Test: Kuhn GA8731 twin rotor rakes

By: Mark Fouhy, Photography by: Mark Fouhy


Discussions always get interesting when it comes to opinions around what the most important job is when silage making time rolls around

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Team Kuhn raking, baling, and wrapping perfection

Different roles within a silage crew demand different skills and experience, and different machinery.

Obviously, the chopper driver rates pretty highly, as they should have the most experience and are operating an expensive piece of machinery. Tractor and bin drivers can be less experienced but still have an important role to play in order to avoid damage to equipment and the landowner’s property.

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Satisfying results: even and tidy rows

Another key role is the mower operator, the first to the paddock and first to find any obstacles that may cause grief to valuable gear. If the mowers is out of action, the whole process comes to a grinding halt. The stack man is also key: without a well-packed pit of silage, the quality of conserved feed is going to be poor, making the rest of the process somewhat a waste of time. And then, of course, there’s the person operating the rake, which is key to an overall efficient job. An experienced person on the rake can tidy up rows making life easier for those to follow with the harvester and bins.

So from the above analysis, it’s clear that each aspect has an equally crucial role to play, and it’s much the same when it comes to machinery. Build quality is vital, as the smallest dud part can stop the whole machine working.

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High clearance when turning over rows at headlands

This month, we’re taking a closer look at the Kuhn GA8731 twin rotor rake. Although the Kuhn range of rotary rakes includes large efficient quad rotor units, this test covers one of the larger twin rotor options: the GA8731.

This model has a working width of between 7.7 and 8.6 metres, which is enough to drag in three mower widths, offering great efficiency running in front of a round, square or conventional baler or loader wagon.

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Spare wheel attached to frame in case of punctures

Test

I headed to Taumarunui to see the unit in action with the guys from Harrison Contracting (who we featured a few months ago with their new Kuhn round baler combi wrapper – clearly, they’re a fan of the brand).

With a relatively kind winter, there were quite a few hectares of early baleage to be done. With an old twin rotor rake and a greater workload coming into spring, the need for efficient, reliable gear is important, particularly given the tight windows of opportunity to get through the workload needs of faming clients.

Given this situation, it was an ideal time to demo a new rake before the season hit full noise. This is where the Kuhn GA8731 comes into the picture. With a good relationship with Graham Anderson from Giltrap Agrizone (GAZ) – one of their closest machinery dealers and stockist of the Kuhn range – a demo machine was organised.

With a Kuhn combi baler already in the fleet, as well as Kuhn plough and power harrow, the Harrison Contracting guys know what to expect from the brand in terms of build quality and also parts and back-up service from GAZ.

With a few paddocks of oats and rye grass mown a couple of days earlier, I was surprised at how dry both the paddock and wilted crop were. First up for the demo machine was rowing up ready for the baler.

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Hydraulic ram to help control 3D movement of each rotor

Getting the Kuhn GA8731 ready for work is quick and easy, with hydraulic locking for transport, which Kuhn call the Stabilift system, the lack of a pull string to release the locks is an upgrade on the old rake on site.

Adjustment of ground height is done with manual crank handle, which in theory shouldn’t really need altering very often. Having hydrualic width adjustment on the go is helpful, as depending on the crop determines how wide you have the rotors to give a suitable row for the harvesting machine following.

The 3D ground following system of the Kuhn rake is something that really impresses me. Using a small hydraulic ram on the front of each rotor prevents the rotors diving into the ground as you lower them back into work, which is traditionally where the main opportunity is for tine damage (other than rough uneven paddocks). I have seen other brands with a jockey type wheel, which runs just in front of the rotor to protect the tines and rotor gearbox.

For this job, our test paddocks were relatively smooth with just a few rolling undulations. As you’d expect, the six wheels beneath the 13-arm rotors kept them running along the ground smoothly, not digging in or dragging extra dirt or contamination into the rows for baling.

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PTO shaft up out of the way of grass

The larger Kuhn rakes (as opposed to smaller farmer type machines) are onto gen III Masterdrive, two stage reduction gearboxes for the rotor drives, which seem to run smoothly and quietly. The drive from the PTO runs up to a high point on the chassis and then splits to the top of each rotor. As the angle is more like 45 degrees rather than a 90-degree gearbox, it shouldn’t require quite as much horsepower. In saying that, on test day the rake was hooked onto a Massey Fergusson 7619, which at 190hp, is enough to almost run three of these rakes, =with the low horsepower requirement from Kuhn being just 68hp (or 50kW).

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Covering the ground, pulling in 8.6m into 2.3m rows

The slightly wider operating width of the Kuhn GA8731 rake over Harrison’s old rake was a big plus, as being able to pull in three rows compared to two-and-a-half results in more consistent rows, making it easier for the baler driver to give a pretty consistent fill to the bale chamber and produce quality bales.

On test day it was hard to show this, given that the paddock had been turned to help with the drying/wilting process. The crop was also lighter, but of high quality, so tested the Kuhn on the tidiness of the job done. In these conditions, it excelled.

I would be interested to see how it went later on with its full three mower widths and a much heavier crop. The rows should just be larger, so the baler just would be making more bales per row, saving time for both the rake and baler tractors driving up and down the extra row or two the old rake would have made.

One thing the Kuhn GA8731 was lacking was a central divider to prevent the fodder being thrown too far one way or another, but maybe this is the way the new models are going and manufacturers have decided that part to be unnecessary.

Operation

The simplicity of the Kuhn rake is a key feature for me. The designers have not overcomplicated things, which means it doesn’t take a rocket scientist to operate it. Important in these times as if need be, a new trainee to the industry should pick it up relatively quickly.

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Folded up, transport height is under 4m

Height adjustment of each rotor is with a manual crank handle and a visual scale, which is pretty standard. Optional hydraulic adjustment is an option with an upgraded in-cab control box, which I would say may be hard to justify the extra expense.

The control unit of the test machine allows the operator to switch between transport and work mode and vice versa, and also the operating width of the machine between 7.7 and 8.6 metres to give the optimal row. The individual operation of the two rotors is a handy feature for awkwardly shape paddocks, particularly triangles, so you can avoid picking up the headland when starting or finishing a run.

Lift of the arms comes up 75cm at an angle of 45 degrees, which should clear even the biggest rows. Being semi-mounted (two-point linkage), along with the rear steering, makes getting in and out of gateways easy, as well as providing good manoeuvrability in the paddock, particularly when turning back onto rows.

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The steering rear axle makes getting through gateways easy

In transport position, the Kuhn is still a relatively compact machine, and with rotors of 3.65 metres, the transport height is kept just under four metres, and there’s still enough clearance beneath the machine so rotors shouldn’t get hung up or damaged on anything. The overall transport width is kept under three metres and the machine comes standard with over width panels and lighting for road work.

As always, build quality of the Kuhn rake is notable, and weighing in at 2.25 tonnes, there’s actually quite a bit of weight there given how much steel structure is in a rake. One handy feature is the incorporation of a spare tyre bolted onto the frame; hopefully, that should get you through the day if the worst happens, or at least until somebody has time to take the punctured tyre for repair and get back to the paddock.

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Hydraulic adjustable width operation on the go

Summary

Much like rugby, silage making is a team sport. If everybody plays their position well, you will have a good result at the end of the day. As for the Kuhn GA8731? I would be happy to own and operate one of these rakes. I think this model would suit a large number of contractors with its ability to cover the ground in a variety of conditions, and with its simple no fuss operation, which is most people want out of a machine.

Kuhn GA8731 specifications

Working width 7.7–8.6m
Avg. windrow width  1.4–2.3m
Attachment/Cat 2-point pivoting lower links/Cat2 & 3N
Rotor diameter  3.65m
No of arms/rotor 13 arms
Tines/arm 4
Rotor drive 2 Stage reduction Masterdrive GIII
Rotor suspension 3D
Wheels/rotor  6 wheels 16x6.50-8
Rotor height adjustment Crank handle
Tyres on chassis 15x55-17
Transport width 2.99m
Minimum transport height  3.99m
Length 6.57m
Weight 2250kg
Power Requirement (kW/hp) 50/68

Pros

  • Simple to operate
  • Low horsepower requirement

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    3D ground following rotors
  • Spare rotor wheel attached to the frame
  • Individual arm operation
  • Compact transport dimensions.

Cons

  • No central divider

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