SEARCHING FOR THE ULTIMATE 2009 CRF450 CLUTCH SYSTEM
THE CHEAP AND EASY FIX When it comes to clutches, there are always cheap and easy fixes. In the old two-stroke days, savvy riders carried spark plug washers and automatic transmission fluid (ATF) with them in case of clutch problems. Today, ATF is out of the question, but spark plug washers still hold some hope. Rather than use spark plug washers as shims, the MXA wrecking crew had 0.060-inch shims machined. We stuck these shims under the four stock UPGRADING THE MATERIALS With the reduced clamping pressure of the 2009 CRF450 clutch, going to four stiffer clutch springs was the bare bones fix. The inherent problem is that stiffer springs mean a sigificant increase in clutch pull. This is no problem for a rider who raced a Maico, CZ or BSA, but modern marketing techniques have favored show- room usability over racetrack performance. The easier the clutch is to pull on the showroom floor, the more likely the buyer is to plunk down his cash. The connun- drum of trying to build a works-style clutch (with the light weight of four springs and a reduction in their supporting mass) was that, without the ability to use the exotic titanium springs of the factory bikes, the spring pressure required to make the clutch bulletproof was too great for the showroom dog-and-pony show. By adding four stiffer aftermarket clutch springs to the stock clutch you get better hookup, but you haven’t addressed all the other issues of clutch performance— issues that Team Honda found solutions to. A local CRF450 racer can get closer to true-to-life works technology, by simply using all the CNC-machined parts that Hinson makes for Team Honda. The three basic parts are the clutch basket, pressure plate and inner hub (the only parts we couldn’t get that Team Honda uses were the titanium clutch springs). In pure function, the Hinson replica of the stock 2009 Honda clutch layout was smooth in release and stiffer in pull. Those two characteristics were to be expected. Since the CNC-machined parts are stiffer and stronger, they flex less, reduce plate stiction and resist notching of the tangs. This allows the plates to move in and out with less friction. And the stiffer clutch springs increase the pack pressure (while making the clutch harder to pull in).
CRF450 clutch springs to preload them. By putting more load on the spring, we upped the pressure of their initial bite against the plates. It is a time-tested trick that almost always helps a slipping clutch. Unfortunately, Honda’s clutch springs seem to be on the edge, and shimming them not only made them stiffer initially, but it turned them into light switches. Instead of firming up the clutch pack so that test riders could meter the feel, the clutch was either on or off. We rejected shimming as a solution. As a corollary, the 0.060-inch shims made the clutch hard to pull (perhaps we could have used 0.040-inch shims, but we were try- ing to get as much clamping pressure as possible). The next fix was much better. We simply replaced the stock clutch spring with specially wound Hinson clutch springs. They were stiffer, and the coils were wound to provide the most progressive modulation possible. By exchanging the four stock springs for four stiffer springs, the clamping pressure is increased (and so is the pull at the lever).