Been playing with an old ZXR250A engine to test some tuning suggestions like increasing the compression ratio of the engine. This engine is number 480, so a very early build that I assumed was high mileage and might be good for parts at some stage. Went to turn it by hand and it was pretty tight, so rather than push it, I dropped the oil (smell was nauseating) and started pulling covers off to see what was what. Clutch was stuck together, so it came out in one piece. Bottom end was mucky to say the least. Once the clutch pack came out the engine turned freely, so I did a quick check of the valve clearances and most were okay, but a few were either way over or way under. Looks like someone put 1.75mm shims in all the valves except a couple. Pulled the head off to practice doing a squish test. Turned the head upside down and put fuel in the valve area to check for leakage. They all leaked from either inlet, outlet or both! So, valves will need to come out if I want to use this head. Cylinder one has some liquid marks (looks like fuel) which should hone out. Cylinder two was more burnt oil than I've seen in a while, so not expecting rings to be worth keeping. Did the squish test, but I am waiting for feedback about whether it was done properly or not. Cleaned up the clutch friction and steel plates. Checked plates were within spec and also springs. All good, so ready for reassembly. Cleaned up sump, oil pickup and pressure relief valve, so bottom end is also ready for reassembly. Need to get some new gaskets before final assembly (depending on how good the top end is).
Did several more squish tests on the old ZXR250 engine. Turns out I was measuring the wrong area. I was measuring the valve recess when I should have been measuring the flat areas (der). Doesn't look like there's much room to move in the standard combustion chamber, so I might leave the whole increase compression ratio exercise for a later stage. Need a few different shims to finish the valve clearances, so in the meantime I will store the shims and buckets externally... And, put the reassembled engine to one side and start on some carbs for another project.
Got the MC19 up in the air to pull the wheels and forks for rebuilding and paint. Tomorrow the rear shock comes out to see if I can figure out a better option than stock. Swingarm is pretty disgusting so I might pull that as well and give it a good cleaning.
Smart boy making use of speshiality tooling ekuipmint. Initially I used 4 inch nails but they kept bending (the steel holder slides down after the DIY castle nut driver is on) so I had to use drill bits
Best to use a rattle gun so you don't break the thread towers in the hub. There is another speciality tool for holding the hub, you could make a basic one, but rattle gun in gear works
I'm not 100% sure. I only ever check cylinder pressure against what the manual says, so you might be right. If it is 12.5:1 then I should be able to run higher octane fuel than the 91 octane everyone says you should run in these engines? Not sure it will give me anymore power without me changing the timing. I'm not at that stage yet, but I do know the ZXR cams are 'fixed' as is the timing wheel, so not sure how to try and get anymore power out of this thing.
While I've serviced quite a few of these, when I did the only one I've tried to hot up, I was impressed at just how difficult kawasaki made it. They really did not want anyone f****** with their engine. You've got to get really creative to change the cam timing - or even the static ignition timing. The usual 5 degrees more advance is nearly impossible with the factory setup. It's even more miniature engineering than most of the 250/4 engines. the FZR for example is loosely thrown together by comparison - and things can be moved around very easily.
Move the pick up coil for timing of ignition. As for the cams, they have about 240-270° of opening (it's in the manual) so be careful messing with it. Depending what you are trying to achieve, but for maximum horsepower in natural aspiration, you're trying to move the the torque up the rec range. Maximum torque is 10,000rpm, maximum horsepower is 15-16k. Maybe a shorter exhaust and something like a Power Commander to adjust the spark in the later rev range?