2:20 PM PT -- Paul doesn't share his ex biz partner's memory of the deal. He tells us, "Unfortunately, Mr. Derbyshire's interpretation of said events is without merit."

Paul Teutul Sr. -- co-founder of Orange County Choppers and star of "American Chopper" -- cost his business partner millions and ruined a future TV project ... according to a new suit.

Thomas Derbyshire claims he and Teutul formed a company specifically to produce a show for A&E called "Orange County Choppers: American Made." Derbyshire says he agreed to fund the project entirely -- up to $3 mil -- but he would own 51% and Teutul would own 49%.

According to the docs ... Teutul agreed to the terms, but a few months after Derbyshire wrote a $1.8 million check to start production, Teutul tried to change ownership to a 50/50 split. Derbyshire says he refused to sign off on the new terms, and production fell apart.

Derbyshire says Teutul was screwing him even before that, though, by striking a side deal with a dog food company, paying his son, Michael, out of the budget without consent and demanding "endless reshoots of himself."

Derbyshire now wants to dissolve the company, and have Teutul cut him a big check for all the money he lost producing a show that never aired.