Part 10 Finishing the Crankcase and starting on the Oil PumpsIn this installment from 'Vixen's Den' you can see the hand finishing of the two crankcases and a start is made on the elaborate oil pump arrangement located off the rear main bearing cap and located in the dry sump.
I use a long flexible extension with my Dremel to remove all the unwanted ridges and blend all the corners what cannot be easily reached by my milling machine. I follow the Dremel work with a selection of Swiss files and pattern makers rifler files. Fine grades of 'wet and dry' abrasive papers are used to smooth and refine the surfaces. I also use disks of 'Scotchbrite' mounted on the Dremmel to frost the surface to an even matt finish. When I am satisfied with the surfaces, I can give the crankcase a light grit blasting with fine alumina grit to create the appearance of a casting. The machined surfaces are carefully masked off and protected with painters masking tape to preserve their 'as machined' surface finish.
I made a start on the Main Bearing Caps. As you can see, there are five and they are all different. The rear bearing cap also carries the battery of oil pumps, which are located in that bulge to one side of the crankcase.
I must have misread my own drawing which resulted in some scrap parts, no, lets call them 'test pieces'. I had inadvertently machined a pump cavity where there should have been a plain bearing. Just look at that main bearing bolt passing through the pump cavity in the rearmost bearing cap....... Dohhhh!
Mercedes have a strange fascination for multiple pumps of all descriptions. In the sump, there is a battery of oil pumps to provide fresh oil for the bearings and several scavenge pumps to scavenge (suck away) the used oil and return it to the external oil tank via the oil filter and oil cooler. You have seen the oil filter mounted on the side of the two stage supercharger. In addition to this set of pumps, there is another scavenge pump for the supercharger, a fuel pump and the main coolant water pump mounted externally at the front of the engine. And, if you like, you can add the two stage supercharger as another huge air pump.
The sump oil pumps consist of a series of simple gear pumps driven from a common shaft. In each pump section there are four oval oil transfer passages outside the pump cavity. Passages are milled into each pump section to connect the pump cavity to the appropriate oil transfer passage. Thin bronze plates divide the pump sections and help control the flow of oil into and out of the battery of pumps.
There are fifteen parts to a pump housing set and each part is slightly different to it's neighbor. It seemed like a good idea to get a bit organised. I have yet to summon the courage to make and fit the pump spur gears, there are just so many of them.
The bronze block at the front of the pump set is the manifold which connects the various pumps to the external pipework. The first pump section supplies pressure oil to the five main roller bearings. The second section supplies pressure oil to the plain bearings of the four camshafts . The third section scavenges (sucks) the used oil from the front of the dry sump through a strainer, which is yet to be made. The fourth pump section sucks oil from the rear of the dry sump through the integral strainer. The fifth pump section sucks used oil from the four cam boxes and also from the clutch bearing housing at the rear of the engine.
Fresh, cooled oil enters the crankcase through the pipe flange on the right hand side of the case. All of the scavenged (used) oil is pumped out of the crankcase through the angled flange on the left side. You can also see the individual oil connections to each of the main bearing caps.
As with the original engines, everything will connected by large and small diameter copper pipes soldered to the individual flanges. I will be waiting until later in the build before I make and fit these pipe connections. They look like a snake pit and will be easily damaged if they are fitted to early in the build.
There are times when I wish that Mercedes Benz could have done things in a simpler fashion. But I must keep reminding myself that in 1939 these engines and cars were at the very cutting edge of motor racing technology, no effort (or expense) would have been spared if it produced a fraction more power.
Stay tuned
Mike