Originally Posted by
sparky4lawndart
in other words... no other changes were made and the motor kicked to 4K RPM with the recommended needles.. 2 out on high and 6 out on low.
The motor ran great for 4 16oz tanks... each time allowing the cylinders to cool to the touch... average cylinder temp 195 +/- 10degrees...
on the fifth tank, approx. 60 seconds after running normally at about 3900RPM cylinder 2 (based on the drawing above) cracked at it's base so I shut off the ignition and found the head of one of the bolts on the floor...
Spectator assessments from the cheap seats agree that it was either running the engine for too long or oil-based hydraulic lock...
Sorry to hear about this outcome...
- When you say it ran great, you mean it was running near optimum mixture or still overly rich (but not stopping)? If it was run lean, then the cylinder might have simply seazed. With any luck, you won't have crankshaft damage and will simply need to replace cylinder/piston/ring.
- Then, the cylinder temps; 195 is F or C? I take it this was during running @ WOT. How did you measure - by IR?
- Also, any chance one of the lower exhaust tubes creating some sort of siphon to allow gravity poolling of fuel/oil? Did you crank the engine by starter or hand?
- Was the air vent of the crankcase free-breathing?