Barnett’s Scorpion Clutch

Tom Johnson
Tom Johnson

The sting’s the thing…

Did I really need a Scorpion for my S&S Panhead, which might make 80 or 85 horsepower, tops? Maybe not, but I have ridden a fair number of miles with Scorpions on other motorcycles, and I flat love them. Engagement is smooth, and they grip like a boa constrictor dipped in Krazy Glue. I’ve never known a Scorpion to slip, even behind an S&S 124 with the lightest of three sets of springs that Barnett provides (two, in some cases). On top of that, neutral has always been there when it’s supposed to be, and shifting’s a breeze. I already had Barnett disks in the four-speed clutch I put together from leftovers, but still wanted a Scorpion.  

Barnett makes them for all ’36-up Big Twins and most Sportsters, with two models to choose from. The basic Scorpion has a stout aluminum pressure plate with six coil springs, but a lock-up pressure plate is also available. Besides the springs, the lock-up uses weights on pivoting levers to increase clamping force on the disks. As the clutch spins faster, centrifugal force swings the weights out, forcing the other end of the levers in against the pressure plate. Grip can be increased by using heavier springs, mixing the light and heavy ones, or adding weight to the lock-up. The real beauty of the lock-up is that it allows the use of lighter springs for a comfortable lever and more controllable leaves at the drag strip- or when a light turns green and you want to smoke the guy next to you without wasting time spinning the tire or climbing down from a monster wheelie. Remember Zarathustra’s Revenge,  the Shovelhead that Indian Larry started on for S&S? I once asked Paul why he and Keino  used a lock-up clutch when finishing it up. He responded with another question- “Is there anything better?” I reckon not.

But as cool as lock-ups are, and I would have killed for one during my nitrous days, the standard Scorpion should be more than enough for pretty much any normally aspirated, gas-burning street engine out there. At the center is a beefy steel hub that spins on a double-roller sealed bearing. O.E. four-speed clutches work well enough with careful set-up, especially with a RamJett retainer (R.I.P., Roger.) or Tamer, but those stubby little rollers in the rattley tin bearing cage can’t touch the Scorpion bearing. Once pressed into the stock basket, the Scorpion bearing/hub assembly supports it more solidly than the stock rig ever could, and freeplay, the bane of four-speed clutches, gets 86’d.  

Moving out from the hub, the clutch pack has several improvements over stock, starting with a steel jutter spring that does its best, if not always with perfect success, to keep things quiet. Next comes a stack of seven each steel and friction disks that more than double the surface area of the stock clutch. Most Horse readers will understand that adding surface area is the best way to increase clutch bite, next to a lock-up, without resorting to rock-hard springs. And if you look at Photo 13, you’ll see that Barnett has obsoleted the hell out of the traditional single-row friction pads we’re used to seeing. Their segmented pattern provides smoother engagement and crisper separation by eliminating problems related to heat expansion, every clutch’s mortal enemy, as well as the possibility of slippery fluid building up between the steel and friction disks in wet clutches. Proof positive is that the segmented frictions usually require less spring pressure than conventional disks. 

All of Barnett’s friction disks, except the old-style BSA and Triumph cork disks, can be run wet or dry, but a word on soaking before we break out the hammers and prybars and get to work. The folks at Barnett recommend against soaking dry clutches. They say that it’s ok, but unnecessary, for wet clutches. If you feel the need to soak regardless, use whatever fluid you’ll be putting in the primary- “Type F” ATF is ok too. What does soaking modern friction disks actually do? Nuttin’, honey. The only justification that isn’t based on religion/superstition/what your Uncle Jimmy Sue the high-stepping transvestite did with his Horex bobber and he never had a problem is that, in models with wet primaries, whether by accident or design, the plates may engage a little smoother. Even then, soaking is needless ju-ju. All you really need is to brush the plates with lube, or just do whatever you were going to do all along before you read this. Bottom line is that you will really have to work at it to fercockt Barnett plates, except maybe for the old cork ones. 

As mentioned before, a thick aluminum pressure plate that carries the six springs holds the Scorpion together. The standard pressure plate is anodized a bright, golden orange color, and a thing of beauty on my mostly black and aluminum rigid. The aluminum lock-up head is polished. Sneer if you will, but I’ve always  thought that polished aluminum was a beautiful thing, in moderation. It’s not my place to speak for Barnett, but offhand I’d guess that using the lock-up on an open primary would be an “at your own risk” proposition, sort of like walking a Bengal tiger leased on a puppy chain. Then again, it won’t fit behind a standard primary cover.

I set the Scorpion up three ways- with an open 3” belt drive, an open chain, and a chain tucked away inside tin primary covers from Paughco. Some of you won’t get this, but the P-motor is quiet mechanically, and I wanted to eliminate as much drive noise as I could to enjoy that. The only time the Scorpion made noticeable racket with the belt was when I disengaged it for shifting, or held it in while waiting for a light to change instead of shifting into neutral. It was quieter than the stock clutch, but still pretty noisy when disengaged- not unusual with open-belt four-speed clutches. The open chain was fairly noisy, and a constant source of fear and fascination for riders I happened to pull up alongside of or pass. For some reason, the friction disks seemed to clatter more against the dogs in the chain basket than they did in the belt set-up. 

I finally found what I was looking for when I installed the Paughco primary covers over the chain- they swallowed most of the drive noise right up. I admit that I missed not being able to bug the straights with a lube-slinging, flesh-hungry primary chain whirl-gnashing its way around pointy steel sprockets but, all things considered, that seemed an acceptable trade-off. Operation of the Scorpion was perfect with each of the three drive set-ups. It was a little noisier than I expected with the open drives, but still quieter than stock. I realize that noise isn’t an issue for many who read this but, as I said, I enjoy being able to hear my P-motor whirring happily away in its own little world. 

Installing the Scorpion is simple and straightforward. The one hang-up for do-it-yourselfers is that a hydraulic press, although not exactly mandatory, would make the job easier. For starters, Barnett recommends pressing the bearing into the bearing adapter. Getting around that by heating the adapter in an oven and chilling the bearing in the freezer was easy enough, but Barnett also recommends a press for installing the Scorpion hub assembly in the clutch basket. I tried the oven/freezer trick again, but the hub dug its heels in and skidded to a dead stop 1/2” short of home. I thought about smacking the hell out of it with my favorite persuader, but decided to use a long 7/16” bolt and nut to pull the adapter on down, instead. The only problem was that the back of the basket was open, so there was nothing to anchor the bolt head. Poking through my scrap pile, I found an old alternator rotor that fit the back of the basket and spanned the opening perfectly. With the bolt and a few hardened washers anchored against the rotor, tightening the nut against washers outside the hub forced it home in about two minutes, with pressure exerted against the steel hub only, not the bearing. 

The same techniques you use for adjusting your present clutch should work for the Scorpion. Typically, that means lightly bottoming the pushrod against the throwout bearing, backing it off 1/2 to 3/4 of a turn, and locking it down. Then, adjust the lever or pedal according to your manual or personal preference. I like lots of freeplay because it makes the clutch engage quicker.  

Installation of Barnett’s Scorpion Clutch

Estimate Cost : 600 USD

Installation of Barnett’s Scorpion Clutch on a motorcycle

  1. Start by removing the old clutch. Remember that the hub nut has left-hand threads. 

  2. I chilled the bearing and heated the adapter before putting them together. 

  3. A hefty snap ring secures the bearing. Throwing over my cheap-o snap-ring pliers for Jim’s pro version was a good move.

  4. I installed the bearing/hub-adapter assembly in the basket with a long bolt and an alternator rotor. 

  5. The instructions call for blue-Loctiting the support-ring screws and tightening them to 5-7 in-lbs. I settled on, “That feels about right.” 

  6.  

    You’ll need a 5-speed clutch-hub nut to install the Scorpion. I used the late’84 – ’89 style.

  7. Take care not to dislodge the key while installing the hub on the shaft. 

  8.  

    Install the hub nut with red Loctite and torque it to your usual specs- 50-60 ft-lbs. should do. Barnett’s hub locker will help.

  9. The flat spacer goes in first.  

  10. It’s followed by the dished jutter, with the concave side (white dot) facing out.

  11. Next goes “Friction Disk B,” which has a different lining than the others.

  12. A steel disk goes next.

  13. The segmented friction disks stand out from the crowd, don’t they?

  14. Torque the pressure plate screws to 14 inch-lbs., then remove all freeplay from the pushrod, back the adjuster out 1/2 to 3/4 of a turn, and lock ‘er down.

  15. Behold- “The Mangler!” Step back, son, it bites.

Tools
  • Torque Wrench
  • Loctite Blue
  • Loctite Red
  • A 5-speed clutch-hub nut to install the Scorpion. I used the late ’84 – ’89 style.
Materials
  • Barnett’s Scorpion Clutch

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