447 CHTs Different.
in 2 Stroke Technical Questions
14 years ago
Is this normal?
Front (flywheel end) cylinder of a fan-cooled Rotax 447 consistently 75F hotter than rear (gearbox) cylinder. This isn't an instrumentation problem as I can swap all components (sensors, wiring, gauges) and get identical results. I've even changed the horrible ring/crimped sensors everyone uses, for proper machined rings with thermocouple wires silver soldered into them (as described in the Rotax installers manual). (THAT was a surprise - new readings were 350/425, rather than the 325/375 I was getting with the old sensors. All of a sudden I wasn't comfortable with the higher reading.)
It's single carb (of course), and I've experimented with tilting the carb slightly, in case it's favouring one cylinder. Also raised the needle to maximum rich. The temperatures are highest at full throttle (6500), and stay the same until below 6000, when they drop to a more reasonable 300/350 in the cruise (~5300).
I've even swapped 447s! Exactly the same readings (same carb though).
Am now considering adding a diversionary baffle into the engine cooling cowl to direct some more air over the front cylinder. The only thing stopping me is why would I have to modify what the great Rotax designers deemed unnecessary?
Both plugs have identical good colours.
Any thoughts?
Dave
Front (flywheel end) cylinder of a fan-cooled Rotax 447 consistently 75F hotter than rear (gearbox) cylinder. This isn't an instrumentation problem as I can swap all components (sensors, wiring, gauges) and get identical results. I've even changed the horrible ring/crimped sensors everyone uses, for proper machined rings with thermocouple wires silver soldered into them (as described in the Rotax installers manual). (THAT was a surprise - new readings were 350/425, rather than the 325/375 I was getting with the old sensors. All of a sudden I wasn't comfortable with the higher reading.)
It's single carb (of course), and I've experimented with tilting the carb slightly, in case it's favouring one cylinder. Also raised the needle to maximum rich. The temperatures are highest at full throttle (6500), and stay the same until below 6000, when they drop to a more reasonable 300/350 in the cruise (~5300).
I've even swapped 447s! Exactly the same readings (same carb though).
Am now considering adding a diversionary baffle into the engine cooling cowl to direct some more air over the front cylinder. The only thing stopping me is why would I have to modify what the great Rotax designers deemed unnecessary?
Both plugs have identical good colours.
Any thoughts?
Dave
