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#1
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? |
#2
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. |
#3
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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. |
#4
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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? |
#5
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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. |
#6
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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. |
#7
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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 |
#8
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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. |
#9
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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. |
#10
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. |
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