So I picked up an old Kawasaki KE125 for $55, its an old dual purpose machine supposedly developing 13.5 Hp at 7500 rpm, figured it could be a reasonable platform for a bucket mainly because of the rotary disk valve inlet.
Measured the port timing and found the following
Inlet 115/55 = 170 deg
Transfers 111 deg
Exhaust 163 deg
Rod length 96mm, big end pin 20mm/50mm
Piston pin to piston crown height 34mm
deck height 1.2mm
So that’s how it arrived but obviously that’s not how it could remain.
I read and absorbed the ESE thread which gave me the basis and links for a respectable engine design, I then acquired a copy of Professor Blairs ‘the basic design of 2 strokes which mostly went over my head but there was also some serious info I could apply to the build.
Settled on a target BMEP, peak RPM and calculated the following STA’s.
9.5 BAR 10750 RPM CONFIGURATION
from Blair calcs
power kW 21.96
exhaust area 0.0147
exhaust blow-down 0.00095
transfer area .01605-0.008
inlet time area 0.018
The disk diameter turn out to be a somewhat limiting factor but the required STA could be achieved using 225 deg duration, likewise the single exhaust port would hamper blow down.
After talking to TZ I decided to run with the Wiseco KX125 piston as they are readily available and had been proven in the ESE bikes. The connecting rod took a couple of attempts to get right (due to the TKRJ catalogue measurements for the KMX125 rod being incorrect) but in the end I settled on a DT125 rod. The cranks required modification thankfully this is exactly the sort of thing Gigglebutton is good at. Next step was to purchase port map analyzer software, found all the STA’s above were achievable - 128deg transfers, 196deg exhaust and 225deg inlet would do the trick.
Set to work cutting and porting, started with the exhaust port then moved on to the transfers which presented the first major design flaw, as standard the transfer ducts have no inner radius. I added epoxy to the inner wall to achieve what I hope is a reasonable curve then widened and changed the angels of the ports. The disk was the easiest mod although I chose not to go all the way to 225deg settling on 215deg for testing.
The carburetion is to be handled by a Keihin PWK and the ignition is a complete system off a KX125 (no money for a ignitech)
So after many months of being side tracked with other things I finally have this motor together so now its off to the dyno to find out if its been worth while!
As a side note I told the wife I could complete this motor for a couple of hundred dollars, I failed miserably but have managed to hide most of the costs
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Originally Posted by kel
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