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Old 07-15-2017, 11:35 PM   #1
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Load/rpm = wear

I think load has much more to do with wear that rpm.

It has a lot to do w noise too. I worked in a powerhouse in Alaska that had a 1440hp Enterprise 8 cyl turbo diesel. It turned at 327rpm and had a 5" thick X 90" dia solid steel flywheel. When they turned on the high pressure water pumps on the dredge it almost doubbled the load. When that happened the sound level went way up .. instantly. Same rpm. The flywheel and govenor only lost 4-5rpm. So the huge increase in noise was load only.

So overpropping to lower the rpm and lower the noise probably dosn't work.
Just my opinion.
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Old 07-16-2017, 12:11 AM   #2
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But the audio character of lower frequency noise is very different, subjective yes but huge for me.

A chug chug of a slow diesel compared to a little chattering petrol genny, no comparison, former could lull me to sleep, latter even at lower decibels makes me want to tear my hair out.
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Old 07-16-2017, 01:08 AM   #3
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The noise increase is simply the engine "going to work", responding to a torque demand. (and burning a good bit more fuel)
There will certainly be more wear under load, higher temps and pressures, but though
quieter, underloading has its downsides too.
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Old 07-16-2017, 03:05 AM   #4
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Interesting question. The 1800 rpm(eg.Kubota/Onan) marine genset is a good example. You hear it "shoulder the load" when you add something substantial, like the microwave or the 2000watt kettle,then it gets on with the job. But, at what cost to its longevity?
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Old 07-16-2017, 08:03 AM   #5
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"But, at what cost to its longevity?"

The modern method of contemplating engine life is fuel burn.

An engine will last say ? 50,000 gallons of fuel.

At 5GPH it will last longer in hours than at 8GPH or 10GPH ,

but if operated as the mfg suggests will produce the same KW hours before the rebuild.

Operated at 50+ GPH will lower the service life , ask any sport fish operator .
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Old 07-16-2017, 09:07 AM   #6
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Load is another word for work. Work done is what wears an engine because it loads all the components more. Higher speed versions of some engines are running faster to produce more work. The increased work is what wears the engine not the speed per se. The speed is how they increase the work potential.

Consider that at 3000 RPM in gear some engines can produce 400 HP. at 3000 RPM out of gear they produce little HP. Which do you think produces more wear?
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Old 07-16-2017, 10:03 AM   #7
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I think each engine has a "sweet spot", or better put a "sweet region" in the load vs rpm chart. In that region, it will last dang near forever. I don't buy that the engine's life is defined by the total fuel burned. That is a very crude and sloppy rule of thumb. I do agree that an engine run at 50% will likely last longer than one run at 75%. And engines tweaked for super high output are not going to last forever.

Interesting that road tractor engines often make a million miles, which at average of 50mph is 20k hrs. They get about 6mpg at 60mph so that is 10gph or about 200hp. Most are around 14liters so averaging 14hp/liter. Pretty light duty, there.
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Old 07-16-2017, 10:45 AM   #8
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Thanks for doing the arithmetic Ski. 20,000 Hrs!!! 14 HP/ liter!! Proves the point light load equals less wear.
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Old 07-16-2017, 11:15 AM   #9
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So far "wear" has been used as ageneral term. Is the most important part of an engine the piston and cylinder? Here the wear is clearly a result of load. The more force from combustion and the resulting force is mechanically exerted on the two parts .. piston and cylinderwall. The force goes way high at high loads. The piston pushes at a considerable angle offset by the crankshaft so the forces on the two are extremly high. Fourtuneatly there is a lot of surface to bear on but very little oil to reduce friction.

But all the moving parts of an engine wear as it runs. When we throw the engine away or remove it for rebuild the pistons and cylinders seem to be the basic reason why. And the wear there is caused by load. So would it be safe to say engines wear out fastest w heavy loads? I think so and the lowest load for a given power output is achieved by higher rpm that lessens the load for each stroke because there are more strokes to share the load.

All the above assumes an engine operated w propper service and good running dynamics like propper warmup and service.
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Old 07-16-2017, 11:49 AM   #10
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Maintenance issues-overheating-and sea age and gross overloading kill many diesels otherwise most engines with some care and some without the care will outlive their owners. The overloading and maintenance are things we control even the overheating is usually related to owner care. As mentioned the industry usually measures life in fuel burn and very few recreational boats will approach that much use. I can see SP fishing boats esp charter boats that run at high speed getting there but very few of the boats on this site. When I first got into the power boat end of boating rather late in life I learned the hard way about overloading. I bought a boat a few years old with 250 hrs on the engine and several weeks later the engine blew up. I then sought and got an education in overloading and exhaust geometry after the fact and too late to save that engine.
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Old 07-16-2017, 11:50 AM   #11
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"Proves the point light load equals less wear."

Not really as trucks are subject to the road conditions.

Maybe in Kansas there are no hills , traffic lights or stop signs, but a lot of throttle is required to get 80,000 moving .

Truck engines make delightful boat motors , because operation for long periods at full throttle is the norm, unlike autos.
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Old 07-16-2017, 11:56 AM   #12
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Here is a fuel map and some commentary on under loading.

https://www.morganscloud.com/series/...for-sailboats/

A diesel is a diesel, dont worry about sailboats in the article
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Old 07-16-2017, 12:50 PM   #13
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I am pleased to read posts regarding engine loading, lubrication, cooling and life-span.

For a long time I've run engines and calced engine life potentials under the following principals:

1. Engine HP number should be no more than 75% of cubic inch displacement number

2 Engine should be run on continuous basis having medium load at no more than 75% of WOT. Heavy load should not be allowed to bog down engine except for quite short duration

3. Engine should be brought up to at least 85% WOT under light to medium load at least once and for no more than a very few minutes in any 25 hour operating period. WOT needs to never be reached but may be done so for very short periods in conjunction with tests being run

4. Engine should always have clean high grade oil installed with continual checks done on continued oil quality and oil changes accomplished at correct intervals. Gasoline engine prior to 1998 [i.e. engines with flat tappets and not roller bearing lifters] should have appropriate volume of zinc additive installed at oil change and again at 50% time between oil changes. 4 OZ ZDDP container is what I use in all my "classic" gasoline engines.

5. Engine cooling system should always be adjusted to maintain engine temperature that manufacturer connotes as being the best.

Happy Engine Use-Life Daze - Art
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Old 07-16-2017, 01:07 PM   #14
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I know it is a thread hijack a bit but the comments here bring a question to me.
Is there really a lifetime for an engine? Or can a wel maintained engine can be rebuilt without limit? (of course excluding any major failure like I forgot t put oil in my engine an I seized). I will provide 2 examples that explain my question. First one, my own engine (well my own boat engine, my own is less strong), it was built when I was not yet born, it has been rebuilt an I do not know how many "real" hours it has, I just know it has almost 1500h since the rebuilt, but for an 50 years old engine it runs damned well and I was not expecting to see this.
Second, I am working for a railway company. One day I was in the diesel shop where loco were repaired and I ask the lead mechanic how long is the life of a loco engine. He was surprised by the question and told me there is no limit on the engine, the limit is the loco itself but engine have an infinite lifetime (then I was the one surprised).

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Old 07-16-2017, 01:43 PM   #15
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Some engines are designed as disposable engines while others are designed to be repaired / rebuilt as often as needed. Remember the old days when a tie rod end could be shimmed to take up for wear? Almost none have had that since the 1970s.

Your locomotive engine is a huge hunk of cast iron and all the parts can be replaced, oversize bored and updated forever. I learned diesel engines back when that was the case. My dream diesel engine would be a 6 cylinder Deutz diesel since you can get repair kits for everything on them, even today. The last one I overhauled (in 1969) ran another 50,000 hours pulling a irrigation pump. The owner wanted it overhauled again...

I still see trash pumps with Deutz diesel engines running them and can ID the engine by sound from a good distance. Keep the oil changed, feed it clean fuel and it will run forever.

Now, they design everything with an expected lifetime, and if you get there, great, otherwise pull and replace. In the old days, washers, dryers, fridges lasted for many years. Now, if you get 8 years out of either of these, you're lucky.

My sister just retired a Samsung fridge due to lack of service. I think it was still in warranty, but it took 5+ weeks to get warranty service on it. Had all the bells and whistles you could imagine but wasn't reliable. Now it is making ice in the garage.
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Old 07-16-2017, 02:00 PM   #16
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Quote:
Originally Posted by stubones99 View Post
Now, they design everything with an expected lifetime, and if you get there, great, otherwise pull and replace.

In the old days, washers, dryers, fridges lasted for many years. Now, if you get 8 years out of either of these, you're lucky.
From an inside source... I understand that amongst big manufacturers of appliances seven [7] years is the magic engineered "failure" number they agree to as best for their goods needing replacement. I'd call that "Enhanced Product Failure" collusion... i.e. to substantially enhance reasons to have new failure prone items once again purchased. Seems very similar to"Price Fixing"... which is illegal!


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Old 07-16-2017, 02:17 PM   #17
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We are on Year 19 with our simple GE fridge at home. I've made a few repairs over the years but nothing too unusual. Ice maker control panel failed and the plastic water hose has failed a couple of times.
We finally replaced our dishwasher after 17 years and our other appliances are all holding up pretty well.

My mother can't seem to get even 7 years out of a refrigerator.
Go figure!
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Old 07-16-2017, 02:27 PM   #18
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Engines with replaceable sleeves are meant to be rebuilt. Sleeveless engines often don't have rebuild parts available from the oem, just after market makers. But any engine can be rebuilt.
I ran many of the old direct reversing diesels like the Enterprise mentioned above. In many way they were better engines. Many had no transmission but were directly connected to the shaft. Most didn't go to 300 rpm, but they have very good economy and would go decades between overhauls in commercial service. Cheap WWII surplus diesels drove most of the companies that made them out of business.
Many commercial fishing boats of my time were over propped. Most cruised at 80% of hp and got excellent mileage. I know of several boats that ran a war surplus Detroit for 30 years w/o overhaul, if ever.
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Old 07-16-2017, 03:58 PM   #19
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Art, I like your 5 points on engine life. One of my current boats has an old international harvester diesel with unknown (likely many, many) hours. It's new to me and I have my fingers crossed that there are many more hours left to go.
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Old 07-16-2017, 04:05 PM   #20
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My engine's (NA JD 4045) sweet spot is 1800 RPM (a bit above 40% load) versus a WOT of 2400 (hull speed achieved at 2200). I try to avoid less than 1400 where maximum torque is achieved.
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