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In Reply to: RE: So what did you do for Father's day? posted by bigshow on June 18, 2017 at 16:18:47
Wife asked me what I wanted to do, and since our boat could use some work that's what I did. 'Tubes Rule' T-shirt brings quizzical looks around the marina.
Follow Ups:
Nothing like mechanical work to clear the cobwebs.
That's one of two Detroit Diesel 6-71N (6 cylinders, 71 cubic inches each) two-stroke, normally aspirated. Five inch stroke, four and a quarter inch bore, designed in 1938 and in production until 2005.
There's a roots blower, that was once more widely known in drag racing (6-71 blower) that maintains approximately 1 psi intake pressure. All four valves in the head are exhaust valves, the intake is through ports in the cylinder wall that are uncovered when the pistons are all the way down. They use conventional sump and pump lubrication.
When the pistons are down the exhaust valves are open and the intake ports uncovered, the blower is purging the cylinder of exhaust gases. As the piston starts back up the intake ports are covered and the exhaust valves close, the fresh air is compressed until the pistons reach the top of their stroke when fuel is injected by the cam driven injectors and burns.. every stroke.
These two-stroke six cylinder engines sound like twelve cylinder four-stroke engines and will not start without the blower.
Later higher output models (6-71TII) have turbos and intercoolers, but significantly shorter time between overhaul.
They guy that surveyed our boat said he's seen 6-71Ns go twenty thousand hours in commercial use without failure.
My apologies as you very likely already know the above, it's just fun to share anyway.
Here's a pic from an 8V-71 in a marina neighbor's boat that was disabled looking for the cause of excess smoke. It still ran and idled smoothly. An "in frame" overhaul has been completed and the smoke has cleared. Unknown if it was fuel or water that caused he damage.
the sharing was fun for me, I dig boats,
In my sailor days, I once sat alongside the Mississippi River with a guy who could tell the different propulsion systems in the push boats passing by, using only the engine noise. I thought that an ok way to spend some time, so don't mind a few diesel stories.
My own diesel experience is varied but slight. MY favorite is the smallest, a lifeboat motor that you pump up air pressure to start, the biggest, the slow speed marine engines Sea land was running in its fast freight container ships.
I was visiting, and went below to check it out. . One huge piston was hanging from a hook on a chain lift, with a pad eye loop screwed into the top. I don't know if the loop stayed there, it looked clean, but this was all new to me.
Each cylinder block is separate, and they stop one piston for maintenance while in port, while the crank continue to turn, the engine never stops, I was told. One of the piston rings was hanging on a dedicated piston ring hook, yellow and limp, like a giant runner band because it was made out of teflon and was round, as thick as a garden hose. . Inside the cylinder block was a cut out, an opening made for a custom inspection ladder, so you can get up to work inside. Not a crew favorite. Made me glad I worked on deck.
My own boating experience is taking a break from 'good times' to frustration with a persistent oil leak. A 1" pipe fitting at the external oil filter housing started leaking and it's very frustrating to have any oil in your bilge water (as you know) because you can't just vacuum up oily water and pour in down the sink.
I took it apart and looked for cracks, nothing found so wrapped it up with teflon tape, which I've since read is not recommended for anything subject to vibration, only to have it start leaking after a couple hours run time.
Again disassembled and inspected, I bought Permatex "high performance" thread sealer ($15) AND the "recommended for best results" primer ($20) then followed the directions exactly, waiting 24 hours before use, only to have it leak after a couple hours.
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