This plunger came to a ugly end through no fault of its own. It's all down to the conrod bearing giving up the ghost then totally coming off the conrod. The owner couldn't understand why the shearbolt had gone then got a shock when he investigated further. 

Pic 1. Wrong side of the track. 

Pic 2. Slightly twisted.

Pic 3. You don't belong there.

Pic 4. No room for a fag paper.