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Detroit Diesel (DD671N) Questions
Not having made any significant displays of ignorance lately that I
know of, thought I'd give it a try: Is there any way to measure compression without removing injectors or other major components on DD671s? Second question: Since the DD671 is a 2 cycle engine, I'm assuming there are no moving valves, just fixed intake and exhaust ports in the cylinder walls. Anyone know if that is correct? If so, I'm also assuming that any loss of compression would have to be from worn rings and/or cylinder bore. Also correct? |
Detroit Diesel (DD671N) Questions
Wayne,
First Caveat: I've never worked on any Detroit Diesel engine (that I can remember) Wayne.B wrote: Is there any way to measure compression without removing injectors or other major components on DD671s? Don't know (shrug) Second question: Since the DD671 is a 2 cycle engine, I'm assuming there are no moving valves, just fixed intake and exhaust ports in the cylinder walls. There are exhaust valve/valves in each cylinder in a two-stroke turbo-diesel. See http://auto.howstuffworks.com/diesel-two-stroke1.htm Also see http://www.marineparts.com/partspages/DETROIT/DET12.HTM for a list of exhaust valve part numbers including for the 671. If so, I'm also assuming that any loss of compression would have to be from worn rings and/or cylinder bore. Also correct? See above. Loss of compression could be due to rings/cylinder, exhaust valve, etc. Good luck with it. Don W. |
Detroit Diesel (DD671N) Questions
Wayne.B wrote:
Not having made any significant displays of ignorance lately that I know of, thought I'd give it a try: Is there any way to measure compression without removing injectors or other major components on DD671s? No not really & you need to use the correct tester of course, which can be pricey it's probably better to just get a tech to test. Second question: Since the DD671 is a 2 cycle engine, I'm assuming there are no moving valves, just fixed intake and exhaust ports in the cylinder walls. Anyone know if that is correct? No it still has an exhaust valve(s) in the head as usual. The air flow is from; the blower pressurised air box on the side through, tangential inlet ports,(uncovered as the piston approaches BDC like the 2 stroke OBs), incoming fresh air flows to help purge any remaining exhaust, the rising piston rises covering the inlet ports, the exhaust valve closes & compression up to fuel injection just before TDC, The power stroke is till towards the bottom when the exhaust valve opens & the exhaust starts to flow It's certainly a "2" stroke but it has most of the elements of a 4 stroke. This is why when I waaarr on endlessly about how bad 2 stroke OBs are, I'm usually careful to say "crankcase transferred 2 strokes" your diesel is not that. The crankcase is not "deliberately":-)) pressurised (not that you'd guess it given the way they throw oil) & the design is very successful. If so, I'm also assuming that any loss of compression would have to be from worn rings and/or cylinder bore. Also correct? The bottom part of the engine is pretty much the same as a 4 stroke, wet sump, pressure oiling etc so save some accident (air cleaner something broke??) you shouldn't expect the piston/ring/bore area to fail out of the blue. The usual suspects are always there, head, valves (exhaust only but they still get burnt). Your first instinct is probably the best a compression test; it should tell you whats happening or least give you some good clues. K |
Detroit Diesel (DD671N) Questions
On Tue, 24 Jan 2006 22:40:54 GMT, Don W
wrote: See above. Loss of compression could be due to rings/cylinder, exhaust valve, etc. Good luck with it. Things are not at a critical state since they are both running well, but the port side engine is taking a few seconds longer to cold start than it used to, so I'm assuming that something is mildly amiss. |
Detroit Diesel (DD671N) Questions
Wayne,
K answered your questions very well, but I'm curious why you think you have low compression, as that rarely happens on a detroit. I suspect an underlying story here. Secondly, that engine has been made for 70 years, there are many variations. Which one do you have? Please note there are many different cylinder heads as well. The older ones are 2 valve and the modern ones are 4 enhaust valves per cylinder. I think you should identify symtoms, if you want meaningful help. Steve "Wayne.B" wrote in message ... Not having made any significant displays of ignorance lately that I know of, thought I'd give it a try: Is there any way to measure compression without removing injectors or other major components on DD671s? Second question: Since the DD671 is a 2 cycle engine, I'm assuming there are no moving valves, just fixed intake and exhaust ports in the cylinder walls. Anyone know if that is correct? If so, I'm also assuming that any loss of compression would have to be from worn rings and/or cylinder bore. Also correct? |
Detroit Diesel (DD671N) Questions
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. |
Detroit Diesel (DD671N) Questions
"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!) |
Detroit Diesel (DD671N) Questions
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. |
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 |
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 |
Detroit Diesel (DD671N) Questions
On Tue, 24 Jan 2006 19:50:34 -0500, "Eisboch" wrote:
Are your 671s turboed or normally aspirated? Naturally 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. You and all of my neighbors. :-) It's like having a pair of Greyhound busses idling in your backyard. 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. They have a reputation of lasting almost forever and can be totally rebuilt in place with new cylinder sleeves, bearings, pistons, etc. It's my understanding that in commercial generator service they frequently go 20,000 hours between overhauls although 4 or 5,000 hours is more typical for marine service. |
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? |
Detroit Diesel (DD671N) Questions
Wayne.B wrote in
: Not having made any significant displays of ignorance lately that I know of, thought I'd give it a try: Is there any way to measure compression without removing injectors or other major components on DD671s? Nope. The way to tell if the compression is good is expressed by: "Will it start?" If it starts on all cylinders...compression is great! Second question: Since the DD671 is a 2 cycle engine, I'm assuming there are no moving valves, just fixed intake and exhaust ports in the cylinder walls. 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; Anyone know if that is correct? If so, I'm also assuming that any loss of compression would have to be from worn rings and/or cylinder bore. Also correct? Worn rings, cracked cylinder head, cracked cylinder sleeve usually starting at the port opening. Look at the exhaust. If it starts steaming after it warms up, the head or block is cracked allowing pressurized water into the cylinder, which turns to steam on the hot piston. It always starts cold with white smoke from incomplete combustion. 2-stroke DDs aren't "environment friendly"....but owner friendly. Shrimp boats running 4-53s may not have any rings at all and they're still shrimping...(c; You can tell when the rings are "too worn". It starts running away when lube oil from the crankcase splashes past the worn rings that are supposed to be wiping it off the cylinder walls before the big bang....and the 2-stroker just runs away wild on its own lube oil! Most exciting...black smoke for miles behind boat...shutting down injection pump makes it go faster! Only way to stop it is shut off its air supply by plugging up the intake, which is very exciting on an engine that may explode in shrapnel any second....(c; But don't let that prospect bother you putting off that ring job another year.... At least it'll never have a turbo-charger fire.... Aboard USS Everglades (AD-24), a nice old 6-71 powered a big DC generator putting out 440VDC for the after gun turret from 1952 that had long since been removed for the stupid DASH helo deck. (We were better off with the gun because at least it worked.) The calibration laboratory I worked in needed a stable AC power supply, even when the ship's AC was awful, so a DC to AC motor- alternator set, 50KVA was installed and wired into the huge, black bakelite DC power panel with the huge knife switches no safety bureaucrat would ever approve of. (The lab actually ran its lighting off a secondary 110VDC, NOISELESS, winding on the genset.) The 6-71 drove the AC M-G set to 1800 RPM (60 Hz - 4 poles) any time we weren't parked against Pier Papa in Charleston. (We used to turn back the speed on the M-G set to 50 Hz so the TV didn't wobble in the Med, under threats of "YOU FIX IT IF YOU BREAK IT" from the Chief Electrician..(c; That 6-71 had over 12,000 hours on its meter on the panel and would almost crank by hand! They are really great engines... Oh, diesel fuel? No problemo. It sucked fuel oil from a 90,000 gallon tank. |
Detroit Diesel (DD671N) Questions
"Wayne.B" wrote in message ... 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 |
Detroit Diesel (DD671N) Questions
On Tue, 24 Jan 2006 20:50:45 -0500, "Eisboch" wrote:
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. That would be the better out come for sure. |
Detroit Diesel (DD671N) Questions
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. |
Detroit Diesel (DD671N) Questions
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. There are valves. Check: http://www.yachtsurvey.com/comparing_diesel_types.htm Courtesy of Detroit diesel! Gaz |
Detroit Diesel (DD671N) Questions
Gary wrote in news:C1EBf.325410$2k.236563@pd7tw1no:
There are valves. Check: http://www.yachtsurvey.com/comparing_diesel_types.htm Courtesy of Detroit diesel! He's right....Sorry. |
Detroit Diesel (DD671N) Questions
Wow!! This goes on and on.
As most everyone has said the most likely culprit is fuel system related. In my experience air leaks are very rare except when the engines have been recently serviced. If this started after servicing the fuel filters an air leak is very probable. Injector tips are another possibility. BTW, injector timing is critical to a DDA running well. You should probably invest the few dollars for a timing gage. If you own the engines for a while you'll need one. These engines are so simple and easy to work on that you would do well to take a course on them. You could learn everything you'd ever need to know in about a 40 hour course. That would include a complete teardown and reassembly phase with a tune up. IMO, these are wonderful engines for the DIY inclined owner. Butch "Larry" wrote in message ... Gary wrote in news:C1EBf.325410$2k.236563@pd7tw1no: There are valves. Check: http://www.yachtsurvey.com/comparing_diesel_types.htm Courtesy of Detroit diesel! He's right....Sorry. |
Detroit Diesel (DD671N) Questions
Wayne,
The only way to check the compression is by removing the injector, their are special tools for this. It's not a difficult job, but you do have to reset the rack, which can be a little difficult if you've never done it before and don't have the tools for it. By the way, two cycle Detroit Diesel's have exhaust valves in the head (usually four valves) and an intake port cut into the side of the cylinder (no intake valves). The blower builds pressure in the intake manifold and when the intake port is open that pressure, along with the open exhaust valves, is what forces the exhause out. |
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 |
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. |
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 |
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. |
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. |
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 |
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. |
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? |
Detroit Diesel (DD671N) Questions
"Wayne.B" wrote in message ... 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 |
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. |
Detroit Diesel (DD671N) Questions
Wayne, when the engine is in the "hard to start condition", and then it
finally starts, does it do so on all cylinders, or does it go thru a period where only 1, 2, 3, etc cylinders are firing for a while before all 6 finally kick in? This could indicate a very slow leak between the injection pump and the injectors. bob Wayne.B wrote: 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. |
Detroit Diesel (DD671N) Questions
On Thu, 26 Jan 2006 15:16:07 -0800, RW Salnick
wrote: Wayne, when the engine is in the "hard to start condition", and then it finally starts, does it do so on all cylinders, or does it go thru a period where only 1, 2, 3, etc cylinders are firing for a while before all 6 finally kick in? This could indicate a very slow leak between the injection pump and the injectors. Usually you can hear one or two kick a couple of times and then they all light up a second or two later. On a DD671 there is no central injection pump. Each cylinder has its own driven by the cam as I understand it. |
Detroit Diesel (DD671N) Questions
In article ,
RW Salnick wrote: Wayne, when the engine is in the "hard to start condition", and then it finally starts, does it do so on all cylinders, or does it go thru a period where only 1, 2, 3, etc cylinders are firing for a while before all 6 finally kick in? This could indicate a very slow leak between the injection pump and the injectors. bob DD671's don't have an Injection Pump. They have a Fuel Pump that supplies a common Fuel Rail, to which each Injector tapes off of. Each individual Injector is then pumped via the Injection Lobes of the Camshaft. Remember this is a 2 Cycle Diesel, not a 4 Cycle. Bruce in alaska -- add a 2 before @ |
Detroit Diesel (DD671N) Questions
Wayne,
One more time, you have a leak on the SUCTION side of fuel pump. Hint, just change the hose! Steve "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.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. |
Detroit Diesel (DD671N) Questions
On Sat, 28 Jan 2006 13:47:22 +0100, "Steve Lusardi"
wrote: you have a leak on the SUCTION side of fuel pump. Hint, just change the hose! Steve Thanks. Is it correct that the leak could also be at the fuel filter gasket? |
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 |
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