To answer your question if Lycoming installed roller tappets in your original Type Certificate (T/C’d) engine this would be considered a major alteration. It would also change the data plate by dash number in some cases.
Engine overhauls can be accomplished to a variety of standards. They can also be accomplished by many different facilities, ranging from engine manufacturers, large repair stations, or individual powerplant mechanics. The selection of an overhaul facility can and does, in most cases, determine the standards that are used during overhaul. The CFR requirement in Section 43.13(a) is that the person performing the overhaul shall use methods, techniques, and practices that are acceptable to the Administrator. In most cases, the standards that are outlined in the Engine Manufacturer Overhaul Manuals are standards acceptable to the Administrator.
These manuals clearly stipulate the work that must be accomplished during engine overhauls and outline limits and tolerances used during the inspections. The only definition regarding engine overhaul is the word "rebuilt.
Rebuilt
The term "rebuilt" is defined in CFR 43.2. The definition allows an owner or operator to use a new maintenance record without previous operating history for an aircraft engine rebuilt by the manufacturer or an agency approved by the manufacturer.
A rebuilt engine as defined in CFR 43.2, "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." All parts used must conform to the production drawing tolerances and limits for new parts or be of approved oversized dimensions for a new engine.
A major overhaul consists of the complete disassembly of an engine, inspected, repaired as necessary, reassembled, tested, and approved for return to service within the fits and limits specified by the manufacturer's overhaul data. This could be to new fits or limits or serviceable limits. The determination as to what fits and limits are used during an engine overhaul should be clearly understood by the engine owner at the time the engine is presented for overhaul. The owner should also be aware of any parts that are replaced, regardless of condition, as a result of a manufacturer's overhaul data, service bulletin, or an airworthiness directive.
The manufacture has the authorization under their T/C to make changes. If you decide to go to Lycoming check you engine data plate when you get the engine back. You may notice the data plate is updated to reflect the major change/alteration.
Second please understand there is a difference in repair and overhaul. What you want is a repaired engine from Lycoming back to new part standards.
