Eric,
The tappet chest covers are aluminum castings-

They are flat on the outer face, but there is a raised boss where the bolt passes through. Also, the edges are well radiused. On the inside they are ribbed.
Notice also, even though the inner face is recessed, there is some light milling to make sure the head of the tapper adjuster screw does not touch the cover (on the left side). The original bolt will have a very small Kingswood trademark, unless it has been polished away.

I have an old stock gasket set, but I do not know who the manufacturer is, or how accurate the material thicknesses are. But the gaskets for the tappet chest covers is a thick pasteboard type material, 0.070" thick. The gasket abuts the crankcase on one side, so rotation is not a problem. Yet it could slide downward, but I guess it was expected to stay tight. After a short while, the gasket probably deformed to the edge of the cylinder casting and that helped keep it in place. Perhaps the factory gasket had a horizontal crossbar across the middle with a hole for the bolt that kept the gasket from dropping down and these aftermarket gaskets I have are a cheap replacement?


I looked in the 1938 spare list and they do call out an oil slinger for both the flywheel and timing side ball bearings.
The self-aligning bearing is to allow the crank to flex at elevated rpm, but the main journals should run true. The self-aligning properties are not to accommodate a bent crankshaft. If the crankshaft is bent, the rod bearings are going to have a tough time and you will also likely experience piston seizures due to the pistons being crooked in the bores and developing hot spots.
I made new cylinder head bolts for my engine. Actually I made them several times over. The originals were quite rusty, so I decided to make new ones in polished stainless steel some twenty-five years ago when I first got my '36 Aero. The place I just started working at the time had a CNC lathe and specialized in stainless steel parts. So I made some out of 304 grade stainless, as I did not think the original bolts were made out of anything special regarding strenght. When I tightened the bolts, I noticed they never did pull up tight but just kept turning, and turning , and turning... I took the bolt back out and the 5/16-18 Whitworth thread was 5/16-16 pitch where the thread exited the tapped hole!

I had underestimated the small (and weak) core diameter of the coarse Whitworth thread. Fortunately it did not mess up the thread in the cylinder. So I made new bolts out of 420 stainless steel and had the fella at work ruin them through the heat treat furnace. Those ended up so hard they were brittle, and the heads popped off one after the other.

I suppose the fella could have heat treated them to a lower hardness, but he only knew one process for each grade alloy and for 420 it was dead hard all the way through! Finally I made them out of 17-4PH stainless, which can be heat treated without getting too hard and brittle (about 46 HRc). I don't think the original bolts were plated, I would have to search them out and check.
Recently I made some for my F28 (1928 600EW) that are also 5/16-18, but a different shape to the head altogether.

There may be a relation between the loose crankshaft and the torn taper. If the crankshaft is jerking about the flywheel is going to be jarred and that will only encourage it to become loose on the taper. However, a poorly fitted taper is sufficient in itself to work loose and start fretting and scoring the surface. Mind you, a loose crankshaft is a catastrophe just waiting to happen.
-Doug
[Strike out comment about tappet adjuster clearance, see subsequent post. 24Oct18 -Doug]