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Old 20-04-2020, 18:05   #91
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Re: How many hours is too many?

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Originally Posted by malbert73 View Post
Internet search shows that the M25 is a marinized Kubota D850.
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Originally Posted by kenbo View Post
That's correct, it's a Kubota D850 a
Are you guys sure? I would be almost certain its a Shibaura 653, that Perkins rebadged into its 100 series small diesel range and the Perama series of marine diesels. They look similar, obvious give away is the different side of the engine of the oil filters.
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Old 21-04-2020, 00:47   #92
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Re: How many hours is too many?

Of course all reciprocating piston heat engines have a design life. Quite simply, the fatigue strength of the connecting rods - and any other components that see cyclic loads, especially reversing loading - have an envelope of the number of cycles to failure.
Probably the most significant variable is the level of stress induced in the component during cyclic loading. A component that is loaded to say 80% of its carrying capacity will last typically much shorter relative to one loaded to 20%. Fully reversing loading is far harsher than partially reversing loading. Load level, load symmetry versus number of cycles to failure relationships are rarely linear.
Heat is another variable - most metal strengths are inversely proportional to temperature. So if you have an overheating engine, at the same power level, components are subjected to operating stresses closer to their failure levels and thus will have a shorter fatigue life. Further, clearances and thus friction will change with increased temperatures, possibly further exacerbating loading conditions.
Metal fatigue is not a new concept. If ICE engine components were made massively enough and carefully kept cool enough, and run at relatively low power levels, I guess you could have a nearly infinite life span. Such engines would be much heavier than desired and would be far more expensive than most typical users would want to invest in.
It would be a rather silly thing to put in an engine designed to last 100 years into a car that will be traded in after 3 years due to stylistic changes. Commercial truck engines are designed to different standards. Recreational boating is a rather small market, and we are lucky that small tractor engines, suitably marinised, often fit our needs pretty well.
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Old 21-04-2020, 07:49   #93
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Re: How many hours is too many?

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An oil analysis wonít tell you engine condition, it may point out some current problems but will not tell you the condition of the main and rod bearings, compression etc.

However if you have an oil pressure gauge, you can get a very good idea of how much wear there is, to begin with the engine should start almost immediately, and with little smoke. That is actually a good compression check cause without good compression they donít start immediately, it takes several seconds until there is enough heat to run and of course they smoke at start up as there is excess fuel to be burned off, thatís an indicator that the upper cylinder/rings could be worn.
Throttle up the engine before it is warm to half max RPM, with cold oil that should tell you the oil pressure relief valve setting, it should hold close to that pressure under cruise, even at full operating temp, maybe not exactly, but within say 10%
Then after itís warmed up well, pin the throttle wide open and hold it there for at least 5 min, boat is underway of course, watch for any overheating and once you have it as hot as itís going to get back down to idle and watch oil pressure, Iíd want to see about 1/3 of what cruise pressure is, if itís real low, that is a strong indicator that the internals have excessive wear and it wonít hold pressure with hot / thin oil due to it leaking out the areas with excess wear.
Now sometimes a slick seller will put straight 50W oil in so that the pressure remains high, so watch for that.

On my motor I pulled the oil filter and cut it open to inspect, and changed the oil before the sea trial so I knew it had the right weight oil.

If you know what your looking for, I maintain you can tell more from an oil filter inspection than most any other inspection method.
There are of course articles and Iíd bet YouTube videos on oil filter inspections, just donít use a grinder or saw to open the filter as that puts a lot of metal in it. Use an oil filter cutter or a pipe cutter, a pipe cutter actually works pretty well.
It would be best to know what the oil pressure specification for a particular engine should be rather than rely on a generalization. The manufacturer should have the numbers. From the Yanmar Shop Manual for the GM/HM engines...
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Old 21-04-2020, 07:56   #94
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Re: How many hours is too many?

It is good to know specific specs, but realize those are min specs, I’d never operate an engine that came close to those min oil pressures, it may live awhile, but your at the min spec, meaning you have a problem, just it’s barely acceptable.
My motor as an example has I believe a min pressure at idle of something like the one above, around 7 PSI, however my old motor idles at 25 PSI. The day I look down and we are idling at 15, I’m going to start investigating, 7 is crazy low.
My high pressure is hit at about 1500 RPM and is about 60 PSI, any RPM above that doesn’t increase pressure.
These are hot numbers of course.
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Old 21-04-2020, 07:59   #95
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Re: How many hours is too many?

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Originally Posted by AndyEss View Post
Of course all reciprocating piston heat engines have a design life. Quite simply, the fatigue strength of the connecting rods - and any other components that see cyclic loads, especially reversing loading - have an envelope of the number of cycles to failure.
Probably the most significant variable is the level of stress induced in the component during cyclic loading. A component that is loaded to say 80% of its carrying capacity will last typically much shorter relative to one loaded to 20%. Fully reversing loading is far harsher than partially reversing loading. Load level, load symmetry versus number of cycles to failure relationships are rarely linear.
Heat is another variable - most metal strengths are inversely proportional to temperature. So if you have an overheating engine, at the same power level, components are subjected to operating stresses closer to their failure levels and thus will have a shorter fatigue life. Further, clearances and thus friction will change with increased temperatures, possibly further exacerbating loading conditions.
Metal fatigue is not a new concept. If ICE engine components were made massively enough and carefully kept cool enough, and run at relatively low power levels, I guess you could have a nearly infinite life span. Such engines would be much heavier than desired and would be far more expensive than most typical users would want to invest in.
It would be a rather silly thing to put in an engine designed to last 100 years into a car that will be traded in after 3 years due to stylistic changes. Commercial truck engines are designed to different standards. Recreational boating is a rather small market, and we are lucky that small tractor engines, suitably marinised, often fit our needs pretty well.

Is metal fatigue of con rods really a limiting factor for diesel engine life? What percentage of sailboat diesels die from broken rods?


I think I generally agree with you, but I think few sailboat engines are actually ever worn out. They fail from overheating or hydrolocking or corrosion mostly, don't they? Or you wear out the cylinder bores or bearings or just the rings, and it's not worth overhauling it.



Sport fish motors might be different, but the way we run our engines I don't think metal fatigue plays much of a role.
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Old 21-04-2020, 08:41   #96
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Re: How many hours is too many?

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I donít know why you guys refuse to listen to what a design life limit is.

So what do you guys think a designer, designs to? The maximum life possible? Of course not, but they donít often design for the cheapest to produce either, there has be something in between, so they do in fact have a design life, which allows a manufacturer to manufacture as cheaply as they can, but their engines still last long enough so that their reputation isnít tarnished, usually, sometimes they get it wrong.
For example for my IO-540W1A5D aircraft engine, it was 2500 hours, but when I tore mine down at 2500 hours, all the ďhardĒ parts met new specs, not serviceable specs, but the specs for a new part, so my engine could well have gone much, much longer than itís design limit, because it was well maintained and operated conservatively.

Design life doesnít mean how long something will last, it is how long it was designed to last under a specified mission profile.
Again, itís a lot like tires, you can buy tires that are rated for 30,000, 40,000 miles etc. that doesnít mean that is exactly how long they will last, a kid may wear out a set of 30,000 mile tires in less than 10,000 miles, where as Grandma may easily get 50,000 miles out of them, but they were designed on average to last for 30,000 miles, and I bet that on average, most do.
Engines are the same way.
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Old 21-04-2020, 08:56   #97
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Re: How many hours is too many?

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Are you guys sure? I would be almost certain its a Shibaura 653, that Perkins rebadged into its 100 series small diesel range and the Perama series of marine diesels. They look similar, obvious give away is the different side of the engine of the oil filters.
Absolutely sure, I've rebuilt a few and replace a few M-25's with the upsized D950 long block. The Perama M20 (18hp) has a bore & stroke of 64mm x 64mm, a square design. The Perama M30 (29hp) was 75mm x 72mm an over-square design. The Universal M-25/Kubota D850 (20.5hp) is also an over-square design but has a bore x stroke of 72mm x 70mm.

As far as I know, Perkins and Volvo Penta were the only marine diesel engine rebadgers to use the Shibaura. Nice smooth engine but not used in the Universal line.
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Old 21-04-2020, 09:07   #98
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Re: How many hours is too many?

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Is metal fatigue of con rods really a limiting factor for diesel engine life? What percentage of sailboat diesels die from broken rods?


I think I generally agree with you, but I think few sailboat engines are actually ever worn out. They fail from overheating or hydrolocking or corrosion mostly, don't they? Or you wear out the cylinder bores or bearings or just the rings, and it's not worth overhauling it.



Sport fish motors might be different, but the way we run our engines I don't think metal fatigue plays much of a role.
Metal fatigue isnít an issue due to correct design, but yes motors if run correctly and correctly designed do wear out as opposed to breaking, and itís the bearings and rings and the bores that do, cause thatís what is supposed to wear out.
It often racing that breaks things, simply because you exceed the design limits.
Sportfish motors almost always wear out too, usually the top end meaning the bores and rings, they lose compression and begin to burn oil like any other worn out motor. They donít exceed limits, just run at or close to the limit continuously.

Ideally and if correctly run and correctly designed pretty much the whole motor wears out about the same time, it does no good of course for rod bearing to be completely worn out and the rest of the motor be almost new.
That is where the design life limit comes in, if everything is designed to the same life limit, then the motor wears evenly if you will.
The design life limit really doesnít mean the motor will wear out at that time, it means hopefully that everything is matched and wears evenly.

Engine design has gotten astonishingly good, computer modeling has advanced it to the point that you can try different things and see how it works, where in the old days you had build it and run it on a test stand, hopefully several engines and do tear downs inspecting at different hour intervals, now that can to a great extent be done in a computer, assuming your company has the cash for the software etc.

But yes most motors die, or are killed, not worn out. You see that is cars too, Iíve known several that would be polished and waxed, but the oil never changed and eventually the motor dies of course.
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Old 21-04-2020, 20:33   #99
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Re: How many hours is too many?

Interesting discussion! I admit I'm not sure how to apply it.

It seems to me that it is going to be a bit of a crap shoot. Yes, maintenance will matter a lot, however there is no way to know how hard it was run.

There is also something I find telling, and that is that in a random search of Yachtworld, in my price range, I didn't come across a single boat with hours that high... I did come across a few mentioned of rebuild or new.

Now, if the trend is low hours, and based on what I've read, the most common use of the diesels in our boats, is terrible for them, then the high hour engine should actually be a better bet.

Except, if the engine has been run hard for those hours then your probably no better off...
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Old 22-04-2020, 00:01   #100
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Re: How many hours is too many?

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Absolutely sure, I've rebuilt a few and replace a few M-25's with the upsized D950 long block. The Perama M20 (18hp) has a bore & stroke of 64mm x 64mm, a square design. The Perama M30 (29hp) was 75mm x 72mm an over-square design. The Universal M-25/Kubota D850 (20.5hp) is also an over-square design but has a bore x stroke of 72mm x 70mm.

As far as I know, Perkins and Volvo Penta were the only marine diesel engine rebadgers to use the Shibaura. Nice smooth engine but not used in the Universal line.
Kenbo, you should fact check before you tell porkies on the internet.

A Perkins M25 and M30 are the same engines except for the bore size. Built by Shibaura. If you had rebuilt them you would know about the Shibaura marks on the pistons. The sharing of almost every single part number.

Here is a link to the workshop manual it might be helpful if you do need to rebuilt one in the future http://www.marinesurveyorontario.com...riesm25m30.pdf
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Old 22-04-2020, 06:04   #101
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Re: How many hours is too many?

The M-25 is a good engine, the weakest link on that engine is the Rube Goldberg manner in which the alternator is mounted and tensioned. If the alternator mounting modification has not been done that's what I would focus on. The mod is available from Catalina Direct. Change the oil and coolant enjoy the boat.
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Old 22-04-2020, 12:16   #102
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Re: How many hours is too many?

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Kenbo, you should fact check before you tell porkies on the internet.

A Perkins M25 and M30 are the same engines except for the bore size. Built by Shibaura. If you had rebuilt them you would know about the Shibaura marks on the pistons. The sharing of almost every single part number.

Here is a link to the workshop manual it might be helpful if you do need to rebuilt one in the future http://www.marinesurveyorontario.com...riesm25m30.pdf
Interesting post. Cowpoos, methinks you are confusing the Universal M-25, a marinized Kubota D850, with a Perkins M25. I've never rebuilt a Perkins M20, M25 or M30. No argument that they are marinized Shibaura engines but they are not the base engine for the Universal M-25 which is the focus of the OP. Sorry for your confusion but you must read the posts of others more carefully before you throw stones.
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Old 22-04-2020, 12:19   #103
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Re: How many hours is too many?

My 2QM20 from 1979 didn't have an hour meter on it when I got it, so no idea how many hours it had on it. I've since put on 1500 hours in five years and it still runs just fine
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Old 22-04-2020, 13:05   #104
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Re: How many hours is too many?

So many times and engine life is only spoken of in hours. While hours are important, it is equally important to look at the calendar. Which is flipping by on a daily basis, even if the engine is not being run.

A new, well built, small diesel engine, that is started and run continuously within its design range, should operate for over 20,000 hours. Provided the fuel is kept clean and the oil is changed within intervals, and general maintenance is performed on schedule.

Real world use sometimes sees engines that are 5-8 years old or older with less than 200 operating hours. This is terrible for the overall longevity and operating hours of the engine. Particularly in the marine environment. These engines will probably not make 4000 hours.

In all those years, seals and gaskets get older and harder and brittle and leaky. Metals rust, corrode and oxidize. Oil in galleries and rings and bearings build varnish and absorb moisture. Fuel breaks down corrodes injection pumps and injectors. Zincs go unchanged.

Worse is the neglect of the ancillary components. Oil coolers, heat exchangers, transmissions, wiring, exhaust systems particularly. Many times it is the break down of parts un-associated with the power generating portion of the engine that lead to the demise of the engine itself. Again particularly exhaust and cooling systems.

Do not concentrate only on hours and ignore the age of the engine. Neglect and lack of use will kill an engine long before its reaching its 'design life'.
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Old 22-04-2020, 13:24   #105
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Re: How many hours is too many?

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So many times and engine life is only spoken of in hours. While hours are important, it is equally important to look at the calendar. Which is flipping by on a daily basis, even if the engine is not being run.

A new, well built, small diesel engine, that is started and run continuously within its design range, should operate for over 20,000 hours. Provided the fuel is kept clean and the oil is changed within intervals, and general maintenance is performed on schedule.

Real world use sometimes sees engines that are 5-8 years old or older with less than 200 operating hours. This is terrible for the overall longevity and operating hours of the engine. Particularly in the marine environment. These engines will probably not make 4000 hours.

In all those years, seals and gaskets get older and harder and brittle and leaky. Metals rust, corrode and oxidize. Oil in galleries and rings and bearings build varnish and absorb moisture. Fuel breaks down corrodes injection pumps and injectors. Zincs go unchanged.

Worse is the neglect of the ancillary components. Oil coolers, heat exchangers, transmissions, wiring, exhaust systems particularly. Many times it is the break down of parts un-associated with the power generating portion of the engine that lead to the demise of the engine itself. Again particularly exhaust and cooling systems.

Do not concentrate only on hours and ignore the age of the engine. Neglect and lack of use will kill an engine long before its reaching its 'design life'.
I can not find a thing wrong with this other than one stored correctly may not suffer the failure, few are.
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