Friday 30 October 2020

Machining the Crankcases – Part 4

Although there would be machining operations later in the project to fix the inner timing case (not yet started!) to the timing-side crankcase, there are 3 unrelated machining tasks that can be completed at this stage.

The first of these is the oil collection volume at the bottom of the crankcases from which the oil is scavenged and returned, via the scavenge pump, to the oil tank.

This consists of the volume itself and a large threaded hole for the collection pipe and a gauze filter to be inserted. This only needs to be in one side of the crankcase and in this case the pattern was made to accommodate this in the timing side.

The second machining operation is the oil drilling that connects the external oil feed to a location midway between the drive side main bearings, where the oil distributor ring will be positioned. This long drilling is not an easy machining operation; the hole passes through a thickened vertical rib and any miscalculation, setup error or "wandering drill" would result in the hole emerging in the wrong place, probably at one of the bearing outers. It worked out that the hole needed to be 70 from the vertical and entered the boss for the external oil feed as shown below

 And after dismounting the casting from the milling machine it had emerged here….

….which was exactly the right place.

The last machining operations are for the camshaft drive spindle bearing and an annulus to be used to position and positively locate the housing (not yet made) for the camshaft drive spindle outrigger bearing. Both of these are shown in the picture below.

To set this up, a pilot hole was first bored on the milling machine as this facilitated accurate positioning, relative to the crankshaft, using the DRO. The timing-side crankcase was then transferred to the faceplate on the lathe where the pilot hole could be accurately positioned on-centre with a dial gauge. A small through-hole to the inner crankcase surface was drilled and this would be used later to locate accurately the position of the oil pump drive on the outer timing case. The annulus was not easy to machine and most of the material was removed using a milling cutter in a tool-post grinder, turning the faceplate slowly by hand, and then finished with internal and external boring bars.

The last operation to be carried out on this part of the crankcase is the drilling and tapping of 3 holes to clamp the outrigger bearing housing but this will be done later when their exact location is known and the housing has been made.

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