ALLEN MILLYARD
Specials builder par excellence Allen Millyard tells us about his saucy six.
Allen muses on the joy of six!
I’ve had a really busy month working long hours on my latest project: a 374cc six-cylinder, twin-cam, short stroke engine that will resemble a 1960s Honda RC174 six-cylinder when it’s finished, not an exact copy but my take on one.
I am using a pair of Yamaha FZR250R engines for base components making and modifying all parts at home, including the 12-piece roller bearing crankshaft, with simple hand tools and my trusty 1970s Colchester lathe and 1950s Elliot Milling machine. This is by far the most complicated and mind-consuming project I’ve taken on to date and I will be talking about this in detail soon. I was also invited to display three bikes at the Classic Motorcycle Mechanics Show at Stafford, the recently completed Kawasaki H1 500LC four-cylinder, S2A 350 four-cylinder, and my Honda SS100 V-twin. I was there both days and spoke to so many people. Luckily my brother Brian came with me to help and did a great job answering some of the questions. Last month I started talking about my Kawasaki H1 500 LC project and how I modified the crankcases and the crankshaft. So with the crankshaft complete it’s basically a standard assembly of the bottom-end. The selector mechanism, gearbox shafts and kick-start mechanism are assembled into the top crankcase ensuring all location pegs are engaged with the corresponding holes in the bearings. At this point I always rotate the gear shafts to check for correct engagement of all gears. The crankshaft is then put in ready for the bottom crankcase to be lowered down. I use Permatex ultra grey on the crankcase joint – this is a gasket sealant similar to the original Kawasaki bond and I find it works well; I also put a drop of Loctite bearing fit on the top of the bearings applied with a small brush. The bottom case is then lowered over the studs and all nuts tightened. When I’m making my bikes I like to retain as many original parts and features as possible to create the illusion of a production bike or factory prototype, so with this in mind I needed to retain the original oil injection system. The Kawasaki H1 engine is fitted with a three-outlet pump that delivers a metered amount of oil to each cylinder via three separate pipes and drillings in the crankcases. The pump is a positive displacement type that is designed to deliver three independent flows of oil; one to each cylinder and it’s not possible to simply add another pipe to the pump or splice two oil pipes together to feed the extra cylinder. The reason for this is the engine creates vacuum during its induction cycle and it is impossible for each cylinder to pull an identical vacuum, so the cylinder with the strongest vacuum will always suck all the oil from a spliced delivery pipe leaving the weaker cylinder starved of oil. Kawasaki changed the oil pump design on the H2B in 1974 with the introduction a four-outlet pump and it is identical in fit to the earlier three outlet pumps. I bought one of these pumps and it fitted straight onto the 500LC engine: perfect I thought, but by using the standard pipes there wasn’t one long enough to reach the left-hand cylinder so I decided to make a new one. I looked on ebay and found some nylon pipe with the required 4mm outside diameter and 1mm wall thickness. The banjos were then cut off the original pipe with a sharp blade and carefully drilled out
with a 4mm drill to remove the remaining piece of pipe that remained in the banjo fitting. The new pipe was cut to length and pressed into the banjo connectors with a drop of Q Bond adhesive to seal the joint. Because my new engine was only 500cc I needed to reduce the amount of oil the pump delivers. I removed the metering cam from the 750 pump and replaced it with the cam from the original H1 500 pump, which fitted perfectly and reduced the amount of oil metered to the engine. Moving on to the cooling system, the H1A 500 was originally air-cooled and my new four-cylinder engine is water-cooled so I needed to fit a water pump somewhere. I initially thought a small electric pump similar to the one I used on my Kawasaki V12 would work, but that would put more demand on the electrical system along with the additional ignition coil and would be too much for the generator to cope with, especially when riding with lights on in traffic. I would need to fit a mechanically driven pump somewhere. I looked at the clutch cover and there it was staring me in the face, I could make a small pump to fit where the now redundant distributor used to be and use the rotor arm shaft to drive it. I no longer needed the distributor because I was fitting a points ignition similar to that fitted to the H1B on the left-hand side of the engine. The rotation of the distributor drive shaft is anti-clockwise which happens to be the same as the Kawasaki KX250F water pump and I just happened to have a rotor and outer cover in my shed left over from my motocross days. I made up the pump casing from a bit of 20mm thick 6082 aluminium plate machined to fit a Yamaha RD250 LC water pump shaft seal and modified KX250F outer water pump cover. There wasn’t much room to work with because the oil pump and rev counter drive is right above, but there was just enough room to squeeze it in. The input feed from the cylinder heads was brought in over the oil pump via a rubber hose and the output was routed out of the front of the clutch cover then behind the right hand exhaust pipe up to the radiator. When fitted, the water pump was no wider than the original distributor and with a bit of cutting and welding I managed to modify the original cover to fit. The engine was now ready to fit into the freshly painted frame with new length bolts and spacers to centralise the engine using existing mounting points. The central two exhaust pipes just cleared the down tubes, so I bolted them in place and then went on to complete a relatively standard chassis rebuild.