Second-hand tractor repair or custom hiring on a fragmented boro rice farm
Rupen Bora farms 3.6 ha of boro rice in four fragmented plots at Nalbari. His 2008 35 hp tractor has 5,800 engine hours; a recent PTO dynamometer test showed 24 hp at 540 rpm against a rated 30 PTO hp. The engine smokes under load and consumes about 8.5 L/h during rotavation, while a neighbour's 45 hp tractor uses 7 L/h with the same 1.5 m rotavator. A workshop quotes ₹85,000 for a top overhaul, ₹1.9 lakh for a short block, and a used 45 hp tractor in good condition is available for ₹4.6 lakh. Custom rotavation is available at ₹1,150 per hour, but the operator is unreliable during the peak transplanting week. Diesel costs ₹92 per litre. Rupen must prepare 3.6 ha within a 10-day window and wants the lowest cost per hectare over the next three seasons, not necessarily the lowest immediate bill.
1. Is the measured 24 hp PTO output by itself proof that the engine needs a major overhaul? Set out the checks and calculations you would complete before approving the ₹85,000 repair.
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No. A 20% shortfall against the rated 30 PTO hp is significant, but it can come from causes outside the engine internals. Before authorising a top overhaul I would:
- Verify the dynamometer reading and correction factors; confirm the test was at 540 PTO rpm and normal engine temperature.
- Check the air cleaner, fuel filters, fuel lift pump, injection timing, injector spray pattern, valve clearance, exhaust restriction and intake leaks. A clogged air filter alone can cost several horsepower and cause black smoke.
- Check transmission/hydraulic drag, tyre pressure and brake adjustment; a dragging brake or starving hydraulic system loads the engine.
- Measure blow-by, oil consumption, compression and injector balance. Only if compression is low, blow-by is high and the simple items are correct is an overhaul justified.
For planning, use the measured power rather than the badge. With a 1.5 m rotavator at 4 km/h and 75% field efficiency, theoretical capacity is 1.5 × 4,000 = 6,000 m²/h = 0.60 ha/h, and effective capacity is about 0.45 ha/h. The 3.6 ha block therefore needs about 8 engine hours per season. At 8.5 L/h that is 68 L, or ₹6,256 per season, about ₹1,738/ha. The neighbour's 7 L/h gives 56 L, ₹5,152, about ₹1,431/ha. The fuel penalty is real but modest compared with the capital cost of a replacement tractor.
2. Compare the three options - top overhaul, buying the used 45 hp tractor, or relying on custom hiring - over three seasons of 3.6 ha each, and recommend one with stated assumptions.
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Assumptions: 8 engine hours per season for the existing tractor; the used 45 hp tractor also achieves 0.45 ha/h; no major breakdown; custom rate and diesel price remain constant; resale value ignored.
| Option | Fixed cost | Variable cost for 3 seasons | Three-season total |
|---|---|---|---|
| Top overhaul | ₹85,000 | 3 × 68 L × ₹92 = ₹18,768 | ₹103,768 |
| Used 45 hp | ₹4,60,000 | 3 × 56 L × ₹92 = ₹15,456 | ₹4,75,456 |
| Custom hiring | 0 | 3 × 8 h × ₹1,150 = ₹27,600 | ₹27,600 |
On pure arithmetic, custom hiring is cheapest, but the stated unreliability during the peak week is an operational risk: a two-day delay in transplanting can cost more than the machine saving. The used tractor is difficult to justify for only 3.6 ha unless it also earns custom-hire income.
My recommendation is a staged one. First spend a small amount on filters, injector and compression diagnosis. If compression is acceptable, do the top overhaul and keep the tractor; this gives control over timing at about ₹1,04,000 over three seasons. If compression is poor, do not put ₹1.9 lakh into a short block. Book custom hiring in writing for at least 1.5 ha as insurance, and use the old tractor only for light work. The overhaul is preferred over the used tractor because the annual work is small and the used tractor's fixed cost dominates.
3. If the tractor is repaired, what operational changes would you make to finish 3.6 ha within the 10-day transplanting window?
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The arithmetic says only 8 hours of rotavation, so the real constraint is not engine capacity but weather, breakdown and water scheduling. I would:
- Sequence plots by water availability, not by distance. Rotavate a plot only when it has received the first irrigation; dry rotavation followed by delayed flooding wastes passes.
- Use a 1.5 m rotavator in two passes rather than four shallow passes, and check blade sharpness daily. Blunt blades increase fuel and slip.
- Keep a one-day buffer: target 0.4 ha/day for 9 days, leaving day 10 for repairs and re-puddling.
- Pre-position diesel, filters, a spare rotor bearing and a mechanic's number. A two-hour breakdown in the peak week is more costly than the fuel saving from a lean mix.
- Book a custom operator for 0.8–1.0 ha as fallback, with a written date. Use the old tractor for levelling or transport while the hired machine rotavates.
- Train the operator to work at 4 km/h and full rated rpm; lugging at low rpm increases smoke and fuel per hectare.
If the overhaul is done, run a 2-hour load test before the season and re-check torque and injector settings. The decision should be reviewed after one season using actual hours, fuel and breakdown records.