One of the great mysteries in sports is how Leon Spinks has managed to make a go of it in boxing, where the code word is "time."

Spinks' pratfalls on the battlefields of hours and minutes are legendary. He has missed appointments by days.

There's a new Spinks now, milder and more grown up.But he and clocks still don't get along.

Watch him now at the speed bag, here in the final days of training before his nationally televised title fight Friday night against world heavyweight champion Larry Holmes.

Spinks' soft-spoken trainer, Del Williams, shadows his fighter like a mother hen with an overgrown, irresponsible chick. A circle of 100 fans hovers around. Spinks is pounding the little bag, working on rhythm. He's grinning his immense grin. He's happy.

"Time!" shouts Williams signaling the end of the exercise and the start of a one-minute breather. Spinks pounds away, oblivious. He's punching and grinning and dancing and moving. He won't stop until he gets enough.

And, of course, a minute later when Williams calls his fighter back for more, Spinks is played out.

Well, some things never change.But there really is a new Spinks in pursuit of the heavyweight title he once held, if only briefly.

Spinks has a new crew of overseers. They took him to the mountains to train for this, his 15th professional fight and the most important one since he lost the title almost three years ago to the man he had wrested it from, Muhammad Ali.

They took him to a northern Michigan ski resort halfway between East and West Nowhere. The Spinks people were the only ones there for six weeks. They trained and worked and worked and trained and only on Monday did they return to dangerous Detroit, Spinks' home.

The challenger was a mere 21 minutes late for his first press conference and only an hour late for his first workout. The latter vexed him.

"I was upset," he said, explaining why he shouted at his manager, Jerry Sawyer, who greeted him wit, "You're late."

"I knew I'd be reading in the press, 'Leon Spinks is late again.'"

Well, what was the problem?

"I went to get my car and I had to go through a bunch of formalities. It was being repaired."

Repaired? The press closed in, sensing the presence of another Spinks transportational saga. He tends to wreck cars.

"Yeah, and let me tell you this time somebody hit me," the challenger chuckled. "And I wasn't even in the car," he added, inexplicably.

Contrary to public perception, Spinks is not a fool. If anything, in his unpredictable visits with the public and the press since returning from the woods, he has been downright witty. He is in excellent shape and evidently ready for the fight of his life, Holmes being in great shape, too.

Some pearls from the challenger:

Spinks on Detroit, when asked what kind of town it is: "I could go into politics and everything else, but basically it's a town."

Well said. Has it become your hometown, Leon?

"No matter how long I live here, I will always think of St. Louis as my home. But I don't want to go back there, ever."

Spinks on has defeat of Ali: "That don't make me King Kong. Anybody could beat Ali. Anybody on God's earth with two feet can be beaten."

Spinks on life (on going wild as champion, getting in trouble with the law, losing the title, the long road back, etc., etc.): "I've learned a lot as a human being, period. Now, when I sit in my corner, I go back in my library (his mind) and think about all my life. It's all there -- the history, section a, b, d, whatever. Then I pat myself on the behind and say, 'Leon, keep going.'"

On Holmes, whose great physical condition some regard as a compliment to Spinks: "If I was fighting somebody like me, I'd be in great shape, too."

On the prospects of this fight going the full 15 rounds: "I ain't going nowhere. So if he ain't going nowhere, I guess we'll both be there."

Don King, who is promoting this fight at Joe Louis Arena as a tribute to the late Louis, claims Spinks' team is helping to make a new man of its fighter.

"He doesn't have a team that will castigate and calumnate (sic) him and toss him to the sharks," said the bombastic King.

"Yeah," said Spinks, "and I got rid of the leeches."

Spinks the boxer is not likely to be much different from the Spinks who defeated Ali on Feb. 15, 1978.He is 27 years old (still young, he keeps saying) and completely trim. His trademark is an undisciplined style coupled with an animalistic survival sense. This child of the harshest ghetto upbringing came through it with a big heart. He's a brawler, a swarmer, and that's what to expect of him, even though he'll be giving away pounds and reach to Holmes.

Spinks on the reach disadvantage and how to surmount it: "How do you escape anyone that swings at you? You move your head."

Spinks weighs a solid 195 and, if anything worries his handlers, it's that he may have overtrained.

He earned this title shot after an up-and-down postchampionship career. He was kayoed in the first round of his first fight after the title defeat, Gerrie Coetzee doing the damage in Monte Carlo. That was two years ago almost to the day and marked the nadir of Spinks' ring career.

He came back, knocking out Alfredo Evangelista in five rounds, fighting to a draw with Eddie (Animal) Lopez and dispatching Kevin Isaac. October, he knocked out the No. 1 World Boxing Council contender, Bernardo Mercado, and gained his second shot at the title.

The feeling among veteran fight followers is that Spinks can beat Holmes, if only, in the code phrase that echoes around the gyms here, "because you never know what Leon gonna do."

But it's a longshot. Said one fight expert, "Holmes is a world-class boxer. Leon just isn't."

The challenger maintains that his tactics will be to cling to Holmes "like a T-shirt," in an effort to avoid the champion's long-armed left jab.

"I got to get inside," said Spinks. "If the good Lord lets me do that without getting hurt too bad, I can get him."

And if he should win, retaking the title that he mishandled so colossally three years ago, what then?

"I made a lot of mistakes the first time. I've been thinking about what I would do. But instead of talking about it, I'm going to do it. And if I'm doing something else that I shouldn't do, then I'm going to be doing it behind closed doors, away from you."

Spinks still has nothing but gums between his left and right upper incisors, leaving a gap four teeth wide. The ladies at the cheakout in the coffee shop at the Pontchartrain Hotel, where he is staying, think that looks ridiculous.

"He has teeth," one said. "He just won't wear them."

"Maybe it's his trademark," said another, "Like Don King's hair."

It takes a big man to ask a former heavyweight champion why he won't put his teeth in. But there are those who think this great, gap-toothed grin is Spinks' biggest personal asset.

When he was done with the speed bag, Spinks eased over to the ring at Joe Louis Arena, a flock of followers hard on his heels. Sweat poured from his head and neck and chin as he wrestled through a shoulder bag on the floor, tossing cassette tapes out as though he were a pooch digging after a bone.

He found Kool and the Gang and inserted it into a gray tape player.

"Cele-e-brate good times. C'mon!"

He grabbed his jump rope and began a fluid, graceful dance. The crowd gathered and the calls came.

"Spinks," they shouted. "Spinks!"

The grin started around the eyes, worked its way across the cheeks, halfway to the ears. It reached the huge, half-toothed mouth, emerging, exploding, consuming his whole face.

It's a wonderful, timeless smile. "He's not plastic," said the man in the yellow shirt next to me, who was grinning, too. "There's only one Leon. He is what he is."