Part 4 By Vince Cutajar

Starting work on the front crankcase casting, I put it in the 4 jaw chuck and centred it as best I could. It's so difficult with nothing really running true. I trimmed the chucking piece of the casting and then replaced the 4 jaw chuck with a collet holder. Clamped the casting (the part that had been cleaned up) in a collet. Turned the front face and bearing housing face to dimension.

I am not really enjoying working on this casting because I can't exactly take any real measurements. Even the crankcase barrel is off centre. I have the feeling that I am doing something not right all the time. I will persevere but I suspect that this will be the first and last time I will work on a casting model.

Turned the spigot and with the crankcase barrel. Being cast off centre it came out not uniform. Drilled and bored the crankshaft hole 12.7mm and then machined the bearing housing for a push fit. Then parted off the casting and cleaned it with the mill.

It's not pretty but hopefully functional.

Next, the crankshaft bush for the front crankcase. Used a piece of bronze from the kit. Turned it 12.7mm and gave it a 1.6mm lip of 15.8mm diameter. Parted it off and cleaned it up. Put back in the chuck and drilled 9.8mm. Now I am not going to ream it because it would end up oversize so the solution was to bore it. only problem was that I do not have such a small boring bar. After rummaging trough the tools I found an small imperial internal threading tool which I do not use, ground it out further to make it even smaller and now I had a small boring tool. Worked like a charm. The hole was bored 10.05 mm.
I then pushed the bush in the cranckcase body and tried it with a 10mm silver steel rod. Good fit. I haven't pressed the ball bearing in yet as I still have some work to do and I do not want to contaminate it with aluminium dust, but seems to work also with the bush.
I started work on the timing cover. Machined on the lathe the outside face and reversed it to machine the other side, but the tool bit was getting too close to the chuck jaws.
How to continue work on the timing cover? At first I was thinking of putting a spacer under the cover in the chuck to take it out some more but at the end discarded this idea as I thought it would would be dangerous if the part flew out of the chuck.

So at the end I ended up using the same method I used for the tappet guides; i.e. fixing the cover to another piece of aluminium and using the rotary table. I figured out that in just one setting I could first reduce the diameter of the cover, then reduce the thickness of the cover and at the end machine the edge recess.

I only managed to get it fixed to aluminium using two 4mm brass screws.

Continued work on the timing cover. Centred it in the rotary table and marked out the desired diameter. Then started milling out the edge with an 8mm end mill. After finishing the diameter I wrote down the DRO X axis reading (2nd photo) which will come in handy when machining the edge recess. I then milled the part to the required thickness.

Next time I will work on the edge recess. Before switching off the DRO I brought back the X axis to zero (Y axis already at zero) and reset the Z axis to zero.

made the recess a little deeper (smaller diameter) as with the original dimensions I was afraid that the wall of the matching recess on the crank case was going to be too thin. Also I noticed that the depths of both recesses (according to plans) were not the same. If I leave them like that the cover would only be supported on the thin wall of the crankcase. Most probably I'll make them both the same size for better support.
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