CYRIL JORDAN is demonstrating for me, over the phone, how the intro lick for 1976's "Shake Some Action" had its roots in Marvin Gaye's "Can I Get a Witness?" He plays both chord sequences back to back on his guitar.

"Can you hear that?" he asks. "I threw a minor chord in the middle, so I kind of changed that famous boogie part."

It's beyond thrilling to hear Jordan dissect one of the great rock 'n' roll songs of all time, by way of one of the other great rock 'n' roll songs of all time. Make no mistake: Flamin' Groovies' "Shake Some Action" is a masterpiece—from those opening bars, in which watery electric guitars swim through reverb to chop out time, to the five-note descending riff that's peppered throughout the song, or from the romantic, forlorn verses, to the three-part rising vocal harmony plucked from "Twist and Shout" that leads into the song's ecstatic chorus. There are scarcely another four and a half minutes in popular music that can best it.

Naturally, Jordan, who was raised on classic 45s during the heyday of AM radio, thinks it's too long. He prefers an equally great demo version recorded in 1973 for Capitol Records, three years before the Shake Some Action LP was released on Sire Records. "It was just me, Chris [Wilson], and George [Alexander]; we went down there, and we got Terry Rae from the Hollywood Stars on drums. And I overdubbed three acoustics played in octaves to give it a galloping strum. It gave it a lot of power. That version's my favorite."

Jordan hopes that the alternate take might turn up somewhere on the next Flamin' Groovies album, which they're slated to record later this year. They've already released a new track called "End of the World," a time-warp tune that bears the trademark Groovies marriage of Byrds chime and garage-rock rawness. Meanwhile, the classic Jordan/Wilson/Alexander lineup—which recorded 1972's "Slow Death," the Shake Some Action album, and two further albums for Sire in the late '70s—have reunited, along with drummer Victor Penalosa, for a string of dates that includes their first-ever show in Portland. Other than a couple of appearances at the Sky River Rock Festival outside of Seattle in 1968 and 1969, Flamin' Groovies haven't really played the Pacific Northwest at all.

"I'm excited about coming up to the Northwest," Jordan says. "You know, Paul Revere and the Raiders, the Sonics, and the Wailers were three of my favorite bands when I was a kid. We'd always heard about that Northwest scene. But by the time the San Francisco scene started in the late '60s there wasn't much coming out of that area at that time, so we never really went there. Now, it's like a whole new music scene. You guys are going to outdo Austin."

The current reunion stemmed from an impromptu meeting between Jordan and Wilson, who hadn't communicated since they parted ways following 1979's Jumpin' in the Night. Oddly enough, it was at a Groovies' reunion show.

"It had been 33 years," Jordan says. "It wasn't anything that anybody set up, it just kind of happened. We would have seen each other a lot sooner... but [Wilson] had moved to England, so that distance kept us apart for all those decades. I was doing the Teenage Head version of the Groovies with [original lead singer] Roy [Loney] and the A-Bones, and we went to London and Chris came to the gig. I saw him backstage and as soon as we saw each other it was tears and hugs."

This Groovies run will focus on the Shake Some Action era and the songwriting chemistry of Jordan and Wilson, which hasn't diminished over the years. "Chris and I are just writing great stuff and the ideas keep coming. When we broke up in 1980 we were far from being done as artists, and this has given us a chance to continue what we were doing back then. We're just carrying on. It's funny, because there are 33 years of time and space between us, but when we got back together in 2013 it seemed like it was the day after we broke up in 1980. It was like time and space didn't affect us at all. It was very strange. Really, really groovy, actually."

It's clear that this Flamin' Groovies chapter is about much more than capitalizing on the past. The band, in all incarnations, has never been fully in step with prevailing musical fashions. Rather, the Groovies have consistently played the kind of music they like best. As with Big Star, who've also been lumped into the "power-pop" category with the Groovies, history has been justly kind to their legacy, but the proof has always been right there in the dusk-lit, interweaving guitars of "Shake Some Action."

"Rock 'n' roll music is not contemporary," Jordan says. "It never has been. It crosses over to each generation."