It doesn't matter that it cost YOU nothing. The rule for SSC engines states:

"2. Engine: Stock .15 cid engine available from normal retail outlets for a non-sale retail price of $60 or less, excluding taxes or shipping. Engine and carburetor must be used in stock condition, no modification allowed - if the manufacturer supplied muffler has a removable baffle it may be removed, but no modifications including adding or removing material from the muffler are allowed. Engine must be classified by the manufacturer for use in R/C flying model aircraft. Engine must be complete with stock carburetor and muffler cataloged for the engine by the engine manufacturer installed. Carburetor must be fully R/C functional as intended by the manufacturer and servo operated."

HTH,
D