I have a question for motorcycle mechanics out there who have enough experience with Hyosung 250. I have 2012 gtr 250 and have increased the displacement to 306ccs. The bike is running flawlessly with a lot more power. I have about 30,000 kilometers on this pistons. I like to increase the displacement to around 350 ccs using Honda CBR600RR(2007 up) which is a perfect match.
I already know everything about compression height and figuring out everything as far as fuel delivery and so on. I like to know, can the crankshaft, specially the pin handle the extra displacment? I know the bearing have no problem. I am not modifying anything else like bigger valves and stuff.
The engine is finished with great results. I have about 1000 kilometers on it with no over heating issues. It runs awesome with 344 cc displacement.
I had to do some modifications to CBR's pistons. The top crown had to be machined flat, the valve groves had to be machined since the piston pin is off center and on the Hyosung twin you have to rotate the rear piston and some machining was required since the Hyosung connecting rod is a little wider. The sleeve was removed and a bigger sleeve with lots of boring was replaced for 67mm ID bore. I used Daelim 250 cc injector with a 10K potentiometer at the MAP sensor. I am also using 50K Potentiometer at the IAP sensor to advance the timing and enriching the fuel a little . If you use all the original Head and below cylinder gasket the compression ratio will be slightly lower than original. I might change the rear sprocket to 41 teeth now since the power is greatly increased. I don't have a lot of pictures. The white clay on the picture is showing the valve indentation. Just to make sure the valve don't hit the piston after machining.