Ariel Owners Motorcycle Club

Twenty miles out from home on a run yesterday when the Square Four Mark 1 engine developed a misfire. No unusual noises from the engine so I nursed it home and found this when I looked inside today. The inlet pushrod for the number 1 cylinder has snapped like a carrot. The witness marks are where it was rubbing up and down after it snapped. The rod has no apparent bending. The only possible clue is the rocker shaft lock collar for the number 1 cylinder is missing a corner. Now I just have to find it.

What sort of head gasket does the engine have? Is there any sign of obstruction in the tunnel?

It has Otto head gaskets which had their final tighten down about 100 miles ago. The head doesn’t have any problems, touch wood.
I took out the push rods from cylinders 1 and 2 and looked down the push rod tunnels with a torch. I’ve looked all around the rocker box, in the corners, and within the springs. I haven’t found the metal fragment from the collar. I may buy a small magnet on a stick and have a poke around with that.
The bike is currently sitting in the workshop while I decide whether to take the head and barrels off.

It might have gone down the pushrod tunnels and that’s maybe what caused the pushrod to brake. Before dismantling the head and barrel I would open up the sump and see if you find something. Poke around with a magnet through the opening.

I will try a small magnet on a stick down the pushrod tunnels. I think the piece of metal is too large to have got past the cam followers, but I will check the sump ‘just in case’.

You’re right of course. Forgot the cam followers are in the way.