ALLEN MILLYARD
A test ride and then the big job of sorting the camshaft out: all in a day’s work for our Allen…
Allen is back on with his sixcylinder Kawasaki
With the lockdown rules relaxed I was finally able to take my Kawasaki Z1 Super Six for a test ride. The bike had been finished for a few months, but I had only ridden it across my garden a couple of times, which isn’t far.
I had a gallon of petrol in the shed so I put it in the tank, turned on the petrol tap and waited a couple of minutes to check for leaks. All seemed fine so I put on the choke, pressed the starter button and it burst into life on fast idle and sounded great. It was a nice sunny day and I had been looking forward to this moment for weeks. As soon as I pulled away and went up through the gears it felt under-geared; I was almost straight into top gear as I approached 30mph and I could drop below 20mph in top gear and it would pull hard with no snatching in the transmission.
The bike has its original size 630 pitch chain and I had fitted the largest available 16T front sprocket and smallest 33T rear sprocket, so in order to raise the gearing even more I would need to make a smaller rear sprocket. I continued with the test ride and found that as it warmed up the carburation deteriorated and it started to hesitate on pick-up from low rpm. I decided to return home and investigate further and it turned out to be a sticking choke plunger on one carb. That was an easy fix.
The next thing I needed to sort out was the final drive gearing, so I had a look in my shed and found a 30T 630 pitch sprocket. It was a spare that I had used on my 8-litre Viper V10 for high-speed runs. The sprocket wouldn’t fit my Z1 hub, but all I had to do was bore out the centre hole on my lathe and re-drill the six mounting holes and it would then be a perfect fit. This sprocket totally transformed the bike and it would still pull top gear below 20mph and cruise effortlessly at 3000rpm, which was now at 60mph. So far I’ve covered around 150 miles. My electronic rev counter conversion was behaving a bit erratically and was picking up stray signals from adjacent ignition components. This is a common problem when fitting electronic rev counters. I sorted this problem by changing the original feed wire for a bit of USB computer cable that has an integral metal mesh shield. I connected the shield to earth at one end and used one of the four inner wires to feed the rev counter from the positive wire of one ignition coil and it now works perfectly. Don’t be tempted to earth the shield at both ends of the wire because this will reduce its effectiveness. Testing continues with short trips most days, gradually venturing further away from home.
Back to the engine build and the next thing to do was to make the camshafts. I had already made the new crankshaft with big-end journals set in pairs at 120 degrees to give a firing order of 1-4-2-6-35, so I would need new camshafts to match this configuration. I had been wondering about the camshafts for a while. It was looking like a complex item to make, but the more I thought about it the easier it became. The two central cylinders would be my datum because the drive sprockets and cylinder 2 and 3 each side of the centre line remained in the standard position with the two lobes on each camshaft at 180 degrees to each other. The next pair of cylinders 4 and 5 were set at 120 degrees to cylinders 2 and 3 so the camshaft lobes also needed to be set at 120 degrees relative to the central pair, one lobe rotated forwards 120 degrees and the other lobe rotated backwards 120 degrees. The camshafts were made from case-hardened solid forged steel so I could easily cut them with my angle grinder fitted with a 1mm wide cutting disc.
With the camshafts cut I set up the individual parts, one at a time in my lathe, and bored a finely machined hole into each part of the camshaft to allow old Kawasaki H2 gudgeon pins to be pressed in up to half their length with an interference fit. With all the bores machined I assembled the exhaust and inlet camshafts with the lobes pressed together at roughly 120 degrees separation by eye.
The next job was to set the camshaft lobe positions accurately in my lathe with a degree disc and dial test indicator. To do this I started with the centre portion of camshaft gripped in the chuck and trued up with the first lobe to its highest reading with the dial test indicator and
the degree disk set at zero degrees. Then I rotated the lathe spindle 120 degrees and holding the chuck still I twisted the second lobe to its highest reading on the dial test indicator. I repeated this process for each lobe, referencing its angular displacement relative to the fixed central lobe to prevent compound errors creeping in.
Once the whole camshaft was pressed together in the correct orientation I double-checked the position of each lobe against the degree disk, then checked the run out of the camshaft by placing it between centres on my lathe and using the dial test indicator the total run out along its length was around 0.05mm, so it was ready for welding.
When you weld metal the joint will shrink and pull tight as it cools, causing distortion, so it was important to tack weld in three positions around the joint first before welding all the way around the joint. I welded the camshaft while it was held between centres on my lathe, with the dial test indicator set up to measure the distortion in real time.
It was quite alarming how much the camshaft was moving out of true during the welding process, but as the weld cooled the camshaft returned true and straight. If distortion remained after cooling this could easily be corrected by doing a small weld at the high point, then as it cooled the error would diminish. This was a time-consuming and lengthy process, but I got there in the end with two camshafts finished and ready to trial fit into the cylinder head. I fitted the white metal camshaft bearings and positioned the new camshafts in place, then oiled the bearings and tightened the bearing caps. The camshafts rotated nicely, which was a relief. I then did a complete dry build of the top end with all valves in place, then very carefully turned the engine over two full turns. I was pleased it turned over smoothly and all seemed to be ok.