[COUPERS-FLYIN] overhaul misconceptions

[glen]

Guys..I did some searching on the net and found this explanation of the difference between a  "factory "zero time" engine" and a field overhaul.  After reading this, I know that when my engine is ready for a re-build, I will find a shop with a good reputation and have a field overhaul.  This article is lengthy but well worth the read.  BTW...John Cooper from Skyport Services was right on target...as usual.   Glen Davis CFII Grumman Tiger N70GD 1946 Ercoupe N3103H                 |-----| _________(*)_________                o  o  o     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 ([EMAIL PROTECTED]) 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:   ? 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.   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:   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?   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!