Almost immediately, it was proven worth while. I took off the internal oil lines...
Note the big lump of split pin about to go through the oil pump? I reckon it must have caught in a corner, it fell out as I took the pipe off.
It turns out that the engine holds the centre stand on the bike too, which wasn't too welcome when, 10 minutes before leaving for work, I was left holding the engine whilst sitting on the rolling chassis to stop it falling over. Eventually I extracted myself and left it looking like a slain animal.
Next day I split the cases. Here is the RH side, dripping in shitty silicone:
Oil pump hole blocked with silicone
Today, I turned to the cylinder head. I needed to knock the valve guides out to measure them, and take out the studs etc for inspection/cleaning. When I turned one stud, it went like this:
Once removed, I found a hole at a funny angle with the remains of a stud in it
To sort the broken stud abortion, I used a dremel and dentist burr type bit to cut the stud remains in two down the axis. They then fell out. Next, using an ancient hand pillar drill, I carefully cleaned the hole out with end mills. First, I used one only just touching the sides to level off the bottom. Then, I went bigger until the hole became round.
End mills and slot drills (milling cutters) are great for righting wonky holes. The flat end is less likely to follow the previous efforts, and having 3 or 4 flutes makes it much stronger. You have to be very delicate though, and be careful-my hand cranked pillar drill is good. Ideally you want a milling machine, but if you clamp it down well a regular electric pillar drill should be OK. Like I say, be delicate.
Hole is now tapped to a convenient size, in this case 7/16ths Whitworth. You could use whatever came close, metric would be fine. Just don't remove more than you need to, and stick to a coarse thread for ally-Whit, UNCF or Metric standard are good. If, like here, the hole has some of the original thread remaining, make sure it is removed. The next step is to fit a plug of ally, so you don't want the recreated hole to break through the side. Finally, I'll use the rocker block and the three good holes to mark out where this hole should be...pictures to follow, if it works.