Apparent overheating Ford Lehman 120

Note that the piston I have shown has about 4500 hours on it.

To mention as probable, "how do you know this is an overheating issue?"

kolive said:

I was recently talking with a mechanic about this potential problem, we have twin FL 120's in our boat. He was recommending a simple external temp alarm be installed on the exhaust elbow to warm of high temps often associated with cylinder 6 overheating issues. The alarm could give a warning and time for shutdown to possible avoid catastrophic failure. I monitor with an IR gun as part of my underway checks. The mechanic said it is a band clamp install with wiring to an audible alarm. Seemed pretty straightforward.

Does anyone have this setup on their engines? The photos and problem associated with this repair have my ears tuned in to this thread.

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Here's one on our SP135. In the PNW, it's called a Norm Switch after Norm Dibble who made and sold them. Norm's retired now but you might ask at Pat's Marine in Seattle where he last worked.

Thanks Larry,

That looks exactly like what the mechanic was talking about. He said they have them at North Harbor Diesel in Anacortes. I will check it out next time I get to our boat.

That thing is kind of like putting a smoke detector in your driveway ... by the time it detects smoke the house is pretty far gone.

If the cause of the failure is anything but a raw water circ pump failure, that temperature switch will never detect it. It is only intended to warn of a raw water supply failure ... period.

The out of focus photo of the piston crown makes it difficult to look for clues (though the shiny bright and clean piston bowl waves a red flag) but I suspect a cause that has nothing to do with raw water cooling or even jacket water circulation. If it were my engine I would pull the injection pump and have it tested.

What do you think the injection pump could do to cause this condition? I mean what could fail?

If an adjustment on the metering collar slips, one cylinder can overfuel. That can overheat a piston. Usually this is obvious at idle, as engine knocks and shakes. An injector nozzle valve hanging open can do something similar. The calibration of the system assumes it takes a good bit of line pressure to open the nozzle valve, if the valve is hung open more fuel then desired is injected. Again, this is usually noticed as a sick running engine. With nozzle valve stuck open, spray pattern sucks.

Dick
When you removed the injectors, did you photograph them? Here is how I did it when removed the injectors from my old Lehman 120 (before it was replaced)
InjectorRemovalNov6,2010

If we had photos of the injectors, it might add some pieces to the story of what was taking place in that and other cylinders.

Second question: did you happen to verify that the bleed off tube was air tight? This is a big item that many mechanics miss because they are not familiar with the specifics of the Lehman 120. When the injectors are installed, the bleed off tube must be correctly installed and verified to be air tight. If not, it will allow diesel fuel into the crankcase oil and dilute it, thereby changing the lubrication of the internal parts of the engine. Bob Smith can tell you more about this and its an item he stresses in his engine class. This photo shows you the test rig used to verify the bleed off tube is installed correctly:
Bob Smith/Pelton Passagemaker University Pic 093
Bob Smith/Pelton Passagemaker University Pic 093

I'm not saying that these issues were the cause of your cylinder/piston failure. I am merely saying that since you are having this work done, be SURE these items are followed properly. There are lots of diesel mechanics out there that dont know this !
R.

That would be a "no" to both questions Ralph. But two separate entities pronounced the injectors ok.

When I took my injectors an fuel injection pump to be rebuilt, the technician told me the injectors were "ok". I queried him further to ask precisely what was the pop pressure he measured. The pressure he gave was HALF of that specified in the Lehman manual. I asked him how he could pronounce my injectors"ok" (ie what was his basis) and he said he used the serial numbers and looked it up in a book. He almost argued with me when I instructed him to set the pressure to be that specified in the Lehman book (and verified by American Diesel Corp).

Another case of why I verify everything and do not trust much in technical areas.....
R.

I guess one does not get to be our age without developing some healthy scepticism. The second place I took the injectors to was American Diesel in Kilmarnock. I figured they should know.

If ADC said they were OK then I would believe it.
R.

ralphyost said:

Another case of why I verify everything and do not trust much in technical areas.....
R.

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Spoken like an FAA technical guy, good.

I'm not sure about that...if they were a different injector than OEM but a suitable replacement and the tech verified by serial numbers from the injector manufacturer...that presents a common issue in the marine world.

My guess is that they were exactly the same but verifying sometimes isn't just one phone call unfortunately.

psneeld said:

I'm not sure about that...if they were a different injector than OEM but a suitable replacement and the tech verified by serial numbers from the injector manufacturer...that presents a common issue in the marine world.

My guess is that they were exactly the same but verifying sometimes isn't just one phone call unfortunately.

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Does OEM even apply on a 30+ year old Lehman for any fuel system parts? Sure, AD or TAD can sell one stuff that should work, but mixing and matching old to new injectors can get interesting.

Regardless of the injector manufacturer, the injectors need to open in accordance with the design of the engine...ie at the pressure and timing of the engine design. If the injectors open early (as is the case with low pop pressure) you are effectively changing the timing of when the fuel is introduced into the cylinder and therefore altering the combustion process.

Definitely not trying to hijack this thread, just a quick question hopefully. In reading the thread and all of the experience and knowledge of components that can apparently make huge differences, is there a book or class to get caught up on how to maintain the FL120? Thanks!
~ Jeff

Jbear said:

.... is there a book or class to get caught up on how to maintain the FL120? Thanks!
~ Jeff

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Well Jeff, there is the "Operators Manual & Parts Identification" book which came with the engine.
On p3 Robert F Smith, Executive VP writes " the most important recommendation I can make ....is "do not tinker"(his italics).....unless you know what you are doing, keep your hands off!"
The rest is more encouraging, deals with routine servicing, fuel bleeding, trouble shooting, etc.
I`d ask American Diesel if there is something more extensive, and newer. There are so many of these engines it would be surprising no one has put pen to paper. There are workshop manuals for obscure auto engines, why not for the FL?

Jeff,

Trawler Fest in Anacortes this May has the Bob Smith 2 day class on the Lehman. I sent you a PM.

Oh, I'd like to get in on that class. Sign up info please?

Trawler Fest is in Anacortes this year again. Registration, from the passagemaker.com site is scheduled to open in late February. The class is part of what they call Trawler University, lasts 2 days and costs $450.00. Google Bob Smith Trawler Fest diesel class and you will get more info on what it I does.

I hear very good things about the class. I plan to do it.

These Fords are basic tractor engines with mechanical IP. There is very little to know about these diesels that any general diesel class wouldn't teach. I have a basic diesel in my truck and that has helped me tremendously to understanding these Fords.

One thing I did was to buy new heat exchangers and I custom ordered larger longer units. This has kept the cooling in check for me.

I am no diesel expert. But I am wondering why nobody is considering low coolant flow to be the cause of this. A partially clogged heat exchanger or obstruction in the cooling system could result in the last cylinder overheating.. Was the coolant pump impeller checked? Was the temperature of the coolant checked entering and exiting the heat exchanger? Where is the engine temperature measured? Is it where the coolant enters the engine or wwhere it exits? Or is it measuring the oil temperature.

I apologize in advance if these are noob suggestions, I am just trying to learn as much as I can.

Scott

Perfectly reasonable questions - I have always advocated a new owner replace the heat exchangers and keep the old ones as spares. Particularly the transmission cooler as it has no warnings if it fails, until the transmission fails. One of the boats I looked at to buy had a milkshake in the trans. From a failed cooler.

bligh said:

I am no diesel expert. But I am wondering why nobody is considering low coolant flow to be the cause of this. Where is the engine temperature measured? I apologize in advance if these are noob suggestions, I am just trying to learn as much as I can.

Scott

Click to expand...

This was discussed in a few of the posts.

I took Bob's Lehman class at Trawlerfest Anacortes several years ago, and it was well worth it. He had the class pull the Simms pump, injectors, and reinstall. Adjusted the valves, torqued the head, and restarted the demo FL120. Lots of fun.