MONITOR ‘BALL HOPPER’ HIT N MISS ENGINE

By Jason Ballamy

I had long fancied doing this engine and would often visit Pacific Model Designs website to eye it up. Unfortunately, they went out of business so it looked like I would not get to make one. I did almost buy one of Lone Star's similar style engines but the opportunity to make one of the PMD kits came up so how could I refuse? Lone Star has since been sold to Executive Model Design. See: http://www.minicastings.com

My engine is of the 4hp version and modelled in 1:3 scale and the photo on the left shows the original.

All but one of the castings were supplied in cast iron, the exception being the carb body which is bronze. These are the castings with a 12" rule to give an idea of size, the plastic bag contains the two timing gears.

The logical place to start is with the crankcase which is quite a hefty lump at 11" tall.
But before I could get going on that my fixed steady needed a little bit of surgery before it could be used for one of the suggested machining processes.
After a lot of careful measuring and marking out I decided on the position of the crank drain hole which was only centre drilled  for now so that the casting could be supported by the tailstock while the head end was adjusted in the 4-jaw to get the outside of the cylinder to run as true as possible then the base was machined.































At this same setting a very light skim was taken off the lower part of the cylinder so the fixed steady would have a surface to run against.
It was then over to the mill where the casting was shimmed up and a squaring cut taken across the base, this would be my datum for most of the other machining.





































The opposite side and then the ends were squared to this first face.

With the casting stood upside down the datum face was clocked true, centre located and the 4 mounting holes drilled a tight fit on some 1/4" Whit cap head screws.






































Back to the lathe and the crankcase was clamped to teh faceplate and set to run true with a DTI against the previously turned portion. When true the fixed steady could now be positioned to add support while the casting was faced and bored, the bore for the liner needs to be about 6" long.































To help with setting the crankcase casting up for the forthcoming milling operations I decided to mount it on a tooling plate. This was clocked true to the mill axis and 4 holes drilled and tapped 1/4Whit and the casting screwed down.







































I then wound the mill head up to the top of its travel and proceeded to drill and tap the nine 2BA holes for the head (5) and hopper (4) studs as well as the dozen smaller holes that allow water to flow from hopper to the water space around the cylinder liner. All done using the DROs PCD function.






































The casting was laid on its side with a parallel under the edge of the tooling plate to set it correctly in the horizontal plane and then clamped down using an angle plate at each end, the one at the base into tapped holes in the tooling plate, at the top I made use of some of the 2BA holes. I then used a ‘little Hogger’ to machine all the surfaces back to the correct distance from the centre line.

A bit out of focus but the holes and slots were added at the same setting.
Here you can see that the top of the bearing housing has been milled. I did these using the same set up but had to do each side separately as they are 5" end to end.





































With the crankcase set at right angles the access hole on the side was faced back and opened up to final size.

I deviated from the drawings here. The pen mark shows where they put the stud hole which was a bit out of place if the cover was going to fit in the right place!
Due to the various overhanging brackets and proximity to the side of the casting I had to drill and tap the bearing cap stud holes from below.
Part 1  part 2  part 3 Part 4  Part 5  Part 6  Part 7  Part 8  Part 9  Part 10  Part 11


 




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