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 Savvy
Owner Notebook:
The Zero-Time Engine Myth
When you exchange your worn-out engine for a factory rebuilt one, you get a fresh new "zero-time" logbook to go with it. When you have your engine field overhauled to new limits, you don't. Does this mean that the factory rebuilt is somehow a better engine than the field overhaul? Don't count on it!
by Mike Busch (mike.busch@savvyaviator.com)
 FAA
regulations permit an engine manufacturer like TCM and Lycoming to
assemble rebuilt engines using "pre-owned" components such as
crankcases and crankshafts, and to furnish them with new "zero-time"
logbooks, so long as such rebuilt engines meet the same tolerances and limits as
a new engine. Such engines are commonly referred to as "factory remans,"
but "rebuilt" is the correct term (as we shall see).
Only the original engine manufacturer is permitted to rebuild an engine and
furnish a zero-time logbook. If you take your engine to a first-rate overhaul
shop, they will overhaul the engine to new limits-very possibly to
better-than-new limits in certain areas like balancing and flow-matching-but
they can't give you a zero-time logbook because the FAA reserves that privilege
only for the manufacturer. Here's what the regulation says:
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§ 91.421 Rebuilt engine maintenance records.
(a) The owner or operator may use a new maintenance record, without previous
operating history, for an aircraft engine rebuilt by the manufacturer or by an
agency approved by the manufacturer.
(b) Each manufacturer or agency that grants zero time to an engine rebuilt by it
shall enter in the new record-
(1) A signed statement of the date the engine was rebuilt;
(2) Each change made as required by airworthiness directives; and
(3) Each change made in compliance with manufacturer's service bulletins, if the
entry is specifically requested in that bulletin.
(c) For the purposes of this section, a rebuilt engine is a used engine that has
been completely disassembled, inspected, repaired as necessary, reassembled,
tested, and approved in the same manner and to the same tolerances and limits as
a new engine with either new or used parts. However, all parts used in it must
conform to the production drawing tolerances and limits for new parts or be of
approved oversized or undersized dimensions for a new engine.
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You may want to read that again, because there are a couple of notable
subtleties to be noted in this regulation. First, the reg talks about "the
manufacturer or by an agency approved by the manufacturer…" However,
neither TCM nor Lycoming has ever given approval to anyone else to rebuild
engines, so in the real world only the factory can offer a "rebuilt"
engine and a zero-time logbook.
Second, note that the regulation requires a rebuilt engine to be manufactured
to new tolerances and limits, but that it explicitly permits the use of
"approved oversized or undersized dimensions." What exactly does that
mean? You're about to find out!
With this as background, consider the following letter that I recently received
from a Part 135 operator in South Florida. I have deleted a few names to protect
the innocent:
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What does "zero-time" mean?
In May of 2000, I exchanged two IO-520-EB engines for
"factory-rebuilt" (zero-time) engine with Teledyne Continental Motors.
What did I get?
As has been my practice since I started my charter company in 1995, I have
alternated "factory overhauls" with "field overhauls" based
on a few assumptions. As you have frequently pointed out in your articles and
seminars, TBO is only a factory recommendation and not any sort of a mandatory
requirement unless you are operating the airplane commercially (as we are). It
is commonplace for aircraft owners to exceed TBO by a considerable margin.
In fact, we do so as well. The local FSDO has approved a TBO extension for us of
200 hours. At that time, we are required by Operations Specification to overhaul
our engines.
In our business, downtime is a huge deal. Taking an airplane out of service to
replace an engine before it reaches TBO is costly not only in dollars but in
creating an equipment shortage as well. We simply cannot afford to lose an
airplane at a critical juncture for an unexpected overhaul. In order to minimize
the possibility of that, we have made it our practice with alternating overhauls
between "factory rebuilts" and overhauls by a local repair station
here in South Florida.
We have done that for the past eight years and as a result, I am proud to say we
have never had an engine not make TBO + 200 hours. In addition when we do a
field overhaul, we insist on new cylinders as well. We have always felt that
although considerably more expensive, we were getting our money's worth with
"factory rebuilts" because when we were told the engines were
"zero time" we mistakenly assumed that meant FACTORY NEW TOLERANCE. We
have recently been made painfully aware -- to the tune of $12,000 -- that is not
the case.
In May 2000, we installed "zero time" factory rebuilts on one of our
airplanes. We ran the engines to 1900 SMOH and removed them for overhaul. We
sent them to the local repair station for overhaul, as per our standard
practice. The shop rejected the crankshaft. I was shocked. We had paid over
$7,000 more than a field overhaul for these engines in 2000.
I spoke to the people at the repair station to get an explanation as to the
condition of my crankshafts. The General Manager told me that typically a
crankshaft is good for about four runs to recommended TBO. According to him,
after two runs to TBO it generally has to be ground to .010" undersize.
Then it will typically make two more runs to TBO prior to being rejected. Since
my "zero-time" wound up being rejected after only a single run to 1900
SMOH, I can only draw one conclusion: the crankshaft not new when it was
installed. When we bought "zero-time factory rebuilts" we expected the
crankshafts to make at least the two runs until we turned the engines in for
"factory rebuilts" again. New cranks for my field overhauls cost me
another $4,300 for a total of almost $12,000.
I will not be buying "zero-time" engines from TCM again. I don't see
the advantage. In fact, I now know the condition of my crankshafts and I can
monitor their life span on my own. Furthermore, I gave TCM two months to resolve
the issue and they ignored my inquiries. They finally responded to the G.M. of
the engine repair station with a one line statement "the engine is long out
of any warranty consideration." Some attitude toward customer service, huh?
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A "zero-time" log is not a zero-time engine!
 While it's true that a factory rebuilt engine comes with a zero-time logbook
while a field overhauled engine does not, it's not for the reason you may think.
When you have your engine overhauled by a field overhaul shop, that engine
retains most of its original parts, as well as its serial number, data plate,
and engine logbook or other maintenance records. When your engine is torn down
by the overhaul shop, all its parts are segregated and kept together, usually on
a big roll-around cart that stays with your engine until the overhaul is
complete. The shop cleans and inspects all the parts, discards the ones that
aren't serviceable, and retains the ones that are (hopefully at least the big
high-ticket ones like your crankcase and crankshaft). The overhauled engine you
get back is legally the same engine you sent in, all cleaned up with lots of new
parts.
On the other hand, when TCM or Lycoming receives a runout core from a customer,
that engine loses its identity. The data plate is removed and destroyed. So are
the logbooks. The case halves are cleaned up, inspected, and added to a big pile
of reusable case halves. The crankshaft is cleaned up, inspected, and added to a
big stack of reusable cranks. The same is true of camshafts, rods, accessory
gears, and so forth. Those reusable parts become "anonymous" because
they're no longer associated with any particular engine serial number.
Sometimes, those parts can be reused as-is. Other times, the parts may be
machined to approved undersize or oversize tolerances before they are reused.
When you purchase a factory rebuilt engine, you have absolutely no way of
knowing whether the reused parts used to build up your engine are standard or
approved oversize/undersize.
Now, when TCM or Lycoming builds up a factory rebuilt, it pulls some
"anonymous" case halves from one pile, an "anonymous"
crankshaft from another pile, and so forth. When the engine is completely
assembled, it gets a new data plate, a new serial number, and a new logbook.
The logbook starts out at zero time-in-service. Why zero? Because there's no
other reasonable figure to put in the logbook! The case halves are certainly not
zero-time, but there's no record of how much time they've accrued. The
crankshaft may not be new, but there's no record of how much time is on the
crank, either. And so on.
In short, the "zero-time" logbook that comes with a factory rebuilt
engine in no way implies that the engine is "newer" or
"better" than a field overhaul. All it implies is that the reused
components in the engine are of unknown heritage. Nobody has a clue how long
they were in service prior to the time then were cleaned up, inspected, possibly
reconditioned by machining oversize or undersize, and reused in your engine.
Where did this myth come from?
 The notion that a "zero-time" logbook somehow implies zero-time parts
is a common fallacy, but you now know that it has no foundation either in fact or regulation.
Nevertheless, I think I can probably guess where this erroneous idea originated.
In the late 1970s and early 1980s, most TCM factory rebuilt engines were
delivered new crankcases, simply because the factory had recently switched from
"light case" to "heavy case" design, and there weren't yet
enough "heavy case" cores available to meet the demand for rebuilts.
In the early 1990s, there was a period of time when most TCM rebuilt engines
were delivered with new crankshafts, because TCM required that older "airmelt"
crankshafts be retired and replaced with newer "vacuum arc remelt"
(VAR) crankshafts.
But those were exceptions. As a general rule you cannot assume that your factory
rebuilt engine will have either a new case or a new crank. In fact, as our
disillusioned charter operator learned, you can't even assume that the crank
will meet new standard dimensions. It says so right in the regs!
| Do you have a maintenance-related
"war story" that you'd like to share with fellow
aircraft owners? If you do, I'd
love to hear from you. The most interesting stories
I receive each month will be rewarded with highly prized Savvy
Aviator coffee mugs, so please include your
shipping address. Also be sure to let me know if you'd like
me to "change the names to protect the innocent"
when sharing your story. |
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