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TBO extension due to modifications

@Ahunt: Regarding your edit: Revision as of 15:49, 29 June 2023

1.) I will not contest your choice of adjectives regarding the engine's higher-than-typical rotational speed,

2.) I accept you replacing:

"With the unusually high engine speeds, these engines, at first, had much lower reliability (600-hour TBO)..." (which, as memory serves, came from another ref, now forgotten)

...with the less-diagnostic...

"These engines were initially given a 600-hour TBO, less..."

3.) Unfortunately, you are mistaken as to the cause of the increased TBO, given the normal evolutionary development of new engines, going through "teething troubles" in early development (resolved by "refinements") -- which even the Rotax 912/914 family experienced, as documented in many places, including the cited source, implicitly, in Mr. Busch's closing statement:

"After 28 years of incremental evolution, product improvement, and TBO extension, these engines seem to be about as bulletproof as anything in aviation."

His assessment of the evolutionary refinement of the engine, and resulting TBO extension, is echoed in detail in Midwest Flyer, August, 2011:

"Increased TBO. If your 912 or 914 series engine was manufactured since the beginning of 2010, you already have a 2,000-hour TBO. But if not, your 1,500-hour TBO engine might be eligible for the 500-hour TBO upgrade with nothing more than replacement of [certain parts]... [Because] since 2006, all 912 and 914 crankcases have been manufactured with the improvements necessary to enable the higher TBO rating. ...check Service Bulletin 912-057-UL for the specifics."

BackCountryPilot forum poster notes problems with early (circa 1997) 914 engines:

"I owned a 914... Have an absolutely incredible number of [Service Bulletin]'s (Rotax seems to crank one out every week or two),... (note my engine was a '97, so much of the problems (cracked cases, carb flanges, sticking turbo wastegates, foaming oil causing valve train problems with the hydraulic lifters etc) will have been solved [in subsequent production units]. ..."

At SportPilotTalk.com, "SportPilotExaminer" "Prof H Paul Shuch, PhD CFII DPE LSRM-A/GL/WS/PPC iRMT" notes:

"Early 912 crankcases (prior to s/n 06.0020) are prone to fretting regardless of flight hours. Fretting can cause oil leakage along the seam between the crankcase halves. ...If you have one of these early design crankcases, lighter props won't help (and the engine will likely not reach TBO)."

He later adds:

"The crankcases that had the fretting issue were made in roughly 2004 through 2006, and we began seeing failures about 10 years later."

The Europa-list forum notes another serious issue affecting early 912s models with certain props: Starting difficulties, and even starting-and-running backwards -- and it reports that later Rotax refinements resolved that problem.

While blog posts are not suitable WP:RS for the article, these posts clearly show -- in part by referencing specific corrective actions by Rotax, itself -- that the 912/914 family had serious problems in early production models, limiting reliability, that were resolved before they could be expected to reach the TBO levels of current versions.

And the notable experts in the periodicals cited are suitable WP:RS.

These are reinforced by the Light Aircraft Association (U.K.) in its reprint of ConAir Sports' detailed "Rotax Service Interval Guide" for the 912/914, which advises, in "Summary of Maintenance... at Each Service Interval":

"600 hours: Note that some older engines were delivered with a 600 hours TBO & they will either need overhauling or some modifications carrying out to upgrade their TBO"

* * *

"1500 hrs: Overhaul required on the majority of engines supplied before 2008"

* * *

"OVERHAUL: In recent years Rotax have been actively looking at service history and following their positive findings they have been able to extend the Time Between Overhauls (TBO) for the 912, 912S & 914 engines. Whilst the news of TBO increases are welcome, the engine has had to undergo some modifications to make it possible. The current range of 912 & 914 series engines are being shipped with a 2000hr or 15 year TBO. Owners of earlier engines can have their engines upgraded to the current TBO however in some circumstances it may not be worthwhile as some major components will need replacing. ... Engines before those listed in the table will probably require some major parts in order to upgrade the TBO"

Finally, the official word: Rotax, itself, has a long list of Service Bulletins / Technical Bulletins specifying certain inspections and alterations (or replacements) required for the 912 A (let alone later models) to reach the longer TBOs, including...

• "SB-912-005" / "Technical Bulletin 912-05 R 2 Special inspection to increase the TBO for engine", which specifies a laundry list of engine part replacements and/or modifications from original design required to qualify for the newer TBO.:

"Subject: Increase of TBO from 600 h/10 years to 1000 h /10 years.

"Engines affected: Generally all engines of Series Type 912 A up to and including engine N. 4,380.693"

* * *

"1.2) State of amendments:

"The following modifications as per list of amendments have to be carried out:

[A list of 14 modifications and parts-revisions follows].

Other similar Service Bulletins on the early Rotax 912 A abound -- many as conditions for TBO extension. Ditto other variants of the engine.

Clearly, the growth in TBO, of the Rotax 912/914 family, was not just due to "operational experience" (as hinted in some P.R. material and pop-fiction) but actual changes ("refinements") to the engines in later production units, and factory or field modifications of older units, per Rotax.

I'll leave it to you to correct your edit, accordingly, please. ~ Zxtxtxz (talk) 04:41, 12 July 2023 (UTC)

Thanks for all the details,  Fixed. - Ahunt (talk) 11:22, 12 July 2023 (UTC)