ALLEN MILLYARD
Allen starts his Super Six Kawasaki Zed!
Ilike to be busy working on a project, especially during the winter months when it’s usually wet and there is salt on the roads.
I have just finished working on a Channel 4 TV programme, ‘Find it, Fix it, Flog it’, which has been taking up a fair amount of my time and I was now thinking about a new motorcycle project, but the problem was my mind was blank. I usually need something to spark my imagination, like a simple comment at a show or seeing a particular bike or engine in a magazine or on-line.
While I was at Stafford show last October I remember speaking to Dave Marsden on the Z Power stand and he reminded me that he had been suggesting for several years that I should have a look at a Z1 engine and make one into a six-cylinder. I initially dismissed the idea, thinking it would probably be just a bit too wide to make a convincing factory-looking bike. I was also seeing a lot of photos of my Kawasaki Z1B 1600 V8 on social media that had been posted by people who had seen it at the Barber Museum in Alabama, USA, where my Kawasaki Z2300 V12, first H1 850 five and first Honda SS100 V-twin are also displayed. This made me think about my V8 and whether I should make another one. I remembered my friend Chris Haliday from Pretech Engineering had a few Z1 engine parts, so I called him, and he said he had a set of 1976 Z900 crankcases, barrel, head, cams and a disassembled crankshaft for sale. We agreed a price and I rode straight over on my Honda ST1100 to collect the parts. They strapped on the back easily, but I was quite surprised how heavy the bits were, including a bit of hollow bar Chris gave me to make the main bearing mandrel.
The following day I was looking at the bare crankcases on my garage floor when I remembered Dave Marsden’s Z1 suggestion about making a six-cylinder, and started thinking maybe it would be feasible after all. I was feeling inspired, preferring a new project to making another V8. I carried out a few basic measurements and then made a couple of cardboard templates to confirm the potential width of the engine, which was 23.5 inches. The bike to compare would be the Honda CBX1000, but I wasn’t sure how wide the engine was so I emailed bike guru John Nutting to confirm. John replied saying the Honda CBX engine was also 23.5 inches. Brilliant, I thought, my new engine would be a similar width to the Honda CBX. The early Kawasaki Z1 was often referred to as the ‘Super Four’, so mine would be a Z1 ‘Super Six’.
I really like the buzz of making a new engine, working out problems and creating a factory prototype look; my mind goes into a blur of flashing images, crankshaft, cams, sectioned parts of crankcase, where to cut, where not to cut, etc. I rarely do drawings and I don’t worry too much about potential problems that could dampen enthusiasm, I just jump in with both feet and make it happen. Christmas was approaching and I needed a few more parts so I could make a start over the Christmas period, so I called Pete at DK Motorcycles to see if he had a set of Z900 crankcases and a crankshaft. Pete had a look around and came up with some suitable parts and they were promptly sent out to me the following day. I now had two sets of crankcases to look at and work out the best options for joining them together into a factory-looking six-cylinder engine.
The more I looked, the more problems I could see and I found myself going round in circles without finding a solution. The main issue was the relationship between cylinder stud spacing, the centreline of the cylinders and the position of the main bearing journals, which were not evenly spaced like they were on my RC374 six that I made in 2017 from a pair of Yamaha FZR250R engines. I wanted to add a cylinder to each side of the engine in a similar fashion to maintain symmetry and also to allow the new six-cylinder engine to fit a standard Z1 frame. I prefer this method where possible so that the bike could be easily returned to original condition in years to come if future owners felt the need to do so by simply removing the engine and fitting a replacement four-cylinder engine. I spent several days considering cutting sequences, but was still having problems visualising the finished crankcases so I decided to strip the second crankshaft to establish what parts could be used to make a new 120-degree crankshaft and come back to the crankcases later.
The Kawasaki Z900 crankshaft is made from eight steel webs pressed together with roller bearing big-ends and main bearings similar to a two-stroke engine crankshaft. This made it easy to disassemble on my hydraulic press.
I first had to machine-up suitable support bars from cold rolled square section steel bar that fitted between the webs to allow the crankshaft to be pressed apart. Four of the webs have an integral big-end and one of these webs is circular and has the primary transmission gear machined on its periphery. The spacing between main bearing journals wasn’t evenly spaced due to the additional width of the primary gear and oil pump drive gear on two of the webs. Whilst thinking about the crankshaft I realised that the spacing of the cylinder liners was fixed and I had to make the crankshaft fit the new crankcases by selective assembly of the parts. With this in mind I reverted back to the crankcases, starting work on the left side, sawing off one-and-a-half cylinders, followed by a similar cut on the right-hand side to remove another one-and-a-half cylinders. Then half a cylinder was cut from each side of the second set of crankcases.
The parts were then trued up to size on my old milling machine until they fitted together. The joints were prepared for welding by chamfering both sides of the casting at around 45 degrees by hand with a file. I then machined a mandrel to clamp in the main bearing journals; this would maintain alignment during the welding process. I then assembled the crankcase parts, checking the cylinder faces were in line with a long steel rule. The crankcase bolts were then lightly tightened, while a few taps with a hide mallet on each side of the crankcases ensured a tight fit of the parts to be welded; the bolts were then tightened fully. I warmed the assembled parts up on my gas BBQ before using my TIG welder to tack weld all around the crankcase joint with opposing welds to minimise distortion, then completing all the external welds. The crankcases were then split to complete the internal welds. Once the welding was complete and while the crankcases were still hot, I filed down the welds that spanned the gasket joint area, then bolted the crankcases back together with the mandrel in place and left them to cool. I then repeated the process on the other side before cleaning up the welds that would be visible when the engine was built.