Then the heads come off, followed by the cylinders.
If you really dig into the engine you get to look at the pushrod lifters.
Ever stick a screwdriver into the spark plug hole to see if the cylinder is at TDC? Here's what you're doing to the piston when you do.
Compare the 912 cylinder (L) to the 912S cylinder (R). Wider cylinder, more compression, etc. Also higher strung.
Here's something cool, the evolution of the Rotax cylinders can be seen in this comparison between the old one on the right, and a newer one on the left. Can you tell the difference? It's very subtle. (The older versions have a sharp edged depression in the cylinder head, the new versions have a rounded head. Rotax found the sharp edge tended to trap lead, leading to hotspots and wear, and uneven combustion, among other things. Neat how such subtle things have such a big effect.)
Rings around the piston.
a pocket for the oil.
Now put it all back together. A cool thing about the engine is that there's very little that can be/needs to be adjusted. The timing is set by the triggers on the flywheel/rotor, the valves are set by the tolerances of the pieces themselves. Being an old Lycoming and Continental guy and having listened to too many urban legends and hearsay, I went into the class with some reservations about the engine, but after listening to the explanations about how the engine was developed, how it's manufactured and seeing how the systems work, I've gone into full on Kool-aid Rotax drinker mode. Still don't like having to balance the carbs, but I can always fly up to Rotec to let them do it. Good excuse for a cross country.
Note the lip of the combustion area, just above the exhaust valve. See the pitting? Lead deposits creating hotspots, leading to pitting of the aluminum caused it.
A newer cylinder showing the same signs of fouling above the spark plug.
And some graphic examples of old cylinders. The one on the left is showing heavy lead deposits and ring fouling after 750 hours of running on 100LL and no Decalin. The cylinder on the right is after 2,000 hours, with the lead cleaned off the top but the rings are completly fouled and immovable.
Here's a best case scenario: 2,000 hours of 100LL and Decalin. The head is fouled but at least the rings are fairly free.
The heads are liquid cooled and (fairly) easily come off and apart, but shouldn't need to be removed in a normal, well maintained engine run on Mogas.
The front fell off. We had some extra time and even disassembled the gear box.
Rotec Canada. Small, efficient office and shop in a beautiful location, they even do video production in-house.
