This is how the new CY F-230 laid out
This is the new Chung Yang Four Bolt F-230 Engine with the cylinder removed. Comparison showed that the 4 bolt pattern is the same as the Zenoah 4 Bolt engines. The Chung Yang will also be released in a 35 x 28 mm size. All other appearances are the same. When checking to see if the Zenoah cylinder would fit, we found that we had to change the 4 cylinder base mounting screws. The F-230 came with some TORX bolts with a larger head diameter than standard Allen screws. The heads of the bolts interfered with fins on the Zenoah cylinder. The Zenoah cylinder fit fine after changing the bolts.
The photo of the piston shows the cut-away skirt design, claimed to improve the breathing by un shrouding the transfer ports. We measured the piston to check for cam and taper. The piston is a totally round design. The intake and exhaust ports on the CY are 180 Degrees opposed, where the Zenoah is offset 5 or 10 degrees. This required that the piston ring alignment pin on the CY be centered, 180 degrees from the exhaust port, while the Zenoah ring locator pin is offset to line up with the off center tang in the intake port. The pistons and cylinders would have to be matched if any cylinder swapping is done. A minor detail is the base holes are .210″ dia. on the Zenoah & .230″ on the CY . At first, when the cylinders would not cross fit, we thought it was because of the hole size. We then discovered that it was the larger heads on the TORX that come on the CY was the only thing keeping the cylinder from fitting. Note, on the engine we received, the outlet on the muffler is top center. This is like the mufflers for the HPI RC Cars. For scooter usage, a different muffler may be needed. Of course, the older 2 bolt mufflers would fit.
CY F-230 Cylinder Removed
Comparing Ports to 2 Bolt
CY has support strut on exhaust port, Zenoah…..none
Micro I.D. Ground Cylinder Bore
Staggered Transfer Port Height, Flat Squish Band
Piston Side Skirt Profiled for improved Transfer Flow
We measured the exhaust and transfer port heights from the base and noted that the transfer port timing was staggered. This is a common practice in high performance 2 strokes. The port roofs are also at different angles. The purpose of this is to stack the incoming fuel/air mixture in different layers in the combustion chamber above the piston. The transfer ports were slightly lower than the Zenoah 4 bolt cylinder compared. This should work better with a stroker crankshaft, as strokers tend to raise the transfer ports a little to high for the High RPM range. The exhaust port was also about 1 mm wider, and slightly different shaped than the Zenoah. We noted that the finish on the cylinder wall was a beautiful micro finish. This is accomplished by a finishing process using I.D. grinding rather than bore, hone, plate & hone. Other manufacturers use the latter process, as it is more economical. The second method leave a much courser finish on the cylinder walls. Left over lines can easily be seen by the naked eye. These lines are from the single point boring bar finish, as opposed to the I.D. Grinder finish used by Chung Yang. The other benefit of Chung Yangs cylinder finishing process is the cylinders are much straighter when checked for roundness and taper. We measured several CY cylinders. They are round and straight within .0002″. We find most of the competitors cylinders to be from .0008″ to .0012″ out of round, and from .0008″ to .0015″ taper from top to bottom of cylinder. A straighter cylinder bore lends to better ring seal and better ring life.