For fans of the franchise, the potential was undeniably potent -- have Johnny Knoxville, Bam Margera, Steve-O and their fellow Jackasses thrust themselves against a 3D canvas, then stand back and watch what sticks.

But while "Jackass 3D" can never be accused of stinting on its spring-loaded arsenal of projectile bodily fluids, neither does it approach that sublime, laugh-until-it-hurts level of gross-out nirvana that made the first two installments so darned irresistible.

Sure, there are moments of vintage inspiration -- and you've never truly seen a ripe outhouse explode if you haven't experienced it in slo-mo real 3D -- but this time around the bits miss a lot more than they hit.

Although those aging frat boys once again fearlessly lay their various body parts on the line, this time their hearts just don't seem to be in it.

Of course, even a half-assed "Jackass" still delivers sufficient bang for the premium buck, but it remains to be seen if the novelty hasn't worn off in the four years since "Jackass: Number 2," grossed $72.8 million, beating 2002's "Jackass: The Movie" by about $10 million.

The 3D effect should help the Paramount release ensure a solid opening weekend, although the final take will likely come up short of its predecessors.

Considering it's been a full decade since Knoxville and his crew first unleashed their unique brand of self-inflicted humiliation on MTV viewers, it's pretty remarkable that they're still coming up with novel ways of hurting themselves.

Following a brief introduction by their old MTV neighbors, "Beavis and Butt-Head" (who, incidentally, are being prepped for a more permanent return), the reassembled "Jackass" gang swiftly get back to doing what they did best -- including giving "gag reel" a whole new meaning.

Again guided by director Jeff Tremaine, the guys start off promisingly in sequences built around a game of beehive tetherball and attempting to pin a tail on a real donkey, but in between there are too many repetitive stunts that fizzle on take-off; stuff that would have been relegated to the closing credits in those previous installments.

Notably less successful are the hidden camera pranks, save for an amusing dwarf bar brawl led by Jason "Wee-Man" Acuna which is eventually broken up by wee cops.

And with the exception of some of those intensely visceral sequences, the 3D surprisingly doesn't bring all that much more to the table, suggesting that, when they're really on, those Jackasses really are a third dimension unto themselves,

For the rest of the time, it could have something to do with the fact that Johnny and his fellow daredevils are all rapidly approaching 40, but what was once so painfully funny too often comes across as merely painful in "Jackass 3D."

Opens: Friday, Oct. 15 (Paramount)
Production companies: MTV Films, Dickhouse Prods.
Cast: Johnny Knoxville, Bam Margera, Ryan Dunn, Steve-O
Director: Jeff Tremaine
Executive producers: Van Toffler, Derek Freda, Trip Taylor,
Producers: Jeff Tremaine, Spike Jonze, Johnny Knoxville
Director of photography: Dimitry Elyashkevich
Production designer: JxPx Blackmon
Editors: Seth Casriel, Matthew Probst, Matthew Kosinski
Rating: R, 94 minutes.