The horizontal, rare and winning twin-cylinder engines – News


Engines with two parallel cylinders have been and still are many. Indeed, for such construction architecture recently some builders have abandoned the V-shaped one, which in recent years had depopulated.

At this point, however, one wonders where the two cylinders should “point”. Traditionally they are vertical (i.e. they point upwards) or are slightly tilted forward. But horizontal, when ever? And instead in the not too distant past there have been some significant examples of the use of this scheme, both among competition and standard bikes.

Perhaps not many fans remember that the first world championship was won in the premier class by the AJS E 90, better known as “Porcupine”, Whose engine had two parallel cylinders arranged horizontally. Well almost, to be precise. On closer inspection, in fact, they were slightly inclined upwards.

This twin cylinder was originally designed with the aim of adopting the overfeed, which was instead prohibited by the IMF after the war. The compressor should have been placed on the back of the base.
The characteristic measures were square (68 x 68.5 mm) and the distribution twin shaft with cascade gear control. The two valves of each cylinder were inclined by 90 °. Given the arrangement of the cylinders, the designers (who initially were Matt Wright is Joe Craig) decided to break with the English tradition. To limit the longitudinal dimensions, they adopted a block gearbox, always of the direct drive type, and a primary gear transmission.

As a result, the crankshaft, which rested on three bench supports, turned backwards. Among the unusual features, the use of forged aluminum alloy connecting rods and a magnesium alloy base stood out. The tree had 360 ° cranks. When, in 1949, the AJS won the world championship, the power was of the order of 48 HP at 7600 rpm.

Twenty years after another 500 with two parallel cylinders arranged horizontally, he made a name for himself at the highest levels by winning the GP of Nations, which was raced in Imola in 1969.
It’s about the Linto, the only bike with distribution at auctions and rockers that has imposed itself in a race valid for the world championship. This racing half liter was designed by Lino Tonti in 1967 with the aim of creating an economic and easy-to-maintain vehicle capable of providing superior performance to that of English single-cylinder engines (Norton is Matchless) and therefore ideal for private pilots.

To build the engine the technician from Romagna had in practice coupled two single-cylinder Aermacchi Ala d’Oro 250, of which, in addition to the heads and cylinders, the connecting rods, pistons, valves and so on were used. Obviously new were the crankshaft (with cranks a 360 °), the transmission and the base. The power of this twin cylinder, which had a bore of 72 mm and a stroke of 61 mm, was slightly higher than 60 horses at around 10,000 rpm.
Linto has had a good spread among the drivers who raced in the world championship, but it appeared when the 500 Japanese two-stroke were already starting to enter the scene.

Several years earlier Tonti had founded his own technical studio which he had named Linto. One of his projects involved a 125 cm horizontal competition twin cylinder3. The engine, which had a twin-shaft distribution, was built in 1952 and has also carried out some tests on the track but unfortunately it has not left the prototype stage.

It is interesting to note that someone else, some time before the Linto 500 was released, had thought of coupling two single-cylinder rods and rockers derived from the series to build a half-liter competition.
It is the Swiss Werner Maltry, which had joined two Motobi realizing the Reima. The initiative was excellent but of this bike, which apparently was built in a single specimen in the early 1960s, brought to the race on a couple of occasions by Paolo Campanelli, nothing was known.

Motobi had built a horizontally arranged two-cylinder engine that was used on a series model called Spring Lasting, built in an appreciable number of specimens between 1953 and 1960. It was a two-stroke that in the first specimens had the admission to rotating distributor. This solution must not have provided good results because it was replaced very quickly by the classic aspiration controlled by the piston. The engine was built in versions of 200 (48 x 54 mm) and 250 cm3 (54 x 54 mm).
The latter in the Gran Sport model delivered 12.6 hp at 6500 rpm. One of these bikes won its class in the Milano-Taranto from 1955.

In the 1950s, talking about horizontal twin cylinders meant talking about Rumi. This Bergamo house has linked its name to a series of brilliant two-stroke models equipped precisely with such splitting and architecture. Over the course of the evolution, the sporty versions of the 125 cm engine3 (42 x 45 mm) were equipped with aluminum alloy cylinders with chromed barrel instead of the previous cast iron ones.

Each cylinder was equipped with two transfer ducts and the piston crown was equipped with a V-shaped deflector. The base consisted of two parts which joined together according to a horizontal plane and the clutch it was located at one end of the crankshaft.
The more sporty Rumi or intended for competitive use were powered by two carburettors and were able to provide very lively performances, which allowed them to obtain numerous successes, among which those in the Milan-Taranto of 1954 stand out, in Motogiro of the following year and in the championship of mountain from 1959.

Between the mid-sixties and the early eighties, some houses built competition bikes with two parallel-cylinder engines arranged horizontally (always two-stroke, of course). Among them only the Motobecane 125 he achieved important results, finishing second in the 1980 world championship and winning several Grands Prix.
There Montesa 250 designed and built by Francesco Villa in 1966 she performed very well on a national level but abroad she raced and achieved quite little (and in any case she had to do with the official Morini and Benelli, if not even with the bikes of the great Japanese manufacturers).

In 1974 it was seen only fleetingly DRS 125 designed by Peter Durr.
Two years later the two-cylinder Bultaco appeared, also 125 cm3, which however has been used only occasionally for a couple of seasons; in fact, for its competitive activity, the Spanish company had focused exclusively on the 50 (ex-Piovaticci), which was actually very strong, leaving out the development of the eighth of a liter (which, however, appeared problematic).

A last quote deserves the Iprem 125 of 1980, which however was short-lived, despite having obtained some good placings.

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