Quote:
Originally Posted by jwasbury
The compression release is nothing more than a lever on the valve cover that forces one of the valves to remain open. You press the starter button, wait a few moments for the starter (doubles duty as the generator) to spin up the massive flywheel, flip down the compression release and she chug, chug chugs to life.
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The compression releases on my 1930 John Deere are two petcocks, one in each cylinder, that open into the cylinder about 3 inches from the top of the head. As the piston moves forward (it's a horizontal engine), the cylinder contents go out the petcocks until the piston covers the hole, the remaining contents are compressed or go out the exhaust valves if it's on the exhaust stroke. As you can imagine, once the engine fires, flames shoot out the petcocks several feet. John Deere decided that it was a good idea to have them point down at a 45 degree angle, so it's fairly common to set your field on fire when starting your tractor.