Holly Buddy Twin (oz14601)

About this Plan

Holly Buddy Twin. Inline twin diesel engine.

Direct submission to Outerzone.

Quote: "Introduction: After completing Ed’s excellent Holly Buddy Diesel engine, I really wanted to build a twin. After looking around for a long time I soon realised there wasn’t that much out there in terms of plans or build logs. I came across the Fig Tree Pocket Twin (oz13722) in the Motor Boys plan book and a Sparey Twin (oz13750) on Model Engine News, but nothing quite ticked the box for me.

I wanted to keep the engine small and that ruled out anything with split conrods and one-piece cranks. That said, the Fig Tree is probably still on my build list at some point in the future! I got chatting to Ed and he suggested I had a go at building a twin Holly Buddy which he had successfully done in the past and still had some paper sketches lying around. From there, a plan was hatched.

We started working from his original drawings and I modelled out/tweaked in CAD. The design philosophy was KISS: Keep it Stupid Simple (or Keep it Simple, Stupid!) and building within reach of mere mortals with typical model engineering workshop setups. This was very much in line with the original Holly Buddy which was key to its success. Simplicity aside, like the original Holly Buddy, the engine starts well and absolutely screams! This is one of the first engines I’ve run outside and been truly worried about disturbing neighbours all the way down the street.

When, after what seemed like an eternity in CAD modelling, I finally got round to making some parts in the workshop, the engine was a delight to build with nothing really that tricky apart from the centre crankshaft and bearing.

We both really hope you have fun making this engine. Please share your story with us on HMEM or YouTube etc. We would love to see another one come to life.

This is also my first-time doing CAD work. As a self-taught amateur (mainly learned for 3d printing), people with an engineering/fabrication background will frown at my adherence to conventions (or my lack thereof). I’m happy to take feedback to continue making the plans better. Enjoy the build! Thanks, Ed and Patrick"

Note see also build log at: https://www.homemodelenginemachinist.com/threads/holly-buddy-inline-twin.33976/#post-390338 for more details, many more great pics, also some video.

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