Valve Spring Retainer
A metal washer that sits on top of a valve spring, locked in place by keepers to secure the valve.
A valve spring retainer is a hardened metal washer that sits on top of the valve spring in an engine's cylinder head. Its primary function is to secure the valve spring and transfer its tension to the valve stem, keeping the valve closed against its seat until pushed open by the camshaft.
The retainer features a tapered center hole. Two small, semi-circular tapered locks (called valve keepers or cotters) fit inside this hole and clamp into a groove near the tip of the valve stem. The upward tension of the valve spring pulls the retainer up over the keepers, locking the entire assembly firmly in place.
Because they are exposed to rapid reciprocating forces at high engine RPMs, retainers must be lightweight and extremely strong. In high-performance or racing applications, standard steel retainers are often replaced with titanium or chromoly versions. If a retainer cracks or if a keeper slips out, the valve will drop into the cylinder, leading to catastrophic collision with the piston and engine failure.