Sawing and welding
Allen is doing yet more sawing and welding on the motor of his Kawasaki ‘Super-six’!
For me the nicest thing about making a new engine is working out how to make it in a way that it looks as factory produced and original looking as possible.
Sometimes I spend hours just looking at crankcase castings, cylinder barrels and cylinder heads trying to imagine the thought processes of the original designer all those years ago at the factory.
I find it helps me focus and see the way forward, and ultimately where to cut and adapt parts, making them fit together and look right.
I had already finished the crankcases and barrels, and the next job was to modify the cylinder heads to fit. I had a rough idea how I was going to cut the two heads and how to weld them back together, but the final details were still a bit fuzzy. I never let that bother me too much, though.
The first thing I did was to cut the first cylinder head in half with my hacksaw, cutting through the centre of the camchain tunnel; not to any particular size, just in half. I always use 18 TPI Bahco Sandflex hacksaw blades for sawing aluminium as they cut really well, last a long time and don’t break.
It’s important to have a good-quality hacksaw blade with sharp teeth to help you cut straight, remembering to let the blade cut and find its way rather than forcing it through the metal.
The two halves of the first cylinder head will be used for the outer two cylinders on each side. I trial fitted them on to the cylinder barrels and they looked great. Next I mounted the right-hand part of the cylinder head on to my milling machine and machined the vertical inner joint, removing excess material and truing up the surfaces where I would be welding to the inner part of the cylinder head. This was repeated on the left-hand part of the cylinder head. With both outer parts machined, I put them on to the barrel and measured the gap in between them with my Vernier Caliper. I then marked out and cut off the two outer cylinders from the second cylinder head, leaving a few mm on each side to true up the surfaces on my
milling machine. The inner part of the cylinder head was then machined each side, gradually removing metal and checking the overall width dimension until all three parts would fit on to the barrels with no gaps at the two joints. This was a critical machining task and took a bit of concentration to get right. I remember my apprentice master saying to me: “Measure twice and cut once,” and this advice was very relevant with this particular machining operation. It’s important that all welded joints are tight with no gaps to minimise distortion. If there is a gap at the joint it will pull together as the weld cools, drawing the two parts closer together and distorting the casting in the process. If you do end up with a gap they have to be filled with a shim of aluminium that has been filed to the right thickness to tightly fill the gap. With the machining completed I filed a 45-degree chamfer by hand on the edge of all the joints about a third of the wall thickness both sides to increase the