A crankshaft spacer is a component that fits between the flywheel and the crankshaft in an engine. It helps to maintain proper clearance between these parts and can also be used to adjust the position of the flywheel. The spacer is typically made from a durable material such as steel or aluminum and is designed to withstand the stresses of engine operation. It plays an important role in ensuring smooth rotation of the crankshaft and can help prevent damage to other engine components.