Ford Lehman Fuel Injectors

I have twin 120 Ford Lehmans in my 44 ft OA.* For some reason the port engine has started to drop off 50 to 100 rpm routinely when running at 2000 rpm plus.* I have almost 4,000 hrs on the 1982 engines.* Is it time to rebuild th injector pump?* Clean injectors?

I was told on the Ford Lehmans to do the injectors at 4-5000 hours - rebuild with new tips.* Can't say about the pump.* Get a hold of Bob or Brian Smith at American Diesel.

For peace of mind I recommend you pull the heads and get them rebuilt. Also good time to inspect cylinders, 4,000 hrs us a lot of run time. I did this at 4,200 hrs and discovered a pitted cylinder that can be sleeved and rebored as well as a malfunctioning exhaust valve.

MVDarlin said:

I have twin 120 Ford Lehmans in my 44 ft OA.* For some reason the port engine has started to drop off 50 to 100 rpm routinely when running at 2000 rpm plus.* I have almost 4,000 hrs on the 1982 engines.* Is it time to rebuild th injector pump?* Clean injectors?

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When was the last time you changed your fuel filters?

Also had injector pumps rebuilt. Unless you can say with certainty the injector pump oil was changed every 50 hrs a rebuild is likely needed.

I would pull the injectors and bore scope the cylinders before removing the head.

And I would do a whole lot more diagnostics before rebuilding stuff.

4500 hours is nothing on a half way well maintained Lehman. I've seen injector pumps go damn near forever before a rebuild without having the oil changed in them on a regular basis.

So rule the simple things out first.

I think you should just spend a dozen boat dollars and just rebuild them both because you'll get a groovy new paint job on them. You could even pick the colour.

Reread what Capt.Bill said and start with your fuel filters.

There is very little useful information in your initial post, such as why you are running over 2000 rpm, what is your WOT reading, what are the coolant temps at WOT? That would help a diagnosis. And reread Capt.Bill's posts.

Capt.Bill11 said:

I would pull the injectors and bore scope the cylinders before removing the head.

And I would do a whole lot more diagnostics before rebuilding stuff.

4500 hours is nothing on a half way well maintained Lehman. I've seen injector pumps go damn near forever before a rebuild without having the oil changed in them on a regular basis.

So rule the simple things out first.

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I'm dealing with all this now. Hence the recommendations.

MVDarlin said:

I'm dealing with all this now. Hence the recommendations.

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Yes I get that. I'm just assuming at least you didn't just start pulling things off willy nilly and rebuilding them before having a firm handle on what needed to be done.

The 50 hour injection pump oil change is a myth.

Even American Diesel and Bomac have put out different info on the topic.

As long as fuel isn't diluting the oil...it could go for thousands of hours....well if not thousand, many hundreds more than 50.

At least one member reported running it for many hours with no oil in it at all.

Like all mechanical things..it needs watching and regular maintenance.....not kissing it goodnite every day.

I cruise in vrry rrmote locations and need reliability. My port injector pump locked up at WOT and caused a runaway. Very scary. So a rebuild was necessary. Being prudent I had starboard injector pump rebuilt as well. It was in better condition. Port engine developed a knock so pulled head and found pitting in cylinder next to exhaust elbow as well as exhaust valve carbon / distress. Replacing piston and sleeving cylinder is next step.

Rear piston knocking?

Probably number 6, most common.

My Lehman manual says change the injector pump oil at 200 hours, other apparently say 50 hours. I figure changing it with changing engine oil is often enough.

My Lehman manual says injector pump oil every 50 hrs, engine oil every 200. They also like to have their valves adjusted every 2000 hrs. That might be what the knock is.

Greetings,
Welcome aboard.

I took Bob Smith's Lehman seminar in Oct 2015. He said to change the oil in the 120s at 50 hours. He said that you could go a little longer if it was not diluted by oil. He said each engine has it's own personality and you should change the injector oil at 50 hours and see if it is diluted. If not diluted then extend the interval a little and see how it is. One member in the class said he has twin 120s. One needed changing at 50 hours and the other routinely goes 100 hours. Fortunately on my SP225s I don't have to change the oil in the injectors.

new2trawl said:

My Lehman manual says injector pump oil every 50 hrs, engine oil every 200. They also like to have their valves adjusted every 2000 hrs. That might be what the knock is.

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Comodave said:

I took Bob Smith's Lehman seminar in Oct 2015. He said to change the oil in the 120s at 50 hours. He said that you could go a little longer if it was not diluted by oil. He said each engine has it's own personality and you should change the injector oil at 50 hours and see if it is diluted. If not diluted then extend the interval a little and see how it is. One member in the class said he has twin 120s. One needed changing at 50 hours and the other routinely goes 100 hours. Fortunately on my SP225s I don't have to change the oil in the injectors.

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Do you know if Bob still does those seminars or did Brian become the new teacher?
My twins - Lucy (Stbd) and Ethel (Port) - never run past 1900 rpm. <2200 hrs on both. Ethel has a little fuel leakage in her injector pump but nothing to get excited about right now. These old tractor motors run forever with a little attention.

Unfortunately Bob Smith passed away. I am not sure if Brian is going to continue on with them. Bob was a wealth of knowledge. It was amazing in the class whenever anyone asked him a question, the depth of his knowledge was staggering.

MVDarlin said:

I have twin 120 Ford Lehmans in my 44 ft OA.* For some reason the port engine has started to drop off 50 to 100 rpm routinely when running at 2000 rpm plus.* I have almost 4,000 hrs on the 1982 engines.* Is it time to rebuild th injector pump?* Clean injectors?

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Its time to check your fuel filters before doing any thing else also if still using the mechanical fuel lift pump check that as well,if it's a serviceable type they usually have a small very fine gauze inside which i have seen gummed up more than once, the injection pump requires a positive pressure from the lift pump to reach full RPM output, (low input pressure-low output pressure-reduced RPM),

OR perhaps few barnacles on the Port prop?

Check the simple things first , by the way 4000 hours for these engines is not a worry if serviced on schedule

The L120 Manuals vary between specifying 50 hours and 200 hours(mine). I settled on 100 hours.

Drain the oil at 50 hours and check condition (measure the volume) go to 100 hrs and measure it again. Its entirely fuel dilution that drives the change interval as the pump is a series of interference fit devices that some fuel can get past. If you did not change your Simms oil regularly in the past, your pump will make more fuel.

Also, the case material (cast aluminum) is very soft, be very careful when removing and replacing plugs. They are very easy to strip out the threads.

If you can find someone with a lathe you can make thread adapters to take a water-maker ball valve to screw into the drain. Then you can thread-lock it and forget about damaging threads ever after. You can also remove the drain pipe on the side of the pump and cap it so you will know the precise amount of liquid when you drain it and you can lose the mess you had in the bilge or catch-cup. I also never removed the level plug, just measured the replacement oil. Make sure your filler cap is the one that has the tiny breather hole in it, essential if you remove the vent pipe.

I usually drained the oil into a ziplock as it fit in the awkward drain area and periodically caught the plug and its washer before the bilge ferret could grab it.

psneeld said:

The 50 hour injection pump oil change is a myth.

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This is in the Ford operation manual.

My engine also used 15W40 oil for awhile.

It wasnt recommended in the manual but lot of EXPERTs including Am. Diesel, Bomac and every other good Lehman mechanic I talked to said modern oil and old manuals are just that...

A lot of recommendations have changed through the years since that manual was written.

Its not about mindlessly changing the pump oil, its about fuel dilution of that oil.

Most engines have volumes of tech order updates or service bulletins through the years..... where are the ones for Lehmans?

Exactly.....

"I usually drained the oil into a ziplock as it fit in the awkward drain area and periodically caught the plug and its washer before the bilge ferret could grab it."


Every now and then - a golden nugget. Thanks.

Wow you're welcome! Just passing on the wisdom of other ancient mariners. I thought I was being ignored again, wasting my time here but occasionally a response like your makes it rewarding.