KAWASAKI KR-1/S
Stan Stephens on part one of a resto/tune up of this stroker.
Editor Bertie received an email from a reader in Australia, telling him all about the classic racing scene out there. The guy said there was a lot of interest in the 250cc production class, in particular the Kawasaki KR-1 and KR-1S, and he wanted CMM’S help with tuning them. As a result, Bertie asked me to write an article explaining the tuning work we carried out back in the day. To begin with, before tuning any engine, it needs to be in good condition and set up properly. What I am going to do is amalgamate articles I have written about stripping, rebuilding and tuning the KR-1 and KR-1S so that all the information is together in one place. I’ll update it all too, where needed. Firstly, I have always been an admirer of the KR-1 and 1S. When they first came out we saw their potential and did a huge amount of development for production racing and Supersport 400 racing resulting in hundreds of race wins and many championships. Unlike today, where there are only Supersport 600 and Superbike classes in the British championships, during the 1980s there was also the Supersport 400 British Championship which was incredibly important to the manufacturers’ small bike sales and up-coming riders. Noticing the success I was having in Production racing with the KR-1, Kawasaki contacted me to prepare the works KR-1 Supersport racers, the Stan Stephens/team Green race team was formed and rider John Reynolds so very nearly won the British Championship. At that time the rules for SS400 racing were for 250cc two-strokes and 400cc four-strokes; I proposed to the ACU (the sport’s governing body) that we should be allowed to race 400cc versions of the current 250cc two-strokes. The ACU asked me to build one so they could evaluate it. I built a 400cc KR-1S and what a missile it was! Needless to say it was too quick and the rules stayed at 250cc two-strokes. The 400cc KR-1S was what Kawasaki should have built. When stripping any engine it is important to diagnose any problems and to do some detective work. The first thing to look at on the KR-1S is the KIPS valve linkage. A little wear and tear is acceptable but if the linkage is falling apart (as most are) there is a problem, as most of the KIPS parts are discontinued. Be careful when removing the linkage from the KIPS valves themselves because the valves are very fragile. They are made from hardened alloy, the spindles are only about 7mm thick and there is a flat on them which leaves about 5mm thickness and then there is a threaded hole through it, which doesn’t leave a lot of metal left. Remove the cylinder head carefully because the KIPS valves usually stay in the barrels and once again, they snap easily. Inspect the head for any damage which would give clues to any problems. Check the head face and the barrel faces for any signs of the head gasket blowing. Don’t take any chances with the pistons – just renew them. The genuine articles are not available but there are good pattern ones like the Mitaka kits. Check the cylinder bores for any damage to the Nikasil plating, look for any seize marks or
blistering, also check for cracks between the exhaust ports and the exhaust boost ports. Any problems, get them replated – never, ever have liners fitted! Next step is to remove the clutch cover and strip out the right-hand side of the engine. If the gear oil is white and soupy, this is emulsified. It is caused by water entering the gearbox, usually through a damaged water-pump seal; check the water pump impeller shaft – if there is a wear groove in it the impeller and the pump seal will need replacing. When stripping the clutch, check for broken fibre plates and/or blued steel plates. If you have any doubt about the fibre plates, replace them. If the steel plates are blued but flat give them a rub over with emery or get them bead-blasted. Check the fingers of the clutch basket for excessive wear, although the KR-1S clutch is very good and I have never seen a worn basket on one yet. With the clutch removed take out the kick-start mechanism and the idler gear and the circlip at the back of the clutch. The gearbox is now ready for removal. The KR-1S gearbox is a cassette type which basically means it can be removed complete without stripping too much of the engine. The gearbox is removed from the left-hand side of the engine. Take off the gearbox outer cover and remove the gearchange mechanism, then remove all the screws holding the outer casing on. Be careful – some of the screws are hiding! The gearbox can now be slid out complete. Check all the gears for any damaged or worn teeth or dogs. Next, remove the ignition flywheel. This requires a special but readily available puller. Then remove the ignition stator and the back-plate. Turn the engine upside down and remove the bolts holding the balance shaft casing. Remove the casing and the balance shaft. Remove all the crankcase bolts, the 8mm bolts (12mm heads) and the 6mm bolts (8mm heads). Remove the lower crankcase and take out the crank. To strip and rebuild the crankshaft is a specialist job and it has to be rebuilt on a special jig to ensure the big-ends are set at 180º and that the centre gear is set with the balance shaft timing mark in the correct place. The problem with the KR-1S crank is that Kawasaki never sold parts for the cranks, only complete cranks and they were horrendously expensive and have been unobtainable for years. The con-rods and big-ends can be replaced with KX125 moto-cross rod-kits; the left-hand and centre main bearings are the same as TZR250 mains and the right-hand main is the same as a 350 LC right-hand main. The seals are obtainable from Grampian Motors in Liverpool. Quite often the mains work loose and wear the centre shaft, I have had some new ones of these made. The major problem is if a big-end has
gone and has damaged the crank-pin which is part of the flywheels. When rebuilding a classic engine whether for road or for racing I prefer to have the crankcases aqua-blasted and all the nuts and bolts zinc-plated. Whenever you have any parts bead-blasted or aqua-blasted, always blank off any threads with old bolts but when you get the parts back still thoroughly wash all the parts off and blow out all the threads with an air-line. Be prepared to run a tap down all the bolt holes if there is any doubt (tap as in taps and dies, not the kitchen tap!). A few golden rules when building an engine; always fit new engine and gearbox seals, always use new genuine gaskets, always use new lock washers, always grease inside seals, always oil all moving parts. Thoroughly clean all the parts and especially clean/blow out all thread holes and clean the threads on the bolts. I clean all the threads on a wire wheel. Remember if you are putting the crankcases together and use bolts with dirt and grease on them, as you screw the bolts in the dirt comes up the threads and is left between the crankcase faces. Don’t grease the threads or the same thing will happen. Another golden rule: always check that everything operates properly at each stage of the rebuild; don’t wait until it is finished. By this I mean when you bolt the crankcases together, check that the crank turns smoothly, fit the gearchange shaft and go through the gears and check they are correct. When checking the gear selection, get someone to help. This is because one has to change gear while the other holds the output shaft and turns the input shaft so the gears will engage. When fitting the kick-start shaft, make sure it works and that it returns. When you fit the clutch, turn it to make sure it is not tight. Continue checking everything as you fit it. With a nice clean bench you’re ready to start the rebuild. Unlike most two-stroke twin engines, when assembling the KR-1S crankcases the crankshaft is loaded into the top crankcase. With the top crankcase on the bench upside down, fit all the bearing locating half rings and most importantly fit the gearbox right-hand input shaft bearing. Lower the crankshaft into the top crankcase and locate the bearing pegs. Make sure you have the case dowels fitted. Smear the bottom case with sealer, I always use Yamabond, carefully fit the lower case and fit the eight 8mm bolts (12mm heads) and the four 6mm bolts (8mm heads). Torque down the 8mm bolts and tighten the 6mm bolts. Next fit the balance shaft, align the timing mark on the balance shaft gear with the mark on the crank gear. Locate the bearing pegs and shields and fit the plastic oil feed in the end of the shaft. Fit the balance shaft casing and torque down the four 8mm bolts(12mm heads) tighten the six 6mm bolts. Make sure to use a counter-sunk screw at the front casing bolt-hole or the water-pipe will not fit properly. Fit the steel water pipe with new greased O-rings and fit the large rubber water-pipe. Time to fit the gearbox. Turn the crankcases up the right way. There are no loose shims on the gearbox; the only shim which looks as if it should go on the input shaft goes on afterwards behind the clutch. There is no gasket on the gearbox – use the Yamabond sealer. Check all the selectors etc. are located still and slide the cassette gearbox in. Fit and tighten all the
cover screws including the two inside by the gearchange. Fit the gearchange mechanism and small spring. Fit the gasket and cover. Now for the clutch side. Fit the circlip on the input shaft (clutch shaft) and the shim. Fit the idler gear and kickstart shaft assembly and the small alloy oil jet. Put the clutch basket on the shaft and fit the shim/spacer, now assemble the rest of the clutch complete but just use three springs and very lightly tighten the three spring retainers so that it is still possible to turn the plates. Now fit the assembly onto the shaft and jiggle the plates and clutch centre so that the clutch plate fingers locate into the outer basket at the same time the splines of the clutch boss line up with the splines on the shaft. It’s a bit of a fiddle. Fit a new retaining circlip. It’s best to fit a new water pump seal. The seal fits from the outside inwards and needs pressing out and a new one needs to be pressed in. If you haven’t got the use of a press you can use a large vice and a socket. Don’t fit the water pump cover on yet because as you fit the large clutch cover you can turn the impeller with your fingers and engage the drive gears. Be careful when fitting the cover that the steel water pipe with its greased O-ring fits properly and that the O-ring isn’t displaced. The outer clutch cover gasket and the water pump gasket are no longer available, it is okay to just use Yamabond, the clearance is okay. Now the top-end. Fit the pistons, rings and small-ends and base gaskets and the base dowels. Fit the barrels but don’t tighten the base nuts yet. Put the head gasket onto the head and then fit the KIPS valves to the head
(all four valves are the same). The barrels only have one dowel per barrel but the head has two dowels per barrel so when you fit the head and KIPS valves to the barrels be very careful and pivot each barrel about slightly until all four head dowels line up (this is why we didn’t tighten the base nuts). Now lightly nip the head bolts down and evenly tighten down all the barrel nuts, then torque down the head bolts. The Kawasaki manual does not explain how to fit and time up the KIPS valves and linkage. I did an article in CMM a few years ago on how to do it – it’s very difficult to explain but I will give it another go! When refitting the KIPS system notice all four alloy pulleys and arms are different and that two of the three small connecting rods are the same length, but the third is a different length. Assemble the KIPS valves in the head with the flats on the KIPS spindles facing roughly forwards. Fit the two pulleys on the centre KIPS valves. The pulley with open and closed on it goes to the side with the valve timing pointer cast in the head. The two outer arms are different to each other and are fitted with them facing inwards. The two connecting rods of the same length go between the pairs of valves and the shorter one goes diagonally between the two pairs of valves. When fitting the counter sunk screws that hold the pulleys and arms to the valves, make sure the flats on the valve spindles go towards the heads of the counter sunk screws. When the KIPS valves and linkages are assembled, check it is all timed up correctly. Turn the pulley to the open position and look up the exhaust ports to make sure the valves have opened the exhaust boost ports. Turn the pulley to the closed position and check the boost ports are closed. Remove the KIPS chambers on the barrels and check the hole into the exhaust port is open. If that all sounds complicated, don’t worry it’s a lot easier to do than it is to explain it!