Kehkou
Active Member
Based on experience, what would you say is the max safe RPM and the max safe temperature for your typical Yuyuan Garden-variety China Girl Doll Happy Time engine? I know this is extremely subjective; the many posts about it here or on that...other site...seem to just wander off-topic and never produce a definitive or even approximate answer. My hope is that this thread will at least provide people with a numerical starting point for entering Multifunction Meter (tach+temp) redline values for our bikes. I'll get things started:
The fastest I have gotten my engine is around 7800 RPM. The stock CDI obviously limits the max RPM. I am also up at 5060' HAMSL with the stock 70 mm jet, so, very rich. I must have an unusually well-balanced crank, because if I modulate the throttle just right to eliminate four-stroking at these speeds, the undue vibrations vanish, and the engine runs quite smoothly. I can probably push 8000 RPM down a steep hill with my unmodded HT but, heh, I ain't about to do that.
The hottest I usually run is between 250°F and 370°F. I was told by another member here that this isn't close to the "danger zone", but never clarified what exactly that "danger zone" is (EDIT: His answer is below under "ANSWERS", and in the first reply):
ANSWERS:
The absolute hottest I ran (recorded) was 399°F, but that was during a runaway condition. I do not exceed 7800 RPM.
The fastest I have gotten my engine is around 7800 RPM. The stock CDI obviously limits the max RPM. I am also up at 5060' HAMSL with the stock 70 mm jet, so, very rich. I must have an unusually well-balanced crank, because if I modulate the throttle just right to eliminate four-stroking at these speeds, the undue vibrations vanish, and the engine runs quite smoothly. I can probably push 8000 RPM down a steep hill with my unmodded HT but, heh, I ain't about to do that.
The hottest I usually run is between 250°F and 370°F. I was told by another member here that this isn't close to the "danger zone", but never clarified what exactly that "danger zone" is (EDIT: His answer is below under "ANSWERS", and in the first reply):
350 is hot but it's not quite danger zone in terms of cylinder/head temps. My Phantom can get that hot pushing it on level ground lol.
ANSWERS:
The absolute hottest I ran (recorded) was 399°F, but that was during a runaway condition. I do not exceed 7800 RPM.
As a general rule with an aluminum air cooled 2 stroke engine (in continuous operation) you want to avoid exceeding 450 degrees Fahrenheit at the head. I try to keep things at 400 and below personally. The "Danger Zone" - aka beyond 400-450 degrees - is where the aluminum starts to lose strength and enters into a state where it can fail.
...which sounds a whole lot like redline of other non-interference engines; no valves to smash up, just the piston etching its name into the bore.I believe I have 17-18 hours on it, and they have all been hard hours. A lot of wide open at 8000 rpm, and recently 9000. I don't recommend doing that of course, and I'm sure it has accelerated the wear on all the components. I'm not afraid to push it though, seeing how it's held up.