Some Surprises Come in Little Packages
It was a gorgeous early fall day. Dabney and the Doctor were taking a drive in a newly-acquired addition to the large Dufus collection, a 1967 Pontiac Firebird convertible with an overhead camshaft, 6-cylinder engine. "You know, Doc, these engines are very rare. Runs pretty well doesn't it?" asked Dabney.
"Sure does. It's a shame the OHC 6 didn't catch on. It would have been a good engine even today," replied the Doctor. "I'm enjoying the drive, but didn't you call me to help out on an engine diagnosis?'
"I did, Doc, and it's got me stumped. I'm not going to tell you what it is until we get back to the garage...it's kind of a surprise," said Dabney.
"Yeah, but I don't like surprises, especially when it comes to cars." Doc said. The Doctor prepared himself for the worst, knowing Dabney had a way of acquiring less-than-perfect vehicles and then encountering difficulties making them run.
"But this one is different. You'll see," said Dabney.
The pair arrived back at the garage and pulled the Pontiac into its assigned space.
"It's over here, Doc," said Dabney as he pointed to the corner work bench. Sitting on the bench was something the Doctor didn't expect, sure enough. Rising from an array of its constituent parts was a 1974 Vespa Ciao moped.
"A moped!" exclaimed the Doctor. "I used to own one of these when I lived for a spell in Boston and boy, was it handy. You could go anywhere and park in doorways and alleys with no effort. Does it have baskets?"
"It sure does," replied Dabney. "We can use this to go on short errands and even to run between buildings here at the collection (Dabney's car collection occupies several garage buildings on the property). That is, if I can figure out why the motor won't generate enough electricity to spark."
The moped's frame was assembled and its motor was mounted in its proper place. The crankshaft was sticking out of the side of the frame, with its centrifugal clutch assembly removed. Dabney had rigged up a 1/2 inch drill so that its chuck could grab the crankshaft and spin it.
"This should be obvious, Doc," said Dabney. "The motor has a generator inside that creates about 8 volts. The current runs through the tail light assembly and then to the ignition coil and up to the headlight and horn circuits. The problem is, when I spin the motor with the drill all I get is about one volt."
"Very interesting," said the Doctor. "This moped's odometer only shows 400 miles, so there's no reason to think the generator isn't working. Let's go through a test to see if any wiring is incorrect."
The two double-checked all electrical connections and then chucked the drill to the motor's crankshaft. Standing on the left side of the moped, both agreed that the forward rotation of the rear wheel necessitated that the motor be spun in a counterclockwise direction. They did so and noticed the faint glow of the filament in the rear light, verifying the circuit was correct, but there was no spark and the voltmeter showed barely over one volt. They spent the next hour checking wires and connections, making sure there were no obvious errors or omissions.
Frustrated, the Doctor said "Let's assemble the wheel's drive pulley and the chain assembly to the pedals. Then we'll put on the centrifugal clutch and spin the motor with the pedals, just in case we're not turning the motor fast enough."
They took their time and assembled the chain and sprockets, along with the pedals. They then put on the rear axle drive pulley and its belt, along with the mating pulley/centrifugal clutch assembly. They adjusted everything for correct tension. Dabney was on the right side of the bike wiping off fingerprints as the Doctor went around to the other side to start the troubleshooting process again.
Dabney looked up from his wiping and saw a weird look on the Doctor's face. The next thing he heard was a howling laugh. The Doctor almost fell down, he was laughing so hard. "Dumb, Dumb, Dumb. Boy are we Dumb," the Doctor managed to spit out between laughs.
"What? Did you find a loose wire or something," asked Dabney.
"No, no. Much worse than that," replied the Doctor. "Come over here and take a look."
"Watch this," said Doc as he cranked the pedals. They both observed the action of the rear wheel as the pedals were turned. The rear wheel rotated forward, of course, but its pulley didn't. Inside the axle assembly was a planetary gear set that acts as a reduction system to give the little motor more mechanical advantage. As the wheel turned forward, the pulley turned in the opposite direction. That, of course, caused the centrifugal clutch - and the motor's crankshaft - to turn clockwise, exactly opposite what they thought.
"We were cranking the engine backwards," said Doc now chuckling to himself. "Brilliant!" said Dabney sarcastically.
And of course, as they cranked the pedals and engaged the motor. The voltmeter showed well over 8 volts and the sparkplug fired just fine. The lights glowed brightly.
"Let's put some gas in her and try her out," said the Doctor.
As Dabney returned to where the Doc was standing, he said "Runs great, Doc. You know, I was just thinking. We don't need to tell anybody about this do we?" Dabney said with a wink.
"Tell anybody about what?...Let's go get some coffee." replied the Doctor, grinning.