Ball Hopper Monitor - Casting Project

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This is the connecting rod model that I made.

I am not sure if I will keep the original hinged rod end, or use a more traditional split cap with two bolts.

The original rod I think had the hinge pin on one side, which I am not fond of.

The idea behind the hinge pin, according to the old catalogs, was so that a user (farmer) could easily and accurately adjust the big end bearing clearance using simple tools, and without requiring any shim stock.

I will definitely make up drawings with a hinged rod cap, but I may use just two bolts, with shim stock on my rod.
0.001" shim stock is readily available these days, and the two-bolt rod cap is a much better design I think.

I checked, and the rod clears the side of the cylinder when the engine is rotated.

The big end of the rod outside diameter also fits down the bore, otherwise it would not be possible to install it, since the hole in the bottom of the crankcase is too small for it to pass through.

The hinge allows for fitting the big end by using the side cover as access, You could not easily access the far side or underneath if a traditional cap and two fixings was used.
I got the valve chamber worked out to where I think it will work well.

I did not want to drill simple holes, but instead wanted good smooth flow characteristics, and also good valve stem support.

The valve chamber houses the exhaust valve, and the exhaust pipe screws into the right side of the chamber.

The exhaust valve exits the bottom of the valve chamber.

The spark plug screws into the upper left of the chamber.

Looking at the carburetor, it appears that it doubles as an intake valve chamber, which strikes me as a bit odd, but an economical arrangement to manufacturer I guess.

I still have to model the carburetor, the governor weight that goes in on flywheel, the valves, and the pulley that bolts to one flywheel.

Other than that, I guess there are some bits and pieces such as springs, and the latching mechanism.

And I have not started on the cam yet.


Looking at photos of a full sized 4hp Baker Monitor, I just noticed that my sparkplug is on the centerline of the valve chamber, and that puts the horizontal hole for it right through the bolt that holds on the carburetor.

The full sized engine spark plug is actually off-center from the carb centerline, and closer to the cylinder.

I have revised my sparkplug location so that it clears the carb bolt area.

This is the beauty of assemblies in 3D modeling.
You can make the surfaces translucent, or more often I just toggle on the wireframe option, and look inside a part as you rotate it in 3D space.
Very powerful feature for sure.

Many modelers put the spark plug on the front of the valve chamber, but for the 4 hp Monitor, it was actually located on the left side of the chamber, and there was a priming cup on the top front center of the valve chamber.

The sparkplug on the left on a full sized engine is actually more towards the centerline of the valve chamber, not extended to the left on a boss as I have modeled it; I think to give a bit more clearance between the sparkplug and the fuel tank, and to get the end of the sparkplug deeper into the chamber.

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I am studying the governor/cam/trip/latch mechanism on the Ball Hopper Monitor.

It is a very odd arrangement in my opinion.

I was under the impression that the cam roller rolled up the side of the cam, but it appears that the high spot on the cam just strikes the roller all at once, basically almost instantly opening the exhaust valve.
I expected something more gradual.

And the cam comes around and strikes the roller with every revolution, and the roller does not stay in contact with the cam except at the cam high spot.

And there is an "L" shaped bracket that I guess is the latch, and it bounces side-to-side at the engine rotates, but does not bounce quite far enough to release the valve unless the governor weight flange pushes on it.

There is a stop protruding from the crankcase, to limit the travel of the "L" bracket horizontally.

The 4 hp full sized engine has a spring to pull the bracket towards the crankcase, but the engine seems to still run well without the spring being attached.

The round cylinder that screws onto the end of the exhaust valve appears to ride in a pocket on top of the rocker arm, with no actual mechanical connection ?

I found a good video online somewhere of the hit-and-miss mechanism on a 4hp engine, and have lost that link.

I think Jasonb also has a video of the mechanism in action.

And there is a small cam to actuate the spark, and a lever cantelievered off of the rocker arm for some reason, which seems odd, since the rocker arm is moving. Perhaps this keeps the contact open and saves battery life when the engine is missing (when the exhaust valve is being held open).

Nothing particularly odd about it, very similar arrangement to other engines I have built such as the IHC Famous Vertical and the Root and Van Der Voort Vertical

The cam follower roller does stay in contact with the cam when the engine is hitting under load, what you have seen is the follower being held off the cam when the engine is missing so it will only get a quick touch by the lobe which is enough to disengage the latch which will release if the weight does not throw enough to reengage the latch again for another miss cycle.

Our well maintained full size and model engines can use gravity to unlatch the latch, a dirty old engine in the field may need the spring to help it.

Never seen another engine model or full size where a tappet is mechanically connected to the cam or rocker arm

The cantilevered lever is simply the insulated contact and gives you somewhere to connect a wire to, probably had a Fanstock Clip on the full size. The contact is held away from the ignition cam when the engine is missing, it was common to have a for of "spark saver" on the old engines as there was no alternator to recharge the battery when the engine was running.
How do I go about making the needle valve and associated jet for the carburetor ?

Would it be better to buy an small gas engine needle valve and jet, and retrofit those into a home-cast carburetor ?

Depends what you have designed it like but if based on the PMD drawings then the needle is simple turning and a lot easier than many other aspects of making the engine.

For the needle do the 3/32" dia first and then angle the topslide for the pointed end. Then turn down some more and cut the thread with a die, knurl the next bit of the parent bar and part off.

Much the same for the needle valvebody/jet just turn the diameters and drill and tap some holes/spigots, small drill for the "jet". If you are casting it then it's easy enough, if fabrication then just solder two bits of brass together to form the basic tee shape.

These engines both full size and model are of simple design and construction you don't need fancy bought in needles and jets.
Here is the catalog cut sheet for Baker calls the "throttle with mixer".

I have worked on all sorts of small gasoline engines for many years; lawnmower engines, 2-stroke chainsaws, 2 and 4 stroke motorcycle engines, 2 and 4 stroke model airplane engines, auto engines, etc., and am familiar with how they work, and am familiar with rebuilding and repairing them.

Back in the day, we had mechanical lifters, and so had to adjust the valves with feeler gauges.
The distributor on engines back in BE (before electronics) had points that had to be regularly checked, set, and replaced, and the dwell had to be set with a strobe light.

Race car engines had magnetos built into the distributor, and there was no battery in the car.
An external battery was brought up to get the car started, but the car ran without a battery after that.

For every gas engine I can recall working on, there was always some sort of butterfly in the carburetor, or a rotating cylinder, to meter air into the engine.
As I recall on model airplane engines, the rotating cylinder also moved the needle valve in and out so that the air and fuel were always introduced proportionally across the entire speed range of the engine.

Carburetors generally had float bowls, needle valves on the float; except model airplane engines, which did not have a fuel bowl on the carburetor, and so would work in any position.

I have studied the Schebler carburetor, and some of those were more advanced than the early hit and miss type carburetors.
I think the crude hit and miss carburetors are better described as atomizers, with a fixed amount of combustion air, and a fixed amount of fuel.

I guess for a hit and miss engine, it was either missing (exhaust valve held open), or it was firing (exhaust valve closing each time the engine fired).
So basically a hit and miss engine runs at design speed (about 400 rpm as I recall), and does not really vary from that speed while under load.
A crude carburetor would work ok if you do not need much speed control.

If the engine has to provide varying horsepower over a wide range of rpm's, then a more sophisticated carburetor would be needed.

I purchases a damaged Schebler just to have one to look at, and it has a needle valve that feeds gasoline to a valve seat.
When the internal valve is pulled open by draft, the hole in the seat is exposed, and fuel is introduced into the airstream.

It seems like the valve and hole in the seat basically act as a check valve for fuel flow.

Some of the carburetors had a damper of sorts on the intake air, to control the air-to-fuel ratio.


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This "throttle with mixer" seems very crude, and there is no apparent taper on the needle valve like I have seen on motorcycle and model airplane carburetor needles.

So for the Ball Hopper Monitor, I think I could easily make a "throttle with mixer".

In the grander scheme of things, I would like to install my ball hopper monitor on the back of a scooter, and ride it around at engine shows, and so I may want a more sophisticated carburetor.

I guess I could use a simple belt drive, and just let the engine run at a constant speed with the belt engaged, and then go into hit-and-miss mode when the belt was not engaged.

I generally ride scooters at a constant slow speed anyway, since we don't want to do the Humpty Dumpty thing.

This is what I have in mind for a ball hopper monitor scooter, for use at engine shows.

Sort of a mobility scooter for old-timers.

The handlebars would be a bit higher, so you could ride it standing up.

You won't find butterflys or barrels in teh carb/mixer a sthese engines are not "throttle governed" they are "hit and miss governed" so there is no need.

There is a slight taper on the needle that you show but no where near a spointed as on say an RC aero engine. That is why it can be hard to make adjustments to mixture on these models and I quite often put a more pointe dend on the valve. Looks like PMD got it very close to original, just missing the tapered outside to the spray bar.

You say you want to ride around at a constant speed then what is wrong with hit an dmiss, it will fire when there is enough load, fire on every stroke when loaded enough and miss when you are going down hill, braking or simply in neutral standing still.

As the tank on the Monitor is BELOW the mixer there is no need for a float valve as the mixer won't flood so you don't need the float valve to shut off the fuel

Yes a Lunk type mixer shuts off the fuel a sthe bottom valve closes due to no vacuum drawing in th eair/fuel and can be used where the tank is a little above the mixer. Just be glad you don't have to ask how to machine one of thos ethey are far harder to do than the monitors simple valve and housing. Though like the gears I get a feeling you are looking for the simple approach of buying something in

What I really liked about the Monitor was that you could actually look into the air inlet and see the little jet of atomised fuel every time it Hit this would be a real shame to loose if you deviate from original just for an easy life, after all you said you wante dyour engines to be as near a spossible a match to full size so people woul dnot know th edifference ifthey could not tel the size, sticking a Walbro on there and removing all the then redundant governor parts kind of defeats the object.
I will have to play it by ear on the carburetor.

I will try to build it like an original 4hp engine, and see how well that performs.

It would probably work ok, and you are right, hanging a small chainsaw carburetor on it would really ruin the look and feel of the engine completely.

I am not worried about the store-bought gears, since once I machine the sides of them and add holes to the larger one, they will match the original gears, and nobody will be able to tell I did not make them.

I think the original large gear had the cam cast integral to the gear, but that would be a little tricky to do, and would probably require an investment casting, and some hardening of the lobe somehow.

I guess I could go old-school on the scooter, and use iron wheels like the old tractors, and give it sort of a steam-punk look, like it was made by a blacksmith.
It would be like a Wierd Al Yankovic "Amish Paradise" contraption, but sure to turn a lot of heads at the shows, and make it much easier to get around too, since I am not exactly a spring chicken anymore.

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Maybe a mix of the style of these two vehicles.

I think a front-mounted engine would make a scooter too top heavy, so it would have to be mounted at the rear, or in the center perhaps, but a center mount would be a bit of a leg hazard, with the spinning flywheels and such.

There would be some advantages to a front mounted engine, so I won't rule that out.

These are not my photos.

I have a brass carbide lamp I could hang on the front.

Getting power transmitted to a wheel will be a bit of a challenge.
I do have some 1:1 helical gears that would work at 90 degrees.
They would have to be mounted just inside the flywheel on the side opposite the valve chamber.

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Perhaps a layout sort of like this; to give it a bit of a chopper/penny-farthing look.

Stand on a platform at the back, either side, just in front of the rear wheel.

Tubular frame, with the engine suspended from it.

I think this would work.
Not sure about power transmission.

Sort of an "Amish-meet-chain-gang-biker" thing.

The tubes either side would double as flywheel guards.

Perhaps a thin pulley inside one of the flywheels, close to the diameter of the flywheel, sort of like how the old motorized bicycles use to be arranged.

I guess it could be a three-wheeler, but I am not really a three-wheeler type of person.

Old school wire rims.

Exhaust my be a bit of a problem; would have to think about that.

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This is my dad riding the Roper steam bike replica that he built, in 2003.

He was never one to sit around in a lawn chair; he had to be moving most of the time.



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I don't see the problem of getting drive to the wheels as the axle and crankshaft run in the same direction why would you need to turn through 90deg.

Your mid mounted option would simply need a belt and pully and just have a sprung idler that takes up any slip when the clutch is released and away you go. Plenty of cylinder type lawn mowers work that way.

The other problem with your mid mount as drawn is that it will go backwards, put the tank at the back and then the flywheels will run in the right direction for forward motion.