Oliver Hart Parr 28-50
Built: 1927–1930 · Series: CROSS-MOTOR-Baureihe
Not the right version? The data comes from vehicle registers holding many near-identical versions side by side. Photograph the data plate — we read make and type from it. Open the scanner e-mail address required
Oliver Hart-Parr Cross-Motor range – transverse-engined tractors from Charles City, Iowa: 18-36 G and 28-50, 27.2 to 37.5 kW, 800 to 850 rpm, kerosene and petrol operation
Hart-Parr of Charles City, Iowa, is credited as one of the originators of the term 'tractor', which the firm coined in its advertising from 1907. The Cross-Motor range denotes the Hart-Parr tractors built from 1918 to 1930 with the engine mounted transverse to the direction of travel; in 1929 Hart-Parr became part of the newly formed Oliver Farm Equipment Company. Model designations such as 18-36 G and 28-50 follow the two-figure convention then common in the United States, naming drawbar and belt horsepower.
Read on 3 more paragraphs
The register lists here 2 versions with 27.2 to 37.5 kW from two- to four-cylinder engines of 8,210 to 11,064 cm³, an unladen weight of 3,323 to 4,715 kg, a length of 3,353 to 3,581 mm, a width of 1,854 to 2,235 mm, a height of 1,549 to 1,638 mm and a rated speed of 800 to 850 rpm.
These slow-turning large tractors were used for ploughing and stationary belt work, such as threshing, on the grain farms of the American Midwest, running on kerosene, paraffin or petrol, the cheaper fuel of the pre-diesel era.
On these nearly century-old machines, the condition of the plain bearings, magneto ignition and cooling system matters, along with cracks in the cast-iron frame; spares come almost exclusively from collectors, tractor clubs and specialist restorers, as no factory service remains.
Sources: SpecCodex register, model data: Oliver Hart-Parr Cross-Motor-Baureihe
Technical data
Engine
| Fuel | Kerosin/Petroleum/Benzincorrect |
|---|---|
| Power | 51 hp (37.5 kW)correct |
| Rated speed | 850 rpmcorrect |
| Cylinders | 4correct |
| Displacement | 11,064 cm³correct |
| Bore | 146.05 mmcorrect |
| Stroke | 165.1 mmcorrect |
| Cooling | water-cooledcorrect |
Dimensions and weights
| Length | 3,581 mmcorrect |
|---|---|
| Width | 2,235 mmcorrect |
| Height | 1,638 mmcorrect |
| Unladen weight | 4,715 kgcorrect |
Drivetrain and chassis
| Drive | rear-wheel drivecorrect |
|---|---|
| Gearbox | 2 V/1 Rcorrect |
| Front tyres | 28" x 7"correct |
| Rear tyres | 52" x 14"correct |
| Top speed | 5.2 km/hcorrect |
Origin and approval
| Construction | frame constructioncorrect |
|---|---|
| Units built | 1,207correct |
Where this model stands
Power-to-weight ratio: 8 kW/t (38 kW / 4.7 t)
Power class: Universal (40–100 hp)
Stronger than 36% of the tractors in the register — out of 15,663 models with a stated power figure.
Calculated from the documented figures above — not a rating.
Frequently asked questions
How much power does the Oliver Hart Parr 28-50 have?
The Oliver Hart Parr 28-50 delivers 51 hp.
How much does the Oliver Hart Parr 28-50 weigh?
The unladen weight is 4,715 kg.
What engine does the Oliver Hart Parr 28-50 have?
4 cylinders, 11,064 cm³ displacement, Kerosin/Petroleum/Benzin.
How fast does the Oliver Hart Parr 28-50 go?
Top speed is 5.2 km/h.
What are the dimensions of the Oliver Hart Parr 28-50?
3,581 mm × 2,235 mm × 1,638 mm.
When was the Oliver Hart Parr 28-50 built?
Production years: 1927–1930.
What to check before buying
- Check the hour meter against the service records — a replaced instrument is the most common gap.
- Compare the data plate and chassis number with the papers.
- Check the weights in the papers against the figures here — attachments change them.
- Check front and rear tyre sizes: mismatched pairs strain the drivetrain.
- Shift the gearbox cold and warm — jumps only show up at temperature.
- Load the hydraulics and watch for sag.
- Ask about parts availability for this build year — the running costs hang on it.
A general list for this type of machine — no substitute for an inspection or an appraiser.
We do not sell machines. We ask the dealers who carry this model and come back with price and lead time.
Request a quote →
We ask the suppliers and come back with price and lead time.
Request spare parts →
This page carries 20 individual figures for this model. They come from 1 recorded source; every figure can be traced there. What we cannot document is not here — we leave gaps open rather than estimate them.
Missing a figure you were looking for? Report it →
Know this machine better? Have a photo, a manual, or know that a figure is wrong? Add it to the register →
Other models in this series
Sources: Wikibooks Traktorenlexikon (CC BY-SA 4.0) (retrieved August 2026) · Values adopted and presented in our own form; changes from the source are possible. · How we check the data
Tractor in 3D section
Turn the model, look inside and click an assembly — each one is explained.
