Franco Morini, Minarelli and Malaguti: the engines used in the 80s and 90s on enduro and stradali 50cc.

 

 

The Franco Morini TA-50 and T4 had the same engine block and 4-speed gearbox, although they differed in the thermal system, which on the TA was liquid-cooled with thermosiphon circulation. The intake was reed valve for both, but characterised by a rather small reed valve. Ignition was for both of them with points. 

 

 

The GS.A is the liquid cooled, forced circulation version of the GS. Compared to the T50-A, it has a new cylinder with a significantly larger reed valve than the previous one and electronic ignition. The gearbox remains at 4 speeds as required by law.

 

 

The air-cooled version of the GS.A, still featuring the large reed valve. Four-speed gearbox and electronic ignition. 

 

 

This is Franco Morini's top of the range and most advanced engine, practically an evolution of the previous GS.A..

The G304 was a long stroke with a light alloy cylinder with a gilnisil treated barrel, reed valve in the crankcase, electronic ignition, pump for forced circulation of coolant, electric starter (as an option) and automatic mixer. The gearbox remained a 4-speed, as required by the Code.

 

The G303 was fitted from 1990 and although it was the same engine, the gearbox only had three ratios due to the law limiting the ratios to a maximum of three. It should be noted that the G303 also changed the internal gear ratio, with the first two gears close together and the third at rest. If a four-speed gearbox were to be fitted, it was advisable to completely replace the gearbox with that of the previous G304 to avoid excessive "gaps" between second and third gears. 

 

 

 

 

The RV4 was eventually the most used engine on Malaguti enduros, here in the version without the automatic mixer. The RV4 was a 42mm long stroke engine and in this parameter, it differed most from the DL4 which was a 39mm short stroke engine. Another difference was the thermic group, square on the RV and round on the DL. (see DL card). Otherwise the RV was quite a technically equipped engine, with reed valve, water circulation pump, mixer pump and electric start (if provided).

 

The Minarelli MR was perhaps the best engine ever produced by Motori Minarelli. The MR stands for Minarelli Racing, as it was almost exclusively dedicated to 80 cc cross racing and enduro bikes. It was a more spartan engine than the RV4, with a more compact design. 

 

MR4 was the abbreviation for the 50 cc road version which, due to the silly regulations of the time (1983-1989, Ed.), was equipped with a 4-speed gearbox. It retained the same long stroke as the MR6 80 cc model, i.e. 44 mm, but combined with a 38 mm bore cylinder. The engine was very good-looking, both aesthetically and functionally, and featured an aluminium cylinder with a nikasil coating, mechanical water pump and straight-tooth primary drive. It was not equipped with reed valve induction and was never available with a mixer, although electric start was available as an option from 1988.

 

The great thing about the Minarelli MR was that since it was related to an 80cc racing engine it could be conveniently tuned by mounting cylinders that were much more powerful than the standard one and also had reed valve admission (photo below). But above all it was possible to increase the number of ratios to six; a great advantage compared to the RV4/3 series that could not be as easily modified, on pain of having to replace the crankcases. 

 

In 1990, the Dune was fitted with a version with a locked fourth gear in order to comply with the law limiting the number of gear ratios to three.

 

 

The DL4 was a very good engine which differed mainly from the RV4 used by Aprilia, due to its short stroke. In fact, while the RV series had a long stroke of 42mm (echoing the P4-6), the DL (along with its air-cooled peer the R3GL) had a short stroke of 39mm.  

 

The DL could boast 5 transfers (the fifth is direct to the crankcase), chrome plated cylinder liner, round shaped cylinder (squared in the RV4), piston with windows, large reed valve (like the RV) and because of the short stroke, it was perhaps a more high revving engine than the RV. The mixer came standard.

 

The DL3 was the version with the three-speed gearbox, fitted from 1990 on the MRX as a replacement for the RV4.