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Mountain Performance, Inc.
12379 South 265 West, Unit B
Draper, Utah 84020

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YXZ Turbo and Clutches

Posted by on 11/2/2015 to YXZ 1000R

MPI YXZ Turbo and Clutches.
Clutch durability and the MPI Turbo. After we have read some of the posts of people asking clutch questions and a few actually having clutch problems (non-turbo units), we have some data and recommendations. We would like to publish our recommendations and observations.

We have had no clutch problems or failures during our development and durability testing. We currently have 2 units, one of which is a full production unit. Turbo’ed from day 1 and used for durability testing. Please note that during durability testing we monitor many readings including Drive Ratio (simple ratio of Engine RPM vs Transmission / Transfer Case output RPM). This measurement will show any Clutch Slippage (even under 1%). After reviewing over 1000 miles of data, this is what we observed:

We observed up to 9% slippage, but for never more than 500mSec (1/2 of a second). After 500mSec, the ratio would become flat (actual value dependent on gear 1-5). Boost was run at 180HP target (actual boost number automatically adjusts based on altitude and pressure); since we average 5000ft here typical production kit boost would be 5psi plus 2.5psi for altitude. Our test unit runs at 8psi plus 2.5psi for altitude. Upon inspection of the clutch discs we saw nothing that looked HOT (which is typically evident of a slipping clutch). Measurement of the 8 larger friction plates ranged from 0.119 to 0.121in and the smaller 3 being slightly thicker 0.121 to 0.122in. The plates were all 0.080in. The newer unit may have been 0.001in larger, but one of the new large friction plates was actually 0.118in (.001 smaller than the smallest one from the durability unit).

Our assessment is: ANY ONE CAN BURN-UP ANY CLUTCH. Hard core riding showed NO DAMAGE or signs of slippage. However, we are not suggesting that the few consumers that have had clutch problems were at fault; perhaps driving the vehicle under water is a bit harder on the unit than we were. For our customers desiring a more heavy duty clutch, we recommend the Barnett Tool & Engineering (aka Barnett Clutches) Yamaha YXZ1000r SXS Clutch Spring Conversion Kit. p/n 511-90-10010 for under $150 list. They also offer Yamaha Clutch Plate Kit p/n 306-90-10092. Contact you Yamaha Dealer or Barnett Clutches.

A word on Rekluse: The package from Yamaha is quite soft. We believe that the setup should be stiffened. We have requested recommendations from Rekluse and they will be updating us. A couple of our testing partner dealers have been very helpful on Rekluse. Typically Rekluse clutches are used to solve slippage problems, this setup seems soft as supplied. We expect Rekluse will have a solution (probably wedges or springs).

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