mm...yes there is. It's called Canadian Aviation Regulations
Which CAR states that maintenance must be performed on an aircraft?
I have cited a CAR which states that flight in an aircraft not maintained in accordance with specified standards, is not legal. I presently own an aircraft which has not been maintained in accordance with the standards, and I intend to fly it. Before I fly it, I will assure that all maintenance is compliant, but I'm not in any rush whatever. In the mean time, there is no non compliance in this regard.
Another example was a plane I saw where the owner's AME had kind of unofficially SMOH'ed the engine with a newly rebuilt crankshaft but because it wasn't done at a Aircraft engine facility (but a Truck facility!! lol) they just wrote that it had "new bearings installed"
Wrong, wrong and wrong. This AME is an idiot plain and simple!
What's wrong with that? If the "SMOH" was "kind of" and "unofficial", it was not "official", and not any kind of overhaul (time since overhaul not zero'd in the log). That is clear. If the record of maintenance said that new bearings were installed, and that was done in accordance with the specified data for the task, that was proper maintenance, and I presume properly recorded in the logs. The description of the work accomplished would provide the required understanding to any reader, for the life of the logbook, as to what was done, and the relationship of the work accomplished to an "overhaul" (not at all close). That relationship [to overhaul] can be clearly understood by anyone reviewing the logs in the future - their purpose. More simply, the log will not show a time since major overhaul as zero, and the engine just keeps accumulating time in service, with work accomplished and recorded along the way - completely normal. If the AME who accomplished this work did it in accordance with the correct instructions, and recorded it with detail and correctly, they did exactly what they should be doing, and certainly are not an idiot! I split my engine, had the crank ground under, and was about to have the AMO reassemble it as a "repair", until I realized that in combination with the upper end work I had also done, the AME could sign out a zero overhaul, if I spent an additional $1000 on some mandatory replacement parts. I did that. But, it was my choice. The "maintenance" of replacing parts in the engine was not required, I chose it, and in doing so, accomplished maintenance with a greater perceived value in the future. It did not really affect the way the engine ran.
If a future person who has, or could come to have, technical responsibility for an aircraft feels that there is missing information about the work accomplished, they will not release the plane to service until questions are answered - which might mean an additional inspection/teardown/ or document review. The system works if the records are accurate.