How to PM: Periodic Maintenance Guide for Furukawa HCR9-DS2 and HCR12-DS2 Rock Drills

For owners and machine technicians — by S. Suvit Trading, Furukawa specialist since 1968

Why PM matters more than you think on these two models

The HCR9-DS2 and HCR12-DS2 were built between 1995 and 2004 — which means every machine on the market today is 20 years old or more. That is what makes them completely different from a new rig.

A new machine that misses a service interval still has material left to absorb the damage. A 20-year-old machine does not. Maintenance is the only thing standing between "a machine that still earns money" and "a machine parked waiting for parts."

The good news is that the ISUZU 6BG1/6BG1T is a purely mechanical engine — no ECU, no common rail — so your own technician can repair it on site, and parts are easy to find because the same engine is used in Hitachi EX200 excavators, ISUZU trucks, and dozens of generator sets. Looked after properly, these machines still have a long life ahead of them.

The key principle: a high-hour machine serviced on schedule is usually better than a low-hour machine that has been neglected — and a full year of PM costs a fraction of a single engine overhaul.

Know your machine first — where the two models differ

The maintenance structure is the same for both, but there are differences that must be handled differently.

Item	HCR9-DS2	HCR12-DS2
Engine	ISUZU 6BG1 (naturally aspirated)	ISUZU 6BG1T (turbocharged)
Drifter	HD609	HD612

What this means in practice:

1. The HCR12 needs turbo discipline — idle the engine down for 3–5 minutes before every shutdown, and be especially strict about oil quality, because the turbo bearing is lubricated directly by engine oil. Shutting down hot = oil bakes onto the bearing = turbo failure.

2. The HCR9 needs harder cooling-system discipline — the 6BG1 has no turbo and therefore less thermal margin, and tends to run hot when drilling hard rock or working continuously. A clogged radiator is the number-one cause.

   
   

Identical on both models: valve clearance 0.40 mm, injection pressure 185 kgf/cm², engine oil specification, fan belt tension, and the entire PM interval schedule.

Recently overhauled machines — the first 100 hours of running-in

If the engine or drifter has just been overhauled, the first 100 hours are the running-in period specified in the Furukawa manual — and this period determines the life of the entire overhaul.

• Do not run at full load during this period — work at moderate load and avoid continuous hard-rock drilling

• Change the engine oil and filter at 100 hours without waiting for the 250-hour interval, because running-in produces metal particles as components bed in

• Check for leaks daily — joints that have just been disassembled and reassembled can loosen

• Recheck fan belt tension after 50 hours, because a new belt stretches

  
  

Skipping this stage is why some overhauls "don't last" even when the parts were good and the technician was skilled.

The PM schedule — just six numbers to remember

Furukawa sets the maintenance intervals at 50 / 250 / 500 / 1,000 / 2,000 hours, plus one more that many people don't know about: 600 hours for the drifter accumulator diaphragm.

Daily / every 10 hours — the best-value 15 minutes you'll spend

• Check engine oil and coolant levels

• Drain the water separator — critical given local diesel quality

• Clean the radiator and oil cooler cores — rock dust clogs them fast; this is the single most important heat-prevention task

• Check/blow out the air cleaner — in rock drilling this may be needed daily

• Check hydraulic oil level and temperature

• Refill the drifter grease (molybdenum grease NLGI No.1) in the auto-greaser tank

• Check flushing air before every drilling start — never percuss without flushing air

• Listen for abnormal noise from the drifter

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Every 50 hours

• Fan belt tension — press midway between the fan pulley and the alternator with a force of 98 N (10 kgf); deflection must be 7–10 mm

• Track tension

• Feed chain tension and lubrication

• Grease: boom, guide shell, oscillating cylinder, rod changer, centralizer (universal grease NLGI No.2)

  
  

Every 250 hours

• Change engine oil + oil filter (see the note on intervals below)

• Replace the fuel filter

• First change of the hydraulic return filter — then every 500 hours thereafter

• Check gear oil levels in the final drive and feed motor

About the engine oil interval — read this carefully The Japanese Furukawa manual specifies 500 hours, or at least once a year. However, the same 6BG1 engine in Hitachi EX200 excavators in actual regional service is commonly changed at 250 hours. For quarry work in Thailand — heavy dust, high heat — we recommend 250 hours. Engine oil costs far less than engine repair.

Every 500 hours

• Change engine oil + filter (if using the standard interval)

• Replace the hydraulic return filter (second change onward)

• Check and adjust valve clearance to 0.40 mm (engine cold, both intake and exhaust)

  
  

Every 600 hours — the interval most often missed

• Replace the drifter accumulator diaphragm — the Furukawa manual specifies replacement every 600 hours, and if any crack, pinhole, or deterioration is found, replace it immediately without waiting for the interval

• Check the nitrogen charge pressure in the accumulator

⚠️ Always fully release hydraulic pressure before checking the charge pressure

Every 1,000 hours

• Assess the drifter for overhaul — the standard interval is around 1,000 hours; shorten it for hard rock or poor flushing

• Change the hydraulic oil + in-tank suction strainer

• Clean the pilot filter

• Change the compressor oil and the oil separator element

• Change the final drive / travel motor gear oil (SAE 90 API GL-4)

  
  

Every 2,000 hours

• Change the coolant throughout the system

• Major drifter overhaul

• Major compressor service

• Inspect the wear plates and the entire undercarriage

  
  

Engine in depth — four values to memorize

The 6BG1 and 6BG1T use identical values throughout; the only difference is the turbo. Commit these four to memory (full detail in Appendix A):

• Valve clearance 0.40 mm with the engine cold — both intake and exhaust

• Injection nozzle opening pressure 18.1 MPa (185 kgf/cm²)

• Fan belt deflection 7–10 mm under a force of 98 N (10 kgf)

• Engine oil 21.5 litres, grade SAE 15W-40

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How to set the valves: rotate the engine until cylinder No. 1 or No. 6 is at top dead centre on the compression stroke (the notch on the crankshaft pulley aligned with the pointer), set the valves on that cylinder, then rotate the crankshaft a further 360° to set the remainder.

Warning signs you need to be able to read:

• Black smoke → clogged air cleaner / low injection pressure / poor spray pattern / retarded timing / excessive injection volume

• White or blue smoke → water in the fuel / blown head gasket / worn rings and liners / leaking valve seats / turbocharger failure (6BG1T only)

• Blow-by — smoke from the breather tube underneath the engine — open the oil filler while the engine is running; if smoke is pushed out heavily, the rings and liners are worn and an overhaul is close

  
  

Drifter in depth — where machine life doubles or halves

The drifter is the most expensive component on the machine, and its life depends primarily on two things: grease at the shank, and flushing air.

Shank lubrication — use molybdenum grease NLGI No.1 on the rod, shank, and sleeve via the auto-greaser, and apply grease to the spline groove every time you assemble.

Flushing air — insufficient flushing packs cuttings tightly around the bit and shank; heat and reflected shock waves travel back into the drifter, wearing the piston and drive components abnormally fast. Never percuss without flushing air.

Accumulator — charge with dry nitrogen only. The charge pressure must be read from the plate on the machine.

⚠️ Always fully release hydraulic pressure before checking

Signs the drifter needs an overhaul: penetration rate down more than ~15% from normal · external oil leakage · abnormal knocking or gas-leak noise · loss of percussion pressure · accumulator will not hold its charge

Hydraulics, compressor, and undercarriage

Hydraulics — cleanliness is everything

Rock drills use high-pressure piston pumps, which are far more sensitive to contamination than ordinary hydraulic systems. Cleanliness must therefore be controlled to ISO 4406 = 16/14/11 — one code cleaner than general industrial practice.

The point most people miss: new oil straight from the drum is often dirtier than the target. Always filter it before adding. Pouring new oil directly into the tank is adding contamination to the system with your own hands.

Filter intervals — the return filter is changed first at 250 hours, then every 500 hours. The in-tank suction strainer is changed together with the hydraulic oil at 1,000 hours.

Compressor — watch the differential pressure

The screw compressor on a rock drill works hard the entire time you are drilling. Key check points:

• Check the differential pressure across the oil separator element — if it keeps climbing, the element is blocked and must be replaced

• Compressor air filter — in heavy dust this needs servicing more often than the manual specifies

• Check the safety valve and the unloader system

• Compressor oil is ISO VG32 — never substitute VG46 hydraulic oil

  
  

Undercarriage and feed system

• Track tension — check every 50 hours. Too tight wears bushings and rollers quickly; too loose risks throwing a track

• Travel motor and feed motor gear oil — use SAE 90 API GL-4; check level at 250 hours, change at 1,000 hours

• Feed chain — check tension and lubricate every 50 hours. A stretched chain throws off feed distance and drills crooked holes

• Wear plates on the guide shell — inspect at the 2,000-hour interval and replace when worn beyond limit. Worn plates let the carriage rock and produce deviated holes

  
  

Adjusting the PM schedule for Thailand

Factory manuals are written for Japanese and European conditions. Local quarry sites are hotter, dustier, and more humid. Adjust as follows:

• Engine oil → 250 hours instead of 500, and send samples for oil analysis periodically

• Air cleaner → check daily; it is the most frequently serviced item in rock drilling

• Radiator / oil cooler → clean the cores daily, check coolant concentration

• Water separator → drain daily, and keep the tank full when parked to reduce condensation

• Hydraulic oil → use ISO VG46 (not VG32, which is a cold-climate grade)

  
  

The six most common mistakes

From our experience inspecting and repairing rock drills, these are what destroy machines before their time:

1. Percussing without flushing air — destroys the drifter fastest, and most expensively

2. Shutting down the HCR12 hot — oil bakes onto the turbo bearing; always idle down 3–5 minutes first

3. Not cleaning the radiator cores — especially on the HCR9, which is heat-sensitive; rock dust clogs cores far faster than people expect

4. Forgetting the 600-hour accumulator diaphragm interval — it falls outside the familiar 50/250/500/1000 sequence, which is exactly why it gets skipped

5. Extending the oil change because "it still looks clean" — oil that still looks clear may already have exhausted its additive package

6. Not logging hours and work performed — you lose track of which interval is due, and at resale you cannot prove the machine's history, which pushes the price down hard

   
   

Summary

If you remember only five things:

1. Clean the radiator every day — especially on the HCR9, which has no turbo and is heat-sensitive

2. Idle the HCR12 down 3–5 minutes before shutdown — or the turbo will fail

3. Change engine oil at 250 hours for our dusty local conditions

4. Don't forget the 600-hour interval for the drifter accumulator diaphragm

5. Never percuss without flushing air — it destroys the drifter faster than anything else

A 20-year-old machine with a complete PM history will keep working for years and still command a price. A machine left to chance becomes a large repair bill in short order — the difference is nothing more than discipline in doing the PM.

Appendix

Appendix A — ISUZU 6BG1 / 6BG1T engine specifications

Item	6BG1 (HCR9-DS2)	6BG1T (HCR12-DS2)
Type	6-cylinder inline, 4-stroke, water-cooled, OHV, direct injection	Same + turbocharged
Displacement	6.494 L	6.494 L
Bore × stroke	105 × 125 mm	105 × 125 mm
Output (industrial rating)	~129 BHP (intermittent) / ~114 BHP (continuous) @ 2,500 rpm	Higher (turbocharged)
Max torque	~313 lb·ft @ 1,500 rpm	Higher
Fuel injection	Zexel A-type in-line pump + RSV governor (fully mechanical)	Same
Cylinder liners	Cromard dry type, replaceable	Same
Valve clearance (cold)	0.40 mm intake/exhaust	0.40 mm intake/exhaust
Injection opening pressure	18.1 MPa (185 kgf/cm²)	18.1 MPa (185 kgf/cm²)
Fan belt tension	Deflection 7–10 mm at 98 N	Same
Engine oil capacity	21.5 litres	21.5 litres
Coolant capacity (engine only)	12 litres	12 litres
Compression ratio	17:1 or 18:1 (ISUZU documents disagree — follow the manual supplied with the engine)	Same

Appendix B — Recommended lubricant grades

System	Type	Grade	Change interval
Engine	Diesel engine oil	API CC/CD (CF acceptable), SAE 15W-40 (10W-30 in cooler conditions)	250 h (Thailand) / 500 h (standard)
Hydraulics	Hydraulic oil	ISO VG46	1,000 h
Compressor	Screw compressor oil	ISO VG32	1,000 h
Feed motor / travel motors	Gear oil	SAE 90 API GL-4	1,000 h
General grease points	Universal grease	NLGI No.2	Every 50 h
Rod / shank / sleeve	Molybdenum grease	NLGI No.1	Continuous (auto-greaser)
Cooling system	LLC coolant (ethylene glycol)	To specification — never mix types	~2,000 h / annually

Hydraulic oil cleanliness: rock drill systems use high-pressure piston pumps and should be maintained at ISO 4406 = 16/14/11 (one code cleaner than general industrial practice). Always filter new oil before adding, as drum oil is typically dirtier than the target.

Appendix C — PM schedule summary table

Interval	Engine	Drifter	Hydraulics / Pneumatics	Undercarriage / Feed
Daily	Oil/coolant levels · drain water separator · clean radiator + oil cooler · air cleaner	Refill auto-greaser · check flushing air · listen for noise	Hydraulic oil level + temperature · check for leaks	General visual check
50 h	Fan belt 7–10 mm @ 98 N	—	—	Track tension · feed chain · grease all points
250 h	Engine oil + filter (Thailand) · fuel filter	—	First return filter change	Check gear oil levels
500 h	Engine oil (standard) · set valves 0.40 mm	—	Return filter (every 500 h)	—
600 h	—	Replace accumulator diaphragm · check N₂ pressure	—	—
1,000 h	—	Assess drifter overhaul · check seals	Hydraulic oil + suction strainer · pilot filter · compressor oil + separator element	Final drive gear oil SAE 90 GL-4
2,000 h	Change coolant	Major overhaul	Major compressor service	Inspect wear plates + undercarriage

About this article

S. Suvit Trading Ltd., Part. has imported, overhauled, and serviced Furukawa hydraulic crawler rock drills since 1968. We provide engine overhaul, drifter overhaul, genuine parts, and maintenance planning for every model of rock drill.

If you would like your machine assessed or a PM plan built for your fleet — including machines bought elsewhere — we are glad to advise.

S. Suvit Trading Ltd., Part. 704 Charoen Rat Road, Khlong San, Bangkok 10600 svtrade.com