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LifeTrac - use of car/truck sourced engines?
  • NOTE ON SELF - I am hoping to build a LifeTrac tractor as early as spring 2011, and no later than summer 2012. To me this is a critical 'feature' if it could be done. I started a thread similar on the old forums which I can no longer find so I am posting this here to hopefully renew interest or inspire new conversation down this line.

    The use of commonly available used gasoline or diesel engines from cars and pikcups has the potential to drop thousands of dollars of cost from the project, from around $5000 to half or less - the purchase of the ~50hp diesel engine was the largest expense when I last looked.

    Such engines are larger and heavier (this is a detriment in some instances when maximum compactness or minimum weight is needed) but I think either the advantages outweigh the disadvantages, or alternately provide an important alternative choice and would be worth parallel development. I would happily be the first person to build one if it comes to that, I just would probably need help on the reengineering of the tractor side of the equation to allow this.

    Some advantages:
    - More weight (this can improve traction, many farmers have to add weight plates already)
    - Oversized and understressed, especially on the larger side of the spectrum such engines could put out the desired 50hp darn near eternally, being designed for much more
    - Lower purchase price. A new even small diesel costs thousands of dollars. You can pick up three junkyard but still running engines for less than that so that even if one blows an injector pump or has some normally expensive to fix individual part go out, you can swap the engine and keep the original for spares or leave it on a stand until it is convenient for you to work on it, or find spare parts for less than normal market rates. I have seen running oldsmobile diesel 350's GIVEN away because people thought they were worthless. (bad reputation due to some fully fixable flaws) I challenge you to find someone to give me a running Yanmar...
    - Ability to use multiple different engines gives more flexibility, for instance you might design around a diesel ideally which shares the bellhousing of a common gasoline engine. If the diesel is simply not running, you could swap in a junkyard gas engine which bolts right up, motor mounts and everything. (for instance for some common General Motors models)
    - Lower repair costs is quite possible, since auto engines can be made in the tens of millions, you can get entire second running engines for less than the price of one part on some other vehicles. Entire longblocks for $150 is not uncommon if you are looking for an engine not of interest to hot rodders, or add a little more for all the electronics and everything and verified running.
    - Shared research for alternative fuel compatibility and such with other land based vehicles, for instance a producer gas carburetor (woodgas/coalgas) or dual fuel system (compressed natural gas added to a diesel) which uses an engine common in auto/truck fleets can be applied to a car. Or alternately research done for that engine on a car can immediately apply to the tractor. The same research could be done for experiments of modifying car engines for slower turning/longer durability (for instance power peak at 1200rpm or even less for notably longer life between rebuilds) and again, could be helped by hypermiling car enthusiasts who are doing the same for street use.
    - Might use what you already have around for other purposes, alot of tinkerers may already have a spare engine, or may pull one out of something and have it laying around as the result of some other project like a hypermiling engine swap.
    - Commonality of parts with auto engines mean any auto mechanic already is familiar with what you want them to fix if you cannot do it yourself. There are alot more small block chevies out there than perkins diesels. This may not matter as much now, but say in a future of serious social instability, if I were in a third world country I bet i'd have an easier time finding small block chevy parts than trying to track down my specific model of small sized diesel. Or you might have the same engine in your road vehicle, so that in a pinch if you HAVE to make harvest, you can pull parts off the road truck/car to keep it running then swap it back afterwards. (this has been necessary for instance in vietnam, it was not uncommon to have to swap the engine into the homebuilt/modified tractors in the late 70's and 80's though then it was due more to severe poverty and having to use what they already had on hand)
    - Potential for longer life with slow speed modifications. (case in point - the Lister diesel which operated at 600rpm has been known in alaska to run 50,000-100,000 hours before requiring a rebuild, literally 6-12 years of 24/7 operation)

    Some examples of what i'm talking about:

    General Motors has perhaps made more directly compatible bellhousings and engines than anybody. You can for instance bolt up inline sixes, 90 degree v6's, small block v8's, big block v8's, and all three types of diesel (the old GM 6.2, the 6.5, and the newer Duramax 6600 for what I understand) to the same small block chevy bellhousing. Motor mounts between several are often shared as well. The second bellhousing is used for the 60 degree v6's (2.8L, 3.1L, 3.4L) and earlier inline four cylenders (like the 2.5L iron duke, based off the small block chevy and known as an incredibly long lived engine - 300,000 miles almost being normal). The Buick-Olds-Pontiac-Cadillac bellhousing can bolt up any of the dedicated engines from the 70's and 80's including most importantly, the Oldsmobile 350/5.7L diesel and 260/4.3L V8 diesel and the 90 degree 260/4.3L V6 diesels which would be the primary reason to run such a bellhousing. However in the example above of swapping in a gas motor to keep running while fixing or looking for a replacement motor, the common Olds 307's from the 80's can be had for nothing, yet should meet the 50hp all day power goal with no problem. (being rated for 105-120hp or so peak, half should be fine for an industrial/marine style high load rating)

    Other unique engines in this series include the still cheaply available Cadillac engines, which were known for being made from one of the best alloys at the time in the iron versions (368 425 472 500 v8's), superior to other engines even in the GM line for the purpose of durability. They also include engines that if weight is still important, like the 4.1/4.5/4.9L aluminum V8 cadillac engines, which are cheap beacuse they were not powerful or in high demand by hot rodders yet would make an inexpensive lighter engine that maintains the ability to later hook up an olds diesel or anything else for instance. Furthermore common bellhousing adapters can let you bolt any of the above three to any of the other above three.

    The Oldsmobile 350/5.7 diesel is still widely available in junkyards and considered to have practically zero value. I've been offered to be given running motors for free. Part of the reason was an extremely bad reputation... one problem was bad fuel quality in the early 80's, this contributed alot to engines at the time dying. But there was also an engineering problem - I believe it was weak main bolts. When combined with the problems from the bad fuel this had the unfortunate problem of spitting crankshafts out of the bottom of the block. :P That is where the reputation came from, but since this is just the cost of replacing a couple of BOLTS this is hardly an expensive modification to do to a still running or rebuilt engine to make it otherwise live a long life.

    The GM 6.2 diesel was not very powerful for a full sized pickup motor but would be more than adequate for a 50hp constant goal. (rated I think 150hp or so normally) The only problem they ever had was being run hard and long at full ~150hp type levels up mountains for instance. Most importantly it is among the CHEAPEST diesels you can buy, either used or rebuilt - you can probably get a rebuilt 6.2 for less than a ~50hp Perkins diesel or maybe about the same price and rebuild one yourself for far less. They are extremely common, among the most common diesels ever made, and again if it ever went out or you simply had to get running immediately for harvest or something, you bolt up a common small block chevy v8 (something like 60 million plus having been made) and run that for the meanwhile. You could also use the 6.5 or Duramax 6600 but they will of course be notably more expensive and overpowered for an application like this.

    The Ford 6.9/7.3L diesels (before turbochargers) are also available for not too much money... a bit underpowered for a pickup (though more power than the GM above), they are notably heavier, more durable, and a bit more fuel efficient. They also weigh more. They should share the same bellhousing as common ford small block diesels giving that same swap out emergency option. (or of starting the tractor on a junkyard gas engine and upgrading to a rebuilt ford 6.9 when money permits)

    There are plenty of other smaller diesels as well, often with good reputations - whether old mercedes or VW's for instance, you could also use any of those, but the total expense of doing so is likely to notably exceed any of the common engines above and they will be far less common in terms of parts and repair costs being imported. However I see no reason to disclude anything - simply designing an engine bay with plenty of room and designed around the multitude of shapes should let you put in pretty much anything you have access too... which can include the originally designed ~50hp Perkins or whatever was selected for the original prototype.

    If one wanted to simply go with common gasoline auto engines you could use 4cyl and v6's of small size as well, picking models which are among the longest lasting, noninterference designs, cheapest to repair, easiest to diagnose, and so forth. An example might be honda 4cyls like used in the civic or slightly bigger cheaper understressed american v6's.

    **Note: all the above comments are from memory, it's possible i've made a misquote or two about engine interchangeability, but if there is interest I will doublecheck facts and verify before anyone does any serious work in that direction.
  • 10 Comments sorted by
  • Vote Up0Vote Down
    November 2011
    Welcome back, Jerry, long time, no see :)
  • Hi :D Where did the old boards even go to? I seem to remember checking them and finding the forums didnt even exist... were the discussions archived somewhere or just lost in a crash or something?
  • Vote Up0Vote Down
    November 2011
    The problem I see with this idea is that it either requires a complete redesign of the lifetrac or it is unrealistic within the basic design.

    The LifeTrac is designed to be hydraulically driven, with power cubes, which are interchangeable with many of the other units of the GVCS-50.  There is no mechanical drivetrain in the LifeTrac.  The drivetrain is made up of hoses full of hydraulic fluid coupled with hydraulic motors.  If you switch to a car engine, you either need a different type of drivetrain, or you need to redesign  the power cube drastically (making it LOTS bigger), or you need to give up entirely on the modular power source idea as pertains to your version of the LifeTrac.

    In any case, the beast you would have at the end of that process would probably not be described as a LifeTrac with any accuracy.
  • If the "power cube" is an essential component, what about using a large sized power cube instead? I could understand if there may not be interest from the mainline, i'm just curious if it would be possible for me to work on the parts relevant to me and coordinate the other parts of the design with others cooperatively.

    I wasn't planning on a different drivetrain, just driving whatever hydraulic pump is currently designed into it and running that from the car engine.

    Worst case giving up on the modular power ability may be an acceptable compromise for me, I don't see alot of engine pulling being likely for what to me would be a daily use implement much of the year. (for snow removal and similar) Having a design fork that in all other ways is compatible with the LifeTrac would be fine for me... I do not think most of the design should need to change much at all other than being i'd assume 18-24 inches longer, and wider to accomodate the engine. I'm not seeking a complete redesign, rather something that uses the existing design as much as possible with only this one change of extra engine room or the accomodation of an oversized power cube.

    I'm not even sure which machines require a removable power cube yet... i'm assuming the tractor, the bulldozer (or is that just an attachment for the tractor?), the microcombine, the car, the truck, perhaps the well drilling rig. The proper cheapness of engine might just let you leave a dedicated engine in each of them though.

    Alternately perhaps a wider range of small diesel (and gas) engines could be supported within the power cube (or maybe already are) since some of my main reasons are about lowest entry cost, understressing the engine, and whole components often being cheaper than parts repairs... have low cost alternatives been suggested? The only disadvantage I see to a larger power cube itself (as opposed to on the tractor) is not being as easy to yank out and replace... for the cost in engine savings I could easily buy a cherry picker.

    I also think it was suggested that eventually the LifeTrac could or would be scaled up or down according to other needs... (it lists 18-200hp for the tractor for instance), i'm assuming a larger powercube would be intended to be used at some point anyways or were multiple (even more awkward) engines and pumps the plan? Perhaps some small design change could make it easy to run more than one size of power cube in the same machine... there isn't even a hood it's mostly surrounded by air outside of the frame. Other than a bit more length, widening the point for the "rollcage" in the back so the vertical supports clear even a large v8 and possibly moving the rear axle back for the weight difference I don't see why much redesign is even necessary to the tractor, and it could still use the smaller power cube easily. All I see above and behind the power cube currently is air.

    If nothing else, i'm wondering if people might be able to say "it would be a good idea for the future, say Life Trac v2.0, but lets just finish v1.0 first" and to have the option be a part of that fork when it gets to that.
  • Vote Up0Vote Down
    November 2011
    Jerry, the old boards are long gone, and especially for this topic, it is a tragic loss, because gone with it are the old discussions over the design choices of the original LifeTrac, back before it was actually built or prototyped.  Most of the folks you will see around here now don't even know where LifeTrac started from (and may not care?).  The new "OSE" seems to have long since left its stated goals from its original roots far behind, and anything said here amounts to talk only, that won't influence the real OSE LifeTrac design, anyway.  They've gotten & ignored much good advice on that, just since this new forum was running ;)
  • Vote Up0Vote Down
    November 2011
    >  The new "OSE" seems to have long since left its stated goals from its
    original roots far behind, and anything said here amounts to talk only,
    that won't influence the real OSE LifeTrac design, anyway.

    While that's true, Allen, it is not necessarily a problem or weakness.  So far, people on this forum are pretty much free to explore whatever aspects of the GVCS (and beyond) they like.  As you know, Marcin has his own plans for GVCS development at FeF.  I don't think that should stop anyone, especially people like Jerry who seem to have the knowledge and skills to extend or alter existing designs.  My main concern is keeping it together as an OSE community outside of FeF.  Feeding back ideas, lessons learned, new concepts, prototype efforts that succeeded or failed all contribute to moving us towards the development of a reliable set of GVCS tools.

    - Mark

  • Vote Up0Vote Down
    November 2011
    Very good points Mark.  FeF and Marcin are only part of Open Source Ecology.  That part has taken on the responsibility of releasing the GVCS-50 as open source designs.  Those designs, being open source may be freely modified, as long as modified designs, if published, are published as open source as well.  Where we sit now, a few years into the process, we are somewhere between the infancy and the adolescence of this idea.  Ideas like Jerry's (and others) are part of the maturation of that idea.  Along with maturation, comes growing pains.

    Some of those growing pains come in the form of documentation that is inconsistent with itself.  This sometimes will lead to confusion on the part of early adopter/modifiers like Jerry.   Case in point:  The present design does not call for a 50hp engine, which Jerry expresses concern about.  It calls for 2 power cubes, each with a 28hp engine.  These engines are running about $700 each at present from the supplier in the Powercube BOM.  Now some of the documentation on the wiki mentions 50+hp engines, but that doesn't reflect the most recent designs.  The understanding is incorrect, but I can understand how one could get there.

    So an automobile or *GASP* truck engine would be enormous overkill for the task.  Even a dinky car engine, like the 1.1 liter Ford Festiva engine is bigger than the entire power cube as it stands now and significantly more than your 50hp output.  Already at that, you will need to redesign the powered-up-power-cube, and allow spacing for what is probably now a bigger hydraulic pump, with bigger quick-connect couplers and bigger hoses throughout the tractor, probably a bigger fluid reservoir.  With all of this you will need to make all of the appropriate calculations for failure levels and determine where cushioning valves need to change so this thing doesn't rip itself apart when circuits are turn on and off.  Absolutely none of this is impossible, but there would be work to be done, is all I am saying, and also possibly some glitches to recover from along the way.

    If you didn't want to depart too wildly from the present design, but you wanted to use a more powerful, easier to source engine, I would direct your attention away from cars and trucks and towards smallish motorcycles in the 125cc-250cc range.  These are engines that fit your power output needs nicely, while being small enough to potentially fit within the dimensions of the existing power cube with slight modifications.  There's going to be some rethinking involved about motor mounts and the alignment of components within the power cube itself, depending upon your motorcycle engine of choice, but you won't have to redesign the entire hydraulics system.
  • Vote Up0Vote Down
    November 2011
    For those who weren't around on the old forums, Jerry Shaw was an active part of the discussion about the LifeTrac design, before it was ever prototyped, and was still just a forum discussion (and it also had an articulated joint in the middle for steering), and he brought up these same concerns about why not use a much more standard off-the-shelf power plant, because the original LifeTrac was calling for a 65 hp diesel engine, and back then, there was NO such thing as a Power Cube even being discussed.

    Not sure we've actually made much in the way of progress since then?

    As far as being overkill, not really, since an automotive engine or a truck engine, for that matter, if they are gasoline-powered, will develop their highest horsepower at much higher RPMs than what is desired, but unfortunately, they also develop their highest torque at higher RPMs too.  Upsizing the power plant would allow a gasoline engine that may produce 180 hp at a redline of 5500 rpm to be run at 1800 rpm, and still have it generate enough horses to be usable for the task at hand, and also improve the fuel economy.  Small-block Chevy engines are world-wide available & cheap, and the LifeTrac could usually use the extra weight too, so it would be a win-win situation to consider and combine them.

    Running a smaller gas engine at higher RPMs will tend to use more fuel, if you actually needed the horsepower or the torque, which equates to more money faster, and often by the population segment that could least afford to spend the cash...
  • Vote Up0Vote Down
    November 2011
    Perhaps a kind of governor or limiter can be added to prevent the auto engine from rev'ing up to a speed/power that exceeds the hydraulic limits.

    - Mark
  • to everyone: I will continue to try to defend my ideas, inspire with possibilities, and argue for why I think my idea is one either worth adopting or beneficial in other ways. Hopefully no one will mind. :)

    to Allen15 1st post: I would like to see some reconstruction from anyone who remembers the old boards to understand more about why it's done "that way", I would like insight into that process. I only remember parts of the discussions myself, and all the talk then was around I thought a 50hp Perkins which at the time was like $2800 if I remember, and some of the wiki still seems to indicate that.

    to mjn: my knowledge and skills are somewhat spotty, I have areas of alot of knowledge and other things that I don't know about. It's the things that I don't know about that i'm seeking help for. I can express the reasons why I think certain auto engines are a great choice (like I just did), I cannot comment comprehensively on tractor design. I would love to know more about the original design process and decisions or forks in the road that were left unexplored or unchosen... i'm sharing my own train of thought so others can see why i'm arguing for what I am arguing for.. even if the tractor needs a redesign i'd want to maintain 100% compatibility with all implements, and use the hydraulics as designed for instance including for drive wheels. By having such a wonderfully simplified tractor design to me it seems pretty obvious why things are put the way that they are, it's just a strong frame upon which to mount an engine, hydraulics, seat, and attachment points for tools.

    to Clifton: I O_o at the small gas engines a bit, small engines like that will have a lifespan of maybe 800 hours before needing a rebuild. They WILL work but I don't know if they will last as long as others may want. They are built as cheaply as possible and not generally even meant to be rebuilt much... one summer of 8 hour a day working and it's used up. This is why garden tractors and such are "light duty", and if the LifeTrac is used light duty like cutting your lawn once a week it should be fine and give the same years of lifespan as a garden tractor has. If it is meant to replace a "heavy duty" small tractor like the type you get from a farm equipment dealer with an 1800rpm diesel instead of a Sears Craftsman weighing 1000lbs with a 3600rpm gas engine it wont though. An understressed car/truck engine will be "heavy duty" for the far lower hp it's being asked to put out. As to auto/truck engines, remember they are rated peak horsepower - what we need are industrial (ie constant full time at that load) ratings... the same reason that a chevy 350 in a car might have 300hp but one in marine duty might be rated 160hp and still be designed with stronger components, it's the duty cycle. If you want a tractor to actually WORK then you can't run a 1.1L Festiva engine at max power - it will not even last 800 hours. The little 28hp Briggs should last 800-1000hrs as most small engines are designed for that but i'm wondering how much longer... for a not often used tractor (yes like my own, yes I might well use the 28hp Briggs as designed then to start, or try to find a used garden tractor and pull it's engine and modify accordingly more likely) it may be fine. For one really intended to WORK with lower long term costs the previously mentioned diesel WAS appropriate... just costing almost as much as a rebuilt car/truck engine of certain background is all.

    The use of a light duty high rpm (all 3600rpm small gas engines are light duty by definition) in the power cube will not guarantee a long life... put it in a generator for instance, run it 24hrs a day and it will need a rebuild within WEEKS. There ARE reasons to favor larger heavier slower turning 1800rpm diesels - they are made for far longer life under the conditions. An understressed auto diesel could turn as slow or slower and last ridiculously long, an understressed auto gas engine would probably last almost as long however, and also be more suited to being powered by biomethane, alcohol, E85, producer gas (coal gas/wood gas), propane, compressed natural gas. Also on the subject of alternative fuels one problem with producer gas engines (one of my personal goals - power this tractor off wood) put out notably less horsepower, like 60% or less. That 28hp Briggs on producer gas would now be putting out more like 15hp without mods, and maybe 18hp with non-cheap mods. It is also far harder to run a "diesel" designed engine off any pure biofuel or gaseous fuel except biodiesel. The best/easiest engine to convert to run off propane/CNG/methane/alcohol is, a gasoline engine. But the small 3600rpm ones will NOT last.

    Also, safe industrial/marine ratings are rarely more than half "auto" (or even pickup) HP ratings, sometimes 40%, occasionally even 33% if the auto version is particularily high performance to start with. If you drop any of those figures lower, especially on a diesel, the engine can last a ridiculously long time because it's understressed. For instance 12V-71 Detroit Diesels used in marine duty... when rated for 700hp or more (which they can be) hot rodded for powerboat use... you'll use them for one season, maybe two, before they die. Tool around and jet ski at 40mph in a 40ft powerboat, have fun all summer and look at a rebuild within 2 years. At high performance they last maybe 800-1000hrs at best just like alot of gasoline engines will. At those power levels the "long life of the diesel" no longer even registers and doesn't even exceed gasoline engines in most cases.

    Run that same 12V-71 Detroit at 350hp like they might be rated in a commercial fishing trawler, and you will still be using the same engine without a rebuild 20 years later despite constant commercial use. At ratings of 1/2hp per cubic inch or lower diesels last substantially longer than gasoline engines. If you can slow the rpm's (through modifications, as I suggested, which means more cubic inches to get the same HP level) you can stretch that even further. The ONLY downsides to using such "oversized" engines are of course the weight and size. And even if it's maybe still eyed as questionable for say the tractor, it's sounding like it could be just right for the dozer which will need to be heavier and larger anyways. In which case if the dozer could use the tractor implements I might just build the dozer first (or at all) since I expect to need earthmoving.

    Put all these things together and a 6.2L GM Diesel is not massively oversized anymore, and although the 6.9/7.3 Ford diesels still would be oversized by then they are common and inexpensive enough now that it's probably still worth supporting. The cheapest of all Olds 350 diesels are probably just about right, and will be the lightest, though they still probably weigh 700lbs or so admittedly. (about the same as a big block gasoline engine) I would avoid the dodge cummins 6BT's for being clearly too damn big (something like 1100lbs and 3ft long??) although the smaller 4BT's (about 700lbs I think) commonly found in UPS trucks and the like are pretty cheap, available, and basically the most efficient small diesel you can even bolt into a large car or truck. (Suburbans pulling 32mpg or greater, and full size RWD cars pulling 45mpg is not unheard of with one) And they take lasting forever into a whole new category if you understress and turn it slow/you'll be giving this tractor to your kids without a rebuild probably.

    The only thing i'm seeking in a design change is the space and weight capacity (ie axles properly under the weight) to potentially allow an auto/truck engine, simply because of the doors it opens. It could be some of my conjectures or things I thought would come of it will turn out to be dead ends, and this fork would be abandoned in the future... if so okay, but it seems worth exploring at least in my mind, and i'm willing to explore it, I just need a tractor that will actually allow me to toy with these things on. There are other reasons why I think a larger and heavier capacity engine compartment is inevitably needed as an option at some point in the future anyways - the talk of making your own steam engines are NOT going to be as efficient per unit of weight nor as small. Or lets say someone has some other made and forged from scratch engine - literally casting and making your own engine is possible, but power to weight ratios are unlikely to match anything current as well. If the compartment is literally oversized now, all of those options are already supported. And so is using the existing power cube(s). The problems of larger size and weight will have to be solved at some future point for any of those spinoffs to work... maybe they'll be incorporated as necessary into GVCS-50 v2.0, based off research of my own design fork to sort out the problems early.

    NO bigger hydraulics would even need to be added - you could literally use the same pump as now, or say two of them (since two power cubes were discussed) - if the pump is fed the same rpm and has enough torque to turn it's demands nothing else needs to change. (it can change, but nothing needs to change - I personally would change nothing) One thing I might do is add the option for a belt drive to change rpm output - a direct shaft drive is always the most reliable and "best", say for a generator head. A vee belt will use a few % power and is potentially something to wear out and break but lets you change the rpms easily. I'd design a larger power cube to run it either way - so that if I changed from say a faster turning gasoline engine to a slower turning underspun diesel I can still use the same pumps and everything just with a different sized vee belt. And I wouldn't even require the vee belt, just have an option for it, or a marked location "if you are building this, and want a vee belt mount it here".

    Nowhere did I state my goals were "more power", just a cheaper understressed engine. Nothing else hydraulically HAS to change nor am I asking anyone to engineer up those types of changes. I think some of the negative reaction is people assuming i'm asking for or wanting something that i'm not... thats why i'm trying to clarify in these posts.

    As to motorcycle engines, they will not last - they have alot of power, they are not meant to be run at those power levels constantly. Many motorcycles are used up by 10-20k miles, only a few even last 50k miles and are usually the slower turning cruisers, and that's just in normal around town cruising at very light loads - not even racing it. (which is what the comparable load would be like)

    To Allen15 pt2: You seem to be agreeing but just to be clear for other readers I would not choose engines which had to be run at high rpm's because the vast majority of them will not last. Peak efficiency is found at maximum torque output, not maximum horsepower output. So what we are generally looking for is engine with low torque peaks (domestic), which are inexpensive to buy (domestic), inexpensive to repair (domestic) and simpler (domestic). Even in foreign countries it is probably better to use a US designed pushrod engine. Some american gas engines have torque peaks in the 1800-2000rpm range, and many could be modified fairly inexpensively (often via "undesirable" parts that hot rodders run away from) to favor even lower speeds as their torque peak. Also at partial throttle the torque peak will normally be lower anyways, and I wouldn't be running the engines at 100% load at the peak. (aka "lugging")

    My goals are 25-50% load at the slowest possible rpm's on the most cheaply obtainable engines, and designing in enough flexibility for the market reality that "most cheaply obtainable engine" WILL change over time. 20 years ago I would have had different selections than now, and 20 years in the future it will probably be something else. By designing for max flexiblity (basically ANY engine from ANY manufacturer, just with a few custom pieces to hook it up) you can have a large long shopping list and choose either the best deal, or in a pinch whatever happens to be available this week for a good price because harvest starts next week, and you just need something that runs and isn't too worn out.

    And a governor or limiter could be as simple as using the vee belt to have an appropriate range of rpm, and simply limiting throttle beyond a certain setting. Ie - max throttle becomes 33% or 45% or something. I'm assuming the load of the pump is fairly constant? If it's not then yes, the pump may spin up to higher speeds if load is suddenly dropped, perhaps moreso than a diesel would. A heavy flywheel would reduce the risk of this getting out of control, or there should be some simple way to hack up a governer which as far as I can tell is just as much of a risk with any other gas or diesel that has been proposed to put in there anyway.

    ***Notes on above: i'm sharing the best knowledge I have on engines because it is an area I have obsessively studied. What I do not know so well are farm tractors... I see no reason moving the rear axle a bit back, extending the frame 2 feet more back, and dropping another 700lbs of weight in place should make the tractor unusable. If it did because of weight favoring the rear tires or something then yes it might require a redesign for a front engine - yes this is alot more redesign than I was planning or hoping for, and yes that may make me abandon the project. If it's just balance perhaps weight plates could be added to the front. Or maybe smaller inline 4/v6's are doable (would add about 200lbs) or even aluminum v8's but the iron v8's and larger car diesels are out for rear mounting. I'm open to discussion. There are still small 4cyl and v6 import diesels but none of them are as widely and cheaply available to buy in a junkyard or repair or modify as the domestics, hence my favoring them. But I see no problems for either "why" to use the engine or that would be created hydraulically by having it, it's just about physically putting the engine on the chassis that I can tell and that's the only thing i'm seeking ideas and discussion about.

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