He explained as he worked, his voice low and even. "An engine like this is a custom instrument. Every part is tuned to every other part. My father set this whole engine around that bracket and that 12 degrees of advance. For forty years, it ran perfect because nobody touched what they didn't understand." He paused. "Then it started to drift."
He pointed to a small component near the distributor, a hand-shimmed contact that controlled when the spark fired.
"This is the piece my father shimmed by hand. Over forty years, the shim wore down just a hair, less than the width of a fingernail. On a factory car, that's nothing. On this car, it pushed the spark just far enough out of time that the engine couldn't catch." He looked up. "That's all it was. A worn shim. A tiny one. The car wasn't dying; it was going out of tune."
"Then why," Boyd snapped, "couldn't forty engineers find a worn shim?"
"Because you weren't looking for one," Theo said without anger. "You assumed factory. So every time the car wouldn't start, you reset it to factory numbers. And factory numbers fight my father's bracket. You weren't fixing the drift; you were stacking a second problem on top of it." He shook his head. "Two wrongs hiding each other. The car couldn't tell you what was broken because you kept changing the question."
Silence. Even Boyd had no answer for that.
"Modern fuel made it worse," Theo added quietly. "It burns a little different than the fuel my father tuned for. A healthy engine forgives that. One already a hair out of time does not. So it just stopped and gave you nothing to chase."
Walter Hayes let out a long breath. "Forty years I've worked on engines," he murmured, "and that is the cleanest diagnosis I have ever heard from anyone at any age."
Theo reached for the notebook one more time. He found the page where his father had recorded the exact shim thickness, the exact spark timing, the exact clearance, all in that careful pencil hand. The instructions to keep the engine alive had been sitting in a 19-year-old's back pocket the entire time forty experts called the problem impossible.
"He wrote down how to save it," Theo said softly, almost to himself. "He knew someday the shim would wear. He left the answer for whoever loved the car enough to look." He touched the page. "I guess that turned out to be me."