Bullet-Proof Barnett Clutch Basket
1. The stock basket, on the left, is cast; including the studs the pressure plate screws onto (A), in contrast to the Scorpion basket, machined from 7075 billet aluminum and hard anodized, and features replaceable steel studs (A). The Barnett basket retains friction and steel plates that offer substantially more cross-sectional surface area than the stockers. The distinctive red material on those friction plates (B), Barnett refers to as “RQ,” which might stand for “race quality,” but more importantly are thermally stable blend of fibers and resins, with excellent porosity, compressibility, and durability characteristics. In other words, great material for preventing failures in high-stress, high-heat applications where shift quality is also a major concern. You’ll also notice that the steel plates are very smooth. A good thing for reasons that might surprise you but we’ll get to that in a minute. In the meantime, notice the difference between the stock pressure plate and the Scorpion version? Beyond the nifty gold color, the Scorpion uses coil springs (C) rather than a diaphragm spring, thus offering a certain tunability that the stock arrangement cannot.
2. The stock setup has a relatively light, fixed-rate diaphragm spring where as the Scorpion kit comes with three sets of six coil springs (42 pound gold, 58 pound gold, 82 pound green, and 100 pound red) that can be used as matched sets or in mixed combinations to get grip and pull in balance and just right for any application. That said, one of the biggest rookie mistakes in a clutch set up is to immediately go with the strongest spring available, which is usually not needed and invariably makes clutch pull at the lever too stout for normal humans. If you really need the stiffest springs provided, you’ll most likely also need to convert from cable to hydraulic actuation. Speaking of hydraulics, it’s during a shift that the greatest demand is placed on a clutch. As the plates slam home, incredible heat (the real enemy) is generated in the pack that doesn’t transfer to the entire clutch all that rapidly. Funny to realize that a “wet” clutch is actually oil-cooled, but essentially that’s the way it works. That’s why pre-soaking the friction plates in primary fluid is crucial. Oil retained in the friction material is squeezed out, taking unwanted surface heat with it. If the plates cannot absorb and discharge oil fast enough, heat builds and glazing (plate imbedding) occurs like brake fade!
3. Given that cooling is important, thinner plates will dissipate heat better than thick ones (notice the difference in plate thickness between the two setups-stock left, Barnett right). Aside from a material that’s almost impervious to this because it can inhale and exhale oil quickly, the best ally in heat control is smooth steel plates. The smoother the surface the more surface to squeegee fluid and pass the heat on and out. In fact the quickest way to destroy a modern wet clutch is to sand or bead blast the steel plates! The second quickest is using springs that will affect this efficient transfer of heat, by making the strength of your hand the factor that alters the plates ability to breathe oil.
4. Even if everything else is cool, the thing that will make a high performance clutch is a basket that won’t break. Three differences you can easily spot between the two baskets is the beefy sealed bearing in the Barnett basket (A), how the hard anodized 7075 metal used makes that cast aluminum stocker look pretty frail, and that the Scorpion basket uses grade-8 fasteners (B), instead of rivets to hold the ring gear. Put another way, the Scorpion basket, though far less likely to need it, is rebuildable.
5. The Scorpion basket weighs in at 8-1/2 pounds, a half pound lighter than the 9-lb factory unit. In itself no big news, but if you’re one who follows the finer points of rotating mass and the flywheel effect, there’s another element of the Barnett Scorpion kit that we need to touch on.
6. You see even though the outside rim of the “flywheel” in the form of the Scorpion clutch basket is fractionally lighter than stock, this super stout hub assembly is anything but light. At 8 1/4 pounds, it’s over two pounds heavier than the Harley hub. However, this heft is concentrated in the center of the rotating assembly. So, inertia is minimized. Since the clutch is the heaviest (and most unbalanced) rotating mass in the powertrain, other than the crankshaft itself, it helps to keep the weight centralized to the mainshaft.
7. Installation is as simple as following the six pages of instructions supplied with the kit. Unless you have a hydraulic press handy, you’re not going to be able to do it at home, since the hub assembly must be pressed into the basket. Pulling the stocker requires no puller, which makes it pretty straightforward. Just be sure to tie the automatic tensioner (arrow) down before you pull the old clutch, compensator, and primary chain off. It’ll be easier to put things back together without fighting that. Seems a shame to cover up a thing of beauty like this, but once the new Barnett Scorpion clutch assembly is installed, you’ll only need fresh primary fluid and a new gasket to button up the primary and go for a ride.
8. All done and you should have a clutch that’s up to anything you can throw at, plus a pull at the lever that’s as light and easy or easier than stock.The pull at this lever is only 9-10 pounds as measured by this hyper-accurate fish scale. Add in the fact that this clutch is holding well over 110 lb-ft of torque, will not slip or grab, and is only working at a little over half it’s capacity, this lever easily controls a whale of a clutch.
9. Speaking of pulling the clutch lever, Barnett has offered the classic black vinyl casing clutch and throttle cables forever. However, with the popularity of people going for that blacked out look, the company has now incorporated black chrome elbows and hardware to create its line of Stealth Series cables.
10. Awhile back we stopped by the Barnett facility in Ventura, California to get one of our project bikes set up with some Stealth Series Cables. While Mike Taylor, president of Barnett, and Joe Snell, head of the Cable Department were taking measurements for our project bike we snuck off to see what we could find.
11. Barnett makes just about everything in-house, so as we wandered around we encountered one of the cable assembly stations. Since they make everything themselves Barnett offers both stock replacement and custom length cables for H-D and aftermarket applications. In 2006 Barnett introduced its High Efficiency (HE) inner wire for ’87 and later H-D cable clutches. The HE cables feature nylon coated inner wire, a High Density Polyethylene (HDPE) inner liner, and are pre-lubed, which aids in smooth cable action and reduced lever effort.
12. Here’s a collection of Barnett’s wide variety of cable fittings in both black chrome as well as mirror chrome just waiting to be assembled. Aside from the black casing Barnett also offers three other casing styles: Platinum Series, Stainless Braided with Clear coat, and Stainless Braid with carbon clear coat.
13. By the time one of the employees found us wandering the assembly floor, our custom length clutch and throttle cables were finished.
14. The Stealth Series clutch cable fits perfectly with the black and chrome look on our project Softail. Even though we routed the clutch cable with a little bit of a tight bend up top, the lever was still easy to pull in.
15. While the black chrome does hold up pretty well, just like regular chrome, you’ll want to be carefull when putting a wrench to the black chrome hardware because it can get nicked and or galled. But we were very pleased with the look, and the action in the throttle was very smooth and it snapped back crisply.
Motorcycles are kinda the last bastion of manual transmissions. The obvious difference between automatic and manual transmissions is the clutch. Wait, scratch that, automatics use clutches of a sort too, so it’s really more about the fact that the majority of motorcycles use a clutch operated by hand, instead of a computer or series of hydraulic valves. The hand clutch (as we know it) is a unique contraption, mostly because of it’s operation and it’s operator, you. Humans are a trifle more erratic in their clutching techniques than any automated system could ever be, which plays into the details of design in good motorcycle clutches. Inconsistent engagement and release and the nature of friction in a “wet” clutch design (especially in big V-twins making prodigious torque at relatively low engine speeds) can lead to a whole host of issues in the pursuit of the perfect Harley-Davidson clutch.
We are very aware of the imperfections and the issues that can arise such as clutch slip, or crappy engagement, and “hanging” on quick shifts. But the real killer is when something comes apart just when you need it most. The thing is, the bulk of these issues we bring on ourselves. Aside from sheer abuse, there are two things common to most clutch woes. First is our propensity to hop up our engines. Seems clear that when you make a lot more power you push the capabilities of the clutch right to the edge, and often beyond. Second, most of us don’t have a clue what those capabilities are in the first place. Lucky for us, there’s a company out there that understands all of this, Barnett Tool and Engineering. And they have been making effective solutions to the problems we’ve just discussed since the late fifties. Even though Barnett is well-known for its control cables, it’s the high-performance clutch components that are a point of pride with the company. Not without reason, since they have really outdone themselves with the Scorpion basket and clutch kit for 2007 and later (six-speed) Big Twins.
