Perkins 4.108 Rebuild, common faults and everything you need to know
One of the most reliable postwar marine diesels - roughly 500 000 built between 1958 and 1992. Cast iron block, CAV/Delphi DPA rotary distributor pump, naturally aspirated. Rebuilt, it will run for another 20-30 years.
The Perkins 4.108 is one of the most reliable postwar marine diesels. Built as an industrial engine and adapted for marine use as the 4.108M. Around 500 000 engines were built between 1958 and 1992. Fully mechanical design, no electronics, a rugged cast iron block. It is rebuilt with standard processes and then runs for another 20-30 years. Three known issues: the rear crank seal leaks (Foley Engines Tech Tip #100), the head bolts tend to seize in the block, and the CAV/Delphi DPA pump needs an overhaul at every full rebuild. We carry out cylinder head reconditioning, cylinder boring, crankshaft reconditioning and complete engine reconditioning in our own machine shop with 12-month warranty. See also our boat engine rebuild hub page.
The Perkins 4.108 at a glance
Sourced from the Hallberg-Rassy Club Perkins 4.108 reference, Perkins Long Service Club, Perkins Workshop Manual, Foley Engines tech tips and TA Diesels service data.
4-series predecessors and variants
The 4.99 to 4.107 to 4.108 development was industrial/agricultural based. The 4.108M is the marinised version.
| Variant | Application | Power | Period |
|---|---|---|---|
| 4.99 (C99) | Industrial / agricultural | 30-37 hk | Mid-1950s |
| 4.107 | Industrial / agricultural | ~43 hk | 1957-1965 |
| 4.108 / 4.108M Current | Industrial + marine | 37-51 hk | 1958-1992 |
| T4.108 (turbo) | Industrial | More power | Advanced variant |
Note - successor: The Perkins Prima series (M50, M60, M80T) was launched in the 1980s and ran alongside the 4.108 rather than replacing it outright. The 4.108 block was more popular and stayed in marine production until 1992. Its last application was the British Army's APU during the Gulf War.
Common faults on the Perkins 4.108
Cross-checked against Foley Engines tech tips (#100, #126), SmokStak, Cruisers Forum, Engine Builder Magazine and kemsoracing technical bulletins.
Rear crank seal leaks
The Achilles heel • High- Symptoms
- Oil traces in the bellhousing, oil drips behind the engine, a dropping oil level between runs.
- Cause
- Foley Engines Tech Tip #100 describes this as the engine's Achilles heel. The original rope-style cotton seal is notorious for leaking and ages quickly in a marine environment. It is replaced with a modern material during a full rebuild.
Cylinder head bolts seize in the block
Classic Perkins 4-series • High- Symptoms
- On disassembly the bolts will not come free without destroying the thread in the block. A classic Perkins 4-series weakness.
- Cause
- Galvanic corrosion between the steel bolt and the cast iron block over decades in a marine environment. Heat and chemical treatments are needed for safe removal.
DPA pump hydraulic governor seal
With insufficient servicing • High- Symptoms
- Rising oil level, diesel-smelling oil, dropping oil pressure.
- Cause
- The CAV/Delphi DPA pump's internal hydraulic governor seal can collapse. Fuel leaks into the engine's oil sump. If the fault is missed, the oil is diluted and the big-end bearings fail. Handled by a CAV-specialist pump shop.
Air bleeding problems on restart
Recurring • Medium- Symptoms
- The engine will not start after a fuel filter change or pump removal.
- Cause
- Air in the fuel lines. Foley Engines Tech Tip #126 documents a specific bleed procedure that must be followed - the 4.108 is not self-bleeding and cartridge-style fuel filters make the process harder.
Cylinder liners wear
High running hours • Medium- Symptoms
- Oil consumption, blue smoke under acceleration, dropping compression.
- Cause
- Natural wear. The 4.108 has dry cylinder liners (which sets it apart from the 4.99/4.107 with wet liners). Wear limit 0,006" over nominal.
Heat exchanger corrodes internally
10+ years • Medium- Symptoms
- Overheating under load, reduced operating temperature, less coolant flow.
- Cause
- Scale and salt on the raw water side, possibly internal corrosion. Note - the 4.108 has no after-cooler since the engine is naturally aspirated.
Perkins 4.108 rebuild prices
Classic 4-cylinder 1.76L engine with dry cylinder liners. Excl. VAT and parts. Main operations - cylinder boring, crankshaft grinding, cylinder head resurfacing - are carried out in our own machine shop.
Cylinder head reconditioning
Bottom end
Full rebuild
DPA pump service
Cylinder machining
| Service | Price |
|---|---|
| Cylinder boring 4 cyl (79,4 mm) | 3 318 kr |
| Dry liner replacement 4 cyl | 6 800 kr |
| Plateau honing 4 cyl | 1 050 kr |
Cylinder head reconditioning
| Service | Price |
|---|---|
| Resurfacing cast-iron cylinder head 4 cyl | 1 590 kr |
| Pressure testing cylinder head 4 cyl | 1 876 kr |
| Cylinder head bolt removal + helicoil | 2 800 kr |
| Valve seat cutting 8 valves | 910 kr |
See also
Other classic marine diesels and related services.
Questions and answers about the Perkins 4.108
What is the most common fault on the Perkins 4.108?
The rear crank seal. Foley Engines Tech Tip #100 describes this as the engine's Achilles heel. The original rope-style cotton seal is notorious for leaking. Secondary faults are seized cylinder head bolts and the DPA pump's governor seal. Foley Tech Tip #126 documents the air bleeding problems after a fuel filter service.
Does the Perkins 4.108 have an after-cooler?
No. The engine is naturally aspirated and has only a heat exchanger - no after-cooler. The heat exchanger can corrode internally, but the after-cooler fault does not exist on this engine.
What is the power output of a Perkins 4.108?
Continuous power: 37 hp @ 3 000 rpm. Intermittent (max) power: 47-51 hp @ 4 000 rpm depending on the variant. Some sources quote up to 55 hp for specific marine calibrations (Hallberg-Rassy Club). The 4.108M is the marinised version.
What does it cost to rebuild a Perkins 4.108?
Cylinder head reconditioning 6 500-9 000 SEK labour. Complete engine rebuild 26 000-42 000 SEK labour, plus parts 7 000-16 000 SEK. DPA pump service is always added at 6 000-12 000 SEK (CAV-specialist).
Is it worth rebuilding a Perkins 4.108 in 2026?
Often yes. Spare parts are still available from specialist British and American suppliers. A fully rebuilt 4.108 gives you another 20-30 years and costs considerably less than switching to a modern Yanmar 4JH or Volvo Penta D2.
Why do the cylinder head bolts seize?
A classic Perkins 4-series weakness. Galvanic corrosion between the steel bolt and the cast iron block over decades in a marine environment. Heat and chemical treatments are needed for safe removal. In the worst case the bolts are drilled out and helicoils are fitted.
How long does a Perkins 4.108 rebuild take?
Cylinder head reconditioning: 1-3 weeks (depending on the bolt problems). Complete engine rebuild: 3-6 weeks in the workshop, plus 2-3 weeks extra if the DPA pump has to go to a specialist CAV shop.
Do you have a Perkins 4.108 that needs looking at?
Call us or send a quote request. Reply within 24 hours. We service all types of boat engines - see boat engine page. All rebuilds with 12-month warranty.