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Old 09-01-2013, 06:34   #1
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Join Date: Mar 2012
Location: NYC Bronx and Poughkeepsie
Boat: Pearson 30 1971
Posts: 11
Decompress for what again?


Many of you have helped on my prior quest to re-start my Yanmar after adding fuel (refueling 20gm20f), leading to success after bleeding the system and my great gratitude. During that time I learned that many people run the starter to crank a few turns with the decompression levers on, in order to bring oil to the cylinders in a cold engine before high pressure operation. I tried to do that but instead of cranking all I got a was a whirring sound as if only the starter motor was working. Is that what it' supposed to sound like with the decom levers on? When I then tried to start with them off it wouldn't start, alhought the batteries were low and the engine had not been warmed due to a drop light in engine burned out. Any insight into this decompression (do it, don't do it, what's the sound, etc?). Thanks again in advance for any assistance on this.

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Old 09-01-2013, 06:49   #2
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Join Date: Oct 2007
Location: virginia
Boat: islandpacket
Posts: 1,881
Yes. That sound is normal. With the levers up you have no compression so the pistons et all turn real easy. You stated that the battery was low. That is a problem. That yanmar has no glow plugs so you have to have a fast strong crank to get the compression to make the heat to to fire the diesel. When you try to start give it 3/4 power and prepair to reduce it as soon as it starts. It wont start with a slow crank because of a lack of compression heat and fuel.
That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.
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