The 4-stroke potato masher
I recently got my hands on an old rotavator, before use I had to make several 'repairs' as it had been sat in a shed for a decade. The starter clutch was prone to jamming, stopping the flywheel and in the process breaking the shear-pin; my solution was to retrofit an electric start feature (read, a big socket, an extension bar and a power drill). The other controls weren't in mint condition either, operation was via yanking and twiddling control cables at the correct time.

Once I'd turned the lawn into a small scale replica of the Somme, my attention turned to the little petrol engine that was now just sat in the garage. After some careful thought I managed to work out that what was missing from my life: a hugely inefficient, cumbersome and risky way to make my lunch. I detached the blades from the bottom, ratchet strapped the engine and controls onto a workmate and made a start on the engine-masher interface. In the end I settled for jubilee clipping the masher to the end of a bit of broom-handle, poking that through one of the work-mate holes and tying a spring on with a piece of string to return it to the 'up' position. The down stroke was powered by screwing a block of wood to the flywheel of the rotavator.

Once I'd lined things up and shaped the wooden block such that it would smoothly push the masher rod down, I got the drill out and started her up. It worked! The masher flailed up and down like a tigger on speed, and nothing seemed to be going wrong. This inspired me go from idle to full throttle, at this point the whole contraption started to topple; I managed to grab it as it went over, cutting the engine by touching together two particular exposed wires. Unfortunately the exposed flywheel had made short work of demolishing the whole masher mechanism; those glorious few seconds of optimism were cruelly crushed as I came to the realisation that I would be forever stuck in a dreary life of mashing potatoes without the excitement of potentially maiming myself.
(madsporkmurderer, Mon 15 Oct 2012, 22:13, 2 replies)

are you sure
It wasn't 2 stroke?
Don't recall seeing any 4 stroke ones.
(speedevil, Mon 15 Oct 2012, 23:40, closed)

Without a doubt,
I had the engine in bits trying to work out why it wouldn't start and watched the piston and valves move as I turned the crankshaft by hand. The small ones tend to be 2-stroke, the larger ones tend to be 4-stroke.
(madsporkmurderer, Tue 16 Oct 2012, 14:51, closed)