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Old 11-26-2021, 12:50 PM   #1
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Does your Ford-Lehman 120 ever "make" oil

Looking over my old maintenance records, I noticed that on 21 October 1989 an oil sample revealed >2% fuel dilution in the port engine. I think that sample was taken after I noticed a slight rise in the level on the dipstick. Over the next three days I put new copper washers on the six injector banjo connections, tested all six injectors, replaced the injector pump, and put new rubber washers on the injector inlet adapters on the side of the engine and hoped for the best. In November the generator also exhibited fuel dilution on its lube oil (resolved with new lift pump), and in February 1990 the PORT Lehman 120 oil sample reported >1% fuel dilution (number 6 injector banjo connection leaking). However, my stbd engine continued to show fuel dilution, but it was getting toward time to load the boat onto the trailer taking it from San Diego to Galveston and thence on its own bottom to Panama City, FL after my military retirement. So, I loaded up a lot of oil and filters to cover numerous oil changes during the 560-mile run to PC from Galveston. Finally, in June 1990, I was told to connect a bicycle pump with an integral check valve to the return fuel line connection at the back end on the engine's head and pressurize the system to a few pounds. With the valve cover off, it was just a few seconds before I spied bubbles coming up through the top of the number 2 injector - the pop test in October had not revealed this low pressure leak. Problem finally solved with a rebuild of that one. Only took eight months to fine that one. After that rash of dilution issues until 2015 when I sold the boat, I never had another fuel dilution issue, but I was truly sensitized to the issue after that!
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Old 11-26-2021, 01:29 PM   #2
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Our Lehman did after I replaced the injectors. I lost oil pressure via the gauge after about 8 hours. I shut it down and checked the oil level and it was 2Ē high. I got towed back to our marina and called around. Bomac Marine said to check the leak off pipe (fuel return line). I had not tightened the pipe at one of the injectors and return fuel was leaking into the oil. Fortunately we didnít get into a run away engine situation.
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Old 11-26-2021, 02:20 PM   #3
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So how did fuel get into the lube oil via the leak off pipe? I'm not real familiar with FL's but on every diesel I've had that leak would just run down the outside of the engine into the bilge. BTDT.
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Old 11-26-2021, 02:34 PM   #4
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Leak off pipe is under the valve cover.

3500 hours since ownership and 200 since rebuild.

Have done the leak down pressure test 2X and no leaks.

O% fuel dilution in the 15 to 20 oil samples sent out.
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Old 11-26-2021, 03:00 PM   #5
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That would do it. All of mine were on the outside.
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Old 11-26-2021, 08:19 PM   #6
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Quote:
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Looking over my old maintenance records, I noticed that on 21 October 1989 an oil sample revealed >2% fuel dilution in the port engine. I think that sample was taken after I noticed a slight rise in the level on the dipstick. Over the next three days I put new copper washers on the six injector banjo connections, tested all six injectors, replaced the injector pump, and put new rubber washers on the injector inlet adapters on the side of the engine and hoped for the best. In November the generator also exhibited fuel dilution on its lube oil (resolved with new lift pump), and in February 1990 the PORT Lehman 120 oil sample reported >1% fuel dilution (number 6 injector banjo connection leaking). However, my stbd engine continued to show fuel dilution, but it was getting toward time to load the boat onto the trailer taking it from San Diego to Galveston and thence on its own bottom to Panama City, FL after my military retirement. So, I loaded up a lot of oil and filters to cover numerous oil changes during the 560-mile run to PC from Galveston. Finally, in June 1990, I was told to connect a bicycle pump with an integral check valve to the return fuel line connection at the back end on the engine's head and pressurize the system to a few pounds. With the valve cover off, it was just a few seconds before I spied bubbles coming up through the top of the number 2 injector - the pop test in October had not revealed this low pressure leak. Problem finally solved with a rebuild of that one. Only took eight months to fine that one. After that rash of dilution issues until 2015 when I sold the boat, I never had another fuel dilution issue, but I was truly sensitized to the issue after that!
Thanks for sharing the knowledge
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Old 11-26-2021, 11:45 PM   #7
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Our Lehman did after I replaced the injectors. I lost oil pressure via the gauge after about 8 hours. I shut it down and checked the oil level and it was 2Ē high. I got towed back to our marina and called around. Bomac Marine said to check the leak off pipe (fuel return line). I had not tightened the pipe at one of the injectors and return fuel was leaking into the oil. Fortunately we didnít get into a run away engine situation.
How does that cause a run away engine?
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Old 11-27-2021, 01:42 AM   #8
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I have also experienced a leaking diaphragm in the lift pump causing the issue. Just another thing to check.
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Old 11-27-2021, 08:05 AM   #9
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How does that cause a run away engine?
Too much oil can can be forced up past the rings and can become an uncontrolled fuel supply. The only to shut it down before there’s any damage is to kill the air supply.
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Old 11-27-2021, 11:15 AM   #10
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Too much oil can can be forced up past the rings and can become an uncontrolled fuel supply. The only to shut it down before thereís any damage is to kill the air supply.
I've been thinking about this for a while.
I ask myself "How would I shut down my Lehman 120 if I had a runaway?"

Wanting to make sure I am always prepared, I figured I would need something to choke the air supply via the air intake filter.


I am thinking of just having a double-bagged shopping bag stowed in the engine compartment near the air-intake filter that I can quickly access and deploy over the air intake to choke off the air supply. Any thoughts on this? Is there a better way? Please advise
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Old 11-27-2021, 11:43 AM   #11
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Too much oil can can be forced up past the rings and can become an uncontrolled fuel supply. The only to shut it down before thereís any damage is to kill the air supply.
Larry, I do not think that can happen. If the rings are so worn to allow oil to pass there then would not be compression for ignition.
I would expect a sudden hydraulic lock occurring and things breaking.
Glad you caught yours before that occurred.
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Old 11-27-2021, 12:43 PM   #12
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I have read where it's the blowby ingested via air intake feed.
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Old 11-27-2021, 12:45 PM   #13
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I have read where it's the blowby ingested via air intake feed.
Happens with turbo seal oil leaks too
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Old 11-27-2021, 12:46 PM   #14
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Never seen or heard of it happening with a Lehman but it does with the 6 series Detroits. I always kept a rag handy to toss into the supercharger if necessary.
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Old 11-27-2021, 12:53 PM   #15
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My business repairs heavy equipment so we get a run away every once in a while. Our way to shut them down is with a C02 fire extinguisher. Works every time and causes no harm to the engine. We keep one specifically for that purpose.
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Old 11-27-2021, 03:54 PM   #16
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ÖI am thinking of just having a double-bagged shopping bag stowed in the engine compartment near the air-intake filter that I can quickly access and deploy over the air intake to choke off the air supply. Any thoughts on this? Is there a better way? Please advise
On a Lehman, if a runaway were to occur, I wouldnít use any bags. Think beyond wide open throttle. Youíd be in neutral with an ungoverned fuel supply. The engine is using/sucking lots of air.

Some air air intakes have a flat surface that you could place a cutting board or flat surface up against the air intake but not on a Lehman.

Iíve never experienced a runaway engine but have talked to a few mechanics that have. Not for the faint of heart imho.
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Old 11-27-2021, 03:55 PM   #17
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My business repairs heavy equipment so we get a run away every once in a while. Our way to shut them down is with a C02 fire extinguisher. Works every time and causes no harm to the engine. We keep one specifically for that purpose.
Thatís the answer. Thanks for that.
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