ALLEN MILLYARD
Allen is once more on with his Super Six Kwak!
The disassembly and assembly of a pressed up multi-cylinder crankshaft is considered by many to be a specialist job, carried out behind closed doors with mystique and intrigue, but it’s actually quite an easy job to do at home if you have a few bits of basic engineering equipment.
With the crankcases finished, it was time to start adapting a standard fourcylinder Z1 crankshaft to fit my new six-cylinder engine. The standard Z1 crankshaft is a pressed up design made from eight hardened steel webs and a central shaft containing the cam-chain drive sprocket. The webs vary in shape and purpose. One web incorporates the primary drive gear; four webs incorporate big-end journals; and the other four webs incorporate the main bearing journals. There are six roller bearings that run directly on the hardened main journals and the hardened outer rings of the roller bearings locate in the crankcases with pegs to align oil feed holes.
The first job I had to do was to strip down two Z1 crankshafts and I was expecting some trouble! I remembered the force required to strip a Z1 crankshaft when I was making my Kawasaki Z1600 V8 over 20 years ago, it stretched the limits of my hydraulic press and I wasn’t looking forward to it. The first thing I had to do was make a couple of support bars from high tensile steel that fit between the webs, making them as thick as possible to take the load required to press the crank-pins and journals from the webs. I had a length of 30mm square EN16 steel bar that was ideal, so I cut off two bits about a foot long, but they would need reducing to 23mm thick in the centre using my milling machine, so that they would fit in the gap between the webs.
With the support bars machined I offered up the crankshaft from under the press until the first web was proud of the support bars and I could slide them into place ready to press out the first crank-pin. To do this I needed a suitable push bar that was slightly smaller in diameter than the 29mm Z1 crank-pin. I have a box of old crankpins that I keep for this purpose. The push bar was then placed on to the end of the crank-pin and then I pumped up the hydraulic press until the ram touched the push bar and resistance was felt. At this point I had a good check to make sure the crankshaft was sitting square, then started to pump up the pressure in the hydraulic system. two tons, five tons, eight tons, then at nine tons, with a huge ‘Bang’, the first big-end journal suddenly moved a couple of mm below the outer surface of the web.
Great, I thought, from now on this one will be easier. I started to build up pressure again, and sure enough at around seven tons it moved again, and after a few more pumps of the lever the first web was free along with the first connecting rod. The process was repeated on the outer four webs of the crankshaft. The inner four webs on the first crankshaft could remain assembled with the two inner connecting rods because I would use this for the inner portion of my new crankshaft. With the first crankshaft stripped I had to completely strip a second crankshaft so that I could pick the required webs and two additional connecting rods required for the new six-cylinder crankshaft.
Once all parts were stripped I cleaned off the tarnish and hardened oil stains with a fine wire brush and brake cleaner, then inspected all the parts for wear or damage. The Z1 crankshaft has substantial, purpose-made roller bearings, and over years of use they have proved to be extremely reliable and rarely need attention. My two donor crankshafts had no signs of condensation damage or wear and the roller bearing tracks still had the original cross hatched lapping marks on the bearing surfaces, indicating a gentle life with good oil. Looking at all the parts, I could see that the central four sets of webs and outer left pair could be made with unmodified original parts, but the webs for the right-hand side would need some modification to maintain alignment with main bearing journals and balance as a six-cylinder engine, which I will explain later on.
I had decided to configure my new crankshaft so that the pistons will rise and fall in pairs at 120-degree intervals, giving a 1-4-2-6-3-5 firing order for smooth running. The first thing I did was to mount the central part of the crankshaft with the central connecting rods three and four on to my lathe in a 3-jaw chuck. Then I set connecting rod four on to a pin held in the tool post to prevent the crankshaft from rotating with the big end at the six o’clock position. I then set up the degree disk and set a pointer to zero. I then carefully traversed the saddle back to disengaging the location pin from connecting rod four and engaging it with connecting rod five, which would locate the web in the correct rotational orientation on the main journal with slight pressure from the lathe tailstock temporarily holding it in place.
The central portion of crankshaft was then rotated 120 degrees, while the new web was held still by connecting rod five that was attached to the pin located in the tool post. A light tap with a hammer engaged the web sufficiently on to the main shaft so that I could transfer the part-built crankshaft to my press to press the new web fully home. I returned the part-built crankshaft to
my lathe and re-checked that rotational alignment between crank-pin four and five was still at 120 degrees and nothing had slipped. The next job was to align crank-pin five with crank-pin two, which had to be aligned together so that pistons two and five would rise and fall together at 120 degrees to pistons three and four.
To do this I used a set of slip gauges and my flat cast iron milling machine table to set up the crankshaft with two of its main bearings resting on identical size slip gauges so that the webs were free to rotate, then clamped crank-pin five on to a two-inch slip gauge and lightly clamped it in place. I then applied light pressure to the crankshaft to hold it in place while I set up crank-pin two by resting it on an identical two-inch slip gauge and lightly clamping it in place. With crank-pin two held in the correct alignment with crank-pin five, I used a couple of G-clamps to carefully engage the web on to the main shaft sufficiently to hold it in place while I transferred the crankshaft to my press.
Once pressed together, I returned the crankshaft to the milling machine and re-checked with the slip gauges as detailed above to ensure crank-pins two and five were aligned perfectly before moving on to the next stage.