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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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  #1  
Old 02-22-2011
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Last edited by chrisncate; 09-22-2011 at 01:33 AM.
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Old 02-23-2011
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About the engine, I notice there you did not specify 2GM20F, the F for fresh water-cooling. If there is no heat exchanger and the engine is more than ten years old, I think you should do a tear down at least to removing the head and see about getting the corrosion out of the head, and if you do that, you may as well do a valve job. How many hours on the engine and was periodic maintenance done? If the oil was not changed as recommended, I would also pull the pan and check the bearings. If good maintenance and fresh water-cooled, I would do a compression check, with and without a little oil squirted into the cylinder. Do not use much or it will artificially raise the compression reading, maybe a half-teaspoon in amount is about right. Some people swear by a leak down type of compression test where a controlled amount if air is put into the cylinder. It gives a more exact reading of leakage as the speed of the starter spinning the engine does not influence the reading of the rate of leakage past valves and rings and the amount of motor oil put into the cylinder to test rings. A leak down compression test is how they test a gasoline airplane engine and the result is percentage readings of engine wear. At 80% in any cylinder, they do a tear down on an airplane engine. My own thinking is that you are looking at relative readings between cylinders when looking for leaking valves or piston rings and going with what the manual for the 2GM20 specifies is good enough. Anyway, if you have a properly maintained fresh water-cooled engine with good compression, just pressure wash or steam clean it and paint it. This assumes an engine with something less than 5000 hours on it. If you do pull the head for any reason, check the cylinder walls for wear with a micrometer. The machinist will have set of these and it is a very quick test which measures cylinder wear. On a well maintained diesel, I would not expect wear as the diesel is a light oil itself and lubricates the cylinder walls
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Old 02-23-2011
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for that engine info. Thanks.

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Old 02-23-2011
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Another thought, if you are pulling the engine and you have noticed some oil in the bilge, now is the time to put new front and rear main seals (crankshaft seals) in and check other gaskets. As a engine gets old, the rubber gets hard and lets oil leak out of the engine.

Also, if a diesel ever runs out of oil, the bearings get wiped out very quickly. It could be argued that if there is no audible warning for oil pressure or automatic shutdown, that the pan should pulled even if good compression and fresh water cooled to check the bearings.
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Old 02-23-2011
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If the engine is not fresh water cooled, no heat exchanger, then take a look here: Corrosion in Salt Water Marine Engines - Part 1
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Old 02-23-2011
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Here's a link that might help with the shaft, stuffing box, and cutlass. There is much to offer at this link, from rebedding deck hardware to wiring termination.
Compass Marine "How To" Articles Photo Gallery by Compass Marine at pbase.com

Absolutely nothing wrong with bronze for chainplates.
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Old 02-26-2011
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What Next on the Engine

Quote:
Originally Posted by chrisncate View Post
Heat exchanger/fresh water cooling
Do you know if periodic maintenance was done? As long as oil changes were done about every 100 hours with oil filter changes at least every other oil change, the engine is probably OK. This is a low dust environment so am not too concerned about the oil filter. I am sure some will think this is pushing the envelope some on periodic maintenance, but I feel that this oil and filter change interval is all right because this is a fresh water cooled engine where the temperature on the thermostat is set higher at about 180 degrees Fahrenheit. This allows the water from combustion to be driven off since the oil temperature will rise above the boiling point of water after running about half an hour with propeller loading (not running to just charge the battery). The water of combustion is bad because the sulfur in diesel burns to form sulfur dioxide and a little sulfur trioxide which form acid when combined with water. Modern diesel contains little sulfur, but this engine is old enough to have used the high sulfur diesel. Modern oils and low sulfur diesel allow longer intervals between changes. However, many boat engines are now allowed to heat up enough to get the water of combustion out of the oil by just maneuvering around the dock so the 100 hour interval is still a good one even on fresh water cooled engines.

If the periodic maintenance was not done, then consider pulling the engine and removing the oil pan to check the bearings. This is a visual inspection. If there is a gray metallic look with no copper or steel backing showing on the bearing, this is good. Even if the bearings look good, they are usually replaced, as bearings are cheap. If the bearings are worn through to the steel backing, then probably the crankshaft will need grinding. Some crankshafts journals (which ride on the bearing material) are case hardened and are very tough. I remember a two-cycle two cylinder Detroit diesel that must have run out of oil as only the steel was left in the bearing shell, but the crankshaft only needed a little polishing. Bearings are a curved piece of metal with a steel backing then copper and finally babbitt bearing material. Dirt in the oil gets imbedded to the babbitt and causes wear of the bearing and journal that rides on the bearing. Acid from sulfur also corrodes the bearings. This lower end work, the pan is on the lower end of the engine, has to be done under practically clean room conditions and I would not trust the average mechanic to do it. Have an automotive machinist do it, as they know about cleanliness and how important it is. The clearance on a bearing is between one and two thousandths of an inch. I piece of paper is about twice that thickness. If you have dirt particles larger than this, you drive the dirt into the babbitt when you tighten the bearing cap down with a torque wrench. Steam clean the engine before taking the pan off.

A compression check is the last thing to consider. If the engine starts easily and runs on both cylinders immediately with no white smoke and strong smell of diesel, then compression is probably all right. If not all cylinders are firing then raw diesel goes out the exhaust and you can smell it. This problem can also be caused by glow plugs that are defective and this is usually the cause. A compression check is simple and I think it should be done anyway as a valve could be leaking a little and the engine will still seem to start all right, but trouble is ahead. One last thing to do is check the injectors. If these have gone several hundred hours, do this check as a defective injector can ruin a cylinder wall from excess heat. An ordinary shop may not have the equipment to check injectors. A place that specializes in overhaul of injection pumps can do this. However, usually a mechanic just replaces the injectors as there is a little more money for them and they do not have to worry about testing. Injection pumps are normally very long lived as long as contaminated fuel has not gotten into them. By the way, I hope you have a very good system for filtration and water removal on your engine. If not, get this added. You do not want the engine shutting down when you need it from contaminated fuel, and also an overhaul of an injection pump is expensive

Last edited by LakeSuperiorGeezer; 02-26-2011 at 09:26 AM.
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Old 02-26-2011
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Hard Starting 2GM20

Quote:
Originally Posted by chrisncate View Post
The p/o ... he told me he did regular maintenance... she starts hard after not being run for a spell and belches lots of white smoke with diesel smell noticeable. We have no glow plug btw..
I did some research on line and found the manual for your engine at Yanmar engine manual download . Download the GM-HM manual which is 60 MB in size.

Without glow plugs, I am not surprised that the engine is hard starting. I found several suggestions on starting. Crack the throttle open one half to three quarters and have your hand there ready to cut the engine back as soon as it catches. Also, if the intake valves are not adjusted according to the manual, see page 58 and 59, it also makes for hard starting. The raw water coolant pump has its own belt so you could loosen it and start the engine; however, there would be no cooling water to the exhaust so that could overheat. The raw water pump impeller will be ruined in ten seconds or so if it is run with no water. The friction heats it up and melts the rubber. The impeller in the raw water pump needs replacement every few years. Also replace the seal for this pump maybe every ten years (not sure about when, making a guess by how long I expect a seal to last) as it gets hard usage with debris in the seawater.

There might be nothing wrong with the engine. Do a compression check. If someone there is a little handy with tools, you could do the check yourself. Take a look at the manual and see if it is anything you all want to try.

Last edited by LakeSuperiorGeezer; 02-26-2011 at 02:33 PM.
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Old 02-26-2011
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New cables from battery to switch and from there to starter can make a huge difference in starting time if they are old as they probably are. New ground cable with cleaned connections at engine ground point as well.
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Old 02-26-2011
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Cables

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Originally Posted by mitiempo View Post
New cables from battery to switch and from there to starter can make a huge difference in starting time if they are old as they probably are. New ground cable with cleaned connections at engine ground point as well.
Cables could be part of the problem. The air being compressed in the cylinders heats the air. This heated air is all there is to start a diesel engine. That’s why a cold engine and cold air makes for hard starting. The faster the spin the more heat in the air in the cylinder. Buy a cheap voltmeter from Radio Shack, the kind of meter with a needle on it. Go from the battery post, it's the battery connection about half an inch round located inside of the clamp for the battery cable, to the other end of the battery cable where it connects to the starter. There will be a copper threaded bolt sticking out there that the battery cable is bolted under. Put the other probe from the meter on the copper bolt and have someone crank the engine for a few seconds. A half volt could be expected, but of course less is better. If the meter moves past zero the wrong direction, reverse the probes from battery post to starter bolt. Do this also on the other side of the battery only run from the battery post with one probe and any metal on the engine for the other probe. The battery cable on this side connects directly to the engine so any metal on the engine will work. If the voltage is too high, clean the connector and battery post with about a 240 grit sandpaper, then put some grease on the post and clamp. This prevents corrosion and with the clamp tightened, the grease is squeezed out where the electrical connection needs to be made. The grease makes for a long and trouble free connection. If you want to be fancy, use silicone dialectic grease from the auto parts store. If the cable is corroded where it connects to the terminal that is clamped to the battery post, replace it. If you replace, consider going to a heavier cable with more copper in it. Battery cables come in different gauges.

Last edited by LakeSuperiorGeezer; 02-27-2011 at 08:20 AM.
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