F510 & F525 – AUTOMATIC COMPRESSION RELEASE
To lower engine compression for easier starting.
Theory of Operation:
The automatic compression release uses fly-weights and a tab to slightly lift the exhaust valve which releases engine compression. The compression release assembly is attached to the camshaft and cannot be serviced separately.
With the engine cranking, the fly-weights (A) are held inward by spring (C) tension. A tab (G) that is connected to one of the fly-weights moves up (away from camshaft) as the fly-weights pivot inward. In this position the tab is held above the camshaft heel (E).
During the compression stroke, with the engine cranking, the tab contacts the exhaust valve lifter (F) and holds it off the camshaft heel a small amount until just before TDC. This opens the exhaust valve slightly just after the intake valve closes to release some compression for easier starting. A stop pin (B) locks the fly-weight and tab in the upper position to prevent the tab from being pushed down by the exhaust valve lifter.
When the engine starts and the engine speed is about 600-900 rpm, centrifugal force moves fly-weight (I) outward unlocking the fly-weight and tab from the stop pin. Now the fly-weights (H and I) overcome the force of the spring and pivot outward until they contact stop pin (B). The release tab moves down (toward camshaft) below the camshaft heel until it no longer holds up the exhaust valve lifter and the engine runs with full compression.