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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. |
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