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Looking for Plans for a Small Diesel Engine

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  • Looking for Plans for a Small Diesel Engine

    Are there any plans out there for a diesel engine with bore between 1.5" (3.8cm) and 3" (7.6cm)? I'm not looking to become a diesel engineer, and design on the fly, I'm just looking to build a normally aspirated, small diesel engine to run periodically, and admire. Maybe, one day, it may be called upon to do some work.

    I would appreciate free plans, but paying is not a problem.

  • #2
    try googling "small diesel engine plans" and/or "homemade diesel engine plans"...


    • #3
      Originally posted by dave_r View Post
      try googling "small diesel engine plans" and/or "homemade diesel engine plans"...
      Funny, but doing so brings you first to this thread and very little else that is of any use to address the OP's question.

      It's interesting to me that this would be the case. I've had the same thought, that it would be sort of fun to build something like that, small enough that I could actually build it, but large enough that it could (maybe) do some modest amount of useful work. Maybe just a few HP, enough to run a small auto alternator and charge a battery or something. But there is little to nothing I've found. I've always supposed that is because diesel engines don't scale down well, and so are difficult to make work but have no idea if that is the actual reason. With all of the expertise and model engineering that goes on in circles like this, you would think this would have been done already and more than once given that so many other sorts of small IC engines have been built in a huge variety of designs.

      Maybe a slightly scaled down version of the famous Lister engine? Is it even reasonable from an engineering standpoint to consider that such a think could work?


      • #4
        No plans here...but a simply amazing model. Check out his others too!


        • #5
          model diesel engine plans
          seems to return usable results.
          Location: Long Island, N.Y.


          • #6
            That youtube engine is exquisite workmanship.

            But not really a diesel, it is more of a semi diesel, as hot tube oil engines are somewhat more related to spark ignited engines, and this seems to even have a carburetor.

            A big issue with small diesel is the injectors. They do not scale well at all. Viscosity does not scale, and lower viscosity goes with lighter oils, more like gasoline.

            So, one possibility would be a Hvid type diesel, which is a diesel, but one that uses a low pressure injection. It injects into a bulb similar to a pre-chamber, but then uses the compression pressure to blow out the fuel, along with some hot compressed air, as the piston descends.

            Neatly avoids close tolerance high pressure injectors, allowing injection during the early compression stroke, yet should give a decent atomization and timing. They were made for a while in full size, but probably were not quite as good as a regular diesel, due to somewhat late injection.
            CNC machines only go through the motions


            • #7
              Yanmar makes a 3.5 kw about 5 hp small equipment engine. Might look at that to see how it is built.


              • #8
                Ahhhh I posted the wrong lest the builder calls it True Diesel. Regardless very fine built engine.


                • #9
                  What about a diesel model airplane engine?



                  • #10
                    1. Search through old issues of Popular Mechanics & Popular Science on Google/books. I know there are plans for gas engines to be found.

                    2. See this site:

                    3. Plans and kits for "sort-of" diesels are available at Hemingway:


                    • #11
                      I have a Fox .36X with a holed piston, and no head I'm planning to rebuild. But, I wanted something bigger. I'll check some of the links. Yeah, Google wasn't much help, this time.


                      • #12


                        • #13
                          Have no idea if this will be helpful or not, so sorry if its a waist of time.
                          If you have modelling/CAD software, maybe create your own prints from a model (if they have functioning ones) ...

                          Theres some more links in this thread:

                          ~ What was once an Opinion, became a Fact, to be later proven Wrong ~


                          • #14
                            Those TWO fully injected diesels are exceptionally nice. And the injectors look to be about 18 or 20 mm long, which is very good in size for them to work so well. Bore 20mm stroke 40mm, also quite small, actually. Kerosene and lamp oil mix is the fuel.

                            I am astounded at how well they work, and look..
                            CNC machines only go through the motions


                            • #15
                              OK, here's what I'm looking for.

                              Picture a Briggs & Stratton horizontal engine, like you find on some garden tool, like a cultivator. Halve that size. Maybe the same size as a weed whacker engine. Nothing fancy. Model airplane engine is way too small.

                              OK. Let's try this. I can do some simple math. What is the starting compression ratio for a compression ignition engine? According to info I can find, it's between 15 and 23. This yields a psi, at 14.7 x CR of between 220 and 340 psi. To give you an idea, the 1967 Buick Gran Sport 400 ci engine had a compression pressure of 120 psi. I know. I owned and rebuilt it. I would have to look to double or triple the psi. I had always wondered why diesels were so darn heavy. More robust crank, con rods, and pistons. More heavily built block and head. Just putting a head with a compression plug on a Briggs & Stratton would lead to a busted con rod and a cracked block.

                              Reading on the diesel cycle, in Wikipedia, it is critical to inject the fuel, rather than have normal aspiration. In a gas engine, the spark plug controls the ignition moment, and this moment is critical. If there is a fuel/air mix in a diesel, the ignition occurs at a point dependent on the fuel composition, the engine temperature, and the compression. Any piece of carbon in the chamber, glowing, can effect this, too. By injecting the fuel into the chamber at the right moment, the designer has control of the ignition moment.

                              I had thought this would be an easy build. Just build a stronger Briggs & Stratton design. Not so. Lotta math. Lotta time expensive and effort expensive trial and error. Lotta precision.

                              Well, it was a neat idea, but I think I'll cogitate on another project, like a stationary engine, or a little steam engine.

                              Maybe, if I run into plans, one day.
                              Last edited by John Buffum; 10-23-2016, 08:47 PM.