Some automotive design innovations last (Otto cycle 4-stroke) and some do not (Bugatti Brescia cam box design). Today I dove into the cam box of a 1923 Bugatti Brescia, a model with which I had not previously been introduced. I had heard of the “banana tappet”, but not held one in my hands.
For some reason, which I have not yet learned, Ettore Bugatti in the early 1920’s thought that the best way to transmit the motion from a camshaft to a valve tip was through a curved stick, a tappet that ran in a block of babbit bearing material that was poured around the steel part in a bronze housing. That is what you see displayed in the above photo.
The Brescia is a 16 valve four cylinder of 1500 cc capacity (1923 kids!). The single overhead cam runs in three bearings in the aluminum cam box, which is bolted to the cast iron monoblock.
Here is a drawing depicting the parts and how they work with the camshaft…
The question I have is, how did they manufacture the bearing supporting the tappets? If one was to simply pour the molten babbit material around the actual tappet, there would be zero clearance for oil to lubricate the part. How did they locate the “buck”, the slightly oversize model of the tappet while they poured the babbit? So many questions.
Apparently there exists at least one specialist that has the knowledge to rebuild a banana tappet carrier, and they will be taking on this restoration challenge. More to come.