Lehman Replacement ?

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Oct 31, 2007
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Vessel Make
Willard Nomad 30'
After all the Volvo, Cummins and old Lehman talk I did a bit of surfing ( very little ) and came up with an interesting possible replacement for the 120/135 Lehmans. Most of the guys with them don't seem to need much more than half power so a full power replacement would'nt make sense and some need a bit more power like perhaps a GB 36 w single eng. Many said they liked the simplicity of the Lehman. The engine I have in mind is a small IVECO. 99 and 148hp, 4 and 6 cyl versions of the same basic engine. CCW rotation, 274 and 409 cu in. Comp 17.5. Weight 992 and 1168 lbs. They are both naturally aspirated and to my knowlege no electronics. I don't see that they are in any way more complicated than a Lehman. They are rated for pleasurecraft use up to 90% power continously so the 99hp 4cyl should work very well for most but if one had a boat where the owner wanted to run his boat at full speed w the Lehman the 148hp IVECO should deliver.
They are availible from maesco.com ( Mid Atlantic Engine Supply Corp.).
Or Klassen Engine Co. www.klassenengine.com. Call Dave Rowland at 1 206 784 0148. I can recomend them as I bought my Mitsubishi there. I highly recomend thier all steel exhaust manifold ( no aluminum ) and optional Murphy switch ( low coolant level warning ) Don't know about flywheel and belhousing compatability to BW ect ... call.

Eric Henning
The Fiat used is a great engine , according to my Euro pals , its used worldwide in some really horrible places where maint is at i minimum.

AS a truck or tractor engine it should take long periods of 20% - 40%power use as well as the Econ o power Ford/Leman marinizations.

Last Sunday went to the Seattle Boat show with main interest to see what engines where being installed in the new trawlers under 60 ft.* Deere was first, Cummins second, Volvo third.* I think its because they make a long narrow low hp engines so twins can be installed and/or walk around engine rooms

At the boat show I was told that Lugger uses Deere engines for many of their models, so Deere decided there was a market and started selling their engines directly to the boat mfg.*

This is what I was told and saw at the Boat Show.*
3 cylinders inline is smooth , the use of a 6 is great as it is smoother.

For reliability take a look at the antique DD 6-71.

7 main bearings , in place replaceable for overhaul , and mostly one side for service (owners choice.)

Reversible with no extra parts , for the twin screw folks.

Hard to beat , although the 1930's design does use more fuel, and weigh more than flyweights.

Easy to lay up , if there is space by the engine.
Anyone looked at the 6N140 that Bob and Brian Smith advertise as a replacement for the lehman at American Diesel. I don't know what they used for a donor engine but I don't think anyone would question their reputation as to dealers.
I believe the AD engine is based on a Ford of England diesel although obvioulsy not the same model that was used way back when for the FL120. There is at least one member of the GB owners forum who has installed one in a twin that experienced a catastrophic failure of one of its FL120s. According to this fellow (and AD) the unmatched pair of engines work just fine together. I believe the AD engine is 150hp.

I don't know what is involved in getting the two engines to match up in terms of engine sync and prop thrust.
I'd think you'd just keep the same prop and reduction gear ratio and then synchronize them by ear.* You might end up with your throttles mismatched a bit at cruise - though if they're governed to the same max RPM, the throttle positions will probably be about the same throughout the operating range.

The new motor will be running at a lighter load, though I think we've pretty well beat the dead horse into submission that these old tractor engine derivatives are pretty forgiving to being underloaded / overloaded / run slowly.
Chris--- While the mismatched engines can be synched up by ear in terms of their sympathetic vibrations (or whatever the thrum-thrum-thrum is), I was wondering about asymetrical loading or thrust when the engines are running at the same rpm. I guess I can answer my own question in that if they're running at the same rpm--- in other words in synch--- the props won't know the difference in terms of what sort of engine is providing the power.

So perhaps my question is more about synchronizing. Is it purely a function of rpm--- when the engines are perfectly in synch and there is no thrumming it means they are turning exactly the same rpm.* <br class="khtml-block-placeholder" />
Or is there more to it than just rpm. If I take a V-8 Cat engine and an FL120 and put them in the same boat and run them both at 2,000 rpm, will they be in sync and there will be no thrumming between them? Or will the powerful V-8 and the not-so-powerful straight-six have other differences that will bring them into audible sync when they are turning at two different rpms?

-- Edited by Marin at 00:49, 2009-01-30
"... both at 2,000 rpm, will they be in sync* ...?

Probably not. Since those engines have widely differing vibration characteristics due to number of cylinders and torsional effects, running them at the same rpm will probably produce a harmonic at several critical speeds. The only reason you can synch two of the same engines is they both share identical characteristics, even then phase becomes a factor as you are probably aware since phase synch is how more sophisticated aircraft engines are synch'ed rather than just rpm.
So if a pair of mismatched engines--- even a fairly close pair like an FL120 and AD's drop-in, 150hp replacement that uses a different base engine--- don't synch audibly at the same rpm but will with differing rpms, how does one deal with the potential asymetrical trhust? If in order to get equal thrust from each prop the engines produce that annoying and often loud "thrum-thrum-thrum" sound from being out of synch, how does one get the mismatched engines in synch and get balanced prop thrust at the same time?

Or am I making a mountain out of a molehill and asymetric thrust is no big deal?
If the propellers are the same and turn at the same rpm, they will absorb the same power and produce the same thrust, they don't know what is making them turn so that is not an issue.

In the case of two different engines, for instance one a 6 cylinder 120 hp engine and the other an 8 cylinder 150, both will produce whatever horsepower the props require as above - both will produce, for the sake of argument, 85 horsepower. But, since the vibration and torsional characteristics of the engines are different, and the rpm at which they produce 85 hp are probably different, they will probably induce some level of a "harmonic" intereference at some speed or range of speeds.

I would think that two 6 cylinder engines producing near the same horsepower would not create much of a problem. Even if the power delivered to the props was different at an rpm that reduced vibration, the difference in thrust could be compensated by rudder at the cost of increased drag and loss of efficiency but unless you*have a*racing trawler who cares as long as your drinks don't walk off the countertops?
There are shaft tachs that would help the matchup , if the gear boxes have a slightly different ratio.

"There are shaft tachs that would help the matchup ..."

That would balance the thrust if the props were the same but if the engines were different they would still contribute to some degree of annoying vibration.

There would probably be some combination of engine speeds that eliminated the synchronous vibrations at the cost of different shaft speeds but like I wrote before, unless the difference was very large, who cares.

The whole thing sounds like it could be a can of worms.
Rick @ Marin,

*** Yes but if you combined a pair of engines that had the same # of cylinders and same cyl configuration like perhaps a 4cyl Deere and a 4cyl Lehman they would probably sync quite well.

Eric Henning
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