The crankcase fixings for the five cylinder rotary required a lot of patience as each cylinder was held in place with 4 off 8BA bolts. However, whilst tapping one particular thread in the crankcase I had broken the tap. This annoyed me so much that the whole engine was put into a bag in pieces and lost for around 2 years whilst we moved house.
The offending broken tap. As you can see it is well buried and looks like I′ve already had a go at remving it
Not sure how well this will work, but I bought a solid carbide end mill.
The solid carbide mill did get the tap out, but the end mill came apart in the process.
As you can see in this picture I resorted to the trusted TiN HSS end mill and used this to finish the machining.
The TiN end mill was still in good condition at the end of the process.
The casing with an aluminium plug back in place of the broken tap.
I glued the aluminium plug in with some very thick instant glue.
With the tap removed and a piece of aluminium in it′s place I then drilled and tapped the 8BA threads to bolt the heads and cylinders down. This just gave me lots of trouble as the aluminium kept stripping. So I drilled the holes out to 3mm and then fitted steel inserts into the holes that had been drilled and tapped 8BA internal thread. This gave me much more secure crankcase fixings for the five cylinder rotary engine.
The bolts looked too bulky so I machined the thread down to 1.4mm diameter in the centre section of the bolt.
The only slight change I would make in retrospect would be to make the steel inserts fit from inside the crankcase so there would be a mechanical hard stop and hence be able to hold a greater force.