First, let me say that these motors are extremely reliable when used in the intended manner. As long as you are not screaming it at top-end all the time, they should last you as long as one could expect from any small engine... However, with many states limiting motorized bicycles to 50cc, we are often pushing these motors a bit further than they were designed for.
Here are some photos of the huasheng connecting rod oil grooves. One of the grooves is about 25% larger than the other, both width and depth. Huasheng and Honda gxh50's are noted for being RPM limited mostly due to the connecting rod and it's limited oiling capabilities. I have also seen breakage at the point noted in the pic. In all of the 50cc 4-stroke bicycle engine failures I have encountered, broken rod or not, the big end on the rod was starting to seize on the shaft. This leads me to believe that the 'current' limitations to spin these motors faster is the small oil grooves. The piston pin oil grooves are sufficient, as it is not rotating a full 360 degrees and oil requirements are much less. If one could modify/machine larger, more uniform oil grooves or possibly drill an oil hole in the end cap it may allow the RPM ceiling on these motors to jump a thousand RPM or more as well as improving longevity for those that use the upper RPM range constantly... Obviously, this is something that would have to be very carefully done, as removing too much material could cause you to throw a rod. Next your limiting factor would be things like valve float, throwing a rod, bent pushrods.
Here are some photos of the huasheng connecting rod oil grooves. One of the grooves is about 25% larger than the other, both width and depth. Huasheng and Honda gxh50's are noted for being RPM limited mostly due to the connecting rod and it's limited oiling capabilities. I have also seen breakage at the point noted in the pic. In all of the 50cc 4-stroke bicycle engine failures I have encountered, broken rod or not, the big end on the rod was starting to seize on the shaft. This leads me to believe that the 'current' limitations to spin these motors faster is the small oil grooves. The piston pin oil grooves are sufficient, as it is not rotating a full 360 degrees and oil requirements are much less. If one could modify/machine larger, more uniform oil grooves or possibly drill an oil hole in the end cap it may allow the RPM ceiling on these motors to jump a thousand RPM or more as well as improving longevity for those that use the upper RPM range constantly... Obviously, this is something that would have to be very carefully done, as removing too much material could cause you to throw a rod. Next your limiting factor would be things like valve float, throwing a rod, bent pushrods.
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