ALLEN MILLYARD
...are the deepest. Allen Millyard gets on with his exciting Z1 Super Six project!
Allen is cutting and creating his Super Six Kawasaki!
When I’m inspired to make a new engine, I have a vivid vision of what I want to achieve and can usually unfold the image in my mind to work out how to make it. This involves visualising how I will modify many parts, and at the same time retain a factory-looking engine.
The Kawasaki Z1 engine was really stretching my imagination to the limit, working out how to add one cylinder each side of the four-cylinder engine whilst being conscious of its width. This left me with many problems to resolve.
Looking at the finished crankcases sitting on my bench really stepped up my excitement and enthusiasm, and focused my thoughts on to the next stage. I had already stripped the crankshafts and had worked out how to reconfigure them from a standard 180-degree four cylinder into a new 120-degree six cylinder crankshaft, so I parked that for the time being to concentrate on the complicated problem of cutting and joining the barrels and heads together.
I always try and avoid the welded joints lining up across components. I prefer it to end up like a brick wall with staggered joints and this is especially important at the first joint between the crankcases and barrels. I had just added a new cylinder to each side of the crankcases, so to stagger the joint I would add two cylinders each side of a pair of central cylinders, creating the new six cylinder block. Before I could start cutting the barrels I had to remove the iron cylinder liners. The liners were on their first oversize at 66.5mm and I was tempted to bore them out to 70mm and use pistons from a Z1000 to give a capacity of 1524cc, but I decided to retain the added strength of the thicker liners. I would be cutting and welding the aluminium cylinder block in the small space between the liners so I would use 1mm oversize Z900 pistons giving a total capacity of 1396cc, which would be just perfect.
Before I could press out the cylinder liners I needed to heat the cylinder blocks up to expand the aluminium, thereby making the liners easier to remove. I was
about to use my blowtorch, when I remembered my gas BBQ. This would be ideal because the cylinder blocks fitted nicely inside with the lid closed. I fired up the BBQ and let it burn for a few minutes to warm up and burn off any residual fat, etc., from the burners, then I placed the cylinder blocks on the grill and closed the lid. After about 10 minutes they were ready so I put on my leather welding gloves to carry them back to the workshop. I set up my hydraulic press and using a suitably sized drift I pressed out all the liners, and due to the expansion of the aluminium, they came out easily. I marked the six liners and respective bores so that I could replace them in their original place in the cylinder block. I waited for the cylinder block to cool then cut one cylinder from each side, leaving a central portion with the two inner cylinders and cam-chain tunnel. I then cut the other cylinder block in half through the central cam-chain tunnel making left and right-hand portions, each with two cylinders.
The next job was to set the central portion of cylinder block on to my milling machine and machine the left and right-hand vertical mating surfaces. To do this I installed my facing cutter into the horizontal spindle; this ensures the machined joint will be at 90 degrees to the mounting surface on the cylinder block. I started to machine the end surface, taking small cuts until it cleaned up.
The critical dimension was the distance between the centre of the cylinders so I calculated the edge-to-edge dimension between cylinders two and three, and then four and five. I then took several small cuts until the dimension was correct. I reversed the central part of the cylinder block and machined the other side to the same dimension. The process was then repeated on the inner surface of the outer portions of cylinder block until they all mated up nicely and fitted on to the crankcases with no gaps at the two joint areas. While the portions of cylinder block were resting on the crankcases I filed the edge of the fins to make them all line up nicely. The welding process was quite tricky. You can’t prevent distortion; you just have to manage it. The first thing I had to do was chamfer the top and bottom surfaces of each part of the cylinder block with a 5mm x 5mm chamfer. This produces a V-joint that will be filled with weld, making a stronger joint. Then I took the parts over to Rob and Doug at RD Cox & Son in Reading for media blasting to remove surface oxidation and grease. I would return for the full vapour blasting process once the welding was completed.
With the parts clean I preheated them in my BBQ to about 150c, and then quickly clamped them on to my milling machine table to hold the cylinder block parts flat and true while I was welding. I then set up my 200A single phase TIG welder and proceeded to weld the top of each joint, and then the fins as far as I could get inwards and the edges of the bottom joint where I could reach. I then
filed the top welds flat with a coarse file, finishing off with a fine file and finally 120 grit Abranet abrasive cloth and file. Then I unbolted the part welded cylinder block, turned it upside down and re-clamped it tight to the milling machine table, then welded the bottom joints and the other side of the fins. The cylinder block was left bolted down to the milling machine overnight until it had totally cooled.
In the morning, while still bolted down, I filed the welded joint smooth, and then unbolted the cylinder block. The top and bottom surfaces were virtually flat and in line when checked with my steel rule, but to true them up perfectly I lapped them flat using valve grinding paste and a cast-iron lapping plate. To do this I placed the cylinder block on the bench and smeared a bit of valve grinding paste across the upper surfaces, then placed the lapping plate on top so I could slide it back and forth using its weight to apply even pressure. It’s really important not to lean on the lapping plate, otherwise the surface will be ground uneven. After a short while I could see an even grey colour to the upper cylinder block surface so I removed the lapping plate and washed off the grinding paste with brake cleaner. It was now perfectly flat so I repeated the same process on the bottom surface of the cylinder block.
I then used my rotary burrs to clean up the welds in between the fins, and finally dressed the outer fin profile with a fine file to finish them off nicely. I then thoroughly cleaned the cylinder block ready to re-install the cylinder liners. I had only removed about 0.002” from the cylinder block upper surface when I lapped it flat, so the liners would be slightly proud when pressed in. This would be fine, because I would be making a special cylinder head gasket from annealed copper sheet and this would help make a good seal on an air-cooled engine. I will explain how I made the copper gasket in a future edition. Next time I willill be tackling t the cylinder head.