3 May 1996

High torque & low weight are Valmet tenets

By Andy Collings

"LIGHTWEIGHT, powerful and plenty of torque," sums up the current design approach of Sisu Tractors.

The Finnish firm has now introduced seven new models to its Valmet line-up, most of them equipped with a new high torque engine and all built with weight economy in mind. One of them, the range topping 160hp, 8750 offers a degree of innovation which is claimed to introduce new technology to the tractor world.

But first, a look at the other models. Now heading the M5 range is the 87hp 865. Powered by a 4.4 litre four-cylinder, turbocharged engine, it weighs in at 3.4t. Aimed mainly at the livestock, no-frills market, transmission choices extend to either an 8 x 4 or a 12 x 8 synchro box.

Features include a new, high visibility cab and an ejector air intake designed to dispense with the more commonly used filtration systems.

Moving up the power range the 115hp 6800 joins the Mezzo line-up and becomes the only Valmet tractor to be both turbocharged and intercooled.

But perhaps the biggest changes are to be found in the higher hp models with the introduction of the Mega 50 series. These not only replace the 8100, 8200 and 8400 tractors but increase the companys power band to 160hp – and beyond.

All are equipped with six-cylinder, turbocharged Permatorque engines, which have been designed to develop a high torque reserve and high torque at low engine speeds.

The Mega series kicks off with the 110hp 8050, which, like the 125hp 8150 and the 140hp 8450, is equipped with a 6.6-litre block.

Standard throughout the series is the use of the Delta Powershift transmission, which offers 36 forward and 36 reverse gears via a 12 x 12 multi-step gearbox and a three-stage powershift unit. Buttons on the gear-stick activate in-range gear changes while a shuttle lever is used for forward and reverse.

Valmet has also uprated its hydraulic linkage control – Autocontrol. Previously analogue, it is now a digital, computer controlled system. This has resulted in greater sensitivity – there are, for example, now nine rather than six settings to control lowering speed and six instead of five for draft control.

But there is now also the addition of wheel-slip control with an implement automatically being slightly raised if wheel slippage exceeds a pre-set 15%. True ground speed is measured by radar and is compared with the theoretical ground speed produced by the transmission.

With 7.4 litres and 160hp under its hood the 8550 should have some appeal for high acreage farmers and contractors involved in heavy draft work. Lift capacity at ball ends is rated at 7t. But for those who require high-power pto, the 8750 might just be a better option. But the Sigma 8750, although having the same 160hp engine as the 8550, has another 30hp for when the going gets tough.

So why not rate the tractor at 190hp? The reason is that the transmission is only able to take 160hp – Valmet choosing to keep the weight of the tractor down under 5.2t ("It is always possible to make a tractor heavier," says the company) and, one assumes, the price.

Instead, the company reasons that if, say, a power-sapping forage harvester is hooked up, the extra power can be channelled through the pto, yet still limiting the transmission input to a safe 160hp. The result is that up to 172hp is available at the pto.

How is it done? Sensors measure the speed of the crankshaft and compare it with the speed of the shaft just before it reaches the pto engagement clutch. Bearing in mind that this is an uninterrupted solid drive any load distortion – twisting – of the shaft can be recorded through a momentary slowing of the non-engine end.

Valmet engineers have calculated that 30í of twist on the shaft equates to a pto loading of 30hp and that, through a control unit, automatically opens up the in-line injection pump to boost engine power by 30hp. Once pto power requirement is reduced, the injection pump is returned to a normal setting.

The result, claims Valmet, is an increase of production by up to 20% when using high power pto implements.

Overall, Valmet appears to have produced some stylish tractors within a popular power band which should find favour with a broad section of the agricultural industry.

New Valmet models

M5 range

865, 87hp, 4cyl turbo, £25,300

Mezzo range

6800, 115hp, 4cyl turbo and intercooled, £40,800

Mega 50 series

8050, 110hp, 6cyl turbo, £43,800

8150, 125hp, 6cyl turbo, £49,300

8450, 140hp, 6cyl turbo, £55,300

8550, 160hp 6cyl turbo,£59,200

8750 160/190hp 6cyl turbo, £61,400

Sigma power explained. Sensors at the front end of the crankshaft compare relative speeds with sensors at the rear end. The degree of twist as power for the pto increases is detected and, when it exceeds 30 degrees (30hp), engine power is automatically increased.

160hp or 190hp when pto demand is more than 30hp. Valmets new range-topping 8750 is able to adjust power output automatically.