Amazing, beautiful detail work Brad! Good to hear you'll show it engine covers off -- it'd be a shame to hide all that fine modeling.
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The engine shown in Patrick's link has its air pump at the back end,which is how I've built mine. What's the chronology?
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Alan, there are so many air pump variations for the Mercedes series that you almost need a photo of the plane you're modeling to be certain how this part was mounted, and which pump version was used. In general, I've found that only the very early D.III-model engines have the pump mounted at the rear of the camshaft tube -- it's a feature I associate with Mercedes engines circa 1915-16. IIRC, that link shows an early D.III because it has the early-style water feed manifold. I think Mercedes moved pretty quickly past this configuration and went to the front-mounted pumps on a redesigned camshaft housing, but kept the rocker arms center-mounted -- the center-mounted rocker arms leaked and sprayed oil, and it appears that they tried several things to solve this problem before redesigning the tube and rocker box assembly so the rocker arms were front-mounted. This applies only to the 160-175 hp D.III version, not the D.IIIa where the airpump (and the rocker arms) were always mounted to the front. Dave Watts or Franzkait can provide the definitive chronology but it's going to be convoluted -- I think I recall Dave saying that there were 5 different versions of the camshaft tube and Franzkait told me that he had seen close to a dozen versions of the pump itself from various manufacturers.