Replacing a Ford Lehman SP135

[jleonard]

"Only difference is the truck and marine black boxes are different"

Not completely true. Some of the internals are different depending on HP and year.
However if used on a trawler at lower power levels the difference won't mean anything.
*I am working on marinizing a 1989 pickup Cummins so I've been thru this.

 

[Nomad Willy]

Larry,
I think that the concept of high rpm small diesels not having much longevity is 90% false.
One of the engines I suggested for you is a 3500 rpm engine and I'll bet it'l go 15000 hrs just as gracefully as a 2500 rpm engine. It may even do that w less noise and vibration. Even at 4000 rpm a modern engine is almost certain to produce less vibration and noise than a Lehman. Engine speed (rpm) dosn't kill pleasure boat engines. Your friends w the Yanmar will probably be just as happy (more if they take good care of it) as they are now when they get 10000 hours on it**** ....if they ever do. Yanmar reduced the speed of some of their engines just for marketing reasons addressing the "high rpm engines don't last" concept. They didn't do it because the engines were better*** ...they did it because their competitors were advertising the old wife's tale. The above is an opinion and not 100% true but nearly so and for all practical purposes especially in the context of pleasure boat engines where as even the highest rpm engines will last 100% as well as lower speed engines*** ...mostly due to the fact that pleasure boat engines die from misuse or/and under use**** ...sitting.


-- Edited by nomadwilly on Sunday 18th of September 2011 06:53:01 PM

 

[FF]

For many engines its piston miles , stroke vs rpm.

Short stroke and high rpm about ballance long stroke and lowish rpm

Bigger medium speed engines will run 600-900 rpm

Ship sized its 90 to 105rpm or so.

 

[JD]

Larry M wrote:


Yanmars to me are not good trawler replacement engines because of the high rpms.* At the rated speed,*it is a 3000 rpm engine.* Their "powerboat" engines are rated for 4000 rpms.

We have*friends who just re-powered their sail boat with the 53 hp Yanmar*for $19,000 US complete and are real happy.



Larry/Lena
Hobo KK42
La Cruz, Nayarit, MX*

*

That sailboat engine is a 3,400 RPM engine and needs to run at 2,700.* The Yanmar in my trawler is a 3,400 RPM engine and needs to run at 2,700.* So why is it OK for the sailboat and not for the trawler?

As Eric said, misuse not use hurts the engines.

*

 

[Nomad Willy]

FF** WWWhhhhaaatttt??????

'Bigger medium speed engines will run 600-900 rpm"
This is a yachting and trawler forum. There is no such engine at all for a yacht that runs at anywhere those speeds. If you're trying to make a point please state it more clearly.
Regarding your comment about "piston miles" it sounds like you're adhering to Marin's theory that an engine is good for so many strokes and then it's dead. Absurd. The force on the piston crown and the resulting force on the side of the piston and the cylinder wall have much more to do w wear than wear than piston "miles". Never heard of piston miles Fred but engineers use piston speed a lot but it's not exactly the same as the total distance a piston travels. What's most desirable (I suspect) is minimum force on the piston crown, minimum force on the connecting rods and bearings and minimum force on the side of the piston and the cylinder wall. All those conditions are meant to the greatest degree w an engine turning at a relatively high rpm (never rpms as there is no such thing as revolutions per minute's) and low load** ...like a truck going up a steep hill in a lower gear** ...little effort is required as there is many more strokes required to do the same work and greater mechanical advantage (the lower gear)........or a boat w a low enough propeller load allowing the engine more strokes to perform the same job w less effort on each stroke. Face it.* If there was no force on the piston and no force on the rest of the mechanical components of an engine it would last a very very long time so anything that minimises the forces makes the engine last longer. Lighten their load w more strokes (rpm) and get the job done w lower engine loadings/forces applied more often (higher rpm).


-- Edited by nomadwilly on Wednesday 17th of November 2010 10:11:10 PM

 

[Marin]

nomadwilly wrote:

Regarding your comment about "piston miles" it sounds like you're adhering to Marin's theory that an engine is good for so many strokes and then it's dead.

No, that's not my theory at all.* What I mean (actually what Bob Munro, the founder of Kenmore Air meant) is that*every engine has a finite life.* The easier you make life for the engine-- by which he meant operating it correctly, not working it too*hard or underworking it--- *the longer that life will be.*

He liked the catchy phrasing--- "A piston is only going to go up and down so many times.* The easier you make life for the engine, the longer that piston will go up and down"--- because his pilots tended to remember it*(obviously I have) and would be more inclined to remember not to abuse the engines in his airplanes.

But he did NOT mean, nor do I, that an engine has a predetermined*and finite number of piston strokes or hours or miles at which point it will crap out.* The life of an engine is determined by a lot of things, not the least of which is how it is operated.* The less it is abused, the longer that life will be.

-- Edited by Marin on Wednesday 17th of November 2010 10:42:01 PM

 

[Tidahapah]

Eric,
The piston speed and forces et all is one of the reasons the Gardner engine is still a very popular choice for displacement cruisers in a lot of countries.
The 6LXB is a 10.5 lt engine developing 127 HP at 1500 RPM.(3:1 box and my prop is turning at 500RPM noice!!!)
For my 48' boat the cruising RPM will be about 1200 and very economic even though it is old technology.
The newer electronic engines I could not have as there is bugger all you can do with them when they play up and that is not nice when you are a few hundred miles off the coast.
We are having this same trouble with the electronic CATs fitted to some of our rig tenders and it is very frustrating for an engineer if you don't have the program or the laptop to connect to your engine to carry out fault finding.

Benn

 

[FF]

What's most desirable (I suspect) is minimum force on the piston crown, minimum force on the connecting rods and bearings and minimum force on the side of the piston and the cylinder wall.

Perfect description of any gas engine.All wrong for a diesel.

The hassle with diesels is the ring sealing is dependant on the load.

The combustion gasses must push the rings in contact from behind the ring.

Without this force , we are back to under loading,huge blow by, oil contamination and slobbering.

The lighter duty the engine is , the less under loading seems to harm them.

The Ford Econ O Power is a classic , "rated" 135 , used at 40 or 60 hp and they last well.

The common rule of thumb is 50% load although 80% is considered to give longer engine life.

Weather a car transplant will suffer from under loading is doubtful as most cars take minor power at cruise.

BMW (Yanmar) may claim its 350HP for acceleration but in auto cruise its probably more like 30 being used.

Weather they will operate at common boat loads , 50% of rated, or more for more than their auto life (2000 -3000) hours is still being proven .

 

[Larry M]

nomadwilly wrote:

Larry,
............The K 42 requires 50 hp to make 8 knots so I think there's no good reason to repower your K42 with any engine over 80 hp. Five hp per ton of displacement should be enough power for almost any full displacement boat.

Eric:* We do have a KK42.* We displace 44,000lbs and have a water line of 39'2".* Using your formula we should have 110 hp engine(?).

To move our boat at 7 knots in calm flat water it takes ~51 hp according to Boatdiesel's power calculator program.* At 8 knots we need 76 hp.* Hobo has two alternators and we run*with paravains the majority of the time.** It is nice to have the power when we are beating into the*wind and seas on the*Pacific when needed.* I'm not saying the FL135 has more power than we need but 80hp is to little IMHO.


<table align="center" cellpadding="2" cellspacing="0" border="0" style="width:100%;border:#000000 1px solid;"><tbody><tr><td align="center" bgcolor="#cccccc">RESULTS </td></tr></tbody></table><table align="center" cellpadding="2" cellspacing="0" border="0" style="width:100%;border:#000000 1px solid;"><tbody><tr><td colspan="2"><table cellpadding="0" cellspacing="0" border="0" style="width:100%;"><tbody><tr><td align="left" colspan="2" bgcolor="#ffffff">**DISPLACEMENT HULL**********</td></tr><tr><td align="right">Hull Speed: </td><td align="left">8.4 kts. *</td></tr><tr><td align="right">Power Required:</td><td align="left">87.3 shp.</td></tr></tbody></table></td></tr><tr><td align="left" colspan="2">**Speed********** </td></tr><tr><td align="center" colspan="2">To Achieve a Cruising Speed of 7 kts </td></tr><tr><td align="left" colspan="2">**Required Power********** </td></tr><tr><td align="center" colspan="2"><table cellpadding="2" cellspacing="0" border="0" style="width:98%;"><tbody><tr><td align="right">At Prop: </td><td align="center">50.9 SAE hp </td><td align="center">37.9 kW</td></tr><tr><td align="right">At Flywheel: </td><td align="center">52.5 SAE hp</td><td align="center">39.1 kW</td></tr></tbody></table></td></tr><tr><td align="left" colspan="2">** Select Engine: **********</td></tr><tr><td align="center" colspan="2"><table cellpadding="1" cellspacing="1" border="0" style="width:98%;"><tbody><tr><td align="center" width="20%" bgcolor="#444444">Rating </td><td align="center" width="20%" bgcolor="#444444">SAE HP </td><td align="center" width="20%" bgcolor="#444444">Metric HP </td><td align="center" width="20%" bgcolor="#444444">kW </td><td align="center" width="20%" bgcolor="#444444">Max Kts* </td></tr><tr><td align="center" width="20%" bgcolor="#aaaaaa">Pleasure</td><td align="center" width="20%">74.9</td><td align="center" width="20%">76.0</td><td align="center" width="20%">55.9</td><td align="center" width="20%">8.0</td></tr><tr><td align="center" width="20%" bgcolor="#aaaaaa">Light </td><td align="center" width="20%">65.6</td><td align="center" width="20%">66.5</td><td align="center" width="20%">48.9</td><td align="center" width="20%">7.6</td></tr><tr><td align="center" width="20%" bgcolor="#aaaaaa">Medium </td><td align="center" width="20%">58.3</td><td align="center" width="20%">59.1</td><td align="center" width="20%">43.5</td><td align="center" width="20%">7.3</td></tr><tr><td align="center" width="20%" bgcolor="#aaaaaa">Heavy</td><td align="center" width="20%">53.5</td><td align="center" width="20%">54.3</td><td align="center" width="20%">39.9</td><td align="center" width="20%">7.1</td></tr></tbody></table></td></tr></tbody></table>


The program calculates the theoretical power required to drive the selected hull form through calm water at the required speed. It is important to note the formula does not take into account wind or wave resistance...

*


-- Edited by Larry M on Thursday 18th of November 2010 11:44:03 AM

 

[FF]

Some folks wonder why some engines seem to suffer less from underloading.

One reason could be the HP difference between pleasure boat advertised and 24/7.

The above example shows a "75" Hp engine rating and a more realistic 53.5 rating.

So cruising at 52.5hp is a fine almost full load that will be quite efficient.

The boat has time limited "extra" power for a big breeze .

This is an excellent example of a properly sized engine .

Using a turboed 350HP would probably cut engine life in half , and easily double the cruise fuel burn.

The reason a "fast trawler" is an oxymoron.

 

[sunchaser]

Underloading problems with a 4 stroke diesel is a myth that will not die.* If concerned, run 80 - 85% off top end rated RPMS for 15 minutes during your daily runs (not at idle either). So long as your water and oil temps get to spec at your selected cruise RPM, you are fine. Oil temp must be above 175 with 185*- 200 a normal no problem*range.

More important than underloading imho is low use and letting sit over winter when not properly prepped. I see on boat diesel that an owner with a 14 year old engine averaging 35 hours per year suggests a class action suit against CAT because of antifreeze in oil --- and rotted out cooling system.

 

[FF]

"Underloading problems with a 4 stroke diesel is a myth that will not die."

National Fisherman was so unconcerned the ran tech articles for 2 issues ,
in an attempt to help working folks specify engines for their duty requirements.

Rather specific recomendations to follow.


Seems the 24/7 pro fish guys have problems the 100 hour a year yachtsman doesn't see.

 

[sunchaser]

Yup, some commercial fish boats do indeed suffer early engine demise (maybe after 15 years) , at near*idling RPMs for hours on end as they pull in and drop off nets and lines.* A properly set up fish boat has an engine big enough to move a load of fish in big seas that may well add 50% or more of the empty weight of his vessel. Most, not all, are set up with internal oil heaters to maintain crankcase temps above 200 during these long periods of very low RPM.

I met one happy fisherman this summer who replaced his very high hour 25 year old DD with a JD that weighed 1/3 as much - more room for fish and no oil drips in the bilge.*Many commercial*boats sit idle for*months on end in the PNW, so "winterizing" or having a buddy run them under load every month*is a must.

Charter fishing boats often have a kicker so they aren't forced to idle their big diesels. A boat I fish on has a 9.9 Merc*with the twin 180HP Volvos*shut down for the 4 to 10 hours per day of trolling.

 

[Larry M]

Charles:* We have ~7k hours on the engine and it runs great.* I'm *hoping to*get another 7K before we*have to do anything.* I agree with your post.**The thread started out as a hunt for*information on the what and what ifs when we do need to do an engine rebuild/re-power.* Once again I have learned a lot from TrawlerForum.com and the people who contribute.* Thanks to all.

Larry/Lena
Hobo KK42
La Cruz, Nayarit, MX

-- Edited by Larry M on Saturday 20th of November 2010 06:26:34 PM

 

[Barney]

Yanma/ Kubota Diesels Vs Case / JD Diesels

Just an observation from a retired Farmer. You hook a set of discs behind a JD /Case etc then hook up the same set behind a Kubota / Yanma diesel with similar HP Ratings the JD/ Case will walk away in a higher gear no trouble. When comparing the engines ,You will generally note that the JD/Case International will produce maximum power at 1700 to 1800 rpm the Kubota /Yanma will both need to be running 2500RPM +. I think these numbers might explain a lot.
If you want/ need long life diesels Non Turbo are way better than anything with Turbo because the stress is substantially less.
Have you ever seen a Turbo diesel working at night, if that doesnt convince you the non turbo will live longer,:: nothing will!

 

[Ken E.]

"Any idea what the cost of a recon Cummins 6bt would be?"

Yes.....I installed a pair of them in 2014. $17k /engine. Another $6k or so will get you a Twin Disc gear. Mine are model 5050, 3:1. An earlier poster mentioned 6bt package deals available with Hurth gears but I haven't heard of this. I am completely happy with this power package. Boatdiesel.com and Tony Athens' Seaboard Marine site can provide lots of info on this engine and it's applications.