RM gearboxes have been specially designed to couple Diesel engines; they allow to operate an utilizer (water pump, compressor, fan…) requiring an input speed different from the Diesel engine speed.
Constructively the RM gearboxes consist of:

  • cast iron casing (aluminium alloy on RM 20)
  • helical tooth, case hardened, shaved (grinded on RM 150) gears
  • shafts are manufactured from high quality steel, case hardened
  • taper roller bearing on output shaft
  • the input shaft is supported by a single bearing inside the casing and therefore it must be driven by a pilot bearing assembled on the flywheel, in case of close coupling to Diesel prime mover.

RM serie includes 6 models and each of them may be provided with an output rotation direction equal to that of input (RM … S), or with opposite direction to that of input (RM … D).

RM … D: reverse rotation units have a primary gear on the input shaft driving directly onto the secondary gear powering the output shaft.

RM … S: same rotation version have an idler gear between primary and secondary gears.

RM gearboxes may be equipped for close coupling to Diesel engines with:

  • overcenter clutch (BD) with SAE housing
  • SAE housing and rigid or flexible coupling (GE, GR)

Freestanding mounting is possible in the BDS execution.


Ratio I
It represents the ratio between the input speed (Diesel engine speed) and the output speed (utilizer speed).
Ratios lower than 1 indicate a gearbox performing as speed increaser, higher than 1 as speed reducer.

Max input torque Me
It is the maximum torque wich may be transmitted on input, corresponding to a theoretical unlimited gear life and to a bearing life (L10) of 5000 hours at least, with an input speed of 2000 RPM.
For clutch/gearbox combination, the max input torque may be limited by the clutch capacity.

Max input speed Ne
It is the maximum speed at the input shaft. For clutch/gearbox combination, the max input speed may be limited by the clutch.

Max power P
It is the maximum power that may be transmitted under normal conditions, without an oil cooling system. The values shown are only indicative in so far as the external factors create much influence, such as: air temperature, possibility of air circulation, environment conditions.

When power is bigger than the listed value a cooling system is necessary.


RM unit selection should be made by taking the input torque and be multiplying it by the service factor:
1,0 light duty (centrifugai pumps, fans)
1,5 duty (4 cyl. compressors, conveyors, hydraulic pumps)
2,0 heavy duty (2 cyl. compressors, mixers, presses)
2,5 very heavy duty (1 cyl. compressors, mills)

The resulting torque is to be lower than the listed value (Me) for selected gearbox type and ratio.
For clutch gearbox combination, the max input torque may be limited by the clutch capacity: see table TECHNICAL DATA FOR CLUTCHES.


Use SAE 90 with EP additives.
Units are supplied without oil; before use fili to the maximum level mark on dipstick.
Oil must be replaced after the first 100 working hours. Subsequent oil changes should be made every 1000 hours or ‘ every 12 months, wichever is the sooner.
Check regularly the oil level.


The maximum oil temperature during continuous operation must not exceed 95°C. It is wise to check this temperature during the first working hours.
If recommended maximum power limits are to be exceeded, RM models 120 and 150 are available with oil cooling system.