Diesel Major Overhaul

[pkrawetzky]

Currently I have a boat with twin Crusader 454's 350HP. Now I consider myself a stickler for preventative maintenance. From changing my oil/plugs regularly to cleaning/flushing the heat exchangers and oil coolers and rebuilding my raw water pumps every 3 years. An ounce of preventative maintenance will go along way. Of course there is more I do but it would just add to my question below.

Soon we are planning on purchasing a much larger boat (50-55FT) which will come with diesel engines. That in of it self is going to a major change for me as I don't know much about diesels but I do plan on taking at least a class on preventative maintenance.

So here is my question. I've seen gas engines go as high as 3000 or 4000 hours when kept in good running condition without a major overhaul or rebuild. So why is it some diesels need a major overhaul every 1000 or 2000 hours? To me diesels are much heftier engines and should be able to go much longer before a major overhaul. At tens of thousands of dollars for each engine, that's a big price tag.

I'm only asking this because I've started to do a lot of research on diesels preparing myself for what's to come. I know some information on the net can be wrong but there is a consistent them with opinions on this.

[bobconnie]

I don't know where you found your specs on diesel hours of operation, but my experince with diesels has shown me that a properly maintained diesel will run why over the amount of hours you put down !! I have had some go 8000 hrs or more !! Of course Im a pretty fair diesel mechanic! But still, even if you need to hire someone to take on the work needed to run them this long it's not to bad a deal !!Theres more to maintaining a diesel then just changeing oil and filters! Valve adjustments and fuel timeing need to be checked as offen as a gas engine! Folks seem to forget that just because they don't have spark plugs they don't need maintaince!! But if you wish them to work right they need to be kept up! also if ya don't want them leaking all over the place ya need to keep them up !! I just sold a ketch with a 471 Detroit with 5000 + hours on it that ran like a fine watch !! and the engine room was oil leak free!! They ALL need to be maintained gas or diesel !! I believe that high RPMs ruin more diesels than anything else!! That and folks seem to think that Fancy oils are the way to go instead of useing good diesel oils ! Just my 2 cents

[sabray]

Bunches of yanmar have had glazed linings at or near 1000 hours. Probably from improper low idle use /break in. I get how you might have heard this. Change the oil run the engine above idle replace the exhaust elbow if its yanmar. Try not to have a turbo. Replace the impeller etc... You will love the diesal.

[pkrawetzky]

Thanks for the info. From the boats I've looked at so far I've seen the following engines:
MAN's
Detroits 6V71, 6V92, 8V71, 8V92
Cummins

The MAN's are where I read every 1000 hours for MOH. That's why I was concerned. Most of the boats have the Detroits. What I've read is they can be "leaky" and "smokey". But I'm guessing as was already stated, routine maintenance would help these situations.

I imagine a lot of this could be covered in a class but I'll need to find one.

[ranger58sb]

Originally Posted by pkrawetzky

Thanks for the info. From the boats I've looked at so far I've seen the following engines:
MAN's
Detroits 6V71, 6V92, 8V71, 8V92
Cummins

The MAN's are where I read every 1000 hours for MOH. That's why I was concerned. Most of the boats have the Detroits. What I've read is they can be "leaky" and "smokey". But I'm guessing as was already stated, routine maintenance would help these situations.

I imagine a lot of this could be covered in a class but I'll need to find one.

A real MAJOR overhaul doesn't happen all that often. That would sometimes include cylinder sleeving, and/or maybe piston resizing, etc.

Overhead set (valves) adjustments are more routine, but even then, the interval is generally quite long. Looks like my manuals are on the boat just now, but from memory it seems like maybe overhead set adjustment is an every-600-hours thing... You can (learn to) do it yourself.

That said, we have a couple boat neighbors with Vikings with 820-hp (?) MANs and they did say their initial adjustment was early -- maybe this is an after break-in thing -- and quite expensive. Can't remember details, but I do remember thinking at the time how proud MAN must be of their engines. OTOH, they seem to work well.

The DDs are 2-stroke engines and I've heard they're less tidy than the newer 4-stroke models like the others you're seeing. They're also said to be less fuel efficient. Doesn't mean a bad thing, just a design outcome.

Annapolis School of Seamanship does diesel classes, if that's a workable location for you.

-Chris

[djmarchand]

If you run a high output, turbocharged and intercooled diesel at the "recommended" 200 rpm off of top, you will be lucky to get 2,000 hrs from them. That would be like running your 454s at 400 HP continuously.

Prop a diesel to run at 100 rpm over rated at wot and cruise at 500 rpm below that which should be 40-45HP per liter and they will live for 5,000 hrs or more.

You do have to keep up with maintenance- air coolers, etc, and make sure that your exhaust system doesn't let seawater back up into the engine.

David

[a64pilot]

You either love Detroit's or hate them. I'm in the I don't love them group, but to be fair if yuo keep up the maintenance with those noisy things they can go beyond 10,000 hours.
I'd go with the Cummins.
All things being equal Diesels will last at least twice as long as gas motors. They are heavier and more expensive than gas motors though, but have you seen a gas Bulldozer or over the road truck lately? Longevity is the reason.

[Capt.Alex]

Detroit Diesels are notorious for short lives because many of them are pumped up to output way more HP than they can handle for any length of time. For example, the 6V-92 can be found from 350-550 H.P The 550 HP ones only last about 1500-2000 hrs before needing an overhaul. The low HP versions can last at least twice as long. The naturally aspirated detroits are nearly bulletproof. The MAN's and MTU's are very dependable and long lasting engines as long as you stick to the maintenance schedule provided by the manufacturer. Most are not scheduled for a complete rebuild until approx. 6000 hrs. Problem is, the regular maintenance is very expensive.

[pkrawetzky]

Lots of interesting info... Maybe it's my understanding of what MOH really is. It sounds like what everyone is saying is there is your routine maintenance (valve adjustments, Turbos, air coolers, etc) and then there is a complete tear down/rebuild. I guess I looking at that routine maintenance as MOH.

It think the best thing I can do when looking at the engine side of things is get the records (if they exist) and have a thorough engine survey done. That in of itself has several definitions but from what I gather includes compression tests, engine/trans fluid analysis, etc.

Don't worry about giving me personal opinions on engine manufacturers. You will always find someone who has an opinion towards a specific one. It's good to hear why they like/dislike a certain manufacturer.

[tdoster]

My opinion is that hours are just one of the factors to use in determining condition and time to rebuild for either gas or diesel. Duty cycles of marine engines are much harder to pin down because too many factors.

But if you took both a gas engine and diesel engine and put them to work 8 hours a day, 4000 hours per year, the diesel would not only outlast the gas engine, but also be more economical to operate in terms of maintenance and longevity, especially when operating at close to WOT all day long.

Diesel engines are machined to greater tolerances than gas counterparts and suffer greatly from the time of start until they are warmed up to operating temperature, and really don't like running lower than the sweet spot up to WOT, whereas gas can run at any range and be happy and more tolerant to the period between startup and full operating temperature.

A sailboat that is started and run long enough to get the boat out of the slip and marina - repeat coming back in. May have less than 500 hours after 20 years, but those are 500 really hard hours on that engine.

[pkrawetzky]

Actually my thought was to only run 10 - 12 knots. By no means would I run WOT for very long. What that equates to in RPM's I'm not sure. The motor yachts we are looking at range in the neighborhood of 65,000lbs and of course each one has a different cruising speed.

[Suijin]

I was on a 44 sloop not so long ago owned by a career merchant mariner mechanical engineer who's a live aboard circumnavigator. The boat has a turbo charged Yanmar 60 hp that he installed 8,000 hours ago. It looks brand new, runs quiet and smooth and according to him he's had no troubles with it at all and all it's vitals are healthy. He rarely runs it over 2200 rpm.

Goes to show it's all about how an engine has been run and the care and feeding it's received.

[HappyMdRSailor]

All I have to say is look for something that has powerplants with low hours, look factory new (clean), had regular maintenance.... This way you assume the care in their infancy and will be able to ensure a Loooooooong healthy life....

Seen 'em all... Man, Detriot, Cummins, Cat... Low and clean??? All the same to me... You will NEVER look back wanting gas plants again....

[djmarchand]

Originally Posted by pkrawetzky

Actually my thought was to only run 10 - 12 knots. By no means would I run WOT for very long. What that equates to in RPM's I'm not sure. The motor yachts we are looking at range in the neighborhood of 65,000lbs and of course each one has a different cruising speed.

A 65,000lb boat means a displacement or at best a semi displacement hull. You don't want to run those over displacement speed- about 9-10kts for a 50' boat unless you own a few oil wells

David

[tdoster]

Originally Posted by pkrawetzky

Actually my thought was to only run 10 - 12 knots. By no means would I run WOT for very long. What that equates to in RPM's I'm not sure. The motor yachts we are looking at range in the neighborhood of 65,000lbs and of course each one has a different cruising speed.

OK, get back up to 10,000 foot level first.

The question is how you plan to use the boat? If you plan any length of cruising, then you may be happier with diesel. If you plan to spend most of the time at the dock and going out for "boat rides" here and there, you may be happier with gas.

Hours are less important than actual condition. A boat with 4000 hours on the engines that just completed the loop by the prior owners with great logs and a good survey with compression is better, in my opinion, than an engine with no history and 400 hours.

When you buy a boat, you should always have an engine survey done by a qualified mechanic who is not the boat surveyor and includes a compression. An issue is always liability, so choose wisely. A good engine survey means someone will need to put a wrench on the engine and anytime you use a wrench, there is a chance you can break something else.