Part 5 By Vince Cutajar

The next operations on the rear part of the crankcase is where I decided to deviate from the instructions in the article. I skimmed the side where the timing cover sits. And then I stopped to meditate on the next steps.

I first put both halves of the crankcase together in my bench vice (with soft jaws). I lined up the outside of both halves as much as I could by eye. Used a couple of toolmaker clamps to hold it together and took it out of the bench vice to have a better look at the line up. I had to do it a couple of times before I was satisfied.

I then took a piece of 10mm silver steel and turned one end 45 deg to make a temporary punch. Put the punch through the front half which was a nice fit, and marked the rear side on the bearing housing. The the plan was to put it on the rotary table for facing and creating the recess for the front half spigot, but could not find a suitable way of clamping it properly. So after much fussing about it was time to try the 4 jaw chuck on the lathe.

Unfortunately, the piece of the casting I wanted to chuck has a slight taper, so pieces of marine three-ply wood were inserted between the jaws and casting so that it could grip the casting better and also avoid scoring the casting with the jaws. Eventually the casting was lined up with the punch mark I had done earlier and the face was trimmed off to dimension. Then the recess was machined and a trial fit was attempted with success. Nice fit without any slop.

I faced off the bearing housing in the casting but left it 1mm higher for further machining when machining the bearing hole. Took it out of the chuck and made a trial fit with the mating casting. Not bad.

Next operation was supposed to drill and tap for the 6 bolts which will hold the crankcase together but am having second thoughts. On the plan it specifies 4BA which I was going to replace with 4mm ( which I already have ) but I suspect that would be cutting it too tight for the bosses (especially one of them). So I was thinking of using 3mm bolts instead.

I cut the recess for the timing cover and milled the bottom to the correct depth. I spent a lot of time trying to line up the casting on the rotary table trying various methods but never being happy with the end result. Finally, after nearly giving up, I had one of those moments.

I am a bit hesitant in describing it, but it did work, so here goes. I chucked the timing cover in the 3 jaw chuck and using a pointed tool in the tailstock, lightly marked the centre. I put the cover on the casting, centring it by eye, and taped it up with masking tape. Put the casting (with taped up cover) on the rotary table and centred it using the centre mark I had on the cover. Clamped it tight, removed the tape and the cover and machined it. I must have been lucky because it worked well.

I drilled and tapped the two holes for fixing the timing cover to the crankcase. I usually insert the tap in the chuck and start the first few threads by turning the chuck by hand and then continue with the tap wrench.

Timing cover is now attached to the casting. I also faced off the bosses on the front crankcase casting in preparation to drilling.

Drilled the front crankcase casting for the six 4mm bolts. Attached both parts of the crankcase castings and secured it with a clamp and using a transfer punch marked where one hole needs to be drilled and tapped 4mm.
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