JOHN DEERES 120HP
JOHN DEERES 120HP
6420S GOES ON TEST
Variable power for this
farmers weekly/Boerderij
tractor test, as
Andrew Pearce looks at
John Deeres 6420S
LAST Novembers Agritechnica produced a raft of new John Deeres. The companys line-up for the crucial 80-150hp class turned around completely, with the 6010 Series swapped for – and youre probably ahead of me here – the 6020 Series. Ten-strong and made in Mannheim with four or six cylinder motors, the newcomers options include hydraulic cab suspension and stepless transmission.
At the top of each range is an S model. These pull the neat trick of tailoring maximum power to the job in hand; and while this is not a new idea – Valmets Sigma system got there first – the logic is not the same.
Valtra starts with a relatively light tractor, builds in extra horsepower, then protects the transmission by limiting engine output in tough low speed work. By contrast, Deere cuts engine power below 15kph. It reckons the 6420S would need more ballast and wider tyres to put 120hp into the soil, which would cancel the tractors topwork advantage. Heavy fieldwork users are directed instead to the six cylinder 6620, with its wider rubber, 5hp more and 650kg extra weight once ballasted.
The 6420S heads the four cylinder range. Roughly equivalent to the old 6410, it delivers a claimed 118hp at maximum and 108hp when limited so is effectively a 120hp class unit. In these times when nothing is allowed to be ordinary, base models are tagged Premium while higher spec versions with CVT transmission are called Premium Plus: this ones the lower-spec Premium. Listed at £48,080 as tested, its aimed at farms wanting 120hp without a six cylinders size and weight.
First impressions
A short tractor, all wheels and tyres thanks to wide Michelins. Visual changes from the old series are subtle; the cabs gained round front lamps, designer air vents puncture a bonnet whose nose wraps round more, welded one-piece rims live under back mudguards which sport a motorbikes flying saucer lamps. Optional air brake outlets hover over a linkage that looks much the same, though a big bulge under the cab rear glass hides repositioned electrics. And the whole bonnet lifts, so no more nose panels to mess with. Change is also afoot in the cab, but more about that soon. Build quality? High, dented only by a loose bonnet sealing strip and a flappy fuse box cover.
THE 6420S only puts out its full power beyond 15kph or when travelling faster than 2kph with something actually working on the pto. This means you cant fool it in draft work by just switching on the shaft, and that for dyno testing a Deere engineer had to whistle up the higher power mode (called high boost in Deerespeak) through a laptop.
Power curves start to diverge only after 1900rpm. Rated speed output at the pto was down on Deeres crankshaft claims by 14.8% at both high and low boost (suggesting high pto losses or that this 63-hr engine wasnt giving all it could), docking the engines card by half a point. Maximum torque (10.4% under the crankshaft claim) arrived spot on cue at 1500rpm. In both modes the engine shows significant overpower (6.2hp high, 11.4hp low), with peaks set sensibly just below the 2208rpm 1000 pto shaft speed.
Constant power bands are wide in both modes; particularly so in low boost where rated speed output is restricted. And specific fuel consumptions promise good economy in work, for while values at rated speed and maximum power fall on the class norm, the six-point averages of 269g/kWhr (high boost) and 273g/kWhr (low boost) are outstanding – probably as the sfc curve rises only slowly towards rated speed. So this is a contemporary engine, showing characteristics which should let it handle heavy pto and draft work without fuss while remaining light on fuel.
The 6420S weighs 5150kg in a class dominated by six-cylinder units where the average is 5800kg. Even set up for work with 850kg of wafers its still light, so delivers a high power/weight ratio for transport and topwork. But if you plan to mount heavy tackle the tractor will need that front weight, as ballasted distribution puts only 46% on the nose.
Whats subjective performance like? The engine is particularly resilient from rated speed to around 1900rpm, then under this settles down behind a wall of torque. Pulling 14.9t the Deere is lively (and the first 40k tractor to crest our main road test hill in top gear), while on steep climbs the motors wide constant power band makes it slow to beg for downshifts. Deep cultivation is handled with conviction despite the maximum power restriction, the motor never sounding unhappy or stressed – constant power is doing its stuff.
THREE gearboxes are on offer. PowrQuad Plus has six ranges and a park position, four powershift steps, cruise control and needs the drivers thumb to push buttons. AutoQuad II adds speed matching, autoshifting and a 50k option, while AutoPowr is a full stepless transmission. The test tractor carried 24/24 AutoQuad II in 40k form.
A tall manual shift lever runs in a clearly defined gate. Out of comfortable reach in two ranges, it clatters between gears and can hang on downshifts, but cant be wrong-slotted when youre in a rush. Knob-top powershift buttons are duplicated alongside the hand throttle so you need not stretch, while the usual Deere direction shuttle lever lives alongside the steering wheel. Powershifting and shuttling are a model of speed and smoothness when the transmission is hot, harsh when its cold.
Eight of 24 forward speeds handle 4kph-12kph fieldwork. Average for the class, this spread is enough – though a potentially multi-role tractor could use more. Good speed flexibility exists around 8kph and 4.5kph but not in the range-change area around 6kph. Small 7% overlaps between field ranges grow to 31% between the two transport ones, while powershift gear gaps are a sensible 20%. Reverse speeds are slowed on this Series so are now the same as forward gears; an improvement, though headland shuttling may need a powershift down. As all powershift ratios are present and correct in reverse, the 6420S hits a true 40k in both directions.
Thats the regular stuff. The clever bits are accurate speed matching on changing main ratios up and down – not novel, but still very helpful in transport – and two-mode autoshifting. The latter is available in any speed range and invoked through a rocker switch. As long as powershift steps are available, normal mode sees the transmission shifting up when revs hit 2250, down at 1800. Eco mode forces upshifts at 1800rpm, downshifts at 1500. Engine speed and throttle position are both monitored, so you can back off the gas in traffic and let eco mode hold a tall gear until you open up again.
Autoshifting works like a charm, thanks to the engines terrific flexibility, the powershifts fast, clean changes and JDs well-judged shift points – although the operator cant vary these, theres no need to anyway. Mode choice depends on the circumstances. For instance, normal mode keeps up outfit speed in hilly land transport, while on the same trip eco should save a little fuel at the cost of journey time. And even though you might expect to use normal mode for heavy fieldwork, eco handles deep cultivation easily despite Deeres suggestion that it should be reserved for light jobs. The 6420Ss bullpower motor is well able to pick up a higher gear then hold it, so the transmission isnt left hunting between ratios. And when it does shift, no appreciable forward speed is lost.
For shaft speed-critical work like chopping or power harrowing, autoshift can team with cruise control (which limits maximum engine speed to an operator-set level) to make a potentially output boosting combination. Self-shifting in normal mode gives no more than 200rpm pto variation, while cruise setting stops overspeed.
There are two transmission gripes. The tractor has to be rolling for autoshift to sense whats going on, so it cant help if the gear is too high when moving away on the shuttle lever. And autoshifting stays active until the operator either turns it off or makes a manual powershift, so you might need to throttle back at headlands to avoid unscheduled upshifts.
JOHN DEERE 6420S
FIELD OPERATION
LIKES AND DISLIKES
• Likes
• Powerhouse engine.
• Quick, well-judged autoshifting.
• Light weight for maximum power.
• Fast, smooth shuttle and powershift.
• Exceptionally quiet.
• Easy, accurate lift controls.
• Powerful hydraulic services.
• Compact size.
• Consistent first-try diff lock disengagement.
• DislIkes
• Thick nose.
• Restricted view to wide implement ends.
• Autoshifting cancelled by manual powershift at headland.
• Diff lock/4WD indication lights only in switches.
• Pto switch clumsy.
• Marginal lift arm visibility for short driver at full drop.
Above left: Lightly revised cab will still be very familiar to Deere operators. Optional sprung passenger seat (foreground) is worthwhile.
Above: Gearshift (left) clatters through defined gate. Hand throttle and linkage control block (bottom) are good to use. Spool levers (centre) are a little sticky; switches for 4WD, HMS II and
AutoPowr gearbox control stack beyond them. Long hitch hook
release lever (far right) is easy to find and use.
Right: Standard Deere instrument panel combines analogue and
digital displays, with read-outs toggled
from a small tag switch on the steering column. Panel adjusts with steering wheel, preserving visibility.
Left: Powershift buttons on gearknob are duplicated on a rocker switch by the hand throttle – no need to reach
for the stick.
Right: New tray helps extend otherwise limited storage space
in cab…
Left: …As does an open slot over the revised roof console, which is home to adjusters for the optional electric mirrors.
JOHN DEERE 6420S
ROAD TRANSPORT
LIKES AND DISLIKES
• Likes
• High power/weight ratio maximises performance.
• Engine flexibility.
• True 40kph top speed.
• Very quiet at all speeds.
• Autoshifting destresses driver.
• Speed matching.
• Little bounce with sprung drawbar trailer.
• Fine brakes.
• High oil flow at low rpm for tipping.
• DISLikes
• Hitch hook visibility marginal for short operator.
• Spool levers sticky for close trailer tip control.
• Main shift lever clunky and a long reach in two ranges.
• Harsh 4WD noise on braking.
HOW THE TEST HAPPENS
Silsoe Research Institute runs the tractor through selected points of an OECD test. Individual data values come from these internationally-standardised measurements, while averages are calculated from OECD test data of other tractors in the power class.
For subjective opinion we drive the tractor for two days. Equipment used with the 6420S included a 4m Dowdeswell power harrow, a 3m Lemken Smaragd cultivator and a
tandem-axle trailer ballasted to 14.9t gross.
Left: 6420s high and low boost power curves begin to diverge at 1900 rpm.
Below: Constant power bands are wide in both low boost and high boost modes.
Flat fuel consumption (bottom) show engine stays frugal right up to rated speed.
Above: Linkage is low on initial lift force. Pto guard flips up, hitch hook pushes out. Air brake couplers (top) are non-standard. Re-positioned electrics panel below back window limits shorthouse operators sight of arm ends at full drop.
Above: Linkage hardware is
easy to use.
High oil flow at low engine revs makes for quick trailer tipping.
DEERES TechCentre has been lightly reworked inside and out. Its still a one-man band, generously wide up front but cramped further back, served by two click-shut doors and decent boxed-in steps. Hydraulic self-levelling cab suspension (£1389) and front axle springing (£2877) are options not on the test tractor.
This Premium model gets new, lighter shaded plastic trim and a monogrammed air chair but not the Premium Pluss CommandArm seat module. Overhead is a full-length, back-opening roof panel and a revamped switch console complete with storage slot above, though stuff has to be wedged in here or it lands in your lap. Up and to the right now lives a modest-sized drop-down box which, unless you specify the optional box for the nearside mudguard, is the extent of stowage capacity.
Space to either side of the seat is minimal, though a usefully deep well has appeared behind it, below relocated fuses and relays. Helpful in a tractor likely to fill multiple roles, 12V supplies, external cable access and control box mountings are well catered for.
In the lower zones nothing much has changed. The steering column still tips and telescopes through a very generous range, sensibly taking the instruments along for the ride and accommodating all driver sizes. Its home to all the air vents plus a small can-cooler compartment. Ventilation throughput is adequate, with air usefully directable from a car-style control. Lacking is a head-level supply and dedicated rear screen demist vents (though rear screen demist is a £211 option), while non-functioning aircon earned the tractor a black mark. On the brighter side the new optional sprung passenger perch is a major comfort booster on rough going but still crams the occupant into a tight space.
Views are a mix. Mirrors are adequate, not huge, and can have electric adjustment and heating. Depending on your physical size the still-bulky bonnet takes up more or less of the forward panorama. The new electrics panel below the back window is quite thick, so shorter operators only just keep sight of the lift arm ends at full drop. Hefty three-quarter pillars and optional wide mudguard extensions cut the view to the ends of close-coupled wide implements, adding interest to implement transport.
But dont be thinking that visibility is poor. The high-set seat, expansive glass and slim main pillars make sure its not, though the 6420S is no fishbowl. A potentially generous spread of working lamps – up to six at the front, four at the back, all present on the test tractor – give good cover, though the optional xenon lamp package should boost distance and clarity.
DATA
Circle, 4WD unbraked average 11m
Torque rise (high/low boost) 32%/43%
Maximum/average/minimum noise under load 73/72.5/72 dB(A)
Max pto power (high boost) 106.7hp at 2103rpm
Max pto power (low boost) 103.8hp at 2100rpm
Fuel capacity 185 litres
Lift capacities (bottom, middle, top) 3090/4650/5078kg
Gears 24/24
Wheelbase 2400mm
Height to cab top 2742mm
Weight as tested, including 850kg wafers 5150kg
Above: Although short for a 120hp tractor, the 6420 has only an average turning circle . Below left: Saucer lamps are part of 6020 Series styling revisions. External controls for pto and lift arms are
standard; mudguard extensions optional. Below right: The cabs fresh air filters can be reached from ground level.
LIKE other modern Deeres weve driven, this one is quiet – very quiet for a four-cylinder. Better yet, the old and irritating steering hiss has completely gone and on the road with the back window open, most jet-plane whine has disappeared… though its still there in reverse. Silsoes meter registered 73dB(A) in the loudest gear close to 7.5kph and 72dB(A) in the quietest, producing a class-leading 72.5 dB(A) average. Engine hum is the main component in a background devoid of tiring low-frequency rumble, and noise rises only in pitch, not volume, with climbing revs. Pto operation raises the level slightly; flat-out transport stays relaxed, leaving harsh, intrusive 4wd noise during road braking the only fly in some particularly smooth ointment.
CLOSED centre, load-sensing hydraulics with EHR deliver the usual range of functions including transport damping. Nerve centre is Deeres long-serving palm-sized block with its easy-sliding depth control, implement fast-in switch and rotaries for maximum lift and drop rate. The prime functions – setability and sensitivity – are fine, with the hydraulics showing smooth, tailorable response to changing draft.
A substantial top link and self-locking, single-side adjusted stabilizers are easy to live with, though the top links storage latch is an acquired taste. Lower down, a hydraulic push-out hook is released from a high-set lever thats much more convenient than some, and the hook itself stays visible to short drivers if kept at trailer ring height until the last moment.
The 6420S extends a range that otherwise spans 80hp-110hp, so lift is relatively low for a 120hp unit. After correction to 90% system pressure, just over 3000kg force is available with lift arms 200mm above the ground; this then rises quickly with arm height to a much more respectable 5078kg maximum. Any capacity crisis should be confined to the initial movement of a heavy implement with low attachment points.
Like others, Deeres £479 optional headland management system aims to take load from the driver by automating repetitive actions. Now morphed into HMS II and finally including pto engagement, it should record a control operation sequence coming on to the headland, then a separate pto/lower sequence coming back into work. Each can be replayed as the driver pushes a rocker switch, the first approaching a headland and the second after turning round.
Very poor handbook explanation stopped us from using the system properly. John Deere acknowledges this, adding that the manual is being re-written for greater clarity. So for the moment we can only list HMS IIs functions – the ability to store and recall triggers from the diff lock, rear lift, two ptos, 4wd and (if fitted) the electro-hydraulic spool valves – and to note that for safety, its disabled when the tractor is standing still. As four button-pushes are needed to memorise even a simple sequence, setup could be easier.
UP to four single/double acting spools are fed oil by a circuit delivering maximum flow (103.3 litres/min) and hydraulic power (25.5kW) well beyond the 120hp class average. The pickup hitch took one outlet to leave the test tractor two top-spec, 300 Series valves. Manual lever positioning is good but operation is quite resistive and sticky, making fine feathering difficult. If you prefer fingertip stuff, electrohydraulic operation and timing functions are standard on Premium Plus models. Flow controls reachable from the cab and the ability to couple pipes under pressure round off a competent system, which allows a generous 35 litres of oil to be drawn off for trailer tipping.
THE 6420S lines up 540, 540E and 1000rpm pto speeds delivered through a reversible, snap-ring locked stub. A steel guard flips up to ease shaft connection, speed selection is straightforward from a reasonably-placed cab lever and dash speed read-out can be switched between analogue and digital. Deeres usual lift-and-turn on/off switch is safe but not as convenient as a simple pushbutton, while a mudguard switch gives standard external operation. The pto feathers in smoothly against light or heavy loads and operation is now programmable in the headland management system.
Above: New louvered bonnet (1) transforms access. Gatling gun aircleaner sits over integrated single-core radiator (3) with slide-out aircon condenser in front. Small unit (4) is fuel cooler. Battery is now easy to find (5). Small covers on either side of engine (6) drop for daily checks. Dont leave one open by mistake when you drive off, though.
ONE TRACTOR, TWO POWERS
An electronically-controlled Bosch VP44 injection pump takes centre stage in the 6420Ss variable-power act. Controlled by brains on the pump and in the cab, it delivers fuel according to forward speed and pto operation. Beyond 2kph and when torque fluctuations in the pto driveline confirm a shaft-driven implement is in work, maximum fuelling releases full power. In transport, the same happens when speed goes over 15kph. But when speed is in the 2-15kph range and theres no signal confirming pto action, the system assumes draft work is happening and limits maximum engine output.
ALL-WHEEL drive is handled by a console rocker switch, and has limited automation: speeds over 23kph (14.3mph) switch it out, speeds under 21kph (13mph) bring it in. The same goes for the back diff lock, which comes out beyond 12kph (7.5mph) and re-engages at that speed. The front diff lock is limited-slip so looks after itself, the back one disengages consistently from a single prod of the toe. Both systems confirm operation only through a switch lamp. Better would be a light on the console, up under the operators nose.
Cab 4
Engine 4.5
Noise, fieldwork 5
Noise, roadwork 5
Transmission 4
Clutch and shuttle 4.5
Linkage and hitch 3.5
Lift performance 3
Hydraulic services 4
Pto 4
4WD 3.5
Diff locks 3.5
Steering 4
Brakes 4
As fieldwork tractor 4
As topwork tractor 5
On the road 4
Daily maintenance 4
Character 5
Scores run from 1-5 with 1 very poor, 3 average for the power class and 5 excellent. The score for character shows the tractors jump in and drive me factor.
INBOARD rear wet discs stop the 6420S, boosted by pressurised oil and with effort spread to all wheels through automatic (and noisy) 4wd engagement. The pedal is firm, has short travel and if stamped on, produces rubber-smoking stops; gentler tactics bring progressive results. The transmissions park position is backed by a handbrake that doesnt engage 4wd, while splitting the pedals means that 4wd isnt engaged when using independent braking.
STEADY on the road and able in the field sums up this Deere. Although steering angle is an unfashionable 52deg, a short wheelbase and deformable front mudguards give the tractor a turning circle of 10.3m in 2wd and 11m in 4wd. On the road the tractor tracks straight and needs very little effort at the wheel: variable rate assistance (to add feel at higher speeds) would be a refinement.
THE new gas-strut bonnet reveals a repositioned battery, a revamped snap-open aircleaner and a single integrated main radiator: the intercooler is a water/air model carried separately on the block. Daily checks are made through drop-down panels (dont leave one open by mistake or a front wheel will savage it), coolant level can just be spotted through the bonnet louvers, while the back axle uses a fiddly dipstick rather than the sight glass found on bigger Deeres.
Filter access is OK, the hubs and front axle use level plugs, and grease nipples on the front UJs and propshaft still need the tractor moved to get at them. Service looks straightforward – and as engine oil changes are now at 500 hours, youll need to do it less often. The handbook is some-and-some, with information usually there but often not easy to find. Helpfully, though, it lists fault codes and how to call them up.
Verdict
Quiet, strong and easy to drive, this Deere brings low fuel consumption and light weight as a bonus. Most of the changes from 6010 models are a step up and the autoshift option potentially boosts productivity.
Fuses and relays now live behind the 6420s seat.