So you want to build your own engine…

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    I have always wanted to make an engine and I took some time over the Christmas vacation period to start one. I kicked around a bunch of ideas and decided I would make one that would be realatively easy to design and make plus look cool. I have no intention of flying it so weight is not an issue. Thus, it would be a somewhat robust bar stock engine.

    I decided on making the engine “square”, meaning that it will have a.625″ bore and a .625″ stroke, which makes it a .19. To look cool, I decided on a rear rotor design, stealing ideas from both ST and K&B. The front bearing housing was designed to use a 1/4″ front bearing and a 3/8″ rear bearing. The crank is a simple design using a half moon counterweight.

    The main case is a two piece unit, so it made it very easy to cut the intake ports into it. The two pieces are bolted together with four, 4-40 screws. I also decided on a side exhaust but maybe should have made it a rear exhaust (more for the cool factor than anything mechanical). Plus, I decided on a schnuerle port with a boost port. I kept these ports reasonably small but in retrospec may have wanted to make them bigger,

    The piston and liner will be conventional steel liner with a cast iron piston. I placed the rod relately high in the piston not unlike what we use in the full size race car engines. This allows a longer rod which should reduce some of the side loads on the cylinder. I also stepped the bottom of the line to locate it in the bottom case.

    The liner has been lapped to size using a technique I have never used before. This was to make an expandable lap out of aluminum. I started with fairly coarse lapping compound and then went to a finer compound for the finish. With a little work it came out quite round and has a very fine cross hatch. From what I can measure, it is round within .0001-.0002″. I normally use a hone but this has always been on a factory piece.

    I will make an internal lap for the piston to get it to size.

    All in all, it has been alota fun. It helps to have a nice lathe and a decent CNC mill with alota tools. I found a website that has been quite useful and has a ton of really weird stuff… It is

    So, hope you enjoy it and will keep you posted on whether it runs or not!!


    A few more…


    And another…


    That’s realy good. Congratulations. It will run of course, as I’m sure you will have timing etc. correct.
    But, you MUST build something for it to fly in.

    How about a scratch built sport type freeflighter about 70in span?

    Bill Shailor

    Now, you have to name it. I’m trying to come up with something… Maybe “Wen-Lorbiecki” after the legendary Wen-Mac powerhouse!
    Happy New Year!


    Not really sure if it will make that much power! Had to say it before Gutai or someone else would say it…

    Have a great New Year (also)….



    John’s Son

    naw , done
    Too Many Beers

    There’s 3 names.
    For a plane, try a Marval. It has served me well this year.

    The engine looks good. What is the all up weight? I hope to see it at the Nats.

    Dean McGinnes


    Nice looking engine. I always wanted to roll my own as well. I lack only three things, talent, knowledge, and equipment> 🙁 🙁

    Any particular reason you went with iron/steel piston-liner technology, and not aluminum piston, and chrome plated brass liner? 😕


    Fascinating project, John, it looks really good so far.

    As one who has dabbled in engine building (I have all the equipment my late father used – he built 4 engines), I thought I might venture an answer to the question about piston/cylinder materials.

    Cast iron and leaded steel are easy to turn on the lathe, can be lapped readily, and work very well together in small engines. High silicon aluminium is far from easy to turn, and then there’s the hassle of finding someone to plate the cylinder.

    I have to echo Gossie’s earlier remark, John, you have to fly it.

    John Buskell


    I’ve thought about it for a few days now

    a Bill Winter VAGABOND.


    I’ve thought about it for a few days now

    a Bill Winter VAGABOND.


    As stated, the cast iron/ steel sleeve is fairly easy to do. I found that I could readily turn the piston to about .0015″ over and then easily lap it to size. It came out within .0001 round, which really surprised me. Way too easy…The steel liner took a bit more work, as you lap, clean, measure, lap, clean, measure until it comes to size. And then, I missed my magic number by .0001 or two.

    The normal ABC p/l assembly needs the liner to be chromed. I had a chrome bath a long time ago and it caused me quite a mess (turns out that not all stainless steel is compatible with the chromic acid). I did not want to send it out as it would take more time. Plus, if I need to make changes, I can readily do it on the steel liner.

    Here are a few more pics of it getting closer to completion. It has a great rock on the bottom and decent compression. All of these things tell me that I got the thing relatively square and true. Has been alota fun so far. When the weather changes I should be able to see if it fires up…

    Because I didn’t have the right tap, I put a standard plug in it. Some time I may change it over to a Nelson plug, which should be better. I also have it ported very mildly, so there is plenty of room there. Who knows, maybe I will make version number two with everything hopped up and make it a flyable version. I can design it so that I get rid of more material in the crankcase and lighten it up. Maybe even go to a rear exhaust with a bolt on extension….


    Gee what happened to all your radiuses??????
    That is the most rectangular engine I have ever seen. Nice work and good effort. What is your timimg??? Did you set your motor up on Nelson criteria in his motor specs? What degree of silica did you use in your piston? Did you centerless grind your piston? I s this an abc or a1cc chrome anodising employment. Did you bush both ends of your rod?
    What is your port timing? Did you employ any emprller cutout in the crank to force feed your ports. Are your ports strictly to the cylinder by edm burn ins? are you using the 11/32-32 unf nelson design for the top end? 1 or2 bubbbles in your head insert?????
    A long time ago there was a carter that used a fuel sling ground into the back of his crank that started all of these empellertype spoon mods.
    Dale Sudgen the Canadian used themon his engines as well.
    How did your crank balance come out? how smmoth is your running ivbration. Doug Joyce had figured out the 2 stroke dynamic balance methods on his Rossi 2 and 3 mods. Impressive
    Please get back and lets swap lies.
    Regards, Clay Parker Bellingham Wa. 360-933-4588


    So many questions with so many simple answers….

    The two engines (I made a front rotor as well as a rear rotor) where done to only prove that I could do it. They all used very simplistic design features.

    The piston and liner were done in steel/cast iron. I do have a fairly nice 0-1″ digital mike good to .00005″ and it was pretty remarkable (at least to me) that I was able to hold .0001″ on the diameter on the piston with some simple turning and home made lap. The liner is, as I said, steel, and the ports were machined in with a simple angle fixture and layout die.

    Timing is early Rossi .15, with about 160 degrees of exhaust timing. I seem to remember that the boost port is about 140 and the side ports around 135….I could be off slightly on those numbers tho. I figured I would not make it too radical as all I wanted was something that would start and run.

    The crank is also steel (1050L I think) and the crank pin was machined via a simple offset slotted bushing that I made and then placed in the lathe. I turned the pin and then polished it to size.

    The rod was outta 2024 T6 and was profiled on the CNC. Yeah, I have a Bridgeport style (knee) 3 axis CNC. I stuck to standard sizes so that the reamers didn’t need to anything special. Both ends are non bushed, again for simpicity. It would have been fairly easy to bush but I didn’t have the good material and thus kept the aluminum with cross drilled oiling holes.

    And, yup, they sure are square! Again, I just wanted to prove to myself that I could make everything fit acceptably and act like an engine. Thus, I didn’t spend time reducing sizes and weights. That is also why I went to the two piece crankcase. This way I could easily cut the bypasses with a simple ball mill. Plus, I could use misc pieces of aluminum I had laying around. It also simplified teh actual construction. The majority of both crankcases were machined on the lathe and the put in the mill to cut the mounting lugs and such- turned a round into a square.

    As can be seen, the rear rotor engine had the cylinder bolted on at is base. The front rotor uses long screws (just like the Cox .15) to hold the cylinder in place.

    Simplicity was the name of the game and as stated, I just wanted to see if I could make everything. I even wimped out and put a standard 1/4-32 plug in them instead of a Nelson.

    If you want to see the front rotor, look at:

    Look in the engine pics on Ron’s website and the two engines are on page 11 and 12…

    Sori I don’t have much hi tech in them, but it did prove I could at least put all the parts in the same place and at least make something that looks like an engine…..Now, I bet ya want to know how they run. Well, we don’t know yet. The reason is, is that I haven’t cut the groove in the piston for the circlip. I haven’t taken the time to grind a small cutter to do it. Maybe this winter…

    Hope this answers a few questions!!


    Here is a finished pic of the engine (actually it was done a long time ago but finally found some pics. Still have not run it, but it sure feels nice! Lots of hand flipping time on it already!

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