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#11
posted to rec.boats,rec.boats.cruising
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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. |
#12
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? |
#13
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. |
#14
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 |
#15
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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. |
#16
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. |
#17
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 |
#18
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. |
#19
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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. |
#20
posted to rec.boats,rec.boats.cruising,rec.boats.building
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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. |
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