Engines > From Plans

Planis Farm Boy Engine

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Hi everyone

Since I always enjoy watching buildlogs, I want to start one of my adaption of the Farm Boy engine.

Some time back i got my hands on a set of drawings of the famous Farm Boy engine from Jerry Howell. I liked the design of the engine a lot and also the fact that it can be made from bar stock.
Since I'm all metric I had to redraw the plans. While playing around on the CAD I figured, I might as well make the engine a little bit bigger than original and so I settled for a scale of 32mm to the Inch. This means the engine will be about 30% bigger than original.

The engine specs are:
 - Bore: 32mm
 - Stroke 44mm
 - Compression ratio 4:1
 - Displacement 35cc
 - Flywheel diam 192mm

Because I've never made a one piece crankshaft before, I decided to start with that one, so in case it is not turning out right I can still abort the project...

To start with I got some normalized S355 bar which will hopefully not distort too much while being machined

The round bar was machined square and then the shape of the crank was roughed out

Then turning the crank pin

Roughing the outer parts of the shaft

Since I've done some wrong thinking :facepalm:, the crankshaft hat to be shortened and center drilled  again

To then finishing the shafts

That's what it looked like so far. I left some material to take a skim cut on the crank webs too.

Moment of truth  :thinking: I think I can live with a runout of about 0.02mm  :)

So I went on with cutting the keyways

And cutting the key accordingly



Looking good!  :ThumbsUp: :ThumbsUp: :ThumbsUp:
I'm looking forward to see this one coming together.  :popcorn:

Roger B:
That's a good start  :praise2: You may find that the runout changes over time as the stresses in the metal release. Generally it can be trued up again.

Brian Rupnow:
Nice cad work and very nice job on the crankshaft.---Brian

Great work! Looking forward to seeing more.


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