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I am looking at buying a craft with an IO-540. It is within hours life to give a couple of years pleasure but it was fitted new 18 years ago. It doesn't seem to have been zero timed yet, so it has averaged a touch less than 100hrs/year (which can be good... or bad)

Without going into the why's or wherefores, even though the engine may have been well maintained, although it will only be used for private flying, I think I would be more comfortable with a complete overhaul/zero timed engine (understanding zero-timed does not necessarily mean like new). The craft seems to be pitched at a price that factors it in.

However, not being too technically savvy, does a zero-timed engine reset its calendar life as well, or is not enough done to the engine to give our regulators faith that it will last another 12 years?

Thanks in advance...
Only a factory can zero time an engine which is why you often see hours SMOH (since major overhaul) if it's only going to be privately used I'd have it overhauled by a reputable outfit here. Our engine was fitted in 1990 when the aircraft was built and has had one major overhaul.
My experience is 'yes' - zero-timed means zero-timed in every sense.

13 years ago I bought an AA5 where the engine had been zero-timed 30 hours before I bought it. My engineer didn't start to do the 'after 12 years' sign-off until a year or so ago.
It is my personal opinion that all the confusion arises because the rules are, in fact, a load of bunkum.
Quite simply, if it aint broke, don't "fix" it !

AIUI, most failures occur a short number of hours after major strip-downs. If it's not making metal (wear and disintegration of bearing-surfaces) compressions are good and well-balanced, leave well alone.
These archaic engines have proven, like the ancient mill-engines, that their relatively slow speed and low-stress,provide a long, trouble-free service-life. many "timed-out" engines find their way in to "experimental /Permit aircraft, where they seem to outlive their owners!

Mags do need periodic overhaul, if only to lubricate bearings, check/change slipring brushes and points and, most importantly, the shellac insulation of the windings.
Carburettor -jets rarely wear unless they have a needle running in them (constant vacuum -type as in Bing, Stromberg,SU. and their superbly engineered Japanese equivalents) - in which case both needle and jet should be periodically replaced, but, again, as the vast majority of running is at constant-speed, the service-life is long and a mixture-control compensates for wear. Float- needles and seats are also a major wear-potential, but, again, only likely to manifest at low revs ,where flooding would show up.

I'd say, use it until any issues present. I've seen sombody put a rebuilt Lycosaurus into a C172 and a cylinder departed rather violently in the overhead......another new engine and a cowling! (I have no idea why they don't Loctite /wirelock /splitpin the base-nuts on the cylinders, the items that are so- secured seem to be very arbitrarily selected,- but i'm not an aero-engineer and so not qualified to dictate such measures on what is, apparently, a not-uncommon occurrence .
Bobcro liked this
One more point. It's perfectly possible to run an engine on condition beyond TBO if it's running well and we did that. It's worth getting an oil sample done at each service as that gives early warning of emerging problems needing further investigation.
After our much reported 'towbar' incident 5 or 6 years ago , our 360C-I-C was torn down for shock inspection at a well known engineers in Southend, and with the Insurance company's approval rebuilt and zero timed using new parts paid for by us.

The engine at the time had been on condition for years and reached 1800 hrs.They paid for the labour : I believe this arrangement can no longer be done. We paid a small 'betterment premium, but we still got a new engine half price.

Despite all the BS about who can and who cannot 'zero-time' an engine , our certificate of release from said Engineers states 'Zero-Timed on (date) and its new logbook started on 0.00.

Good enough for me.( I had great fun doing the 'running in' when out planned engineer let us down.

Issue with Lycomings I've seen is that they are more likely to corrode over time than fail due to higher numbers of hours.
Yes - once over TBO hours they need careful monitoring for ware (so compressions, oil consumption, bits in the oil etc).
The main corrosion worry is the cam shaft - it doesn't sit in oil when the aircraft is stationary, so after a couple of weeks of not running, the oil film disappears leaving it open to the elements and it corrodes. Engine should really be inhibited if it wont be run for a few weeks, but few people are going to do this. So it would be the age of that engine I would be worried about. it would need a good internal inspection to know whether corrosion is an issue.
jerry_atrick liked this
The intention is to buy and then part it out - either equity or non-equity... Not for profit, but just to share the cost a bit (I don't fly enough to warrant owning it outright).

Re Lycomings - a share in a PA28 I bought into years ago had to be overhauled (they zero-timed it) well before its hours or years limits; it wasn't used that much and could sit a couple weeks or so in between use, esp in winter. I was surprised as I was under the impression Lycomings were pretty well bullet-proof (the magnetos they used are a different story); of course, up to then, I was in school run PA28s that rarely sat idle for too long.

As it turns out, the craft I am looking out had gone under offer moments before I called to put in a firm offer - those are the breaks - but a similar steed has turned up, this time with an O360 and you guessed it - it's on extension about to go on-condition. A careful inspection of the flying logs to see if it spent a lot of time idle is probably well worth the time. Though if I go for this one, the next question will be about replacing an old bendix skymap unit and a bunch of old 25khz/mode c things with the latest gadgets...
jerry_atrick wrote:The intention is to buy and then part it out - either equity or non-equity... Not for profit, but just to share the cost a bit (I don't fly enough to warrant owning it outright).

An aside, which is an observation on terminology:

I'd normally take the phrase "part it out" to mean "break it for spares and sell the bits". Looks like you mean "sell shares in it".