I have recently heard claims of reliability problems with the fuel-injected Rotax 912iSc engine. Anyone else have heard about this? Somewhat surprisingly the problems are said to be not with the fuel injection and electronic engine controls but rather with the gearbox.
I would expect the gearbox to be the same as in the carburetted 912 variants as the rated power is the same. Whether the engine is carburetted or fuel-injected should not matter for the gearbox, should it? Neither should manual or electronic engine controls matter.
AFAIK the electronic fuel injection and ignition was designed by Rockewll Collins that’s top notch aircraft grade engineering
Everything else is just motorcycle grade engineering 
We have one iS in a club plane. Rockwell Collins or not, we found undermentioned original Rotax-installed/spec’ed main wires to the ECU from the generator. Visible heat damage on the insulation, and a cause of many hours of fiddling. That’s an early iS though. I don’t think there are more problems on the iS than the carbureted ones, but when there IS a problem, it’s a really big deal to find the root cause. The weak point on the Rotax is traditionally the carburetors, but they are also easy to fix, a known thing. This ECU is just a black box, and nobody knows anything about them, hardly Rotax themselves.
People here usually upgrade their standard Rotax engines to Edge Performance FI and/or turbo, even on brand new planes/engines instead of going iS.
I don’t think there is any connection between FI and gearbox, and even the standard ignition on non-FI Rotaxes is electronic (non magneto type). Gearbox problems are usually due to running on leaded fuel or using wrong oil. That happened a lot to the Tecnam (certified) in the club. People filled it up with Aeroshell If there is a connection nevertheless, then rest assure, Rotax has no clue what the bug should eventually be.
Awkward. If anything, the chance of the carburetted engine causing problems of the gearbox is bigger because the carbs can become unbalanced and the gearbox does not like that at all.
You mention recent claims. I looked on https://www.rotax-owner.com/en/forum and can only see discussions on this topic that are years old and presumably no longer an issue?
LeSving wrote:
I don’t think there is any connection between FI and gearbox, and even the standard ignition on non-FI Rotaxes is electronic (non magneto type). Gearbox problems are usually due to running on leaded fuel or using wrong oil. That happened a lot to the Tecnam (certified) in the club. People filled it up with Aeroshell If there is a connection nevertheless, then rest assure, Rotax has no clue what the bug should eventually be.
There are plenty of Aeroshell oils – in our 912iS we use AeroShell Oil Sport Plus 4…. it’s the most recommended oil type due to the additives which are aimed to reduce wear in the gearbox…..
Airborne_Again wrote:
I have recently heard claims of reliability problems with the fuel-injected Rotax 912iSc engine. Anyone else have heard about this? Somewhat surprisingly the problems are said to be not with the fuel injection and electronic engine controls but rather with the gearbox.
I have a Rotax 912is and this statement is correct, the earlier versions of the 912is had some problems with the gearbox (unusual high wear). Mine has been replaced with the new version. The new version has an oil spray nozzle.
In my opinion, it’s a great engine, but if it has a problem it’s very hard to find.
jvdo wrote:
Mine has been replaced with the new version. The new version has an oil spray nozzle.
So in your experience the new version works reliably?
Airborne_Again wrote:
So in your experience the new version works reliably?
The old one was reliable, it didn’t cause any big problems. It just had a lot of wear, at about 500h we experienced vibrations.
It turned out to be a known problem so it had to be replaced.
The new one is only 20h old, so it’s too early to say.
I don’t have a picture of the wear of the dog gear itself. However, as you can see from this picture, the general condition was not great.
On this picture you can see the oil nozzle that was added on the new version.
I found this post from 2018 on another forum, I think this information is correct:
“The 912iS fix before now was just to install the same parts and hope they didn’t wear again. Some had to replace gearbox parts 4-5 times. Rotax identified the issue as poor oil distribution in the gearbox, but especially on top and forward. The fix is now a new gearbox with a new oil spray nozzle mounted in the front to spray oil on top. You can see this in the new Parts manual. The gearboxes are just now coming out. Part of what took so long was the extensive testing that took thousands of hours to make sure it would work.”
As an owner of an aircraft equipped with a 912iS, I asked the producer about the issue. He indicated that bearings within the gearbox had been replaced on numerous gearboxes, including the one in my own aircraft, and that Rotax were aware that these parts could fail so have decided that once I notice the vibrations, I will probably buy the new gearbox rather than keep taking it apart and replacing bits.
I just feel it’s pretty poor for Rotax to note a design issue and not compensate, even partially, the owners for the upgrade required to eliminate the issues caused. Having said that, still love the engine….. averaging 16.8l over the last 30 hours, cruising at around 120KTAS…
