0 material differences · fewer than 12
Tractor oneInternational Harvester 6661972–1976No measured PTO figureTractor twoInternational Harvester 6861976–1980No measured PTO figure
Which should you choose?
We will not advise between these two machines, because their power is identical, with the same weight or the same engine, which usually means one machine sold under two names; any difference below comes from how each source describes it. The figures below are side by side so you can judge them yourself; each says whether it was measured, claimed or declared by its source.
Field by field
0 material differences · 13 fields identical or within 5%, which is not counted as material
| Field | 666 | 686 | Gap |
|---|---|---|---|
| Engine | |||
| Engine power, claimed claimed | 66.1 hp | 66.1 hp | — |
| Engine declared | INTERNATIONAL HARVESTER C-291 | INTERNATIONAL HARVESTER C-291 | — |
| Maximum torque declared | — | 220 lb·ft · 298 N·m | — |
| Transmission | |||
| Top speed declared | 18.6 mph · 30 km/h | 18.6 mph · 30 km/h | — |
| Clutch declared | Pedal-operated dry single-plate clutch | pedal-operated dry single-plate clutch | — |
| Hydraulics & hitch | |||
| Pump flow declared | 12.0 gpm · 45.5 L/min | 12.0 gpm · 45.5 L/min | — |
| Rear PTO speeds declared | 540 rpm | 540 rpm | — |
| Weight & dimensions | |||
| Unladen weight declared | 8,199 lb · 3,719 kg | 8,199 lb · 3,719 kg | — |
| Wheelbase declared | 103.0 in · 2,616 mm | 103.0 in · 2,616 mm | — |
| Length declared | 161.0 in · 4,089 mm | 162.0 in · 4,115 mm | — |
| Width declared | 87.0 in · 2,210 mm | 89.4 in · 2,271 mm | — |
| Ground clearance declared | 21.0 in · 533 mm | 21.0 in · 533 mm | — |
| Turning radius, braked declared | 12.0 ft · 3.66 m | 12.0 ft · 3.66 m | — |
| Fuel tank declared | 123.9 qt · 117.3 L | 123.9 qt · 117.3 L | — |
Height is not in this table. It is not one measurement: the sources measure it to different points — over the cab on some machines, over the steering wheel or the exhaust on others — and the same tractor measured two ways can differ by most of a metre. It appears here only when both machines' figures carry the point they were measured to and it is the same point, which is not the case for these two. Each machine's own page prints its height as its source gives it.
International Harvester 666 sources
- Source: Traktorenlexikon, “IHC 666”
- Source: Traktorenlexikon, “Farmall Farmall 756”
- Source: Traktorenlexikon, “Farmall Farmall 666”
International Harvester 686 sources
- Source: Traktorenlexikon, “IHC 686”
- Source: Traktorenlexikon, “Farmall Farmall 756”