lathe to bore the cylinder at the sort of engine size you are talking of which will come out at 1/2 scale. The main casting will be almost 16" tall which will nee dmounting onto a face plate and supporting with a fixed steady to bore the cylinder. add to that about 9" of boring bar sticking out the tool post and room for the saddle will need plenty of length.

What about casting capacity, you made the pop corn engine flywheel smaller as the volume wa smore than you could handle won't that be the case again?
I am studying the Ball Hopper and VJ Monitors, trying to get a better feel for the engines, and how to machine them.
I will have to review JasonB's build.

I have found a lot more old information about the VJ engine, including an exploded view, but I don't really understand all the differences between the VJ and the BHM. I think the VJ is a headless design? and the BHM has a head hidden under the hopper.

Mounting the crankcase/cylinder in the lathe may be a problem.
I haven't studied this enough to know yet.

I can use a #30 bilge in my furnace, and brimful it will hold 94 lbs of iron.
The usable amount of iron in a B30 is probably in the 45-60 lb range.

I will have to look at the heaviest casting, and make sure it would fit in that range.
The runners, risers, and gates add a significant amount to the pour capacity requirement, and can be as much as half of the total melt, laying it out as I do.

If the waterjacket is like you say, then I think I would core it.
I believe the core was supported by holes in the sides of the mold, which were then either plugged, or used as water entry/exit points I guess.
(I re-read Jason's post, and this is what he states).

I still don't have a good mental concept of that wonky spark plug and valve chamber, and I guess the carburetor bolts onto the chamber.

I have never made an IC engine, and so the arrangement of things is pretty foreign to me, compared to steam engines.

Upper valve I think is intake, gravity open ?
Lower valve is exhaust is seems.

It looks like on some BHM engines, the cam gear is not on-center with the centerline of the engine.
Am I imagining this?

Seems like the crankcase/cylinder could be stood upright, and bored vertically on a mill.
It would have to be a pretty rigid mill, with some depth to it.

The VJ design seems even more odd than the BHM design, with the valve chamber and carburetor cast into the headless cylinder?
The VJ seems like it would be more difficult to make patterns for and cast.

Last edited:
It probably would be wise to stick with a 12" diameter flywheel, for many reasons, some of which JasonB mentions.

A 12" flywheel would give an approximate frame/cylinder height of 13 inches, overall engine height of 22 inches, hopper of almost 7 inches diameter, and a bore just over 2".

I think this would be the scale to use.

I would be tempted to make the Monitor logo part of the 3D print. I have done this with software as simple as Designspark Mechanical, and as complex as Solidedge. DS needed a bit more work than SE. With DS I had to scan the logo, import the image into FreeCAD and draw round the text, save it as a STEP file to import into DS. It was long winded, but worked. I believe SE could do the whole process. Draft can be included when the text is extruded onto the surface. When I tried Solidworks a few years ago I found that it would create a larger degree of draft than either DS or SE.
This is the best photo I have found of the logo, I guess because it is straight on.

Not my photo, and I am not sure where I found it.



  • s-l500.jpg
    22.2 KB · Views: 5
I forgot one very important step in my description of creating a logo. Inkscape. I would use your photo, crop it, convert to black and white (grayscale) and then use inkscape to trace the outline of the bitmap and convert it into a STEP file. Much better than trying to draw around something like a logo.
One advantage of all the software mentioned here and above, they are all free, except for Solidworks, I think.
Water space core would only have 4 quite delicate radial slots to locate from the top an dthe single small drain off lower down. It becomes complicated to locate the core as the print also needs to allow for the print for the main cylinder bore core. You may have to have a ring running around the 4 slots that can be bonded onto the main core but then you need a complex core box.

Top valve is atmospheric inlet that just gets sucked open as the piston goes down

Several of the Baker engines had the crankshaft offset from the cylinder axis.

Think of the valve box as a cylinder head with two valves and a spark plug in it, carb mounts to the inlet sid eof the inlet valve, muffler to the exhaust

If you can scan the image of the logo and trace/convert it you just nee dthe outline and your CAD should then be able to wrap it around the tank. You then extrude that with some draft. As Lee says it would be a much better way than trying to stick something onto a basic 3D print otherwise you may as well just turn the tank pattern from wood an dstick bits on.

Tis is an example of wrapping text, it was laid out on a flat plane some distance from the cylinder each red square represents the text and then wrapped onto the surface


  • wrap.JPG
    51.2 KB · Views: 5
pat you will have to overcome your Facebook Fobia and then you will find image slike this. Hopper removed showing teh "head" and the radial slots around it
head off.JPG
Ah, that is the photo I was looking for.

No, I will die before I use facebook or google; way too big-brotherish for this oldtimer.

Thanks for the picture though, that is a crazy way to mount a cylinder head for sure.
I guess the outer gasket has no appreciable pressure on it, since it only has to contain the water in the hopper.

The design does yield a water-cooled head from a simple head design without cores.

For the water jacket core, I would just 3D print the cylinder and jacket in 3 pieces, and then clamp them together to make the core.
The top would also probably need to be a retract.

I have a 2D trace of the Monitor logo, but I am not up to speed on getting that onto a curved surface.
I have the trace if anybody wants to play with it (PM me).

Last edited:

Latest posts