T&T: Lehman 120 Life Span?
pac...@att.net
Vic Kucera
Pacific Star
Ketchikan, AK
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Ken Williams
Bob Smith says with good care, 20k hours! Mines just broke in at 3200
hours. Excellent, reliable, simple engine I must say!
Respectfully
Ken
KK42
Continuum
Faure, Marin
and sweet talk?
Anything can and will break unexpectedly. But assuming maintenance
carried out in the manner for which these 1950s vintage engines were
designed (ie, frequent), and operation in accordance with the philosophy
of the engine's design (ie, conservative), the Ford Lehman 120, if used
regularly, is said to be a 12,000 to 14,000 hour engine. That means
between major overhauls. It does not mean that's how long it will run
with little more than routine oil and filter changes.
>From everything I have learned from people like Bob Smith at American
Diesel, the Lehman 120 has three relatively high-wear items that will
need periodic overhaul or replacement. These are the coolant pump, the
original, two-part Jabsco raw water pump, and the Simms injection pump.
The coolant pump is no different than the coolant pump on a car. The
vulnerable item is the shaft seal, as this will eventually wear out and
allow the pump to leak coolant. One way to prolong the life of the seal
(and bearing) is to not put a heavy side load on the pulley with the
drive belt. You don't want it loose enough to slip obviously, but you
don't want to over-tension it or try to power some monster alternator
with the same belt. Fortunately, the coolant pumps are available new
and are not expensive ($129). Good idea to buy and carry a spare.
The original, two part Jabsco raw water pump is a problem waiting to
happen. The problem is not so much the Jabsco pump itself, but the
drive unit that couples the pump to the engine. This drive unit, which
was designed by Lehman Brothers and made specifically for the Lehman
120, was the best solution at the time. However it apparently was very
difficult to manufacture. In fact Bob Smith told me yesterday that it's
the only component on the Ford Lehman 120 to have had a factory recall.
The Jabsco 5850-0001 pump is still available new as are parts for it, so
it can be rebuilt if necessary. The drive unit is no longer available
new-- they can only be rebuilt. And according to Bob, rebuilding them
is a rather iffy proposition, so a rebuild is likely to not have a very
long life. What happens is the bearing(s) in the drive unit gradually
wear which in turns allows the pump end of the drive shaft to wear and
eventually break.
The solution is to replace the whole deal with a new Johnson one-piece
pump. These are available from American Diesel (and I assume other
sources) and the cost per pump is about $360. It's a simple, bolt-on
setup. The only change necessary is to install a longer hose between
the pump and the oil cooler because the Johnson pump is shorter than the
original two-piece pump setup. The hose is included in the pump kit
from AD.
The Simms injection pump slowly wears out because it's the nature of the
beast. The lube oil in the pump's sump only lubes the drive mechanism.
The jerk-injection plungers (or pistons if you will) are lubed in their
bores by the fuel they are pumping. As the engine is used the plungers
and bore walls slowly wear down and more and more fuel can get by them
and dilute the lube oil down below in the sump. Every pump except
possibly a newly overhauled one will dilute its lube oil to a degree.
But eventually the dilution will get severe enough that the lubricity of
the oil in the sump becomes compromised. Also, the pressure behind the
"shots" of fuel being sent to the injectors will start to fall off.
When all this happens, it's time to have the pump overhauled.
The Simms pump is the single most expensive component on the engine, and
this plus the fact that just about every pump is putting at least some
fuel into its lube oil makes it imperative that the oil in its
self-contained sump be changed at the recommended interval of 50 hours.
Yeah, yeah, I know there are people on this list who say they go 200 or
more hours between Simms pump oil changes and have had no problems.
Well, nothing has a problem until it breaks. The pump's sump holds very
little oil and it takes no more than 15 minutes to change it, so there's
no real reason not to do so and thus help maximize the service life of
the pump. I've changed the oil during a cruise when the 50 hours are
up--- it's no big deal.
The single greatest enemy of the FL120 is heat. Obviously things like
the little oil and transmission heat exchangers have a finite life and
should be changed periodically. And when you change them, don't skimp
and get the cheapo exchangers, spend a few dollars more and get
cupro-nickel exchangers. They last a lot longer. But the raw water
pump impeller-- Jabsco or Johnson--- should be changed periodically.
Hoses should be monitored for leaks. If the engine should overheat,
shut it down until you can determine the cause. Don't just assume it's
a faulty sender or gauge, although these are certainly possibilities.
The manual says the lube oil in the FL120 should be changed every 200
hours. That's fine, but I've never had an automotive, marine, or
aircraft mechanic tell me that fresh oil is bad for an engine, so we
change the oil and filters on our FL120s every 100 hours. Compared to
the cost of rebuilding a diesel or repowering the boat, new lube oil and
filters every 100 hours is free.
Bob Smith knows of FL120s that have gone in excess of 25,000 hours
before needing a core rebuild. However, these engines were in constant
service with (I believe) the Washington State ferry service (powering
generators, perhaps?) and received excellent servicing and maintenance.
In recreational boat service where they are run less frequently, they
won't deliver that sort of life. But if maintained and serviced
correctly, run conservatively, and not allowed to just sit for long
periods of time (unless they've been properly pickled) 12,000 to 14,000
hours is not an unreasonable service life to expect for the core engine.
The most important thing to remember about the FL120 is that this is a
1950s engine with 1950s metallurgy, 1950s (British) design practices and
manufacturing techniques, and 1950s service and maintenance intervals
and requirements. So if you treat them as though it was the 1950s,
you'll have great success with them. If you try to operate them as
though they were no different than the modern Cummins, John Deere, Cat,
etc., in your boating buddy's boat, you'll most likely have a lot of
grief with them.
______________________________
C. Marin Faure
GB36-403 "La Perouse"
Bellingham, Washington
John Walsh
purchase a cruising boat. Is there someone out there who could write a
similar summary on the life expectancy of 375 hp 3208TA Cats that are used a
lot of Grand Banks and some Hatterases?
John
S/F Profishent
Deale, MD