Douglas,
As mentioned, on the exhaust valves of the DT they originally used three springs. #4994 is the 350EW spring that I previously mentioned and it was used as the innermost spring. So technically #10012 should have been labeled the 'intermediate' or middle spring. But it is the inner spring on the inlet valve.
I don't think the valve timing on the exhausts was anymore radical than the inlet, so the purpose of the third spring on the exhaust was (besides wearing out the exhaust lobe quicker!) likely due to the realization that the heat was going to make the exhaust springs degrade in spring rate more quickly. LDMCC members can buy new DT valve springs via the Club. They should also have the EW springs, if you want to go triplex on the exhaust. The road bikes seemed to get by with just the duplex set.
Douglas had another way to combat heat transfer to the valve spring. Underneath the very large flange of the valve guide is a thin insulating mica washer. How effective it actually was, I am not so sure. With the enclosed valve gear models (1932-35) there was a air break between the roof of the port and the floor of the valve spring pocket that probably was more effective. Unfortunately the design also introduced a few new flaws!
"Superlock Washer" was the term then for what we call a Thackery washer, or double coil washer. Two of the engine mounting bolts I posted a picture of earlier have their super lock washer. The other has a modern single coil lock washer. These are getting hard to find now, as only a few smaller sizes used on fifties and sixties British sports car carburetors seem to be still in production. In the larger sizes you have to keep an eye out for second hand hardware.
Engine breather. This is a small fitting of aluminum and brass that screws into the drive side wall. It vents oil mist onto the primary chain. If the chain breaks, it usually is broken off. The following picture is of a 1934-35 crankcase, but it used the exact same breather. There is a light spring and a sheet metal disk inside that serve as the one-way valve.
-Doug
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