Machining the Front of the Crankcase
Machining the features at the front of the crankcase requires precision because three gears and their bearings are mounted here. For the gears to mesh correctly they need to be precisely spaced from each other. The position of the front crankshaft bearing holder has already been machined and all of the features on the front need to be precisely placed with respect to it.
Below is an image of the front of the crankcase and it can be seen that there is a lot going on there.
Before starting the machining I go to the surface plate and carefully characterized all of the dimension of the assembled crankcase, using the center crankshaft hole as my master datum. I created a detailed sketch with the dimensions of the actual part, the actual size of the crankshaft bearing holder hole and its relation to all sides of the part.
Then the crankcase is mounted in the vise vertically and squared to the axis of the CNC router. I spent an afternoon checking and rechecking the alignment and touching off the part aligning it to all of the axis of the CNC router. I used the dimensioned sketch to check the alignment several ways using them to double check each other. Then I slept on it.
The next morning I rechecked the centering of the crankcase in the CNC vise, then ran the set of programs machining the front. The machining on the front took 25 minutes and the machining of the holes took another 8.
Below is a picture of the CAD model and the resulting machining of the front of the crankcase. One of the small bearing has been test fit. There is a second bearing not installed equidistant below the crankshaft.
Then I machined the two crankshaft main bearing holders, one is mounted on the front of the crankcase and another on the rear. Below I am test fitting the crankshaft ball bearing for a nice snug fit.
Then I turn the features on the outside of the bearing holder and test fit it into the crankcase, again to a nice snug fit.
Below are a couple of pictures with the dummy crankshaft installed in the engine with the two main bearing holders supporting it.
I heave a sigh of relief. The most critical features of the crankcase have been completed and I am satisfied with the precision of alignment on the different sides.