A primer on the Sportster Spring Plate, AKA “Grenade Plate”.
A grenade plate sounds like something you’d find on an armored military vehicle. Unfortunately this has become the nickname for the Spring Plate in the clutch pack of many Harley-Davidson Motorcycles, including the Sportster and Evolution Engine powered big twins.
It’s picked up this unfortunate nickname due to it’s propensity for failure. It is known to regularly come apart and damage the surrounding clutch plates, clutch basket, and other components inside the primary.
What is the “Grenade Plate” and why does it fail?
The Sportster Spring Plate is found in the center of your clutch pack. As you can see in the image above, it is made up of 2 steel pieces sandwiching flat springs, and the whole thing is held together by brass rivets. This design provides a gentler, more forgiving feel to the factory clutch. However, the brass rivets often become fatigued and start to fail. When the rivets in the spring plate fail, the pieces are typically flung outwards against the clutch basket, damaging the surrounding clutch plates and cutting grooves in the basket itself. At this point, the whole clutch assembly as well as the basket itself must often be replaced.
How Do I Know if my Grenade Plate is Failing?
A slipping clutch, or a clutch that refuses to stay adjusted is a common symptom. You may also find aluminum, steel, or brass shavings in your primary oil. Inspect the clutch pack right away if any of the signs are present. A special clutch spring compression tool will be needed to disassemble the clutch pack.
How Do I Get Rid of this Sportster Spring Plate?
The Screaming Eagle replacement clutch, and many aftermarket clutches like this Energy One Clutch solve the problem. They do so by eliminating the spring plate and substituting two additional steel plates and one additional friction plate in it’s place. The replacement clutches won’t feel as light or as smooth as OEM. However, many riders prefer the feel of an aftermarket clutch.
You should at least consider the spring plate delete on any evo powered motorcycle. However, it should be pretty much mandatory for a performance oriented evo build.