Private equity firms circling the $74 billion loan book at Silicon Valley Bank may find that the Federal Deposit Insurance Corp. is unwilling to sell the assets — or at least not at bargain-basement prices. 

More than half of the bank’s lending program — $40.5 billion as of the fourth quarter — consists of lines of credit to firms backed by capital-call commitments from their investors, according to bank documents. Those loans typically have terms of one to two years, with low interest and default rates, meaning they’re not likely to deliver high-octane returns.