A tale of two camshafts -
or two tales of a camshaft.
We built the camshafts from EN40, nitrided for hardness. The cam acts on a "penny" sat on the so-called cam-follower. The cam-follower is an inverted "bucket" which presses on the flat top of a little mushroom tappet. Its short stem presses the end of the valve stem. The cam-follower slides up and down in a thick steel plate, which fits snugly in the cam box.
We knew that oil would get under the cam-follower and into the well for the valve spring. Usually, this is drained away to the sump.
We decided to keep the oil in the box containing the cam assembly and drilled galleries to get it squirted back to the top.
What we found (in the early days when we couldn't even start the engine) was that the engine turned over OK but after a
variable time, odd noises came from the cam boxes, getting more and more unpleasant. When we took the tops off to have a look, there was nothing special except the cams looked a bit battered.
One evening, imagining I was the oil being pushed around, I saw that the cam-follower acting like a piston, was pushing oil back to the top, passing the junction between the bottom of the cam box and the steel plate. The oil squeezed into that and with the large surface area,
lifted the whole plate up, till it was able to meet the rotating cam lobe.
Fixing the plate to the floor solved that. Sounds obvious but it was quite mysterious.
Tale No 2. Worse. The engine was turning at about 3k rpm - its max - and it clanged to a halt, sounding very expensive. Stripped down (good little engine) it had taken this hammer well. The Audi inlet valves were an interesting shape and had stopped the piston. Bang.
I was puzzled to find when I opened the cam boxes that on the inlet side, the oil had all gone (simple seal failure, I think) and the "penny" mentioned above was ground into a slight wedge shape. The work required for the cam to slap open the penny and cam follower had got too great without lube, so the cam drive had failed and the valves jammed part open as the piston came up.
Never run a car without oil.
So a bit of work but it gives an opportunity to think about combustion chamber design (heady stuff).
More anon....