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″ strok. 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!!

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