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Old 25-05-2009, 12:59   #1
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Turn Diesel Over by Hand?

I have Yanmar 2GM20F, 2 cylinder, and can turn it over by hand pulling on the Vbelt. I thought diesels had so much compression that it would take a "hulk" to turn over by hand. It is a small engine, though. I'll feel better about it if someone just tells me it's normal. Thanks!
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Old 25-05-2009, 13:25   #2
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No!!!

With the compression ratio of a diesel, you should not be able to turn the engine over easily, if at all. Diesels that are designed to be hand cranked have compression releases that allow you to turn them over, however. Some Yanmars came with compression releases, maybe yours is one and they are activated. Look for a lever for each cylinder somewhere around the valve cover of the engine.

You didn't mention whether the engine runs.

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Old 25-05-2009, 13:45   #3
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Compression Release

This engine does have compression release levers, but they are not engaged. I adjusted the valve lash and had to line up the timing marks on the flywheel by turning the crank pulley by hand. The engine was running before, but took a while to start up. Compression might be low. It's not starting now, but I have to retry bleeding the fuel system.
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Old 25-05-2009, 13:46   #4
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Are you sure the crank is actually rotating? You shouldn't be able to turn it over with the v-belt. My guess is that it is slipping and you are just turning the alt and water pump.

If the crank pulley is turning you have something major wrong, sometimes there is woodruf key in the nose of the crank that keeps the pulley from spinning which might be stripped?

I see your latest post. Ya, crack the injector lines till you get fuel coming out and make sure the starting battery is charged up.
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Old 25-05-2009, 13:56   #5
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Crank

The crank is rotating. I pulled the head off earlier to inspect it and the pulley definitely makes the pistons go up and down. The valves and seats had some pitting in them, so maybe there's some compression loss there. My guess is that the carbon buildup increased compression and helped it run. Now that I cleaned it, there may not be enough compression. Maybe it's time for a head/valve job.
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Old 25-05-2009, 14:07   #6
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Sounds like it is time, on 2 cylinder you should be able to turn it over with a wrench on the crank bolt but it should take some effort and be jerky. One last thing maybe to check is that the head gasket got reinstalled correctly???

Send the head off to a rebuilder and have them inspect it for you, they will be able to tell quickly if the valves are seating properly. If the engine is already out of your boat it wouldn't take much to get the short block rebuilt, new bearings, hone the cylinders and install new rings. Prolly have time to do that while the head is getting rebuilt. If it is that bad you will really enjoy your new rebuilt engine
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