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Lets talk Diesel engines

Old 06-10-2021, 09:50 PM
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Originally Posted by ChrisandKristin View Post
Even if you know how to run the rack on a Series 71 you need the timing pins for 'em to set the injectors. Very few mechanics have those in their toolbox anymore with the advent of electronic engines. And setting the governor and syncing the injector control links on a V-block is more of a black art than a science.
This is the truth. The pins are like 20$ but the knowledge to tune one well really is a skill.

I've seen a lot of poorly repaired ones runaway in the last few years. As the Detroit mechanics get older and older, general diesel mechanics that don't have the knack can have a hard time with them.

Detroit parts are cheap, but the quality of reliabilt parts arent genuine dd parts. Repowered my 52 footer because of this factor alone. Love operating detroit powered boats, especially in the fisheries with lots of maneuvers. But lots of the replacement parts were flawed, enough we took on the task of new iron.


A 2100 rpm na 8v71 may be a great little 318hp motor, but it will require an entirely different drivetrain to the gassers. None of this stuff is cheap. I just put a short shaft assembly into an existing boat one size bigger. Bearing plus glass, plus shafy and adapters was still thousands. That's the easy cheap stuff. Start adding on props, gears, gear adapters, exhausts, it can spiral. Even with super cheap mains it would be a tough sell.


As for using old takeout Volvo's.... just skip the middleman and get into financial masochism.


The small cummins make the most sense. Find a salvage rig and buy the whole shooting match and adapt it. Might find the same with 671s but it's less likely. Lot higher chance of finding an 03 f150 with a rust free body than a 79 f150.... just sayin.
Old 06-10-2021, 10:52 PM
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I agree with putting the Cummings in simply for resale value. The 671s will probably be the easiest since they were an option but then it still just has an old set of 671s. I actually like volvos but that would be like repowering an outboard with evinrudes good luck finding a buyer down the road. Would love to see a photo of what you did with the dash on your mustang. If you do do it hope you do a repower thread
Old 06-11-2021, 03:13 AM
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So you’re saying there’s no way it’ll cost you $100k. So that must mean you’ve run the numbers. What did you come up with? What will you have to buy and how much do you expect it to cost? I expect you will not address this question directly but we’ll see.
Old 06-11-2021, 06:24 AM
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Originally Posted by Comfisherman View Post
This is the truth. The pins are like 20$ but the knowledge to tune one well really is a skill.
When you set the pin in the hole on the injector body and brush the flat over the spring retainer the "feel" of how much drag you have as you turn the rocker adjusting screw, and consistency from one injector to the next, will determine the accuracy of the timing. Same with the links - you can run the rack on one bank on a Vee and think you got it perfect. But how much pressure you put on the governor link when you set the other bank will determine if the fuel rate is identical on all 6, 8, 12 or 16 injectors. You get one injector tight by 1/4 of a screwdriver blade width and you'll have a loose rack on the whole other bank. The engine will run, but it won't run like one tuned by a pro.

Runaways are caused by a binding metering barrel in one injector. There's only three moving pieces in a Detroit injector, but they were never designed for today's ultra-low sulfur fuels. Engines in service today have had the injectors replaced with remans with hard-chromed barrels and plungers, or they soon will when they experience a stuck injector. If the buffer is set properly and the engine still has significant governor roll at idle when it's cold may as well pull the rack shafts, rockers and injectors and find out which one is binding before it becomes a problem. 12V's and 16V's have some governor roll when they're cold by design, simply because the same governor used on the 6V's and 8V's is driving that many more injectors. But once again, experience tells the trained ear if it's right or not. Somebody who doesn't know what they're doing can screw up a Detroit really bad and then the engine gets a bad rap. But properly maintained and tuned, we got a couple 16V149's on generators with 30,000+ hours on them, never had the oil pan or a head off since new. They have outlasted the hour meters.
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Old 06-11-2021, 07:53 AM
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I have a '79 with naturals in my backyard I'd sell. Fresh rebuilds (not a repair-this was a 40K rebuild down to the bare block by 30 year Detroit mechanic, new Detroit heads, Reliabuilt kits, accessories all rebuilt, custom stainless risers), Northern Lights generator. Needs grunt work now: soft goods and exterior work. It was my dad's boat, had it in my mind to make a Fish/Dive boat out of it but I just don't have the time.
Old 06-11-2021, 08:25 AM
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So if the testimonials of the rank and file here (some of whom do this for a living and other whom have learned the hard way) haven't deterred you.......Well then you just not looking at the facts with an open mind.
I personally think this is an unobtainable goal for all the wrong reasons with an unrealistic budget restriction.
That being said.....Please have at and prove us wrong. A build thread would be advantageous and appreciated by all that follow.
Best of luck and please keep us updated.

Tony G
Old 06-11-2021, 08:38 AM
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I suspect that what's really happening is that the OP doesn't want to go boating. He wants to go mess with engines.
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Old 06-11-2021, 09:00 AM
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Originally Posted by chainsaw42 View Post
So you’re saying there’s no way it’ll cost you $100k. So that must mean you’ve run the numbers. What did you come up with? What will you have to buy and how much do you expect it to cost? I expect you will not address this question directly but we’ll see.
As I don't have the boat here and haven't chose the exact engine I plan to install the best I can do is a WAG. Here is what I have been playing with based off the set of CAT engines I found with transmissions.
CAT Engines and Trans: $28K
Shafts: $2000 (Don't know the exact size and length I need yet but went over kill on the site I found)
Hangers: $1600 (Again without know exactly what I need I went with the high side of what I found on the site and the plan would be to find a Hurricane boat and pull some to use.)
Props: $5000 (I already have another set of props that are much bigger than what's on the boat that I can possible use. Until I pick a for sure engine and trans setup there is no way to know if they will work. I could be low on my price here but this is ball parking from my searches.)
Fuel filter and line setup: $2000 (again could vary based off engine requirements.)
Miscellaneous parts for moving the beds and placing the engines: $2000
Total: $40,600 for full swap out. Even if I take the advice of everything someone tells you and double my budget I am still at $81,200 which is still a long ways from the $100K. Are there things I am forgetting and don't know about yet? I am sure! The sad part of this entire post is that I have spent way more time reading and trying to defend my decision to do this swap than getting the information I was looking for. I get that a lot of the people that bring it up respectfully are genuinely think they are trying to help. I do appreciate the concern and wisdom. Also letting me know all the stuff I would need to change. Had someone said all of this a year ago I would not have known half the stuff I needed to change. I have been learning as much as I could over the last 2 years about these boats. Does that give me the vast knowledge that some here have? No but I am learning. That's why I came here and asked the question. As you will note in my original post I said I was opening a can of worms. That meant exactly what this thread has turned into. Not helping someone with the information that want but questioning the person on what they are doing and why. So there you go I answered your question that has nothing to do with my question to begin with. If you don't have any information to help me then please don't add to the clutter I already have here. I am done debating if I should do this or not. If I can figure out what engines I am going to go with maybe I will decide I don't need to do it. I am sure there are going to be 50 more responses to how there is no way my numbers make sense but I will not bother with defending myself to the nay sayers any more. Now if you know of major parts I am missing please feel free to inform me so I might add them to the list of parts to buy.
Thanks


Old 06-11-2021, 11:27 AM
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Crane to pick the old rustbuckets out of there once you get then out of the salon. Bigger crane to move the diesels into the boat. Frame to lift the old motors out, move them back 10 feet where the crane can get to them and then move the new motors forward. Chainfalls etc...
New shaft logs for larger shafts.
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Old 06-11-2021, 11:41 AM
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Add a good amount of $$ for exhaust plumbing. Maybe I'm wrong, but I don't think it's as simple as a rubber hose on a diesel. Maybe an N/A diesel, but anything with Turbos will need some special consideration. There was a yanmar swap into a 32 Luhrs posted on this board that I believe had a lot of trouble with exhaust.

While I don't think installing new shafts is voodoo, I do think it may be the area you'd want to spend for an expert on.

Also does 2k for shafts involve the machining? cutlass bearings, seals? Do you need larger water pickups for the diesel and possible aftercooler? Bigger sea strainers?

Generator?
Old 06-11-2021, 12:04 PM
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I just replaced most of the hose clamps on my smaller boat, $1,500 for stainless constant-tension clamps. There are going to be dozens of that category items you are going to run into. This thread might be a can of worms, but it will help you think of a lot more details than you are likely to know, without having ever done major work on a boat this size.
Old 06-11-2021, 04:39 PM
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You sound kind of sensitive. No reason for that. People here including me are just trying to give you what you asked for...advice. I honestly thought you were going to say you can do it for 10 or 20k.

As far as 'which' engines...when you're on a budget and money is the number 1 constraint, I would say don't worry about the exact motor and just be ready to pounce when a pair of something that will work well comes up for sale used in really good condition for a reasonable price. That is going to be an extremely rare occurrence so don't make it a once in a lifetime event by limiting it to a particular model.

that said for someone on a budget who is doing all the work himself, nothing beats a mechanical cummins as far as easy to work on, reliable, parts that are super easy to get your hands on, parts that are relatively cheap, and tons of good advice readily available for the DIYer online for free. but I wouldn't hesitate to throw in a good pair of cats for the right price and I'd even hold my nose and buy volvos if everything about them was good.

but, before you ever drop a dime on this you better figure out what you got in that boat. I know you're convinced you got it for a 'steal' but there is a saying that the most expensive boat you ever own is the one you bought the cheapest.
Old 06-11-2021, 05:01 PM
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You are going to have to pay $50 to access the site but boat diesel dot com has a lot of running takeouts posted in the for sale section. As a bonus you may find someone over there who has actually done this before.
Old 06-11-2021, 06:10 PM
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Originally Posted by tad117 View Post
I agree with putting the Cummings in simply for resale value. The 671s will probably be the easiest since they were an option but then it still just has an old set of 671s. I actually like volvos but that would be like repowering an outboard with evinrudes good luck finding a buyer down the road. Would love to see a photo of what you did with the dash on your mustang. If you do do it hope you do a repower thread
need to refresh your brand names.
Old 06-12-2021, 02:00 PM
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Originally Posted by tad117 View Post
The 671s will probably be the easiest since they were an option but then it still just has an old set of 671s
Nothing wrong with an old set of 238's if they fit in the hole. But 6-71's sound a bit different than the 60 deg v-blocks and for a sport boat I think you'd be disappointed in the power compared to what a pair of 454's can do. Too bad you can't stuff a couple v-blocks in there. The 5.9 Cummins engines are ok, will usually fit in the hole that a 454 came out of. But they are a medium-duty engine with their sleeveless block and non-articulated one-piece pistons. The 8.3 Cummins has wet liners but is really no lighter than a 8V71.
Old 06-12-2021, 02:13 PM
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Other stuff that comes to mind that you haven’t mentioned or is light on detail:

Throttle and shifter controls - are they compatible and if not you’ll have to buy and install new gear.

Shaft couplings.

Shaft seals.

Raw water intakes - are they of sufficient size and will the current location allow installation of new engines.

Do the used engines come with exhaust mixers? They aren’t cheap.

Exhaust and muffler will have to be a bespoke design.

A few grand for engine mounting hardware seems light on.

Props - you might be lucky and buy a used set that work perfectly with the hull/engine/transmission combo but most likely you’ll end up spending money to have them tuned or maybe have to buy a new set that are specced properly to get the right performance.

If you have the head space in the engine room then an inline six like the Cummins B series will give you much more access and working space around the engines than a V8.
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Old 06-12-2021, 04:35 PM
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Respectfully, that is the poorest reason to switch propulsion. Many folks are very bad at assessing risk. I had a guy scared to go in the boat due to sharks, even though there hasn't been a single shark related fatality in Mass in my 30 plus years of boating.
But it doesn't occur to him he's far more likely to die in a car accident on the way to the marina.
If you want to be safe, be smart and reduce real risks, not one in a million things for people who follow basic safety rules.
Old 06-12-2021, 08:45 PM
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Spending $100k because you are worried about a gas powered boat seems insane. Replace all fuel fittings/hoses, make sure bilge blowers are good, and go boating. You will be 3 years in and over $100k, with unknown engines, will have had no use of the boat, and it will be worth nowhere near what you've spent. If so worried, sell this one and buy a diesel powered boat.
Old 06-13-2021, 04:36 AM
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Just do it.
Old 06-13-2021, 12:50 PM
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Major engine compartment rewire.

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