Auto Diesel (Yeah, again, but...)

Yes it can happen, if you are an idiot.

 

This is an interesting and informative thread.Should your engine exhibit signs of reversion,you will have to fit a dry tail pipe.The only guarantee.

 

So,!!! do we have it now then? All agreed? There should not be water in an exhaust manifold-cylinders rings and spark plugs are not wet from sea water. As the web site states, what ever reason could cause it, reversion should be checked for and can not be tolerated.
So are you going to put this car engine in a boat or what?

 

jack frost - yeah.
All the talk about 'marine' engines has been informative, and I have actually learned a lot. As was suggested way back, I checked the internet, and I made phone calls, and I found that, since I am in the middle of the prairies, where there simply are no 'marine' engines available, the shipping costs alone for a used (and in need of rebuild) marine engine would be as much as the purchase price of engines that I can pick up here... used car or truck engines that I know how to work on. And, as a bonus, there are a ton of tractor engines, nice, clean, used diesels usually with transmissions, and spare parts as near as the local small town dealership, within a couple hundred miles of my house.
Will it be an elegant installation? Perhaps not. It will be basic, open and easy to work on, everything carefully installed and safe as houses. It will be affordable, clean and functional and will power my light, streamlined displacement hull, as fast (5-7 knots) as I need it to. I have the skills and tools to work on the installation, and, since the power requirements are relatively small, and the engine I select will be relatively large, I will never have to run it at 90% capacity, so the whole over-driven aspect of marine vs automotive engines will never arise. The torque curve of the engine I select will allow me to swing a large enough prop, fast enough, to give me the speed and power that I need. The rest is a mess of non-issues.
I originally asked a question about why the experts all said that a gas or diesel automotive (non-marine) engine had to work so hard, compared with 'marine' engines. My question was answered early on, and my decision was made then. The rest of this thread is personalities.
To all you professionals out there, good luck. Build 'marine' engines and sell 'marine' parts.
I'll be building an engine and buying parts. At J.C. Whitney or Sears or my friendly neighborhood junkyard.

 

Ok then have a go, You have a reasonable argument for it, see how you feel in a few months time. You say that you can get spares a few hundred miles away? So wheres the water? I assume you going to put it into some water when its done? Or are you going fishing up a river or some thing. Good luck -enjoy your self.

 

Might go fishing, might just loaf along through some of the big lakes around here, might spend a few weeks just lying on the deck in the sun, bobbing on the hook. Might head out through the Great Lakes to the ICM, or might not.
The thing is, I can afford to do any of that. If I waited until a 'marine' engine was available, I couldn't. I couldn't be sure of replacing any expensive 'marine' parts, if they went bad. Not only the cost, but the time involved in locating, shipping, etc.
I specifically asked about an automobile engine in a displacement hull. Not planing, displacement. Slippery, smooth, graceful. Especially, and this is the statement I wanted clarified, about the experts saying that an auto engine in a boat had to run at 75-90% power all the time to match the power of one of the mystical, magical 'marine' engines.
That didn't make sense then, and it doesn't now. It wasn't until the posting that said that marine engines are built small, and therefore, had to run at high power output to move the boat, that I realized the truth.
A small engine working hard equals a big engine working easy.
I've always heard that there's no substitute for cubic inches, and I bet it applies for 'marine' engines as well as non-marine engines.
All the warnings about everything going to hell in a handbasket if I don't have eutectic pistons or some such other part or system just doesn't track. Sure, some of the old hands and vested interests here are going to resent that statement, but ask me, briefly, if I care.
'Marine' parts are expensive. I understand supply and demand. And research costs, too. So, if a dealer or manufacturer or salesman wants to preach marine engine conversions to the congregation, fine. (BTW, Vested interests aren't necessarily a bad thing, despite some people feeling guilty and defensive about being one.)
At the end of all this, which I consider this to be, I got the answer I needed, and I've made my decision. Will I be happy with it in a few months time? Absolutely. I believe that care and intelligence in building, applying and maintaining a sytem counts a whole lot more than 'magic' parts or special fluids.
The assurance that, in the event that something does go wrong, I can safely, cheaply and quickly repair any malfunction, find replacement parts anywhere, and afford to actually acquire those parts, and in a timely fashion, too, counts for a whole lot more to me that the privilege of telling the world I have a 'marine' engine, approved by a vested interest.
Enjoy myself? Can't be helped. I enjoy most things.

 

I am sure your little motor will be fine, Kubotas are a popular conversion. sounds like you have the emotion and tenacity to get you through. Yeah you know! big marine engines are hellish expensive so its pretty normal to buy just enough horse power for the job. Take a look at how much more a 250 will be from a 200 and some times its just a case of injection alteration. But unlike your project a power boat will usually need 100% of its power to get it onto the plane -then you can back off to 70% if your lucky. If you get it wrong then its a case of re-pitching the prop and then the top speed suffers and you have a dog that needs full power all the time to keep it on the plane. Oh by the way, talk to your prop man before you buy the engine, Its the prop that pushes the boat not the engine. He will tell you how much HP the prop will absorb and what RPM, then with that criteria in hand you can choose an engine and gear ratio. If you do it the other way round as all first timers do, your prop man will not like you very much for asking him to make a prop that gets you out of the crap. It might be too late. But you seem to be in safe terratory going oversize and asking for only 5-6 kts.
Seeing as your a fan of the marine industry Ill;e tell you a story you will like. All the small outboards of Evenrude and Johnson 2.5 HP are a 3.3--3.5 just restricted. They simply have a small washer with a smaller hole lodged in between the carb and the intake. Pull the carb, pluck out the restrictor washer with a screw driver and you have a 3.5 This gives you 20% ish more power. The timing is a slight different but you alter that by the point gap. I have done a few . Takes about 1/2 hour.The Mercs are the same too only they fit a slide that is too big to clear the port,-- cut it down and you have un- restricted it. I am not sure how much extra they charge for the higher HP model. This will of course mess with your warranty. I think I just got myself in trouble? Oh well.

 

Thanks jack frost. That's something I had never considered. I thought props were kind of like tires - get something that fits, slap it on and motor off. You saved me a whole bunch of time and money and frustration.
About the 'restrictor plate' outboards... why would someone do that? I can understand when Nascar wants to level the playing field, but an outboard? That seems counterproductive, if not downright stupid.

 

So they can sell horse power as though they were selling it by the kilo. We are not supposed to know about it. They want us to think that a 2.5 Hp is different from a 3.5.
I think I am right in saying that the old Evenrude /Johnson 80-through-115 were all the same block ,just differed carbs, timing, exhaust. But a new set of carbs on a 80 did not a 115 make , its a bit more than that. A new set of carbs would be more than the difference between the 80 and the 115. I am going back quite a few years here I dont know whats happening today.They have us by the short and curly;s --they always have. If no one comes back at me on this I must be right, you know what this forum is like if you say some thing wrong.

Oh, also check where your going to fit the rudder, you must leave some space for it. There are some critical dimensions to adhere to, too close to the prop etc The dia of the prop away would be a safe start. Also dont get the prop too close to the hull 1/6 of diam, min, seems to come into mind. Again your slow speed should keep you clear of total catastrophies . There will be some web sites that will help you on this. Hydraulics are real easy, you will be able to buy a kit with all in the box. But I guess you would prefer a cable job.

 

Man, you are a warehouse of ideas and information! Thank you.
See, this is what this board should be about!
BTW, I just realized another example of the value of even a simple transmission. A 3.5hp rototiller slams a whole handful of tines through the soil pretty intensely. A boat motor can't encounter that much resistance swinging a prop. Wish I had realized that before.
The prop dealer would be able to advise me about the clearance dimensions, etc., correct?

 

That isn't entirely true. They offer different sizes to meet different needs. Some boats have a max HP. The companies simply detune an engine to fill his void rather than design a whole new engine Engines are routinely detuned to increase longevity. Look at a 671 VS 671 TI. Finally this is normal in all areas from lawn tractors to car engines.

 

Thank you, woodboat, for all your help. Your comments made a big difference. They helped point me in the right direction.
And your most recent posting is absolutely correct. Anything that has a motor is manipulated to adjust the power according to the pervceived need... or market. Again, thanks.

 

Errr well the prop man will be able to advize you on clearances but its not really his job. Thats the boat builder. You need a book, there must be hundreds on this subject. If i were you I would be trying to go for a very slow prop speed. Dont skimp on the shaft size, I would not go to 3/4 for instance,its probably within the torque limits but its a bit thin. You would most likey un-true it if you touched ground. I would go inch or more, Again talk to the prop man and tell him your requirements. There are some bits and pieces that are not normally made like shaft log -stuffing box etc but I guess you could if you know what to make. Try to keep the shaft short as possible or you may get 'whip' and need more support bearings. Your extra thick shaft and slow speed will keep you further away from this problem. Try also to keep the shaft at 10 degrees, that would be reall good, more than that is ok but I would'nt go over 15 if you really dont have to.

Dont forget about thrust-- the prop pushes the boat by pushing up the shaft into the engine and the engines into the hull. Marine engine mounts accomodate for this. Tractor stuff most likely will not. But if youre stuck you can strap the engine so that it can move but not forward , it only needs two mountings straped.
Dont forget a thrust block and bearing, or thrust bearing in the gearbox. This thrust thing will kill your gearbox in minutes.
Keeping water out of the boat might seem a problem which is what the log and stuffing box does. A stufing box is an antiquated method of stuffing greased string onto the shaft like a water tap. I have made some deep sea jobs recently for 2 inch shafts and have run now for over 100 hours and not a drop has yet to enter. Sooo easy to make.
Have you got the boat yet?

 

The thrust bearing is basically a conical bearing mounted in the drive line, usually in pairs, one for forward thrust and the other for reverse, correct? To relieve the strain on the transmission, which, as you say, isn't built to take it. I don't have them yet, but I do have some ideas...
Yeah, my thought was to go with as big and slow a prop as possible, and, since I tend to want to overbuild anyway, a nice stiff prop shaft is a must. Two inches wouldn't be out of the question, as a matter of fact. Is a stuffing box similar to a cutless bearing? I have some ideas about them, too...
The boat is mostly piles of wood right now. I've been recuperating from surgery, and looking foward to getting the green light to start putting it together.

 

Auto Diesel (yeah,again,but...)

The rule for supporting shafts with bearings.20 40. No closer together than 20 times the shaft diameter.No further apart than 40 times the shaft diameter.?