Front Cover –
The front cover seals the front of the crankcase and houses the oil pump and three gears, the crankshaft pinion, the oil pump gear and the valve timing drive gear. The features in the front cover hold two ball bearings for the gears need to precisely align with their partner bearings on the front of the crankcase.
Machining the front cover has several challenges, the foremost is aligning features on both the front and back sides. A secondary challenge is the tight quarters and fine details on the front face of the cover. The mating surface of the crankcase was machined in one setup, so the bearing holding features and the mounting holes for the front cover are well aligned. I will do the same on the front cover, machine the bearing features and the mounting holes in the back in one set up. Then I will load a piece of fixture stock in the mill, and machine holes matching the eight mounting screw holes in the front cover. I will then screw the front cover front side up with four of the screws, and machine as much as I can. Then I will put in the other four screw, remove the first set of four screws, and machine the balance of the front cover.
Below, the inside of the front cover is being machined. This is a straight forward set of operations because they are essentially a copy of the set performed on the front of the crankcase.
Below is an image of the finished inside machining.
I then use a band saw to remove most of the material on the front side of the cover, following up on the mill to provide an accurate surface to start with on the CNC router.
A fixture block is loaded into the CNC router vise. I perform a finishing operation on the top to flatten it and provide a known surface with respect to the CNC Z axis. Then the six mounting holes are machined and tapped. One of the holes was used as the X and Y axis zero set points and the top surface becomes the Z axis zero set point.
Below the roughing pass begins
I used a 1/4 flat end mill for initial roughing and machining of the horizontal flat surfaces. Then I used a 3/16ths ball end mill to machine the curved outer surfaces, and finally a 1/8 inch ball end mill to create the fillets around all of the features. I either used a dull 1/8th inch ball end mill, or did not properly match the spindle speed with the surface speed, but I was disappointed in the finish of the radius operation. Oh, and I hit the screw holes with a 3/16th flat end mill to create the counter sinks.
Below is the front cover mounted on the front of the engine.