Peter wrote:
unless an independent engine shop is outright crooked, they will not reassemble an engine as “overhauled” which is outside the manufacturer dimensions and other guidelines, and the shop has an incentive to reveal all under-spec parts it finds because they make the trade margin on replacing them
I don’t think there are manufacturer dimensions for overhaul, there are instead limit dimensions and guidelines for ‘serviceable’ and ‘new’. Overhaul means take apart, inspect and put back together, as defined in FAA terminology. The owner’s opportunity to operate independently in maintaining a serviceable engine (which means exactly that) is an asset which is eliminated when a factory TBR program is forced on the owner by the manufacturer. That drives up costs in conjunction with the TBR program also eliminating competition between engine parts suppliers.
The shop doing aircraft engine work can be any A&P mechanic, even one on working on his own engine, and whether it’s that or an engine overhaul facility, the best and most proper incentive is to serve the owner of the engine and his needs. I don’t think (for example) that throwing away expensive sole-sourced parts that may be barely outside new limits after 2000 hrs serves the paying customer.
Yes; one would think e.g. Thielert would have a much better grip on what goes on.
But I would make two comments:
)On a slight tangent, it will be interesting to see the TBR increases on the diesel engines materialize. With the engines going back to the manufacturer after their stated life expectancy I’d imagine the process can be much more reality-based than for the avgas engines the manufacturer hardly ever gets to see / inspect. Then again, the absolute number of engines in the sample pool might be the same, or even with a disadvantage for the diesels, given the numbers in circulation.
What I heard is that this 1200hr TBO might be the result of the turbo installation pushing the slightly small engine too hard.
I have heard the same about IO540 engines with 10:1 pistons (for the US Exp market) making only 1200-1500hrs before making metal.
Here’s what Continental Motors Intl. has to say about TBOs :
TBO periods were established on most CMI engines beginning in the 1960s. Since that time, CMI
has made significant engineering improvements to virtually all major engine components. CMI
has refined manufacturing processes and implemented computer numerical controlled (CNC)
machining tools enabling CMI factory engines to meet higher standards than possible when CMI
engines were originally granted FAA Type Certificates. These improvements have enabled CMI
to increase TBO limits for many of our new and rebuilt engines
USFlyer wrote:
TBO is arbitrary
It is not… There is a whole branch of engineering sciences devoted to the subject of service life prediction of thermal and mechanical heavily loaded machine items. However, simple equations to link mechanical and thermal induced stress to durability of certain items.
The TIO-360-A appears to be an anomaly in having a 1200 hr recommended TBO when compared the -C series engine with 1800 hr TBO. I’m not sure of the exact differences between -A and -C suffixes, I thought it was maybe just conical engine mounts, but there appears to be something funny with this particular -A suffix engine to have such a low TBO. Other variants with TBO that low have understandable issues like narrow stem valves or geared propeller.
PS Some links seem to indicate the -A means angle valve, i.e. completely different cylinder heads, maybe that is it. There are surely a huge number of O-360 variants.
Yes; I was wrong in saying Mooney used that one; they use Conti instead (as per the linked thread). But my Q stands: how is such a (very short) TBO determined?
The only lycoming turbo that mooney has been using is the 270HP TIO-540 in the TLS/Bravo. Getting the cylinders liquid cooled by going the Bravo mod changed the engine from a cylinder eater towards not needing top overhaul at mid-life (typical for turbo, at least Continental).
The other turbo mooneys, the 20K or the acclaim are using continental turbo engines. A TIO-360GB/LB or MB for the M20K and a TIO-550 for the acclaim.
There are also aftermarket turbo kits for the M20C-E-F-G-J. These are based on the original lyco IO-360A (or O-360 for the C) plus typically a rajay turbo.
My experience from ROTAX 914 turbo is that the TBO was stated low in the beginning (1000hours) and has been increased step by step (1200-1500hours) towards 2000hours when the company gained more and more experience with the fleet and the real failure modes.
The first turbo ROTAX had issues with crack in the crankcase and oil pressure sensor failing. Otherwise, well maintained, these are no issues engines and make TBO and beyond without issues.
