SailNet Community banner

1 - 20 of 28 Posts

·
Registered
Joined
·
3,550 Posts
Discussion Starter #1
I have a Yanmar 3gmD and have gone through the engine replaceing fuel lift pump, fuel and air filter, cleaned fuel tank, added new fuel, added Racor filter/water seperator. Engine starts easily and runs great. Only problem at full throttle only can get to 2400 rpm. Engine is rated for 3400 rpm. Engine is in an S&S 34 sail boat. At 2400 boat moves at about hull speed in 5 foot seas and 20 knot head wind. Power seams ok for boat at 2400 rpm, but manual says at this rpm hp is about 14 hp. At 3400 rpm should get 20 rpm. Manual says injector pump could be the problem.

Any other ideas for low RPM? Could the throttle be adjusted to get full rpm?
Thanks, Casey
 

·
Senior Member
Joined
·
19,489 Posts
Are you sure the prop is clean - and properly sized/pitched? Are you starting to develop black smoke at that rpm?? Is this a new phenomenon?
 

·
Registered
Joined
·
3,550 Posts
Discussion Starter #3
I recently cleaned and bottom painted hull and cleaned the prop. I bought the boat 4 months ago and from what I know the prop is original. Boat was built in Austrailia in 1978. Engine looks to have been installed in about 1980. Prop might be wrong but if it is it has been in the boat for 30 years. The engine may have always run like this, the last owner could not give me much information on the boat. The prop rotates freely by hand (no binding) and I have no abnormal vibration. The boat has been around the world recently (via panama, and cape of good hope) so the system is workable- I just want to make sure it is not going to hurt the engine long term. The engine does produce a white / grey smoke at all rpm's both high and idle. I have replace the thermostat (which was totally corroded) but this had no effect on the engine running. The engine does produce a kind of burning odor from the exhaust but the engine temperature seems ok (no high temp light and engine and exhaust can all be touched with the hand for several seconds without being too hot. Engine buns no oil and at 2400 rpm burns about 1/3 gallon per hour (at 6 knots) which seems normal.
 

·
Registered
Joined
·
3,550 Posts
Discussion Starter #6
I did look into the mixing elbow- it looked clear. Also, all cooling water lines are new. and the inlet strainer is clean. Looks like adequate cooling water is coming out the exhuast outlet.

I imagine the fuel injectors are original and never been serviced. Could white / gray smoke be from un burned diesel coming from a poor spray pattern from worn fuel injectors?
 

·
Registered
Joined
·
5,680 Posts
I have not tried to go to max rpm at in neutral. Could I damage the engine by going to max rpm with no load?
There is no problem revving the engine in neutral. I think most of us assumed the rpms you were reporting were in neutral.

If it revs right up to 3200-3400 in neutral (I suspect it will), you have all the signs/symptoms of being over-propped. That is not good for the engine, so you should change it even if somebody else went around the world like that.
 

·
Registered
Joined
·
3,550 Posts
Discussion Starter #9
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?
Thanks, Casey
 

·
Registered
Joined
·
5,680 Posts
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 +.
 

·
Super Moderator
Joined
·
6,752 Posts
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.
 

·
Registered
Joined
·
488 Posts
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?
Thanks, Casey
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.
 

·
Registered
Joined
·
3,550 Posts
Discussion Starter #16
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.
Thanks, Casey
 

·
Registered
Joined
·
3,550 Posts
Discussion Starter #17
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?
Thanks
 

·
Blitz - 34'Seidelmann
Joined
·
6 Posts
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.
 

·
Registered
Joined
·
3,550 Posts
Discussion Starter #19
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.
 

·
Registered
Joined
·
2,249 Posts
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
 
1 - 20 of 28 Posts
Top