Crankshaft – Poppet Valve Single

crankshaft
crank and gear for my single cylinder 4-stroke

The crankshaft for the poppet valve single cylinder engine has been machined from mild steel and includes timing gear machined directly on the shaft. 

Three views of the roughed out crankshaft

This started with a piece of hexagonal mild steel, why hexagonal? Well, I bought a job lot of mild steel on ebay and as it machines so well this is what I selected for this part.

The webs of the crank are just wide enough to still fit a 3-jaw chuck. Note the use of the rotating centre to align this perfectly.

I started the machining in the Warco WM240B lathe.

Re-aligning the crank in the lathe allowed me to later machine the bearing surfaces to size.

As the crankshaft and timing gear were in one part I had to make the bearing large enough for the gear to fit through. This meant I needed a ball bearing with a large ID.

I have to say, the finish of the crankshaft is superb. A clean cut, burrs removed from the edges and a quality thread cut into the end.

The crankshaft for the poppet valve single shown from different angles. Note though that the big end pin is missing.

About Nigel 336 Articles
I've been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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