Our new columnist on camshafts!
Our new columnist on why three just ain’t good enough!
Ihave made quite a few Kawasaki specials over the years and always strive to produce a factory-fresh, period-looking machine using (where possible) all original parts, but this time I wanted to do something a bit different.
Looking at a pile of 1971 H1-A parts in my friend Neil’s workshop that he was thinking of selling, got me thinking, maybe I could rebuild the parts into a prototype futuristic version of the H1 500 that Kawasaki could have made with a water-cooled engine? Kawasaki did in fact make a fourcylinder two-stroke prototype show bike with a square four configuration in 1972 but I’m not sure it was anything more than a concept mock-up, so I thought why not make something similar that works? Making a square four would be possible but would require new castings to achieve a factory-looking engine so the next best thing would be an inline four. I agreed a price with Neil and collected the parts the following day. I have seen several four-cylinder Yamaha engines that were made by grafting a pair of RD250 engines together and I initially thought I would do the same and put the completed engine into the Kawasaki H1-A chassis. This would make a nice bike but I had this nagging problem that kept me awake at night, the finished bike would have a Yamaha engine and no matter how hard I looked at it, it just wouldn’t be a true Kawasaki and would be wrong for my ‘prototype’ look. The shape of the engine was completely different and even if I disguised it a bit it would still look like a Yamaha engine. Then it came to me in a flash: I should graft a pair of water-cooled Yamaha 250LC top-ends onto extended Kawasaki triple crankcases to make an inline four. ‘Problem solved’ I said to myself. The Yamaha 250LC barrels and heads were made around 1980 so would be perfect for my new ‘futuristic’ look four-cylinder engine and I already had a pair of damaged H1 crankcases in my shed, which were perfect to cut up and make the four cylinder engine, so I set about cutting, machining and welding. A quick search on ebay located a pair of early Yamaha RD250LC barrels and heads, which would look just right. When they arrived the first thing I did was see if they would fit on the cases but they didn’t; they weren’t even close. The liner protrusion wouldn’t fit into the H1 crankcases, the transfer ports misaligned, and the stud spacing was different. To solve the problem, I removed the studs, set the crankcases up on my 1954 Elliot milling machine and bored them out to allow the LC barrels to engage with the crankcases. All four barrels then fitted and looked brilliant, but the stud holes didn’t line up, the transfer ports didn’t line up and I could see past the barrels into the crankcases in places. ‘Oh well’ I thought, I wasn’t expecting it to be a simple job so the first thing I did was weld up the existing stud threads, drilling and tapping new threads in the right position. I also fitted Heli-coil inserts because I was threading into welded material in places. The studs were then re-fitted and LC base gaskets lowered down and scribed around to mark the new transfer port shape. Several areas had to be welded up and the whole transfer port reshaped to match the LC base gasket with rotary burrs. The barrels now fitted nicely but there was another problem, the bore spacing on the H1 crankcases was slightly wider than the Yamaha crankcases so the one piece Yamaha head would not fit, this was solved by cutting the heads in half and adding a section of pre-bent aluminium plate and welding it back together. At this point I started to think about the crankshaft, The Yamaha RD250LC has a 54mm stroke and the Kawasaki H1 500 has a 58.8mm stroke so that
outlawed the use of the Kawasaki crankshaft flywheels because the Yamaha barrels are designed to work with a 54mm stroke and I wanted to retain the original 54mm x 54mm bore and stroke. I had a look at the Yamaha RD250 crankshafts and decided that because they were roughly the same size as the Kawasaki crankshafts the easiest way was to convert them to fit. The bearings were a different diameter, which was easily resolved by sourcing new bearings with the required sizes to fit the Kawasaki crankcases and Yamaha crankshaft, and the Yamaha labyrinth seals were turned down on my lathe to fit. The generator stub shaft and drive side stub shaft on the Yamaha crankshaft was also machined to Kawasaki dimensions to allow them to match up with the Kawasaki primary drive and generator rotor. One last thing I needed to check before I built the crankshaft was that the piston reached the top of the bore when the crankshaft was rotated. To check this I assembled one set of flywheels and fitted them in the crankcases, then fitted one barrel base gasket and piston to see. The piston fell short of top dead centre by 5mm so I had two choices: fit a longer connecting rod or remove metal from the crankcases. I could safely machine one or two mm from the cases at most which ruled that option out, but luckily I managed to source new connecting rods that are 5mm longer and would fit the Yamaha crankpin and little-end bearing. Once fitted the piston rose and fell perfectly in line with the top of the barrel at top dead centre: again, problem solved. I’ll be talking more on this next month. cmm
“One thing I needed to check before I built the crankshaft was that the piston reached the top of the bore when the crankshaft was rotated. To check this I assembled one set of flywheels and fitted them in the crankcases...”