Honda GX-31 Mini 4 Stroke Engine

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engines run since 05/27/07

2005 - The GX-31 engine was originally developed by Honda for their weed whacker line and for their Harmony tiller. Since then it has been adapted for numerous other uses including portable pumps and even small vehicle propulsion. It features the ability to operate in any position - even upside down. It is quiet, given its high RPM operation.

I'm using this engine for a number of applications including a tiny Cordless Battery Charger (TM). Many people seem to be curious about how Honda made such a small 4-stroke. I was too so I took it apart, camera in hand.

I apologize for the rather poor quality photos. I owned a low quality Kodak point'n'shoot when I made these photos. I'll replace them with better pix as soon as I can.

Be sure to REFRESH each page on this site as I'm adding content on a daily basis.

The power output side. The centrifugal clutch shoes are attached directly to the flywheel.

This shows the output side with the clutch output shaft and housing made by Staton Small Engines. This adapter enables the engine to be used for things like go-karts, scooter, generators and the like.

Closeup of the Staton unit. A very high quality product.

Starter side with the outer housing removed.

Tiny valvetrain plus a view of how the flywheel and clutch mate.

More detail of the flywheel and clutch shoes.

The valve cover. Note the steel inserts designed to prevent over-tightening of the bolts.

Closeup of the valve train.

Another closeup of the valve train. Note the dime used to set the scale.

Carburetor and cylinder detail.