Here are the photos of the sheared Villiers pump crank after a stone came through the suction hose and locked the impeller. Also the 2a grooved key and a cropped image of the bolt threads showing the original paint on them.
The clean cut on the crank vividly demonstrates what can happen when an engine suddenly stops stone (pun intended) dead and the energy created by momentum of the reciprocating parts has nowhere else to go.
Once got a mixer for it’s drum, my old one had started to rust through. The mixer had a Briggs & Stratton engine that would fire, but not run. Was not bothered, as I had a rescued Honda to fit on. But when I had 5 mins free thought I would get the B&S going. But no go, I subsequently revisited it a couple of times, could not understand why a nearly new engine with good compression, a big fat spark and fuel would only pop and bang for a minute or so. Decided to take off the flywheel to check the ignition timing and the alloy key had half sheared. The drum had stopped suddenly, the flywheel still was able to move and it probably saved the engine. It now runs as sweet as a nut, but have it stored away with no use for it. Have been told to always fit a genuine B&S alloy key, never a steel one.
Have a Clifford Mk1with a Villiers 25c. I re-fitted the flywheel using only light taps on the T bar of the socket and glad I did. When using it I hit a stone that stopped the engine and moved the flywheel on it’s taper. Otherwise the 25c crank could have sheared. My Howard Gem has a pin in the shaft from the clutch that is there to shear if the rotors stop suddenly. Some plough and cultivators have shear bolts too to protect the implement. The grooved key and roll pin follow the same principle.
The paint of the threads should put to bed any thoughts that this engine had had it’s cowl off (and by extension the flywheel), since the day it left the Alcon works in 1951/2. A further inspection revealed the felt behind the stator plate, although I fail to see the relevance of it. The roll pin and grooved key are factory modifications most likely done at the JAP works in conjunction with Alcon. It could be a one off, or part of a small batch, who knows. The grooved key is designed to shear and the roll pin that prevents the pulley from being tightened hard against the flywheel, will let it turn if the engine stops dead. Better a sheared key than a sheared crank. On a portable pump used by ill informed operatives, a solid steel key I would describe as a “recipe for disaster” a sheared crank “untold damage”. The roll pin only has to resist against it’s own rotational inertia force whist the engine is running and the action of the starter rope from static. Not much. It’s primary purpose is to prevent the pulley going tight against the flywheel, so it is free to turn if the key shears.
This will be my last post on this subject (JAP 2a flywheel removal) until I have got the engine running. Am not going to descend further into a ding dong battle on this forum about whether the roll pin and grooved key are factory modifications, or a bodge by a mechanic, or the merits or otherwise of a key and pulley arrangement designed to shear. Nor does the fact others may not have seen such a set-up before. In the grand scheme of things, it makes no difference anyway. The important thing is to take care with the re-fitting of the flywheel to ensure the crank does not move over, everything is correctly aligned, there is no resistance or rubbing. It will be during this assembly process when a final decision will be made whether to tighten the pulley against the crank, or re-fit the roll pin. Current thinking is I am attracted to the idea of maintaining a shear capability due to my own experiences and observations. Also would like to put it back to the same specification it came from the factory. Want to use the engine as a test bed for an energy transfer coil conversion. It may have a use for it as an irrigation pump for my Evenshower oscillating spraylines, but it will need to demonstrate comparable fuel efficiency with my existing modern pumps. Being brought up in the market gardening industry it was drummed into me that a strainer should ALWAYS be used on the suction hose of a pump because if it sucked up a stone it would wreck the pump set. I still think the roll pin and grooved key were a factory modification to trial the idea of introducing a shear element into the design. But was quickly dropped, probably due to the cost. If others take a different view, I am totally unconcerned and will move forward with working on the engine as I see fit.
