FITS:YAMAHA RAPTOR 660R ALL YEARS:
The Raptor 660 when modified is capable of very high H.P. We designed a clutch kit to match the needs of higher H.P. engines. This kit is the same as our STD heavy duty kit with the addition of even a stiffer spring than what comes in our heavy duty kit. The stiffer spring helps with the additional power the 660 can make when big bores and stroker cranks are added. This kit would also be recommended for heavily ported stock stroke engines making more than average H.P.
We have been an ATV dyno tuning facility since 1999. During this time we have logged over 15,000 dyno runs on ATVs. From the beginning, the most common thing we saw from quad to quad was that the clutch would slip under heavy load. This is instantly noticed when a quad is being dynoed, because the rear of the bike is strapped down to the drums on the dyno so that the tires do not slip and you can register horsepower.
When the tires are unable to spin freely like they do in the dirt, the entire load of the motor is held solely by the clutch. If it is weak, poor quality or badly worn it will break loose and the motor will rev up and the quad cant put all the power to the ground.
1. We use cork style friction plates with a metallic base. We have tried all the different friction compounds available and these were the most durable. Kevlar type frictions had good wear properties but glazed over very quickly and started slipping compared to cork.
2. The steel plates are the most important component in the strength and durability of a good quality clutch kit. The steel plates are full plates which give maximum contact area with the friction plates. Our steels are smooth on both sides, most clutch kits like TUSK have dimpled or textured steel plates. THESE STEEL PLATES DO NOT LAST AS LONG AND DO NOT HOLD AS MUCH HORSEPOWER AS SMOOTH PLATES. "Dimples" are concave in shape reducing surface material causing less contact area and premature clutch slippage. We have done tests where we had quads that had a slipping clutch (the clutch that was in it was new). We took the dimpled steels out and replaced them with smooth steels and the clutch stopped slipping.
3. Springs are equally important, we use a spring that is 10%-15% stiffer than stock. This helps with pressure on the friction and steel plates limiting clutch slippage.
4. For the Raptor 660 we have replaced one of the (2) larger I.D. frictions with a full size friction plate. This allows the larger I.D. friction plate and wave washer spring to be removed & replaced with a full size friction plate. This will give you more contact area and capable of handling higher H.P. The purpose of the wave washer spring is to cushion the clutch engagement, removing it is a common practice and will not affect the performance of your clutch. We still include the (2) larger I.D. friction plates so you have the option to install the clutch which way you choose This is the only clutch kit on the market that offers this option.