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The 400ex is capable of making 40+ H.P. when big bores and stroker cranks are used. Standard clutch kits will not last long with that kind of power. We designed a clutch kit to handle the abuse of a higher H.P. engine, we took our std heavy duty kit and added a stiffer set of springs. The clutch pull is stiff but not so extreme that hand fatigue is an issue. We also recommend this clutch kit for dune riders. Sand dunes are very hard on clutches and can cause the same wear that a high H.P. engine can cause.

We have been an ATV dyno tuning facility since 1999. During this time we have logged over 15,000 dyno runs on ATV’s. 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 can’t put all the power to the ground.

We have come up with a clutch kit combination that has worked well over the years and finally are able to have the kits made to our specifications.

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 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 which reduces surface material and contact area causing premature clutch slippage. We have done tests where we had quads that had a slipping clutch. We took the “dimpled” steels out and replaced them with smooth steels and the clutch stopped slipping. Dimples are concave in shape which reduces surface material contributing to premature clutch slippage.

3. Springs are equally important, we use a spring that is 20%-25% stiffer than stock. This helps with pressure on the friction and steel plates limiting clutch slippage.

Our clutch kits are not the cheapest kits available, but we feel we have created a truly custom high performance kit at a reasonable price.

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