Anthony,
Strictly in terms of preventative maintenance, a pilot who is not working under the supervision of a certificated mechanic, or who does not hold a mechanic certificate, is restricted to the list of items called out in 14 CFR Part 43, Appendix A, part (c).
This list is not carte blanche authorization to perform the maintenance items listed, however. Several stipulations apply. The pilot is under obligation to perform the maintenance to the same standards any certificated mechanic would perform it, and to do it in strict compliance with a current (and present and available) set of maintenance instructions from the manufacturer. The pilot must use the proper tools, taking care to adhere rigidly to the specifics in the maintenance instructions. No complex disassembly may be involved.
Completion performance standards as given in the manufacturers data must be followed, as well as any industry standards such as those spelled out in AC 43.13 1B/2A. Maintenance log entires must be made, and filled out properly, as failure to do so invalidates the airworthiness certificate for the aircraft. All regulations applicable to a certificated mechanic also apply to a non-certificated mechanic performing the duties of mechanic, and this includes the pilot doing preventative maintenance.
Any maintenance not listed in Appendix A may not be undertaken by the pilot as preventative maintenance, without specific authorization from the Administrator, or unless under the supervision of an authorized mechanic.
If you don't have access to Appendix A, PM me and I'll post you the relevant section.
