A Hoax in Time — Keith Laumer

When Chester W. Chester IV inherits a hundred acres of rolling green lawn surrounding a fifty-room Neo-Victorian eyesore crammed with his Great-Grandfather's Invention, his friend Case Mulvihill, ex-carny hand, was curious. Visiting the house, they discover that the giant computer, filling not only the former wine cellars but a system of caverns underlying a large part of the county as well, is still in working order, busily coding and storing information in accordance with the last instructions of Chester's long-dead ancestor.
When Chester types a question on the computer's keyboard, it at once recognizes him as the descendant of the inventor -- and permits him entrance to the secret inner chamber which is the actual nerve-center of the gigantic thinking machine.
Case at once envisions a quick fortune to be made from the great computer, which can seemingly answer any question put to it -- but Chester reminds him of the outstanding inheritance tax due to the Internal Revenue Bureau before Chester can legally take possession: several million credits -- due and payable now!
Experimenting further with the computer while sampling Great-grandpop's wine stocks, Case and Chester discover that the machine has the capability of presenting remarkably lifelike scenes on the Tri-D wall of the control room. A chance remark of Chester's suggests a scheme to Case: he and Chester will propose to the Internal Revenue Bureau that they be permitted to operate the machine on a cash-admission basis to raise the needed tax money. But rather than offering a mere information service, they will convince the IRB officials that they have on hand a real, live, TIME MACHINE!

This is the original version of Keith Laumer's epic time travel novel, The Great Time Machine Hoax, as it was originally serialized in the pages of Fantastic Magazine in the summer of 1963. This version features considerable differences from the novel version.