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Kubota B7100HST Troubleshooting

The Kubota B7100HST is a 2WD or 4WD compact utility tractor. This model was manufactured between 1977 and 1997. The tractor was designed in 2 versions: B7100HST-E (2WD) and B7100HST-D (4WD).

The Kubota B7100HST powertrain system components: a 46.5 cu.in (0.8L) Kubota D750 4-cycle vertical 3-cylinder indirect injection naturally aspirated water-cooled diesel engine with a maximum power of 16 hp (11.9 kW), and two-range hydrostatic transmission with infinite forward and reverse gears.

Max forward speed: 3.5 mph (5.7 km/h) using low range or 9.1 mph (14.5 km/h) using high range, and max reverse speed: 2.4 mph (3.9 km/h) using low range or 6.2 mph (10.1 km/h) using high range. The open center hydraulic system used a gear pump with fluid flow rate of 3 gal/min (11.4 l/min). The hydraulic pressure is 117 bar (1700 psi).

The two-wheel drive models are equipped with 4.00x9 front tires and 7.00x16 rear tires. The 6.00x12 (AG) or 20.5x8.00-10 (Turf) front tires and 8.00x16 (AG) or 29x12.00-15 (Turf) rear tires are used for tractors with four-wheel drive. The wheelbase is 54.6" (1390 mm) for 2WD models and 55.1" (1400 mm) for 4WD models. The Kubota B7100HST is compatible with a Kubota B1630C front-end loader with lift capacity to full height of 510 lbs (230 kg) and breakout force of 780 lbs (353 kg).

Engine Troubleshooting
Engine will not start or hard to start
Fuel filter is dirty - Replace the filter element
Closed fuel supply valve - Open supply valve to inject fuel
Air in fuel pipes - Bleed fuel pipes
Faulty or dirty injectors - Change fuel injectors
Damaged fuel injection pump - Replace or repair injection pump
Engine has low compression - Inspect cylinder block and change worn parts
Engine stalls during operation
Engine is cold - Warm up the engine
Air in fuel lines - Bleed fuel lines
Bad fuel injection - Check and adjust
Fuel filter is dirty - Filter maintenance required
Fuel injectors are defective or dirty - Check fuel injectors and replace if required
Diesel engine stalls after starting
Incorrect setting of fuel injection pump timing - Check the fuel injection pump timing setting
Fuel filter is dirty - Change filter element
Fuel injector nozzles fault - Replace fuel injector nozzles
Fuel injection pump is damaged - Repair or change injection pump
Dirty air cleaner element - Service or change air cleaner
Engine stops at low idle speed
Incorrect low idle speed adjustment - Correct the settings
Fuel injection pump damage - Rebuild or change fuel pump
Clogged or damaged injector nozzles - Service or replace nozzles if required
The valve clearance is not adjusted - Adjust valve clearance
Engine overheats
Low engine coolant - Top up coolant. Check and repair damage to the cooling system if required
Cooling system is dirty or cooling components are damaged - Flush cooling system or replace faulty parts
Engine oil level low - Checking oil level and add if necessary
Fan belt tension is not adjusted or belt is worn - Replace or adjust belt tension properly
Thermostat malfunction - Install new thermostat
Diesel engine is losing power
Fuel injectors are defective or dirty - Check fuel injectors and replace if required
Fuel injection pressure is incorrect - Check the fuel injection pressure and adjust if necessary
Air filter element is clogged - Clean or replace the air filter element
Oil filter element is dirty - Change or clean engine oil filter element
Diesel engine is overloaded - Shift to lower gear or reduce the load
Valve clearance is wrong - Need to adjust valve clearance
Low idle speed setting is not correct - Normalize low idle speed
Fuel hoses or pipes are dirty - Clean fuel hoses and pipes
Engine compression too low: Valves are faulty or leaking - Change the valves
Engine knocks or noises
Unadjusted fuel injection pump timing - Adjust injection timing
Dirty or defective injector nozzles - Install a new set of well-balanced nozzles
Insufficient engine oil - Fill up the engine oil
Engine is not fully warmed up - Normalize the temperature by warming up the engine
Main bearings or crankshaft failure - Need to install new components
Broken or defective piston rings - Replace the piston rings as required
Flywheel screws are loose - Tighten the screws firmly
High engine oil consumption
Oil leakage: Seals or gaskets are wearing excessively - To repair leaks, replace worn parts
Oil viscosity is incorrect - Use oil of correct viscosity
Seized or wear piston rings - Change the piston rings as required
Valve stems or guides are damaged - Valves need to be changed
Scuffed pistons or cylinder liners - Check liners and pistons, replace as required

Electrical System Troubleshooting
Battery does not charge
Battery is worn - Battery replacement required
Battery cable harness damage - Check battery cables for damage, change or repair
Loose or corroded cables and terminals - Tighten or clean cables and terminals
Belt is worn or belt tension is incorrectly adjusted - Change belt or properly adjust belt tension
Starter turns slow
Low battery capacity - Low battery charging, charge as required
Battery does not hold charge - Service battery or change it
Bad battery electrical wire harness - Check wires for malfunctions, repair or replace
Corroded or loose battery cables and terminals - Service or tighten battery cables and terminals
Starter motor won't turn
Battery power is low - Recharge the battery
Discharged or faulty battery - Change or recharge battery
Starter motor is defective - Repair or replace starter
Disconnected or incorrectly connected cables - Inspect battery cables and connect correctly

Hydrostatic Transmission Troubleshooting
Excessive HST transmission noise
Fluid level is too low or fluid is dirty - Change fluid or top up to proper level
Speed control rod linkage is damaged or unadjusted - Adjust or repair rod linkage
Relief valve is faulty - Change the valve
Transmission overload - Reduce loading
Worn or damaged parts of the transmission - After disassembly and checking, replace worn components
Transmission fluid overheats
Oil level is low - Add transmission oil as required
Transmission fluid filter is plugged - Change or clean the transmission fluid filter
Cooling components are damaged or clogged - Inspect all cooling components and service or change if necessary
Excessive transmission load - Load needs to be reduced
Power is insufficient
Fluid level is low - Fill system with correct transmission fluid level
Charge pressure is insufficient - Test charge pressure
Defective or worn relief valve - Install a new valve
Transmission oil leaks
Broken gaskets or seals - Seals and gaskets replacement required
High pressure inside the transmission housing - Repair or replace worn parts
Oil return tube is clogged - Inspect tube and service if required

Hydraulics Troubleshooting
Hydraulic system overheated
Improper hydraulic system pressure setting - Set the pressure properly
Main relief valve incorrect adjustment or failure - Set up or change the relief valve
Hydraulic oil contamination - Change the oil
Air leaks in hydraulic system - Check the suction line, pump seals, and fittings
Hydraulic fluid pressure is low
Hydraulic oil level is insufficient - Fill the hydraulic system with oil
Hydraulic fluid filter element clogging - Change the hydraulic filter element or service if required
Faulty hydraulic oil pump - Check hydraulic pump flow and replace pump if necessary
Defective or not adjusted hydraulic control valve - Adjust properly or change
Hydraulic cylinder failure - Inspect the hydraulic cylinder parts for damage or wear and replace if required
Hydraulic piping leaks - Identify leaks in the system and repair it
Three-point hitch lifting is too slow or cannot be lifted
Hydraulic fluid level is low - Add fluid to the hydraulic system
Cold oil in hydraulic system - Wait for oil to warm up
Hydraulic fluid filter clogging - Change hydraulic filter element or clean if necessary
Hydraulic pump is defective - Check the pump capacity and replace pump if required
Main relief valve failure or incorrect setting - Set up or change the relief valve
Damaged or incorrect adjusted hydraulic control valve - Change or set correctly
Hydraulic cylinder is defective - Inspect cylinder parts for wear or damage and replace if required
Suction pipe is damaged or loose - Repair or change
3-point hitch won't drop or drops slowly
Hydraulic control valve block is not set properly or defective - Set correctly or replace
Faulty hydraulic cylinder - Inspect cylinder components for wear or damage and change if required
Hitch rock shaft is damaged - Replace the shaft
Internal mechanical malfunction with hitch - Replace faulty or worn hitch components
Hitch is lowered or raised jerkily
Air trapped in the hydraulic system - Check the suction line, pump seals, and fittings
Hydraulic fluid is contaminated - Fill up with new hydraulic fluid
Hydraulic pump failure - Check the pump performance and replace it if required
Defective or not adjusted hydraulic control valve - Adjust correctly or replace
Hydraulic cylinder failure - Check cylinder components for damage or wear and change if necessary

Steering System Troubleshooting
Hard Steering
Steering knuckle or steering column is stuck - Inspect steering column and knuckle, replace worn parts
Steering gearbox components are worn - Replace defective components of steering gearbox
Faulty drag link or tie rod - Replace or repair
Insufficient lubrication in steering box - Need to lubricate the gearbox
Not adjusted toe-in alignment - Check and adjust toe-in
Tires are not correctly inflated - Inflate tires as necessary
Excessive steering wheel free play
Steering column bearing or shaft is worn - Change faulty parts
Steering linkage assembly is worn or loose - Repair or replace steering linkage
Worn steering gearbox bearings - Replace the bearings
Front wheel hub bearings or steering knuckles are worn - Change hub bearings or knuckles
Damaged or worn steering tie-rod ends - Change faulty part
Tractor pulls to right or left
Worn or loose steering linkage assembly - Repair or replace steering linkage
Defective steering knuckle bushing - Replace knuckle bushing
Uneven tire pressure - Inflate the tires properly
Toe-in adjustment is incorrect - Adjust toe-in correctly



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