I've posted about this before, so at risk of repeating myself....
Had an (almost complete) engine failure in a C152 whilst PPL training last year. Flying solo circuits at an airfield some way from base. Initially thought that the problem was plug-fouling, as the rough running felt very similar to that caused by a fouled plug. After leaning out the mix and running at full power with the brakes on, the problem cleared (or so I thought) so it was back to the runway for departure back to base.
Approx. 4 miles from departure airfield and with around 25 miles to run, the engine suddenly began shaking very violently. At circa 1500ft and losing height around 300fpm at full power, my only option was to return to the airfield I'd just left and get to the first available runway. Thankfully after turning around I was lined up long-final on runway 22 (not the runway in use). Made a straight in approach just as the last power died away - the engine cut completely just short of the hold point on the taxiway.
Turned out to be a sheared cylinder bolt, resulting in one cylinder coming clean away from the engine. The strange thing was that the engine temp and pressure didn't drop until I was only 1 mile from touchdown, so there had been no prior indication of a major failure.