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Old 05-29-2012, 09:23 AM   #41
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... After a while I remembered reading what someone really smart wrote about backpressure on this forum (maybe FF?) and how it would prevent starting in this situation. I had Bill crack the hose to the top of the exhaust manifold and it started right up...
Can someone explain this? Why would there be back pressure at the exhaust manifold when the engine is at rest?
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Old 05-29-2012, 10:12 AM   #42
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My understanding of it, and I could for sure be wrong, is that turning over the starter (and engine slowly) fills the exhaust manifold with water therby stopping airflow through the exhaust. The engine can't run without air. By pulling the hose the vacuum is broken and the water runs out.

Again, it worked for me, but my understanding of it is likely pretty rudimentary.

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Old 05-29-2012, 10:54 AM   #43
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As you all have probably figured by now, (Bob especially) I'm not a great troubleshooter, but I felt good about that day.
I may be able to occasionally pass myself off as an internet expert but if so it comes from years of being a bumbling fool around a variety of machinery.

The most recent one I had that stumped me for most of a day was a morning fail to start on my Onan MDJE that had been running fine the evening before when we shut it down. 7:00 AM - time for breakfast - no Onan. It rolled over just fine but no fire. Fuel tanks are full. There's fuel running at the intake side of the injection pump but no volume on the output lines.

I won't make it into a game. Later in the day I figured out that the fuel running at the injection pump was head pressure from the tanks but it wasn't sufficient to act as charge pressure to the pump. Replace the lift pump and it fired right up.
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Old 05-29-2012, 10:59 AM   #44
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I see that sometimes on my main engines. The lift pump will develop a slow leak from a failed gasket, it still pumps, but not hard enough to start the motor.
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Old 05-29-2012, 08:53 PM   #45
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Fun game. Thanks Doug for the entertainment.

So are lift pumps a spare part that a person would normally carry onboard a diesel powered boat?
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Old 05-29-2012, 09:39 PM   #46
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No problem, it was fun and I learned some things.

I do keep a spare lift pump (well actually, I changed out one that was still working fine, but getting a little age, I keep it as a spare) but I wonder if mine go more often than other peoples. I've had 2 on each engine fail in 7 years.

Mine are pretty cheap though and quick to change. About $125.

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Old 05-29-2012, 10:35 PM   #47
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Bobofthenorth, Thanks for bringing up the subject of lift pumps. Mine is more than ten years old. I think it's time for a preventitive replacement. My spare is probably at least that old so I better just buy two.
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Old 05-29-2012, 10:47 PM   #48
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You need to learn how to break problems down and rule out possiblities. You don't start into a problem with a theory that immediately requires massive disassembly or intervention.
Very concise description of the best approach to troubleshooting.

To it I would add that it is essential for effective troubleshooting to really understand how the piece of equipment in question works. Not just "how to turn it on" but how it's functioning inside. Because if you really understand how it and its components function you can do a huge amount--- if not all of--- the troubleshooting in your mind. And then zero in on the few or maybe only one thing that could be causing the problem.

On a particularly frustrating day having to do with toilets not long after acquiring our old boat I bellyached to the GB broker who found the boat for us that I was getting tired of dealing with stuff and wished I could just pay someone to do everything. He said that while that can be nice, the downside is that he sees lots of wealthy owners with beautiful late-model boats who haven't got a clue how anything on the boat works. And sometimes you can't spend your way out of trouble, as when something important fails mid-cruise miles or days from a mechanic. Working on the boat's systems yourself, he said, teaches you how it all works, which means you learn what can go wrong, which means you learn how to diagnose and fix it.

And he was absolutely correct. It doesn't make working on toilets any more fun but it removes the worry and frustration and "why is it doing this?" fear.

We currently have a very bizzare issue with our fresh water pump. While I don't know how the pump innards specifically work, I am 99.999 percent sure I know where the problem is because I understand the boat's fresh water plumbing system. And after analyzing what's going on and eliminating every other cause, to paraphrase Arthur Conan Doyle I have eliminated all the other possibiilties so the remaining one, regardless of how improbable it seems, must be the solution to the mystery. And I didn't have to tear the boat apart to get to this point.

When I fly a plane I don't bank the plane by turning the yoke. I know how the wing works and what it needs to do to the air in order to bank the plane and thus change the direction the plane is flying. I visualize what I want the air to do around the wing to make it bank. And in order to make the air do what I want it to do to bank the wing, I have to turn the yoke.

There is a difference between the first sentence in the last paragraph and the last one. Subtle, perhaps, but it's the difference between simply doing something because you think or were taught that that's what you're supposed to do, and doing somehting as a result of understanding the "system" well enough to know the exact action it will take to achieve the desired result. I believe that same philosophy should be applied to troubleshooting.
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Old 05-30-2012, 07:13 AM   #49
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Very nicely written, Marin, with even a nod to the world's greatest detective thrown in (well maybe him and Travis McGee).

I would also humbly add that the first step to hiring a professional repair person, if you choose to do so, is to do some troubleshooting yourself. "My boat won't work" just isn't enough info. Plus around here, you just can't hire anyone to do a lot of the stuff I have to do to my boat, at any price.

Personally, I enjoy a good percentage (though not all) of my boat work. As I've owned it, my skills have improved and I enjoy it more, now that I don't always feel so clueless.
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Old 05-30-2012, 10:25 AM   #50
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So are lift pumps a spare part that a person would normally carry onboard a diesel powered boat?
I'm likely an exception but I carry several. I have spares for the Onan on both the boat and the bus. I have spare Lehman lift pumps and rebuild kits on the boat and I have a spare Detroit lift pump on the bus. They're cheap and they can stop you "out of the blue". An injector pump will (usually) wear out slowly with lots of warning but the lift pump can fail just because.
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Old 05-30-2012, 01:21 PM   #51
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We carry a spare lift pump for each Lehman.

VERY important, however, is to also carry the tools to change it. In the case of the Lehman 120, it takes a specially ground-down wrench to get some of the attach and hose hardware off of it. So don't just buy a spare part and think you're covered. You may need a special or modified tool to change it.
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Old 05-30-2012, 03:11 PM   #52
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Greetings,
Mr. Marin. I have had occasion to change a Lehman lift pump on the go, as it were, but I don't recall the need for any special tools. What I DID have need of and what wasn't anywhere to be found in any of my spares was a replacement 5/16-24 nut when one of the two decided to play hide-and-seek somewhere under the engine when I dropped it! At LEAST 5 of every size from 2-56 to 1-14 but nary a 5/16 (now have 6 on board).
I would humbly suggest in the list of spares and to keep thing on the less expensive side, a trip to Lowes or similar and buy an assortment of regular grade nuts and bolts to keep in the "stash". These need not be the best or "official" fasteners, mightn't cost a lot BUT may get you home. Seal 'em up in empty PB jars (plastic) with a shot or two of oil or in the case of our British and Australian brethren, empty Vegamite or Marmite containers....Oh boy, here we go again!!!!!!
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Old 05-30-2012, 04:20 PM   #53
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As I recall what works best on the nut that Marin is referring to is an open end ignition wrench. Not something everybody has in their toolbox and as a matter of fact I didn't have one either. I got mine off with two different combination wrenches because each happened to have just a slightly different offset but I put it back on with a borrowed ignition wrench. And when I get back to the boat I will have a set of those because whoever dies with the most tools wins.
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Old 05-30-2012, 04:35 PM   #54
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The issue with the lift pump isn't the size (measurement) of the required wrench but its thickness. You need a pretty thin wrench to fit the space. A tappet wrench will work or an ignition wrench. A friend ground down a regular wrench for me.
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Old 05-31-2012, 10:32 AM   #55
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I also changed the lift pump in my Lehman without any special tools other than what was in my toolbag. I don't recall a specially ground wrench and I don't own ignition wrenches. Maybe the wrench I used was thinner than standard.
I didn't save the old lift pump even though it was still working. I considered it trash. I did however build a filtering system and installed an electric pump that can function as a lift pump should the need arise.
And there is also the outboard engine squeezball rig that can be the backup to the emergency lift pump. Yes I have friend who once helped run a boat back from Martha's Vineyard to Rhode Island using a squeezball rigged up to a Perkins diesel.(Their forearms looked like Popeye's after the trip)
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Old 05-31-2012, 10:47 AM   #56
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The fuel filters can be had from NAPA and are quite inexpensive. Worth changing.
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Old 05-31-2012, 11:10 AM   #57
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If you have a fuel polisher onboard, you can set the pump to pressure charge the motor in an 'emergency' scenario where the lift pump fails.
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Old 05-31-2012, 11:28 AM   #58
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did I miss it? why did the engine stall in the first place?????
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Old 05-31-2012, 12:26 PM   #59
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I have a problem with a starter on a 3208 n.a. Cat.

About 50 % of the time when I turn the key she spins right up and starts in about a 1/2 second. other times I get nothing. I hear a click from the fuel solinoid but nothing. I have to use a screw driver to jump the solinoid and the she will start right up.
Voltage is good on all connections.

When the starter is ingaged the solinoid pushes a lever on a large spring to push the gear into the fly wheel .

Could it be rust on the inside of the starter at the lever and spring?
While throwing parts at the problem
I replaced the solinoid and had to pull the starter to do this I noticed an excess of rust when the starter came off.

Do you think this could be my issue?

SD
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Old 05-31-2012, 02:26 PM   #60
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That part that engages the starter to the flywheel used to be called a Bendix and yes, they can get sticky. I need to keep the one on my Onan on the boat lubed regularly. Its a real prick to get at so I usually stick the little red pipe on my favorite can of miracle lube and wave it around in the general direction of the Bendix. My warning that I need to do it again is a couple of fail to starts. On mine engaging the key again usually corrects the problem as long as I don't go too long between spray lubes.
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