Lehman 120 Piston slap

Marin said:

Scott- Thanks much for the update. I did not know they were still doing this, or had started doing it again. I was going off a discussion on the GB owners forum some years ago where the discontinuation of the replacement engine was announced.

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I heard that as well (perhaps here on TF) that's why I asked him.

I think it's a no brainier to drop in a new and improved FL-120 instead of rebuilding one unless the shop is very well known, and then I would question it.

Bob has improved all the weakness out of the engine and as the old ones can and do go 10k hours plus the replacement unit would be the last time you did it.

I wonder if the 6N140 engines will run gracefully at 80% load 24/7? That should be at least 2300rpm propped to 2500. Considering the source I wounder if anyone would have the inclination to do it. If I had one I would'nt be interested in running that hard but I'd sure want the engine to be capable of doing it. And if the boat needed the power I'd want to run it 2000 or 2100 as a normal cruise. And if it didn't need the power I'd be wanting a smaller engine. Re powering is a great place to be .... the only time one has the choice of how much power to employ.

Understand that the 150 hp base engine that American Diesel is using is NOT the same Ford Dorset diesel that the FL120 is based on. The Dorset was taken out of production several decades ago. What AD is using is a modern, in-production Ford diesel that happens to have the same footprint and mounts as the designed-in-the-1950s Dorset.

So it's not like they've created an improved FL120. What they have is a brand new, marinized diesel engine that as luck would have it, has the same footprint and mounting system as the old 120 hp Dorset.

I believe, but I could be wrong, that the main motivation behind doing this was to provide a drop-in replacement engine for the owners of boats with two FL120s who'd had one of their engines fail catastrophically.

Several folks on the GB owners forum have done this in past years and according to them the 30 hp deference between the engines has no operational effect. I don't recall if there was any compensation reflected in the props.

They are using the Ford Dover base in their ADC engine it is very similer (same crank,pistons rods, etc) some but not all part interchangeability. The blocks are named after the English city's they were manufactured in.

It is really an improved FL120 or Sabre 120 but the older Dorset block is not what was available when they bought out the remaining stocks the Dorset block was.

Bob told me they are for most intents and purposes the same, hey he is the guy that makes them.

As you know the 120 Dorset was first used in trucks and did not like the constant speed changes and lugging by bad drivers.

The Dorset was a 135 HP natural engine that found use in many places from pumps to power units and farm equipment.


Both engines are long out of production.

Tech Tips From Dr Diesel

Manyboats, my Operators book says the continuous (24hr) rating is 92.8hp (68.8Kw) at 2500rpm for my 120hp Ford Sabre


Dover block


Dorset

Good information, Scott, thanks. I had gotten the impression from Bob that he was using an in-production engine for the base engine of his 150 hp replacement. I didn't know he'd bought up an existing stock of the old Dover engines.

Oh well I guess I should have said substitute injectors for spark plugs and # 1 cylinder for # 6.... It didn't seem that difficult.
A relatively cheap way to investigate the noise might be revealing, before throwing a bunch of money at a rebuild or repower.

Scott,
That looks like a dyno statistic ... 93hp at 2500rpm. The equivalant running an under propped boat at 2500rmp. I had a Sabre 120 and they had good information. Thirty hp down (almost 30%) is (I think) considerably lower than most engines ... I should probably say most modern engines but I really don't know.

But that stat of yours may show that load is a much more limiting factor that rpm. Most trawler formers feel that rpm is what kills engines ... probably because rpm produces so much noise.

manyboats said:

Scott,
That looks like a dyno statistic ... 93hp at 2500rpm. The equivalant running an under propped boat at 2500rmp. I had a Sabre 120 and they had good information. Thirty hp down (almost 30%) is (I think) considerably lower than most engines ... I should probably say most modern engines but I really don't know.

But that stat of yours may show that load is a much more limiting factor that rpm. Most trawler formers feel that rpm is what kills engines ... probably because rpm produces so much noise.

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Agreed, RPM won't hurt an engine (within working limits) in fact it puts less stress on it then high pressure and low RPM (Lugging) RPM is needed to make power and while noisy can lower temps, fuel consumption and wear.

I consider lugging an engine a crime, learn to down shift or prop it right.

The longest lived engines such as fixed RPM generator units run for years within a narrow RPM band at a constant power output, very similar to what our slow speed trawlers could be doing.

When I bought my 6N140, I recall Brian (or reading somewhere) that ADC imported and registered a slew of engine block serial numbers. In this way they were able to get around the (then) new EPA requirements and still offer for sale their naturally aspirated engines. Plus, the 6N140 made sense as an affordable replacement for the thousands of FL120s out there in trawlerland.


Regarding this engine being "over powered" for under 40' displacement trawlers--I couldn't disagree more; Would you rather have a smaller engine running at 2200 rpm to make hull speed; or a larger engine capable of reaching hull speed at 1650 rpm? Besides, there is nothing like extra horsepower for running against a 3-knot current or having the "umph" to turn your bow into a 20 knot head wind. However, I do regret that ADC wasn't able to do with the 4 cylinder Super Lehman (rated@80hp) that they did so well with the old FL120.

Marin said:

That's a great word, Peter. I think I'll start using it in conversation. It's right up there with one of my all-time favorite words that unfortunately I have little call to use, and that's "strategery."

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You're welcome Marin…feel free. Just as long as you give me credit and don't attribute the word nucular to me…that I would object to. Actually, I like strategery, as it happens, (says Pete, fighting his laptop's attempts to correct the spelling), so I'll give you credit for that if I'm allowed to use it..?

Piston slap can be tolerated in many cases. There is a piston skirt to bore tolerance that on some can be pretty generous. Since the #6 tends to run hot, and aluminum expands faster than iron, running tight clearances is a recipe for piston seizure. On some engines I build, I like to go on the sloppy side of the tolerance to avoid scuffing and seizure.

I don't know the clearance tolerance for the ford, but 0.005" extra may be ok especially if previous problem was seizure.

If noise goes away or diminishes once warm, can't see any harm in just running it. Probably won't wear much faster than normal.

NWboater wrote;
"Besides, there is nothing like extra horsepower for running against a 3-knot current or having the "umph" to turn your bow into a 20 knot head wind."
Never never have I done any of that w my full displacement 30' Willard. I bucked 40 knot winds and 7' seas for hours along Texada Is and ran at 2 to 3 knots bucking the tide in Knight Inlet. In heavy going I've always reduced power 300rpm ... never increased it. There may be a need or want for extra power but I've not found that need w the Willard. In fact I could have done everything I've done w the W30 on 5hp less.

Manyboats, seems you have all the answers.

Ski in NC said:

Piston slap can be tolerated in many cases.....
I don't know the clearance tolerance for the ford, but 0.005" extra may be ok especially if previous problem was seizure.
If noise goes away or diminishes once warm, can't see any harm in just running it. Probably won't wear much faster than normal.

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Looks like the old slapper is good to go.

BruceK said:

Looks like the old slapper is good to go.

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Great one Bruce

nwboater,
It's my opinion and mostly my observation.
And it applies more to FD than others.
Another opinion is that the need for extra power comes directly from our automotive culture where we have and use (mostly or to a great extent) a great deal of extra power. I just bought a VW Jetta and it definitely has considerably more power than I will probably use other than accelerating very hard just for the fun of it. And of course the need for more goes far beyond HP. Heat, money or the excess in capability of your flashlight or your i-pad, anchor and w just about everything we seem to strive for excess.

Did you ever swap injectors around? You may have an injector (or pump) injecting too early in that cylinder causing some clatter. If its the injector, swapping it to say #1 may cause the noise to follow. That would indicate the problem is with the injector and not the piston (or IP).


I would assume the oil report would show physical internal wear and rule the injection system causing the issue.

manyboats said:

nwboater,
It's my opinion and mostly my observation.
And it applies more to FD than others.
Another opinion is that the need for extra power comes directly from our automotive culture where we have and use (mostly or to a great extent) a great deal of extra power. I just bought a VW Jetta and it definitely has considerably more power than I will probably use other than accelerating very hard just for the fun of it. And of course the need for more goes far beyond HP. Heat, money or the excess in capability of your flashlight or your i-pad, anchor and w just about everything we seem to strive for excess.

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Thats because just enough can get you into trouble and having a bit in reserve for the unexpected can be a very good thing.

How would you like to fly with me if I always landed with less then a gallon of fuel remaining in my tank? Hey we had enough.

Or that time you misjudged the rate of closer of the truck while entering the highway and your engine had a reserve of horsepower to prevent a wreck.

Over the years our survival instinct has tough us that it is better to hunt saber toothed lions with more folks then we really need.

SCOTTEDAVIS said:

How would you like to fly with me if I always landed with less then a gallon of fuel remaining in my tank?

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See I take great offense to this. My instructor always taught me "any landing you walk away from is a good one!"

Skinny, I am waiting for the oil analysis and the expert mechanic before moving forward. I just don't have the knowledge to distinguish a fuel knock from a piston slap. I'm leaning towards the slap because of the smaller piston and the knock fades as the engine comes up to temp? Mike

Hang in there Mike.

Busterbrown said:

Skinny, I am waiting for the oil analysis and the expert mechanic before moving forward. I just don't have the knowledge to distinguish a fuel knock from a piston slap. I'm leaning towards the slap because of the smaller piston and the knock fades as the engine comes up to temp? Mike

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I'm interested to see what the oil analysis has to say. I would think "piston slap" would show elevated aluminum PPM due to piston wear. I've seen wrist pin bushing wear cause a significant knock- but I would think the prior repair attempts would have addressed this (I assume it uses a floating wrist pin).


1983 Present 42 Sundeck
Twin Lehman 135's

Oil Report

That's not looking great. My understanding is that the values represented are in parts per million. The normal average value is not shown, but the lab certainly thinks the aluminum (piston), iron (cylinder liner), chrome (rings) and tin (could be rod, main or cam bearings) are elevated. So much for piston slap- as in noise. To me, this clearly shows wear and if you are considering repairing this engine, the sooner the better. Pre failure.


1983 Present 42 Sundeck
Twin Lehman 135's

For an engine with 90 hours since rebuild of one hole I don't find the numbers too surprising. If the hone job was done with the type of hone I suspect then the wall finish would be of the sort that would have to "break in" and iron and chromium would be expected. The aluminum is also to be expected as the piston is a loose fit in the hole. Also, it would seem to me that if the hole was originally bored .020 over and then honed after the seizure of the second piston that it is very likely to be over the .020 so we could be talking about a very loose fit.
The bearing metal (tin, copper) is higher than I would like to see but...
Tin will show after a rebuild and copper, well might be this bearing might be other bearings no way to tell for sure which bearing.
All in all (with out hearing it run) I would think that your choices are kind of like this:
1. Run it and see if the noise gets worse or stays the same and sample the oil every 100 hours to try an establish a trend. I think a failure is possible ( the piston may seize again) but not all that likely. You limp home if it does quit.

Option 2- pull it down now, and go through it again or replace it with a different engine either used or rebuilt ( this would assume that something is so wrong with this one that it could not be repaired). Either way seems like an engine overhaul is very possibly in your future.

I think I would be tempted (trying to put myself in your place) to run it Budget also comes into this, of course.
It either keeps running ( you win) or it dies and you rebuild it. Of course, you have to decide if that is going to stress you too much to live with. Some people can live with the nagging worry and others can not.

The mechanic looked and ran the engine. BryanF you called it, the mechanic said the oil report is not as bad as it looks and he has worked on hundreds of these engines and some make more noise than others. Because the knock fades away as the engine grows and runs smooth under load just run it. Take an oil sample at 100 hours and call him with the results. Thanks everyone for all the input. Mike

A single, unique oil analysis is a waste of time. You need trends. Look in the holes and look for damage. None visible? Carry on.

Busterbrown said:

The mechanic looked and ran the engine. BryanF you called it, the mechanic said the oil report is not as bad as it looks and he has worked on hundreds of these engines and some make more noise than others. Because the knock fades away as the engine grows and runs smooth under load just run it. Take an oil sample at 100 hours and call him with the results. Thanks everyone for all the input. Mike

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Glad to hear the good news. Keep us posted after the next sample.


1983 Present 42 Sundeck
Twin Lehman 135's

Thanks, Steve will do I should be able to put another hundred hours on her by July. Mike

BusterBrown,
Just for S and G
I'm sure this doesn't apply to your engine at all- but am going to post a couple of pictures and hopefully a short video of a #1 piston we pulled today in a mid '80s Hyster forklift with a 192 Ford Industrial GAS 4 cylinder engine. Compression was 130-150 all 4 holes.
The customer does most of their own maintenance (or non maintenance) and none of my guys actually ever remembers hearing it run in the past. The engine had seized- and the owner and I agreed to lift the machine, pull the pan and determine if it could be repaired low dollar, as in polish the rod journal and roll in new bearings. Turned out #1 was seized, and loosening the rod cap allowed us to turn the crankshaft. The rod bearing inserts had not "spun" inside the connecting rod, and the rod journal was actually in pretty good shape. It was a little puzzling- the oil pump feeds from the center of the crankshaft yet #4 rod bearings and the rear main journal did not look oil starved (we assumed it had run out of oil). Damn this is a long story. My thumb's getting tired.
Anyway, Polish one rod journal, new rod/ main bearings- torqued, new lube filter and fill with oil. Started.
The engine had a definite knock. Pulling the #1 plug wire (effectively taking the compression load off of the cylinder) did not quiet it.
Holy cow- I think we have some "piston slap" going on!!
My guy Ben pulled the pan again, removed the head, and this is what we saw. Ugly...
We have piston gaulding (imagine THAT oil sample), I suspect piston slap, and extreme wear on the connecting rod piston pin bushing (video if it makes it). I'm not sure why the piston originally began to seize, but I believe the rod bearing and wrist pin failures were a result of it. Thought some of you might get a kick out of the pictures. Sorry, no luck with video so grabbed a screen shot.


1983 Present 42 Sundeck
Twin Lehman 135's