I decided the leave the stud with the screw extractor bit inside for another day. So I started to remove the old gasket from the boiler flange and also remove the broken studs that hold the element into the boiler end plate.
But first is the boiler flange gasket. It started out being a right pain. No matter where I poked around I could not get in and under the gasket. Once you get under the gasket you will find that they usually come out in pieces. Eventually I got a sharp chisel under and was able to work my way around.
Here it is half way through chipping it away. The most important part of this is not to gouge any deep scratches into the flange otherwise it will make life difficult for sealing later.
By the way I am removing this underwater or at least under a running tap just in case the gasket has any nasties inside.
Eventually it was all clean, leaving just the rusted out studs which will be done another day. You will note that the boiler is still dirty inside, it will go back into the acid bath again now.
Ok so now it was time to tackle the 6 rusted studs that hold the element into the end plate. Here they are...
I briefly tried to unscrew them, I thought one last go using the double nut technique but they didn't move at all. So drilling was the only option. Thankfully this one would be a bit easier because the end plate is flat and easy to hold in place.
So it was the same routine as before. I used the angle grinder to cut the studs off, then dressed them up with a file, centre punched in the centre, then drilled a pilot hole using my centre drills. Here is the progess after doing my first hole, which was 4mm.
In the last post I mentioned about using good quality drill bits. This time I tried a different bit, I used one of my step drill bits as they are very sharp and make mincemeat of these rusty bolts. So I used the step drill up to about 6mm. After that I then put a 7mm bit into my drill press and accurately drilled them out to 7mm ready for the M8 tap. The benefit with this is you make sure the hole is straight and true, much better than by hand.
So now it was time to tap the new M8 hole. By far the best way to do this is to use the drill press to start the tapping - but obviously the drill press is not powered up.
I set the plate under the drill and then secured it in place (not shown in the photo). With one hand you pull the drill lever so the tap goes down into the hole, with the other you hand you turn the drill chuck clockwise so that it starts to tap into the hole. After a few turns you can loosen the chuck and take out the tap and endplate.
The point of using the drill press to start the threads is to make sure they are straight and true. After that you retire to the workbench and finish tapping by hand. Remember use plenty of cutting fluid to protect the tap and you also "must break the chips" I like to do half turn clockwise followed by half a turn back to break the chip.
So here is the first hole successfully drilled and tapped, testing with a new M8 stud.
And eventually I got to this....
It took about an hour from start to finish and I was VERY pleased with the result. So on that note I finished for the day. I'll explain more about how I dressed up the end plate tomorrow.