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Komatsu S6D125 PC400-5 / PC400-6 / PC400-7 / PC400-8 Cylinder Head Core Differences

News 2026年 7月 1日 22

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All 4 excavators adopt 6D125 series 6-cylinder single-piece independent cylinder head (1 cylinder head per cylinder, total 6 pcs per engine)

but engine generation, casting numbers, internal cooling passages, exhaust flange, gasket, valve train and fuel injection ports are not interchangeable.

First, let we have a look the upper side of the 4 kinds cylinder head photos.

From The above photo, we can notice there are have difference hole in different position.

Cylinder Head Part Number Table (Bare Head / Head Assy)

PC400-5 (S6D125-1)

Bare Cylinder Head (without valves): 6150-11-1100 / 6150-11-1102

Full Cylinder Head Assembly (with valves & guides): 6150-11-1010

Matching Cylinder Head Gasket: 6150-11-1810

PC400-6 (SAA6D125E-2)

Bare Cylinder Head: 6151-11-1102 / 6151-12-1100 / 6151-12-1101

Full Head Assy: 6151-11-1110

Matching Head Gasket: 6151-12-1810

PC400-7 (SAA6D125E-3)

1. Bare Cylinder Head: 6156-11-1100 / 6156-11-1101
2. Updated universal casting: 6251-11-1200 (compatible PC400-7 & PC400-8 partial versions)
3. Matching Head Gasket: 6151-12-1810

PC400-8 (SAA6D125E-5 Electronic Injection)

1. Exclusive Bare Cylinder Head: 6251-11-1100
2. Universal replacement casting: 6251-11-1200
3. Matching Head Gasket (unique thickened steel multi-layer): 6251-11-1810

Item	PC400-5	PC400-6	PC400-7	PC400-8	English Name
Intake Valve	6150-41-4100	6151-41-4100	6156-41-4100	6251-41-4100	Intake Valve
Exhaust Valve	6150-42-4200	6151-42-4200	6156-42-4200	6251-42-4200	Exhaust Valve
Valve Seat Insert	6150-11-1320	6151-11-1320	6156-11-1320	6251-11-1320	Valve Seat Insert
Valve Guide	6150-11-1310	6151-11-1310	6156-11-1310	6251-11-1310	Valve Guide
Valve Stem Seal	6150-17-1510	6151-17-1510	6156-17-1510	6251-17-1510	Valve Stem Oil Seal

1. Fuel Injection Port Design (Most Obvious Distinction)

1. PC400-5 / PC400-6 / PC400-7: Mechanical inline fuel pump, small round injector hole, no high-pressure common rail oil channel inside head casting.
2. PC400-8: Electronic common rail system, extra internal high-pressure oil gallery, larger injector mounting hole, casting wall thickness reinforced for high fuel pressure.

2. EGR Cooling Water Passages

1. PC400-5: No EGR water channel on cylinder head side, simplest casting.
2. PC400-6: Single small EGR cooling hole, basic EGR layout.
3. PC400-7: Double enlarged EGR water flow passages, thicker cooling walls for long-hour mining load.
4. PC400-8: EGR channel + DOC exhaust treatment auxiliary hole, extra cooling cavity for post-processing heat dissipation.

3. Exhaust Manifold Flange

1. PC400-5/6: Thin single-layer exhaust flange, 4 fixing bolt holes.
2. PC400-7/8: Reinforced thick exhaust flange, 6 bolt holes, anti-crack casting optimization for turbo high temperature.

4. Cylinder Head Gasket (100% Not Interchangeable)

1. PC400-5: Thin copper composite gasket, part 6150-11-1810
2. PC400-6/7: Medium steel composite gasket, part 6151-12-1810
3. PC400-8: Thickened 5-layer steel high-pressure gasket, exclusive PN 6251-11-1810, prevent rail engine high pressure leakage

5. Internal Cooling Water Jacket

1. PC400-5: Simple straight cooling channel, easy overheating under heavy load.
2. PC400-6/7: Optimized spiral cooling channel, uniform temperature distribution.
3. PC400-8: Full surrounding closed water jacket, specially designed for electronic engine high combustion temperature.

6. Compatibility Summary

1. PC400-5 head only fits S6D125-1, cannot swap with -6/-7/-8
2. PC400-6 head fits SAA6D125E-2 only; cannot install on -7/-8
3. PC400-7 head (6156-11-1101) works for E-3; 6251-11-1200 cross fits PC400-7 & partial early PC400-8
4. PC400-8 exclusive head 6251-11-1100 only for SAA6D125E-5 common rail engine, zero compatibility with -5/-6/-7 mechanical engines

For the Photo, we can clear find , 4 different parts number, there are differece in the hole.
That is to say, they can’t repalcement each other.

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