Rebuilt vs OverhauledOverhaul and Rebuild are terms commonly used in Aviation to refer to the condition of a part. People in the Aviation industry often use these words interchangeably; it is easy to see the parts as the same and generally the overhaul is less expensive. Often people are left asking, “why should I get a Rebuilt unit when an overhauled is the same for less?”. The two terms are different because of the type of work performed. An Overhaul means that a part is disassembled and examined, parts are replaced as necessary according to the manufacturer’s overhaul manual. To consider a part in Rebuilt condition it must be brought back to factory new specifications as per the manufacturer. Contrasting the two definitions highlights the disparity between Rebuilt and Overhauled. The differences between a Rebuilt and Overhauled Slick magneto also shows how the two work processes will affect the condition of the magneto you receive. The purpose of this post is to help show differences in the two services from a technical perspective.
Certain parts are required to be replaced in both the Overhaul and Rebuild processes, such as the points, capacitor, oil seal, rotor gear, and impulse spring, so these parts are not worth going in depth on. The parts in question are the coil, impulse coupling assembly, block and gear. During the Rebuild process all of these items are replaced 100% of the time with new parts from Champion. The Overhaul manual states, “Additional parts may require replacement depending on conditions as determined during magneto inspection.” For the coil the extent of inspection is “inspect for visible radial cracks” and testing “for primary and secondary circuit resistance and continuity” according to the Champion Manual L-1363. Testing the resistance and continuity is objective and easy to see when the coil is outside of tolerances but visually inspecting a part for cracks relies on a judgment call whether the part should be replaced. The same issue comes up with the impulse coupling assembly, block and gear inspections. In total for these two parts the Overhaul manual calls out for inspection of eight different aspects of the parts. These inspections are based on a technician visually checking for cracks, rust, pitting, damage, or loose parts “using acceptable procedures” per the manual. These inspections rely a large amount on technician visual inspection which can introduces subjectivity into the overhaul process of the magneto.
Further complicating the Overhaul process is that the manual states, “discard all parts removed for overhaul replacement and REPLACE WITH NEW CHAMPION AEROSPACE PARTS.” The Overhaul manual itself is requiring for the Slick Magneto to be replaced by all new parts. Now you may be asking yourself, why don’t more vendors just go ahead and replace all these parts with new items automatically? The answer is because some vendors use DER manuals which allows them to use serviceable parts instead of new. Champion advises the use of these techniques is problematic, “Salvaged magneto parts, reworked parts obtained from non-Champion Aerospace approved sources, or parts the service history of which is unknown or cannot be authenticated, may have been subjected to unacceptable stresses or temperatures, or have other hidden damage, not discernible through routine visual or usual nondestructive testing techniques.” Well maybe some vendors can get around this by using Champion parts from used Slick magnetos but Champion goes on to state, “service worn parts should never be used to troubleshoot or repair a magneto, nor should original parts be replaced by used service worn parts on magnetos being returned to service.” So we are left with the manufacturer stating only to use new replacement parts for all overhauls as deemed necessary by a technician. The best solution is to go with a Rebuilt magneto that is going new replacement parts used every time. Additionally, the rebuilt magneto is going to come with the same 1-year warranty as a new magneto because of the quality of the works and parts.
From a technical perspective, it is clear to see the contrasts in a Rebuilt and Overhauled Slick magneto. During the rebuild process, the magneto is consistently replaced with high quality parts no matter the situation. The Overhaul process allows for interpretation of what is acceptable wear on the parts and is often replaced with serviceable parts to complete the overhaul. The manufacturer’s manual is clear on that the parts should already be nearly rebuilt when they are serviced every time. The question to ask yourself next time you are looking for repair of your Slick magneto is do you want to leave it up to chance of what parts may go into your magneto or do you want the certainty that comes with have all new parts in your Rebuilt Slick magneto?