What is the realistic Time Between Overhauls for the popular Rotax 912S? Realistic cost? Any Repair Stations know what they're doing on these? And any significant maintenance issues to look out for?

Thanks. cubscout

2000 hrs and plenty of authorized Rotax repair stations. Don't know a cost as I don't know anyone who has ran one all the way to TBO yet. I think Steve in his Highlander and Tom in his S7 could answer this part better.

That's kind of a loaded question that would be near impossible to answer. Too many variables.

I have personally seen 912 motors with 3000 hours on them, never opened and running strong. Maintenance and frequent usage are just as important as in a "certified" engine, though they are far less prone to being corrosion-destroyed by sitting than a Conti or Lyc.

Maintenance: Using the proper (motorcycle) oil and (Rotax) filter of course is important. Also since there is liquid cooling the proper coolant is key. Green glycol coolant will quickly damage the motor's water jacket and pump. Rotax says either Dex-Cool type or Evans waterless type coolants are the only acceptable options.

If the motor sees a steady diet of 100LL, it is important the proper precautions are exercised. (Mineral based oil and 25 hour changes) This would prevent lead build-up in the crank case and gearbox (they have a common oil supply). A lead dispersant is also recommended to be added to the fuel.

If you are using waterless coolant (i.e. straight glycol), be aware that this provides another potential fuel source for a fire if there's a leak. And there are a *lot* of coolant hose connections in a 912/914 installation. In the typical glycol/water mix, the water will at least keep the coolant from fueling a fire until the water is driven off as steam. The 914 also has a built in fire igniter with the red hot turbo.

Rumor has it that parts cost is $12K or so.

Cubscout,

Talk to Chris Dillis at centennial - now owns Aspen flying club - used to own skyraider aviation at erie - they were operating 2-3 rotax powered lsa for instruction. He spoke very highly of the maintenance record of the engines - and the evektor (now totaled) flew to TBO of 2000hrs and was going very strong. So strong rather than overhaul - sold the engine to a non-commercial pilot building an experimental and bought a brand new engine. Commercial operation required engine overhaul at TBO - otherwise he would have kept on going. I spoke to the new owner of the engine at LMO and he was happy with it - don't recall his name. Of course as soon as they got the new engine the plane was wrecked.

During a seminar by Phil Lockwood at Airventure last summer, he told the story of one of their 912 motors they brought in for overhaul. It was a regular runner and it was out to TBO, no other reason for overhaul. This particular engine needed no hard parts other than rings. The pistons, cylinders, bearings were all still in Rotax like-new spec, showing no wear. They replaced the rings and soft parts (hoses, seals, etc.) and zero-timed the motor.

I thought it was pretty impressive.

Av8r3400 wrote:During a seminar by Phil Lockwood at Airventure last summer, he told the story of one of their 912 motors they brought in for overhaul. It was a regular runner and it was out to TBO, no other reason for overhaul. This particular engine needed no hard parts other than rings. The pistons, cylinders, bearings were all still in Rotax like-new spec, showing no wear. They replaced the rings and soft parts (hoses, seals, etc.) and zero-timed the motor.

I thought it was pretty impressive.

That is amazing. I once read an article someplace, (Sacramento Sky Ranch? I dunno) in which the author insisted that we can zero time the engine but we can't zero time the parts. He was talking about metal fatigue. I think he was talking specifically about cylinders though IIRC he mentioned cranks and rods too. I know a fellow that has 13000 hours plus on the crank in one of his IO-320-B1A. The airplane flys all the time though, and the crank in the other engine only has 7000 hours on it. Still, that's a bunch.

What is it exactly that compels us (part 91) to replace everything that moves in the engine?

EB