It's time we revisited the guys at Rigid Industries in Mesa, Arizona, to see their latest addition to the '08 Yamaha Rhino 700 they're providing for our giveaway. Their building the UTV with some cool goodies, then it's all to be given away to some lucky reader of our UTV specific mini-mag SideBySource. In each issue we're detailing a piece of the build up and you can go to Rigid's website (www.rigidindustries.com) to fill out an online entry form. The winner will be drawn at random at OFF-ROAD Magazine headquarters on September 10, 2009. Limit one entry per household address.
In our last issue we showed you the tuned performance package that Rigid installed. This kit included an intake with K&N filter, Dynatek Digital Ignition ECU, and DMC dual exhaust for a substantial bump in power output. Now it's time to optimize the transfer of that newfound power to the tires.
The Rhino uses a continuously variable transmission (CVT) to provide the gearing needed from slow speed takeoff to high speed cruising. A belt is driven by a set of sheave pulleys that have the ability to change their effective size (and thus overall gear ratio) by allowing the tapered pulley faces to change width, making the belt ride on a larger or smaller pulley circumference.
A clutch sheave on the primary (drive) pulley sandwiches the belt between the tapered pulley faces. At low speeds, the pulley halves are fully separated and the drive belt sits low on the faces emulating a small pulley diameter. This provides slow speed and high torque. As the rotational speed of the engine (and pulley) increases the pulley faces move closer, creating a larger effective pulley diameter for the belt. This make the Rhino go faster.
The transition of the pulley faces on the primary sheave is controlled via weights that move outward centrifugally as engine speed increases. This affects the rate at which the transmission drive ratio is increased. The weight size is chosen to match the power output of the engine.
When the engine power is modified, it's best to also change the gearing curve of the clutch assembly to get the best power transfer. This is done with custom machining of the clutch sheave assembly. Rigid recommends installing a modified sheave to increase top speed and gain a small increase in bottom end torque. They say this is the drivetrain upgrade that gives you the biggest bang for your buck. A modified unit can increase top speed by 7-8 mph, and a few hp more with other engine mods. Follow along with our installation this month as Matt Weiss upgrades the Rhino and shows you what it takes to install a sheave kit.
We just found out that GBC will be supplying the tires for this build and we'll include info about them in a future article. Next month, we'll show the addition of a full rollcage and soft top to the UTV so keep watching ... and don't forget to enter to win the Rigid Industries built Yamaha Rhino! SBS
 Here are the kit components...  Here are the kit components in the sheave upgrade kit that Rigid sells. It includes a machined sheave, new heavier weights, Teflon weight sleeves, and a stiffer spring to be placed behind the secondary (driven) pulley. The kit also includes a replacement set of clutch springs that can be installed as an option. This mod requires additional work to gain access to the wet clutch portion of the engine. The new springs increase engine stall speed (point of clutch engagement) from about 1300 rpm to about 2000 rpm to allow the engine to rev higher before the Rhino takes off. |  Notches are machined in the...  Notches are machined in the sheave housing as seen here. This allows the weights inside to travel out further and allow the pulley plates to closer tighter. This in turn causes the belt to ride higher (on a larger diameter) on the drive pulley and results in higher overall gearing and top speed. |  To start the installation,...  To start the installation, the driver seat and part of its mount were removed, as was the top engine cover. Next, the vent tube and outer pulley cover were removed, and the outer sheave support unbolted. With the drive pulleys exposed, the nut on the secondary pulley was removed with an impact driver. |
 The kit comes with a small...  The kit comes with a small "belt bolt" that's threaded into the secondary pulley to force the pulley plates apart and allow for easy removal of the drive belt. Note that some belts are directional, so it's a good idea to observe which way it fits. This is also a good time to check belt condition and consider a replacement if the belt is suspect. |  With the bolt removed from...  With the bolt removed from the primary pulley shaft, the sheave assembly can be removed and the secondary pulley assembly can be removed as well. |  With the secondary pulley...  With the secondary pulley on a bench, Matt used an impact driver to slightly break tension on the nut holding the spring on the back in place. With the nut loosened only, he used the spring compressor tool (foreground) to push on the spring and allow removal of the nut and the stock spring. |
 A new stiffer spring was installed...  A new stiffer spring was installed on the back of the pulley. The heavier spring keeps greater pressure on the secondary pulley plates to keep the belt from slipping which can cause the drivetrain to loose some power. |  The stock primary sliding...  The stock primary sliding sheave was disassembled by removing the screws and the sheetmetal stopper plate. An O-ring also sits under this cover and gets reused upon reassembly. |  Here you can see the cam plate...  Here you can see the cam plate that holds the round, moving weight inside the sliding sheave housing. |
 Grease is added to the weight...  Grease is added to the weight slots of the new sheave housing and the new weights with Teflon sleeves installed are dropped in place. Some UTV sheaves are run dry, but Yamaha recommends installation using their Yamalube grease. The original cam plate and stopper cover are reused. |  With both sheave assemblies...  With both sheave assemblies bolted back on their shafts and the belt reinstalled, the sheave support was bolted back on while ensuring the feet tabs fit correctly in the engine recesses. Final assembly of the outer cover, vent, seat assembly, and engine cover are in reverse order from disassembly. The whole process takes less than two hours and can be done by someone with reasonable mechanical skill. In addition to basic hand tools, it helps to have an impact driver and the spring compressor tool. | |