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#1
posted to rec.boats,rec.boats.cruising
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Detroit Diesel (DD671N) Questions
"Wayne.B" wrote in message ... On Tue, 24 Jan 2006 19:17:09 -0500, "Eisboch" wrote: Ain't boats fun? Eisboch (grandkid #5 is a girl!) Congratulations! We are still at #0 but both sons are engaged so that's a good start. Yes, small air leak is a possibility under consideration. This issue is fortunately not at a critical state yet but I like to stay on top of things so I don't get a failure when I'm in the boondocks somewhere. Are your 671s turboed or normally aspirated? It's funny when you get to know how the various engines sound. I can identify the sound of those 671s anytime I hear them start up. A friend has a pair of normally aspirated 671s in a 1972 Hat 38 - actually a conversion from original gas engines. They have over close to 10,000 hours on them and run like a top. Great engines. Eisboch |
#2
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
Eisboch wrote:
"Wayne.B" wrote in message ... On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi" wrote: I think you should identify symtoms, if you want meaningful help. It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt within the last 1,000 hours or so by the previous owner. My port side engine is taking longer to cold start than it used to, sometimes needing 8 to 12 seconds of cranking. It used to start on the first or second turn even when stone cold, and the starboard engine still does. If it has been run within a day or two it still starts very quickly. There is very little exhaust smoke at startup even when cold, and what little there is goes away quickly. The engine is running well and making full power as far as I can determine. There's a guy at our marina who had a somewhat similar problem for a couple of years. Turns out he had a very small air leak in the fuel supply line for one engine. It would run fine after starting, (I assume because the leak was overcome by fuel, but that is pure speculation), but was hard starting. Ain't boats fun? Eisboch (grandkid #5 is a girl!) Hi again, you say it's making full revs??? a fixed pitch prop is an excellent dynomometer so if it were seriously down on compression I think you'd see it in the top end max revs performance. I think before you go too much further you might check the fuel supply especially as you say it starts easier after a day, but by then it's well cold so any mechanical defect in the compression etc would still be there. Seems granddad Eisboch is on the trail here (he's having a good day???:-)), fuel filters are a good source of air leaks also. It might be slowly allowing the fuel to go back down the lines & air in. These engines as with many Cummins, don't have an injector pump in the commonly known sense, they have a moderately pressurised fuel rail not unlike the one in your petrol car. Along this rail (they call it a fuel manifold in the manual) the unit injectors are sited. There is a restriction in the fuel rail outlet to maintain feed pressure to the unit injectors, if the fuel rail isn't properly pressurised by the gear pump supply it won't start ......... easily. The injectors are driven by the camshaft & rocker arms the same as the valves are & do the final pressure increase & injection all in the one movement (pump injector combination). You can imagine if your fuel system, the gear fuel rail pressure pump as mentioned (which is also the lift pump usually), the fuel rails & the unit injectors themselves, get any air in there it will need a few turns to pump it through & clear it. Once started they can live with a tiny airleak becasue it just goes straight through the system & out the return line. K |
#3
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
"K. Smith" wrote in message ... Eisboch wrote: "Wayne.B" wrote in message ... On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi" wrote: I think you should identify symtoms, if you want meaningful help. It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt within the last 1,000 hours or so by the previous owner. My port side engine is taking longer to cold start than it used to, sometimes needing 8 to 12 seconds of cranking. It used to start on the first or second turn even when stone cold, and the starboard engine still does. If it has been run within a day or two it still starts very quickly. There is very little exhaust smoke at startup even when cold, and what little there is goes away quickly. The engine is running well and making full power as far as I can determine. There's a guy at our marina who had a somewhat similar problem for a couple of years. Turns out he had a very small air leak in the fuel supply line for one engine. It would run fine after starting, (I assume because the leak was overcome by fuel, but that is pure speculation), but was hard starting. Ain't boats fun? Eisboch (grandkid #5 is a girl!) Hi again, you say it's making full revs??? a fixed pitch prop is an excellent dynomometer so if it were seriously down on compression I think you'd see it in the top end max revs performance. I think before you go too much further you might check the fuel supply especially as you say it starts easier after a day, but by then it's well cold so any mechanical defect in the compression etc would still be there. Seems granddad Eisboch is on the trail here (he's having a good day???:-)), fuel filters are a good source of air leaks also. It might be slowly allowing the fuel to go back down the lines & air in. These engines as with many Cummins, don't have an injector pump in the commonly known sense, they have a moderately pressurised fuel rail not unlike the one in your petrol car. Along this rail (they call it a fuel manifold in the manual) the unit injectors are sited. There is a restriction in the fuel rail outlet to maintain feed pressure to the unit injectors, if the fuel rail isn't properly pressurised by the gear pump supply it won't start ......... easily. The injectors are driven by the camshaft & rocker arms the same as the valves are & do the final pressure increase & injection all in the one movement (pump injector combination). You can imagine if your fuel system, the gear fuel rail pressure pump as mentioned (which is also the lift pump usually), the fuel rails & the unit injectors themselves, get any air in there it will need a few turns to pump it through & clear it. Once started they can live with a tiny airleak becasue it just goes straight through the system & out the return line. K I think some people put pressure guages before and after the fuel filter. You would know what the pressure is when starting and if the fuel filter is getting clogged. |
#4
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
I agree with the fuel system diagnosis. Have you changed the fuel filters,
checked the fuel water separator etc. Fredo "K. Smith" wrote in message ... Eisboch wrote: "Wayne.B" wrote in message ... On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi" wrote: I think you should identify symtoms, if you want meaningful help. It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt within the last 1,000 hours or so by the previous owner. My port side engine is taking longer to cold start than it used to, sometimes needing 8 to 12 seconds of cranking. It used to start on the first or second turn even when stone cold, and the starboard engine still does. If it has been run within a day or two it still starts very quickly. There is very little exhaust smoke at startup even when cold, and what little there is goes away quickly. The engine is running well and making full power as far as I can determine. There's a guy at our marina who had a somewhat similar problem for a couple of years. Turns out he had a very small air leak in the fuel supply line for one engine. It would run fine after starting, (I assume because the leak was overcome by fuel, but that is pure speculation), but was hard starting. Ain't boats fun? Eisboch (grandkid #5 is a girl!) Hi again, you say it's making full revs??? a fixed pitch prop is an excellent dynomometer so if it were seriously down on compression I think you'd see it in the top end max revs performance. I think before you go too much further you might check the fuel supply especially as you say it starts easier after a day, but by then it's well cold so any mechanical defect in the compression etc would still be there. Seems granddad Eisboch is on the trail here (he's having a good day???:-)), fuel filters are a good source of air leaks also. It might be slowly allowing the fuel to go back down the lines & air in. These engines as with many Cummins, don't have an injector pump in the commonly known sense, they have a moderately pressurised fuel rail not unlike the one in your petrol car. Along this rail (they call it a fuel manifold in the manual) the unit injectors are sited. There is a restriction in the fuel rail outlet to maintain feed pressure to the unit injectors, if the fuel rail isn't properly pressurised by the gear pump supply it won't start ......... easily. The injectors are driven by the camshaft & rocker arms the same as the valves are & do the final pressure increase & injection all in the one movement (pump injector combination). You can imagine if your fuel system, the gear fuel rail pressure pump as mentioned (which is also the lift pump usually), the fuel rails & the unit injectors themselves, get any air in there it will need a few turns to pump it through & clear it. Once started they can live with a tiny airleak becasue it just goes straight through the system & out the return line. K |
#5
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
Wayne.B wrote:
On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi" wrote: I think you should identify symtoms, if you want meaningful help. It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt within the last 1,000 hours or so by the previous owner. My port side engine is taking longer to cold start than it used to, sometimes needing 8 to 12 seconds of cranking. It used to start on the first or second turn even when stone cold, and the starboard engine still does. If it has been run within a day or two it still starts very quickly. There is very little exhaust smoke at startup even when cold, and what little there is goes away quickly. The engine is running well and making full power as far as I can determine. Change the fuel filter, and if that doesn't help, look for a leak in your supply lines. -- "A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3 |
#6
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
On Tue, 24 Jan 2006 18:59:06 -0600, dazed and confuzzed
wrote: look for a leak in your supply lines. Any advice on how to do that? |
#7
posted to rec.boats
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Detroit Diesel (DD671N) Questions
Wayne.B wrote:
On Tue, 24 Jan 2006 18:59:06 -0600, dazed and confuzzed wrote: look for a leak in your supply lines. Any advice on how to do that? visual first, are they wet? Check all nuts for tightness. Clamps for tightness, hoses for leaks or cracks. It could be as simple as a banjo bolt washer that has compressed.... As I cannot see your installation, I can only give generalities. I've seen it be as simple as a fuel filter gasket with a small pit in it. The seal worked under pressure, but left a bit of air into the system when everything cooled off and the pressure dropped. Do you have any high points in the system where air could collect? Do you have a mechanical fuel supply pump or an electrical one? Hoses or hard pipe from the tank(s)? If you have a leak, it is currently a small one from your symptoms. If it was major, you'd have real trouble starting at all. -- "A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3 |
#8
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
"Wayne.B" wrote in message news On Tue, 24 Jan 2006 18:59:06 -0600, dazed and confuzzed wrote: look for a leak in your supply lines. Any advice on how to do that? Thinking about it, why not just fire up the hard starting engine then, using a small container of fuel and an acid brush or similar, lightly wet each fitting on the fuel lines from your Racors forward to the last fitting you can get to on the engine. Watch for *suction*. Sort of the opposite of a pressure bubble test for leaks. I don't know if this would work, but it might. Or, talk to someone who, unlike me, knows what he is talking about. :-) It seems logical though that if that engine is otherwise running fine, you are getting your RPMs and you are not producing smoke more than the other engine, that a compression problem due to rings or valves is not likely. Eisboch |
#9
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
Wayne,
This is simple. You have fuel feed leakdown on that engine. On the detroits, you have a gearpump that draws fuel from the tank and pushes the fuel through a strainer and then a filter. From the filter it enters the Cylinder head where it passes through a cast feed log. Unused fuel is turned around and again passed through the return log in the head. From there it is returns heated to the tank. Fuel pressure at the out side of the pump should be about 45 lbs. Your problem is that the feed line to the inlet of the pump is draining back to the tank. Probably a very small leak in that line. Steve "Wayne.B" wrote in message ... On Wed, 25 Jan 2006 00:31:55 +0100, "Steve Lusardi" wrote: I think you should identify symtoms, if you want meaningful help. It's a 1981 Johnson & Towers marine conversion, supposedly rebuilt within the last 1,000 hours or so by the previous owner. My port side engine is taking longer to cold start than it used to, sometimes needing 8 to 12 seconds of cranking. It used to start on the first or second turn even when stone cold, and the starboard engine still does. If it has been run within a day or two it still starts very quickly. There is very little exhaust smoke at startup even when cold, and what little there is goes away quickly. The engine is running well and making full power as far as I can determine. |
#10
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
"Steve Lusardi" wrote in message ... Wayne, This is simple. You have fuel feed leakdown on that engine. On the detroits, you have a gearpump that draws fuel from the tank and pushes the fuel through a strainer and then a filter. From the filter it enters the Cylinder head where it passes through a cast feed log. Unused fuel is turned around and again passed through the return log in the head. From there it is returns heated to the tank. Fuel pressure at the out side of the pump should be about 45 lbs. Your problem is that the feed line to the inlet of the pump is draining back to the tank. Probably a very small leak in that line. Steve Wayne, I might add that the guy with the similar problem that I mentioned before also had DD671s, FWIW Eisboch |
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