Final day, and more examples of lead poisioning in an engine.

HI-ho, Hi-ho, it's back to work we go.... First you pull off the intake manifold.(The safety glasses not only indulge my paranoid side about my eyes, but they've also got "cheaters" built-in, so it takes care of two birds at once.)

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.

Theory, meet Practice

Day Four, and it's time to leave the books behind. We were greeted with 3 engines (two 912's and one 912S) and a bunch of tools.

No race, no competition, just a group of people interested in learning what makes the engines work.

Roy and I teamed up on a 912. Roy is an instructor at the A&P school next door, they're thinking of making it part of the curriculum and he's here to learn about Rotax engines. He was kind enough to answer questions I had as we went along, too. We started by disassembling the back of the engine which contains the electrical equipment: rotor, stator, ignition triggers, starter, starter gearing, and also the water pump.

The engines use few gaskets, and most bolts are not safety wired, they fit just by the tight machining tolerances. Of course, that means taking them apart can really require some elbow grease....

In some cases, elbow grease just ain't enough.

The starter clutch is fascinating. Most GA airplanes use a Bendix type starter, which has some limitations. For instance, it's a delicate act of learning just when to back off the starter switch when the engine catches, and you can damage the starter if you accidentally engage it when doing a mag check at high rpm.

Rotax doesn't use a normal starter. Sure, they have a starter motor, but instead of the Bendix gear they use a really cool ring of egg shaped bearings/cams called a Sprag Clutch that is driven off friction from the starter gear, causing the bearings/cams to engage the crankshaft via friction. When the engine starts running the crankshaft advances ahead and off the bearings/cams, and the starter gear freewheels on the crankshaft. If the starter is accidentally reengaged it will spin the freewheeling starter gear, and the cams will just ride along the surface of the faster spinning crankshaft. I'd like to know who came up with that system.

The engine is built to such close tolerances there are very few gaskets in it, and very little sealer is even used. Even when sealer is used, barely any is applied. Here some Loctite is applied to the ignition housing assembly prior to reassembly. 

During a break a gent brought in his newly flying airplane, using the new 912is fuel injected engine. Note how small the 912is is compared to a similar Continental or Lycoming engine. 

Back to the shop, we've reinstalled the stator and timing triggers, and starter motor.

And the rotor/flywheel completes the assembly. No, we don't take them out and run them, but tomorrow we'll be taking cylinders off.

In the back of the shop, a pristine rebuilt 914 sits, waiting for a buyer. sigh.......

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Get the lead out

Day Three, and here's how you check the torque on the prop gearbox. With a carefully measured 6' BFS and a fishscale.

 

Every wonder what's inside the gearbox? Once you see everything apart and learn how it's designed, your ability to operate the engine goes up exponentially.

The engine is designed to run on ethanol free autogas, but for convenience people will run 100LL avgas. Problem is, 100LL is not really "low lead", but has a considerable amount of lead in it. You can add Decalin to help the lead from sticking, but once it's in the engine it remains there. Here's some lead fouling a gearbox

And a turbo that had been run for 2,000 hours on pure 100LL, fouling the wastegate. 

Turbo inlet vane. Spins at 70,000+ rpm, makes engine very very happy on a hot day. 

Stacks and stacks of engines, waiting to be shipped. In 1982 Vernon businessman Ron Shelter talked Rotax into producing aircraft engines and created Rotec Research Canada, in 1988 Rotax went into production full time. There are about 3,600 Rotax 912s sold each year, and about 400 914s.

Doing a compression check. Why is the engine on a truck? 

Here's why. In the afternoon the class adjourned to a taxiway and we ran the engine

 

After we had a chance to run the engine, Mike sent us inside and "broke" it, then we came out to troubleshoot it.

"Are you SURE that's the problem??"

 

With a couple hints, we figured it out. This was the end of the 3 day class, tomorrow we start the 2 day Heavy Maintenance class. Cool.

...

Nothing like "hands on" to really understand something.

Gives me flashbacks to when I was a kid and Dad gave me a screwdriver and a cast metal airplane, that kept me occupied for days and started my love of working with my hands. I think I wore that thing out taking it apart and putting it back together again.

 

Wait- where are the green, blue and purple parts?

Always fun doing it with a friend.  Mike, another gent, and I are the only homebuilders in the class, the other 7 are professional mechanics sent here by their companies.

Success. Before we started the teardown I was completely lost about how the Bing carb worked, not a word he said during the formal class made sense to me and I didn't want to slow the class down. I went to the instructor during the break, and asked him to explain it in simple "Damn it, Jim, I'm a pilot, not a mechanic." terms. A few minutes later he had explained it to me in a completely different way, the light went on, and I understood it. The mark of a good instructor.

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