Los Angeles ? Building $200,000 motorcycle masterpieces is the hook to lure viewers to “American Chopper,” but it’s the father-son bickering that revs up the Discovery Channel’s reality show.

Each week, Paul Teutul Sr. and son Paul Jr. fire up torches and grinders to begin work on their latest creation, which they design either for show or private clients. Weeks of drafting a plan, painting, chrome-plating and assembly are crammed into one or two hourlong episodes.

But the real tension of the show, which airs at 9 p.m. Mondays, revolves around the verbal jousting and name-calling between anal-retentive Paul Sr., owner of Rock Tavern, N.Y.-based Orange County Choppers, and son “Paulie,” the shop’s creative whiz.

The tattooed Teutul — his bulging arms swinging from broad shoulders poking out of a tank top — doesn’t hesitate to spew rapid-fire insults such as “Knucklehead!” and or a sarcastic “Picasso!” when his son leaves a mess or misses a deadline.

The 54-year-old father with the gray, walrus mustache is an obsessive clean freak: “I just don’t get it. What’s so hard about keeping things organized?”

He’s also the boss: “And don’t forget who writes the checks around here.”

Paulie, 28, manages to take the ridicule in stride, explaining that creating a work of art takes vision, concentration and time. Pausing to consider leftover tools and debris would stunt the process.

“Be a professional,” Teutul barks.

It’s a wonder they don’t start throwing punches.

“I’ve gone off on him off-camera, too,” Teutul said in a telephone interview from his New York shop. “I don’t hold back. But I blow up for about 15 minutes, then it’s over. We get along a lot more than you think.”

Paul Teutul Jr., left, works on a new chopper under the watchful eye of Paul Sr., in this scene from Discovery's American

Clark Bunting, general manager of the Discovery Channel, said: “I would argue the center of the show is the father-son relationship, and they also happen to build bikes.”

Jay Leno, who’s got an Orange County Choppers bike in the works and is a big fan of “American Chopper,” said the Teutuls are really loving.

“In an hour of the show, they may get on each other’s case for three minutes. But then you have another 57 minutes left, so no more (confrontations) than anyone else,” the “Tonight” show host said.

The Leno bike design is still being worked out and a future episode will focus on it.

The Teutuls recently visited Leno at the hangar-sized garage in Burbank where the comic keeps his stable of more than 150 cars and motorcycles.

“That was really something,” Paulie said.

When the Teutuls showed up on the “Tonight” show recently, they rode in on a pair of custom beauties, one of them their famous Black Widow Bike. Other theme-bike creations include their Jet Bike, Comanche Helicopter Bike and Fireman Bike, built in memory of the firefighters killed in the Sept. 11, 2001, terrorist attack in New York City.

The Teutuls unveiled the Fireman Bike at a New Orleans motorcycle show, and the warm reception tugged the emotions of the gruff dad.

“You know what? I cried. I’m not afraid to admit it,” Teutul said.

Orange County Choppers has also built custom bikes for Wyclef Jean and other celebrities, including professional sports stars. But the Teutuls try to respect their clients’ privacy and don’t name-drop. Most of the theme bikes they build are used for display at motorcycle events.

Besides “the Pauls,” the show’s other characters include Teutul’s 24-year-old son Mikey, who’s described as “phone-answerer and trash taker-outer and so much more,” and Paulie’s childhood friend Vinnie DeMartino, a custom bike fabricator.