Yanmar 3gmd Max RPM - Page 2 - SailNet Community
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post #11 of 28 Old 10-18-2010 Thread Starter
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Prop is 14 inch 3 blade. If it is over propped can the existing prop be trimmed down?
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post #12 of 28 Old 10-18-2010
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They can easily reduce the pitch. I think you're stuck with diameter though.

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Living aboard in Victoria Harbour
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post #13 of 28 Old 10-18-2010
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Originally Posted by casey1999 View Post
Prop is 14 inch 3 blade. If it is over propped can the existing prop be trimmed down?
As mitiempo mentioned, you'd usually start by having the pitch reduced on the existing prop. If it turns out the diameter is too large, you might need to downsize (but 14" doesn't sound too large).

Michigan Wheel is a good resource for learning about prop sizing and pitch.

First things first, though. Test the RPMs in neutral. Hopefully you'll crank right up to 3200 +.


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post #14 of 28 Old 10-18-2010
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1- Confirm the engine will run to 3600 RPM in neutral (I believe this is the "one hour" load RPM for the 3GM)

2- Confirm with a photo tach that the tachometer is reading correctly

3- Make sure your fuel filters are clean and the exhaust elbow is not restricted.

4-Confirm bottom and prop are clean

If all the above check out then the prop is most likely over-pitched. This can usually be fixed by a pitch adjustment but with a high of 2400 on an engine that should be able to hit about 3400 it may require more than just pitch adjustment. A very rough guideline is 200-300 RPM for every inch of pitch adjustment. It is unlikely you can take 3" of pitch on a prop that has possibly been re-pitched at some point in its life span.

You should be able to attain at least max continuous, which is 3400 on the 3GM, or max one hour rating, about 3600, at WOT with a clean bottom and prop.

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Last edited by Maine Sail; 10-18-2010 at 05:09 PM.
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post #15 of 28 Old 10-22-2010
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I will check max rpm in netral and let you know. It will be a few days till I get back to the boat. Could white / grey smoke be unburned fuel from bad fuel injectors? would bad fuel injectors lead to below spec horse power output?
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White or gray smoke is engine oil, either past worn piston rings or valve seals. Unburned diesel fuel is black. If the engine doesn't use any oil you may be seeing steam in the exhaust, another symptom of being over-propped.

A bad injector would have much more noticeable symptoms besides not being able to reach max rpm.
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post #16 of 28 Old 10-22-2010 Thread Starter
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White or gray smoke is engine oil, either past worn piston rings or valve seals. Unburned diesel fuel is black. If the engine doesn't use any oil you may be seeing steam in the exhaust, another symptom of being over-propped.

A bad injector would have much more noticeable symptoms besides not being able to reach max rpm.
I think you could be right on the white smoke being steam. I am going through the engine (it is 30 years old and problably not gotten the best maintinance). Engine anodes with total corroded away, the thermostat was very corroded and blocked. There may be water passages that are blocked. I will attempt to clean the water passages (engine is direct sea water cooled). I will also try a vinegar flush to see if that helps. I am also going to try Stanadyne Performance diesel additive to see if that helps to clean the injectors and lubricate plus add some cetane.
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post #17 of 28 Old 11-01-2010 Thread Starter
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Ran the engine in neutral at the dock and got up to about 2700 rpm. Engine seems to be running good. The max rpm in neutral seems about the same as rpm in forward gear. I am going by the yanmar gage tach (have not had a chance to verify with another tack). Exhaust color seems normal at all rpm. For now seems ok. Engine will produce power I need at 2700 rpm- will verify with a tach. Did notice no fuel comes out of the fuel injector fuel return line to the tank. Lift pump is new as are all filters. Return fuel line is clear. Could it be that injector pump is not putting out maximum fuel and therefore limiting the rpm? Injector pump is original 30 years old.

A problem I have is trying to get the the two zinc anode plugs out of the engine block. I got the one in the head out with dificulty, but I am starting to round off the other zinc plugs with the socket wrench. I tried PB blaster penetrante oil with no success. The plugs have probably not been removed for 20 years. Probably heavy corrosion. I am a little afraid I migh damage the block by taking extreme measures to get the anode plugs out- Any ideas?
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post #18 of 28 Old 11-01-2010
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Zincs: Had the same problem years ago with mine. Never got the one out of the head flange - just changed out the whole flange. The two in the side of the block are hard to get to since behind the yanmar fuel filter and the fuel pump. I always make it a point to remove and check them when I replace the fuel filter and only use the proper sized socket (think it's 23 or 24 mm) with a breaker bar for leverage. Also, keep trying with the PB Blaster or Freeze-out. If this all don't work, you can try an impact gun - they have electric ones that are large but work in a pinch if you have the room.

When reinstalling, use never-seize type grease (at auto stores) to help for the next time you need to take them out.

Let us know how you make out.
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post #19 of 28 Old 11-05-2010 Thread Starter
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I tried everything to get the anode out of the block- nothing worked. I tried Freeze out and did not help. The head is so rounded I think it will have to be drilled out.
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post #20 of 28 Old 11-06-2010
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the tach on my 3gm was completely worthless - i replaced it but wouldnt rely on it for testing. use one of those photo tachs to make sure you are reading what it is really doing
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