Not in boxer, not in line, not in V, not the L: it is in monoblock

2023 Author: Nicholas Abramson | [email protected]. Last modified: 2023-09-01 00:15

Some time ago our friend Nestor put us on the track of this unconventional engine. Specifically, it is a engine mounted on an Ariel Square Four 500cc. The Square Four was manufactured between the years 1931 to 1958. Some 45 HP models were delivered at about 5,500 revolutions per minute. A total of 15,639 units were manufactured and some of these were equipped with a novel engine for the time when the cylinder distribution was "in frame" or monoblock, as its own designer called it.

At present this engine has disappeared due to the great design problems that arose. But I would have liked to try a motorcycle with this engine that every half turn of the cylinder has an ignition. For now I will have to settle for listening to how it sounds in the videos that are hanging on the net to appreciate the difference with a more traditional design engine.

Actually the arrangement of these four pistons is simply the union of two motors of "2 in line" placed next to each other. Linked by a gear system where we can see that cylinders 1 and 4 belong to one engine and number 2 and 3 are from another engine. They also have their own AB and CD crankshafts linked together with two large sprockets (A and C). We can also observe that each motor has its own flywheel (V and T). They did not complicate trying to make a single piece to move all four cylinders in one go.

The first design problems in this engine began shortly after its birth, since the rear cylinders had certain temperature problems not being able to cool enough. Transferring that heat to the stock and making it bend easily. Thus in 1937 the engine was redesigned to improve these problems and at the same time the displacement was increased to almost one liter (995cc).

The engine was created by Edward turner in 1928. Turner presented his “monoblock” engine to the BSA and they rejected the project outright. But Jack Sansgster invited him to join Ariel and so on 1930 the first Ariel Square Four 500cc with a monoblock engine is born which is now a true collector's item.