When are compression release brakes adjusted?

Compression release brakes, also known as jake brakes, are typically adjusted when the engine components involved are cold. The reason for this is that as the engine and components heat up during operation, they expand. This expansion can change the clearances and tolerances between various mechanical components, making it difficult to achieve the precise settings needed for optimal brake performance.

When adjustments are made while the engine is cold, the components are at their minimum dimensions. This ensures that the clearances are set to the tightest possible specifications, allowing for proper engagement and disengagement of the compression release mechanism when the engine is operating. If adjustments were made while the engine is hot or under oil pressure, it could lead to incorrect settings that might impair the performance of the braking system, potentially causing excessive noise or mechanical issues.

Thus, choosing to adjust compression release brakes when the engine is cold allows for the best possible performance and reliability of the braking system.