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Old 06-02-2019, 01:46 PM   #1
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Dead Lehman 120

Ahoy all,

We have a 34' Marine Trader, single 120. The whole boat underwent a complete rebuild over the last 5 yrs and we just launched a couple of weeks ago.

My 120 seized the other day with about 3000hrs on it. I'm contemplating a complete rebuild of the 120 ($11K) vs buying a marinized rebuilt 90 ($7K). Looks like a fairly easy transplant. (I don't recall what the ratio is in my Paragon, which is fairly new.)

Has anyone repowered a 34' or 36' trawler from the original single 120 Lehman to the newer Lehman 90 4 cylinder?

I'm looking at the hp curve in my Lehman book comparing the 2 engines and it shows that when I run at 1600 rpm/ 7kts I'm at 70 hp. Would I burn less fuel with the 4 at 2000 rpm vs the 6 at 1600?

Would I also have to reprop if I made the transition?

There must be some smarter folks than me out here in virtual trawlerland that know this stuff!

Thanks! Capt Harry
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Old 06-02-2019, 02:57 PM   #2
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Ahoy all,

We have a 34' Marine Trader, single 120. The whole boat underwent a complete rebuild over the last 5 yrs and we just launched a couple of weeks ago.

My 120 seized the other day with about 3000hrs on it. I'm contemplating a complete rebuild of the 120 ($11K) vs buying a marinized rebuilt 90 ($7K). Looks like a fairly easy transplant. (I don't recall what the ratio is in my Paragon, which is fairly new.)

Has anyone repowered a 34' or 36' trawler from the original single 120 Lehman to the newer Lehman 90 4 cylinder?

I'm looking at the hp curve in my Lehman book comparing the 2 engines and it shows that when I run at 1600 rpm/ 7kts I'm at 70 hp. Would I burn less fuel with the 4 at 2000 rpm vs the 6 at 1600?

Would I also have to reprop if I made the transition?

There must be some smarter folks than me out here in virtual trawlerland that know this stuff!

Thanks! Capt Harry
I speak no first hand knowledge on the subject.
Some points to consider, the possibility of changing out the transmission and changing the prop.
IF you do a total rebuild, you know everything about the engine, transmission and prop.
Change out the main engine, you are stepping into the unknown.
Again, I stipulate I have no first hand knowledge on anything. You might want find a paid consulting marine engineer with experience with small recreational boats.
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Old 06-02-2019, 03:44 PM   #3
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My first thought is what is up with your current engine? Its odd to hear that one just seized up - the worst failures I'm hearing/reading about seem to be the engine is running but badly, and its rings that have self destructed or some such thing - but the engine is still a runner.

The situations where the engine is seized seem to be related to water getting where its not supposed to be, like back through the exhaust.

Have you thoroughly troubleshooted the engine problem? If its a hydrolock problem from an exhaust water issue you'll want to figure that out first.
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Old 06-02-2019, 04:04 PM   #4
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I agree w mr fract ..,
Thought;
You may want to keep a 6cyl just because I hear the 4’s are w plenty of vibration.
Thought; With the 4 you will burn less fuel but doing the same work not much. Loosing heat will burn more fuel and two extra cylinders is an extra heat sink.

But you should find out exactly what’s wrong w your engine.
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Old 06-02-2019, 04:54 PM   #5
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First troubleshoot that 120. Lots of things can "stick" an engine, and not all are fatal.

Second others that the four banger is a good bit rougher and unsocial. Running hull speed the burn rate on a four will be only a little better, not enough to force a decision.

I doubt you are using 70hp to go 7kts, probably more like 30.
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Old 06-02-2019, 05:11 PM   #6
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My engine acted like it was seized but it was just broken spring pieces jamming the flywheel. The spring pieces were from the dampner plate. Before the engine siezed, I had several episodes of sounds like the engine was coming apart...right around 3000 hrs on a rebuilt 120.


The episodes occurred randomly over a 100 hour period.
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Old 06-02-2019, 05:15 PM   #7
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PS has reminded us of the dreaded damper plate. You will have to disconnect the trans anyway so you can see.

It takes a certain amount of fuel to make a given horsepower, you will not save much if any fuel. Fuel is one of the cheapest recurring cost on these old clamcrushers so don’t worry about it. I know nothing about the 4 but the 6 is usually pretty strong except for cylinder 6. You already have all the marine conversion parts for the 6, why not just buy a long-block from a reputable industrial or agricultural outfit, with a warranty and stick it in? Lots of work, not a little money but most or all of the work can be done by you or get the yard to swap out the blocks for you. Good time to change the trans oil and install new engine mounts. Maybe even paint in there. Don’t forget to MEASURE the oil and re-mark the dip stick!

Just think of all that lovely new coolant, new oil, new filters and a fresh injection pump. Yum.
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Old 06-02-2019, 06:26 PM   #8
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I'm solidly in the rebuild camp (unless a piston has gone through the side of the block) I think it's important to determine what the failure is before making any decisions.

I'm not convinced the P90 would work. There is a dramatic difference in the torque between the two so pushing a 20,000 lb boat with a smaller engine means you will be running at the top end of the power curve to go slower. Running hard will take years off the life of an engine. If they designed it with the 120hp, keep it at 120hp. The money you save now by putting in a smaller engine will probably be lost if you ever sell the boat.

If you end up taking the engine out, send the transmission out for a rebuild. Clutch plates and seals are relatively inexpensive. Removing the transmission is the hard part so once you have everything in place to pull the engine, pull transmission.
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Old 06-02-2019, 06:49 PM   #9
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I have made 7 round trips FL to NJ at 6.3 knots (1700 rpm +/-) burning around 2 gal/hr...thats about gross 35 to 40hp if the rule of thumb formulas are really ballpark..



I have the 40 Albin, single, 4 bladed prop.


I have thought about dropping down to 90-100 hp if I ever need another engine...I AM convinced it would be fine if you run slow....but the economics would have to be more than a couple thousand to not just drop in another 120.
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Old 06-02-2019, 08:08 PM   #10
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Find out what is wrong with the Lehman first! Also if you are going to have the engine out, either for a repower, or a rebuild, have your original fuel tanks been replaced? Might be a good time to consider new ones while the engine is out. Just a thought.
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Old 06-02-2019, 08:36 PM   #11
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You have to know what killed the present engine before setting up its replacement for the same failure.
3000 hours on a Lehman is premature death. It certainly did not wear out.
Water ingestion through the exhaust? Damper plate failure? #6 cylinder overheat? It would be worth a couple hundred to have a mechanic to borescope the cylinders.
Put me in the rebuild 120 camp after finding the failure cause.
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Old 06-02-2019, 09:38 PM   #12
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High Wire I don’t think I’ve ever heard of one wearing out by a TR member.
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Old 06-03-2019, 06:28 AM   #13
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Thanks all for your input.

We've finally splashed Wabi Sabi a couple of weeks ago after having the boat here at home for about 5+ yrs. She was completely rebuilt with the intention of extensive cruising when me wharf wench finally retires in 3 yrs.

She ran great when we launched, successful trip 10 min up river to the marina where I'm completing projects. The gauges and alarms were NOT attached (that was the day's project). I ran her at about 1800 rpm for about 15 min and she was getting noisier. I quickly backed the throttle off and she dies. Let her cool for a day and the breaker bar will not even budge the crank.

A local diesel shop suggested that the oil pump needed to be primed after a 5+ yr sabbatical and that #2 main probably seized. They've seen this before, they say.

Brian at Am Diesel also recommended pulling the tranny to see if those pesky dampener springs clogged up my flywheel, which I'll check tommorow. I did drain and filter out my engine oil and I found specks of metal shavings.

The trans was rebuilt a couple of hundred hours ago, so that's a-ok.

I'm heading down Tues morning to first back off the tranny and to start preparing the engine for removal.

Honestly, with all the blood, sweat and tears I've spent on the old girl, the idea of a shiny brand new rebuild doesn't sound too bad to me....
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Old 06-03-2019, 07:49 AM   #14
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You ran the dngine with no gauges or alarms hooked up? No secondary measurements taken regularly after start and shortly thereafter?
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Old 06-03-2019, 08:21 AM   #15
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You ran the dngine with no gauges or alarms hooked up? No secondary measurements taken regularly after start and shortly thereafter?
Yup, my thoughts exactly.
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Old 06-03-2019, 02:53 PM   #16
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Ya know, it wasn't my finest hour, ok. Scheeeze, you guys are tuff.

I have no one to blame more than myself. But this query isn't a request for opinions on how stupid I was (ha), it was if anyone ever downsized the main to a 90 Lehman….

I was monitoring the temp with a non-contact thermometer. Hoses never saw 172*. The engine always had decent oil pressure (never heard of priming an oil pump, if that's the case), and, as I said before, the purpose of running the engine WAS to hook up gauges. But, alas, sh*t happened.

Still heading down in the morning to pull the tranny to check those pesky dampening springs and then start prepping the engine for removal.

Should the engine be ka-ka, I'm buying a fresh 120 rebuild from Bomac.
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Old 06-03-2019, 03:54 PM   #17
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Yeah, what’s with the blaming you guys? None of you ever get caught?

Is the flooring still up like that? Piece of cake to do that engine swap and even if you rebuild, you can do most of the work in situ. Just pull the block out for line boring and any other machine shop stuff.

Let us know your decision and take tons of photos?
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Old 06-03-2019, 04:19 PM   #18
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Ya know, it wasn't my finest hour, ok. Scheeeze, you guys are tuff.

I have no one to blame more than myself. But this query isn't a request for opinions on how stupid I was (ha), it was if anyone ever downsized the main to a 90 LehmanÖ.

I was monitoring the temp with a non-contact thermometer. Hoses never saw 172*. The engine always had decent oil pressure (never heard of priming an oil pump, if that's the case), and, as I said before, the purpose of running the engine WAS to hook up gauges. But, alas, sh*t happened.

Still heading down in the morning to pull the tranny to check those pesky dampening springs and then start prepping the engine for removal.

Should the engine be ka-ka, I'm buying a fresh 120 rebuild from Bomac.
I think your on the money with a fresh rebuild, takes all the possible variables that come with re powers. Iíve seen these go bad and result in vey disappointing performance... yes if you get the science right and but the 120 is just a tried and proven work horse.... how good will it feel having a basically brand new engine as you motor off enjoying your boat. Good Luck and keep us posted
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Old 06-04-2019, 02:37 PM   #19
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I've never heard of priming an oil pump on any engine. I'd like to know more about that if that was an actual requirement for the Lehman, and exactly how you are supposed to do that? I've rebuilt and started a good number of engines and have never had the oil pump fail to deliver oil pressure on initial cranking. Monitoring temp and oil pressure manually for a few minutes run should have been sufficient.
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Old 06-04-2019, 03:29 PM   #20
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Humph…

Couldn't get the plate off to expose the flywheel. Apparently somewhere along the line the 4 bolts under the discharge for the heat exchanger rusted so badly they are no longer a 9/16. More like a rusted round head. Came home for more tools including an angle grinder. What fun.

Yeah, sbman. That's what I thought too. I've done a lot of engines in my life and NEVER heard of priming an oil pump. WTH?
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