Porting a china girl
- Thread starter johnsteve
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Steve Best
Well-Known Member
First of all, the pin, needle bearing and rod are of low quality. Secondly, we tend to put a huge load on them as we "hotrod"our engines by increasing compression and rpm. Third, we tend to low amounts of low quality oils so the the pin runs hot and suffers metal fatigue.
If you (1) use a better quality pin and bearing from the beginning (too late for that rod), (2) a good oil like Maxima 927 Castor oil at 32:1 and (3) keep the compression ratios reasonable your pin (and piston and cylinder) will last a long, long time. I know this from my own experience.
Those are some wild looking transfer ports, how do they work?
ben4221
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- Sep 17, 2017
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yeah i got some good quality castor oil and new pin and bearing in there now haha i feel sorry for the poor rod but and the transfer ports work well like that, the rings do wear down rather quickly though from the ends of them opening up in the transfer port window but rings are very cheap so its not really a problem. ill put up some pics of the port shapes ive made the most power with
Steve Best
Well-Known Member
Your exhaust port looks great but the transfers are too much. You are losing power.
Here is the deal: The unblemished cylinder above the highest port is where your torque is made. As you cut into it you diminish your torque. So that everything happens at once, the top line of the ports HAS to be straight.
Most important is that the exhaust port is tallest port line in the cylinder. This is because you want it to open when pressure is the highest to start exhaust action. If the transfer is the highest port, the exhaust action will start down the transfer port. Terrible for power.
ben4221
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yeah it doesnt look like it from the photos but the exhaust port is 2mm higher than the transfer ports, heaps of port work has been done to the crank case to allow the charge to flow up through the transfer ports better and i found it best to have the top line of the exhaust port straight but its not ideal for a 2 stroke withe only 2 transfer ports to have to the top line of the transfer ports straight, its should be on an angle so that it shoots the intake charge toward the back of the cylinder, most 2 stroke motorbikes have reed intakes into the crank case and heaps more transfer ports, most importantly one right opposite the exhaust port that is the only time the transfer ports should have a straight top line. its better for performance to have the intake charge spiral up the cylinder away from the exhaust port instead of just straight out the transfers and out the exhaust
