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#21
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
In article ,
Larry wrote: No valves. Intake ports and exhaust ports open as the piston passes over them near BDC when the blower recharges the air and blows out the dead gases. Piston rises cutting that off, approaches TDC, cam rack in the head opens injection just as compressed air reaches 1200F and KAPOW!, we're on our way down again after this god-awful loud knocking noise also indicating compression is great, making enginemen smile...(c; Well it is obvious that Larry has never wrenched on a Scream'in Jimmy of any kind, or he would have known, that they ALL have Exhaust Valves, in the HEAD, under the VALVE COVER.... where the Injectors ARE...... Me |
#22
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
Wayne,
1st: on a 671... no smoke usually means compression is fine. If compression was bad, you would get smoke on startup until they warm. if it warms and they still smoke badly... you need a rebuild fast... If it runs after fuel is shut off or it runs away then you needed a rebuild last year. 2nd: Do you have Racors? Is the fuel level in the tank ABOVE or BELOW the injectors? If the answer is YES and BELOW then go buy a Racor rebuild kit or at least buy the washer that sits over the metal ball. That washer will disfigure over time causing the ball to not seat and the fuel will drain back into the tank. Also make sure all other seals, especially the top seals are in good shape (A rebuild kit comes with all new seals) 3rd: Is the engine turning over the normal speed? If not, batteries may be low. A slow turnover will cause an engine to slow start. 4th: DO your exhaust ports have the heat sheilds over them? If not, you can use a temp gun to find a bad cylinder. If not, you can play with the fuel rack with the cover off to find a bad cylinder. (Not recommended unless you know what you are doing or have 6 fingers on your right hand) BUT AGAIN... no smoke means you probably have 6 good cylinders. 5th- Spend 90% of your time playing with the inbound fuel system. A few hints: While the engine is running.. everything PAST the lift pump (The first pump after the racor) is under PRESSURE. Check this area first for leaks while the engine is running-higher speed the better. Everything BEFOre the lift pump is under SUCTION. This is harder to find because there will be no visible fuel most of the time. (See #2) You can put some semi-viscous liquid around the seals and see if it is sucked in but that can be difficult to see. (Spit, clean oil, etc) Don's waste your money on a compression check ($500 +++) until you have tried most everything else Have fun... I am in a similar situation with one of our boats but we have smoke and 1 bad cylinder.... kind of a smoking gun... Ed ed at Estrobel dot com Wayne.B wrote: On Tue, 24 Jan 2006 20:34:46 -0500, Larry wrote: No valves. Intake ports and exhaust ports open as the piston passes over them near BDC when the blower recharges the air and blows out the dead gases. That's what I thought but everyone else says there are exhaust valves in the head. |
#23
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 |
#24
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. |
#25
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. |
#26
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 |
#27
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
On Thu, 26 Jan 2006 10:00:09 +0100, "Steve Lusardi"
wrote: 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 Thanks, good description. I think I'll start by replacing the engine mounted fuel filters and gaskets since there seems to be a consensus that the problem is somewhere in that area. The fuel tanks are 75% full right now which puts the fuel level above the engines, so that should rule out an issue with the Racors if I understand this correctly. |
#28
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
On Thu, 26 Jan 2006 04:50:08 -0500, "Eisboch" wrote:
Wayne, I might add that the guy with the similar problem that I mentioned before also had DD671s, FWIW Thanks, do you happen to know how he located the leak? |
#29
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 Thu, 26 Jan 2006 04:50:08 -0500, "Eisboch" wrote: Wayne, I might add that the guy with the similar problem that I mentioned before also had DD671s, FWIW Thanks, do you happen to know how he located the leak? I don't. Next time I go down to check the boat, I'll ask. Eisboch |
#30
posted to rec.boats,rec.boats.cruising,rec.boats.building
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Detroit Diesel (DD671N) Questions
On Thu, 26 Jan 2006 06:38:42 GMT, "Calif Bill"
wrote: 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. I have vacuum guages on the suction side of my Racors to provide a warning if they are starting to load up. Everything looks normal there. |
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