Ford Lehman 120 seized piston

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DeliveryCaptain

DeliveryCaptain

Member
Joined
Sep 20, 2023
Messages
18
Location
Los Angeles, CA
Vessel Name
Bear Flag
Vessel Make
'81 Her Shine 40
'81 Her Shine 40. I'm sure this has been discussed at length here somewhere, but I couldn't find it. We bought the boat knowing the starboard engine #6 piston was seized in the cylinder (yes, we got the boat for a good price). There seems to be enough room to drop the oil pan and slide it forward enough to get at the connecting rod. The head is off the engine, so I'm thinking of sectioning the piston by drilling holes in it and removing it from the top. If the cylinder wall isn't too damaged, hone it, new piston and rings, and reassemble. I'd like to hear from anyone who has successfully dealt with this issue without pulling the engine.
 
I had Lehmans in a previous boat. They silt up, impeding coolant movement, around no.6 especially but there could be other causes. I had mine flushed when temps rose. I recall other stories of this issue on TF but not of a fix in situ. My recollection is the problem ended up more extensive. But if you can get access above and below and the block is not so damaged it needs reboring or has other more extensive damage, why not give it a go. You could try searching for old L120 threads.
 
Yes, number 6 is the price child. Have you tried American Diesel for advice?
 
I had one get stuck on a Lehman 275 due to a valve implanting itself in the piston crown. We drilled and chiseled with little care because it was sleeved.

I imagine the same can be done with the 120, but with extreme care to not damage cylinder walls. If you do, some machine shops have a mobile boring machine. I’d call around to find one and price it prior to attacking the piston—your back plan,

That said, since you have access to the top of the piston I’d heat it and the surrounding cylinder wall with a torch, then fill with penetrating oil. Trying barring the crank a bit. If needed, let sit a bit then try again. Once out, you’ll want to check the cylinder roundness and the crank journal surface as well as that on the rod.

Brian at American diesel can provide a piston, rings and bearings. Since the head is removed, now is a good time for the machine shop to do a cable job. Brian can provide the needed parts there too.
 
In my earlier boat, a GB42 with twin FL-120s both nº 6 pistons seized. I helped the mechanic that replaced them, with the engines in place and the boat in the water.

With the head removed and the connecting-rods loosened and lots of Kroil he drilled the tops of the piston and ran a cable to pull up on the piston. I stood above the engine, astride the engine opening to the salon, and pulled up with a 4:1 pulley system. While I pulled the mechanic tapped the piston head with a hammer and the piston eventually released.
 
Xlantic said:
In my earlier boat, a GB42 with twin FL-120s both nº 6 pistons seized. I helped the mechanic that replaced them, with the engines in place and the boat in the water.

With the head removed and the connecting-rods loosened and lots of Kroil he drilled the tops of the piston and ran a cable to pull up on the piston. I stood above the engine, astride the engine opening to the salon, and pulled up with a 4:1 pulley system. While I pulled the mechanic tapped the piston head with a hammer and the piston eventually released.
Click to expand...
Xlantic, that sounds like a great plan. I have Kroil and a small chainfall. Were either of the cylinder walls damaged?
 
There was some scoring in the cylinder walls but it was not a problem. I used the boats for several years afterwards without issue.

This was almost 20 years ago so I do not recall if the mechanic honed the cylinders or not but it seems to be like a good thing to do.
 
Before you do anything, call Brian at American Diesel.

He is the ONLY FL EXPERT.

Web site AmericanDieselCorp.com the phone number is there. He usually responds better to phone calls.

Good luck with your project.
 
I am getting curious now. I also have FL120's, but never heard the story of cylinder 6.
Can anyone explain what the problem is, so that I can prevent this from happening ? Or are there any good fixes that I can use already now ?
 
It is the lowest cylinder and the closest to the exhaust elbow. So it is the first cylinder to suffer any raw-water intrusion issues.

I would guess it is a problem not limited to FL 120s. But on the FL 120s, don't know if it the case with other engines, the exhaust elbow also closes-off the coolant channels at end of the cylinder block. So, a bad exhaust-elbow gasket or loose fasteners could let coolant into the exhaust manifold and on into the cylinders.

The first line of defence is having a well-designed exhaust system and an exhaust-elbow in good condition, with good gaskets and properly torqued-down fasteners.
 
Last edited:
Thanks, there is indeed not a lot to be done about that. I already had to change an elbow last year, but problem is that you cannot find new ones anywhere. So the replacement I have was already used before, hope it will survive.
 
Ok, I will contact him again and hopefully he has them now. Also still waiting for heat exchangers and oil coolers, apparently difficult to get to for him as well
 
Mambo interesting to hear about the oil coolers, I just sent him an email inquiry yesterday on a replacement oil cooler but haven't heard back yet.
 
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