I noticed that I scaled this engine by 14/12, to get to 1/2 scale.

This threw off the exact shaft size of the crankshaft, so I make a new 3D model for it.
I noticed from photos that the crank webs are tapered, apparently with a curved surface taper, which would mean the original crankshaft was cast.

I add the curved taper to my crankshaft webs, since I intend to cast it in ductile iron.

I worked round-robin, starting at the crank pin, crank pin bearing, then the main crank bearings.

That is as far as I got.

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I have photos of a red and gray 4hp BHM.
One shows a stop that is radial, on the top of the governor weight (the red engine), and the gray engine does not have this stop, but instead has a C-shaped boss on the inside of one flywheel spoke.

I am going with the gray engine design; ie: the C-shaped stop that limits the travel of the unhinged end of the governor weight.

The governor weight needs some fillets added, as you mention.

I am working on an assembly of the crankcase, crankshaft, crankshaft bearings, gears, flywheels, and valve chamber, so I can coordinate vertical alignment of the centerline of the exhaust valve stem down to the associated boss on the top of the rocker arm.

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Pat it was nothing to do with entrapped air. As stated it was due to a long unvented core. I am not sure where you are getting the position of th egate from as it cannot be seen in any of those photos of the casting

The Foundry did recast another from the batch of three with a vented core and that was fine. Turns out the Foundry owner left the initial job to someone with less experience and he did not vent the casting. When the owner did it himself with the vented casting it was fine.

I am studying phtoos of the rocker arm tonight.
This is a relatively small part, and located behind the flywheel and larger timing gear.
Rather challenging to get a good look at it.

This video has been a big help with looking at the fine details of a 4hp engine.
If the video is slowed down, the movement of the mechanisms can also be studied.
See 7:12 for the rocker arm.
Also at 3:52.

Looks like the ignition contact is screws to the bosses on the outer bottom end of the rocker.
There is a latch block that bolts onto the inner end of the rocker arm.
And a roller wheel inside of the arm over the cam.

Looking at 4:42, perhaps it is an optical illusion, but it seems that the inner end of the rocker arm is offset in towards the crankcase, when compared with the pushrod that rides in a recess in the top of the rocker arm?

I need to start a new assembly, and work out the vertical alignment of the cam, rocker arm, valve pushrod, valve chest and valve rod centerlines, etc.

I think I can see what is going to with the rocker arm.
I will attempt to make a 3D model tonight.

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<a href="https://www.youtube.com/watch?v=igHwlFFY2Us" target="_blank">http://www.youtube.com/watch?v=igHwlFFY2Us</a>

yeah free issues!!!

Think they send you the next few issues too, at least they used to. If you already have a subscription  they extend it a few issues. When all is done, you need to do an article!