Issue 32 : Sept/Oct 2003
Many diesel engines aboard sailboats have compression-release or decompression levers on top of the engine for each cylinder. As their name implies, these levers hold open the engine valves and prevent normal compression within the cylinders. Although seldom used, they can become very important when you find that your batteries don’t have enough juice to turn over the engine for starting. It is then that those decompression levers are worth their weight in gold.
Since diesel engines have very high compression, they require lots of amperage from the battery to turn them over. If the batteries are too low for the job, or if the batteries and engine are very cold (cold batteries have less cranking capacity, and a cold engine is harder to rotate) you’re left stranded — that is, unless your engine has decompression levers.
By opening these levers and eliminating engine compression, the engine can usually be turned over by the starter, even when the battery is very low. Then, once the flywheel is rotating at a decent speed, and while still holding in the starter button, a compression-release lever on one of the cylinders can be returned to normal. Usually this cylinder will start the engine running, and the levers on the other cylinder(s) can then be thrown into the compression position.
The trouble is, to do this requires more than one person: one in the cockpit operating the ignition key or starter button and another next to the engine to throw the compression-release levers at the proper time.
Since I frequently singlehand my boat, I have installed an emergency starter button inside the engine compartment next to the engine. This back-up starter button can be operated with one hand while the other hand is on the decompression levers. This push-button-type momentary switch is wired across (in parallel with) the engine control panel’s starter button (if there is one) or across the starter terminals of the key-switch.
Thank you to Sailrite Enterprises, Inc., for providing free access to back issues of Good Old Boat through intellectual property rights. Sailrite.com
