Mercedes OM651 Rebuild, common faults & everything you need to know
A complete guide to Mercedes' 2.1 diesel - a common-rail inline-four with DOHC, 16 valves and a cast-iron block, in single-turbo or sequential two-stage turbo (Biturbo) form. From the balance shaft module's timing chain, injectors and swirl flaps to power builds, with workshop prices and clear common-fault guides.
- VIN verification before delivery
- Delivery time normally approx. 1 week
- 12 month warranty on the engine
Robert has built and reconditioned German turbodiesels for over 30 years, and that is the experience we build on. The OM651 is Mercedes' widespread 2.1 diesel, fitted to everything from the C-Class and E-Class to the GLK/GLC, Sprinter and Vito/Viano. It is a common-rail inline-four with DOHC, 16 valves and a sand-cast cast-iron block with an aluminium cylinder head, force-fed by a single VNT turbo at lower power levels or a sequential two-stage Biturbo on the 220/250 CDI variants. The engine is known for a characteristic cold-start rattle from the timing chain tensioner - the chain sits at the rear together with the balance shafts' gear drive, the same exposed location as on several other German diesels. Beyond the chain, the injectors and swirl flaps wear, and the EGR system clogs with soot. We do everything from cylinder head reconditioning and turbo reconditioning to complete engine reconditioning with our own machine shop and a 12-month warranty.
The OM651 at a glance
Shared base data for the OM651 family (the 2.1-litre engine; a smaller 1.8-litre variant was also fitted in the A/B-Class). Variant-specific power and torque figures are listed in the table below, cross-verified against Mercedes' own technical introduction documentation and at least one independent source per value.
| Power | Forced induction | Torque | Typical example | From year |
|---|---|---|---|---|
| 100 kW (136 hk) | Single VNT | 350 Nm | C 200 CDI | 2009 |
| 120 kW (163 hk) | Single VNT | ca 360-380 Nm | Sprinter / Vito | 2009 |
| 125 kW (170 hk) | Single VNT | 400 Nm | C/E/GLK 220 CDI | 2009 |
| 140 kW (190 hk) | Single VNT | 440 Nm | V-klass / Vito 250 BlueTEC | 2014 |
| 150 kW (204 hk) Biturbo | Sequential two-stage turbo | 500 Nm | C/E/GLK 250 CDI | 2008 |
The power and torque figures above are identity data (the engine's output, not tightening torque), compiled from Mercedes' own technical introduction documentation for the OM651 and cross-verified against independent spec databases. The top engine variant (150 kW/204 hp/500 Nm) was launched in the C 250 CDI as early as autumn 2008 and is factory-documented with exactly these figures. The Biturbo variants use two fixed-geometry turbochargers controlled pneumatically via a boost-pressure flap and wastegate, not a variable turbine.
Torque specs
We only publish torque specs we have been able to verify against an actual factory page. For the OM651 we have not yet completed that verification against the Mercedes factory manual (WIS). We never guess and never borrow another engine's values. If you need tightening torques for a job of your own, get in touch and we will find them in the correct factory manual before your job begins.
Common faults on the Mercedes OM651
This is what we see most often when an OM651 comes in. Symptoms, causes and how we fix it.
Timing chain & balance shaft module - cold-start rattle
Notorious OM651 fault • Critical- Symptoms
- A short rattling or clattering noise on cold start that goes quiet after a second or a few seconds once the hydraulic pressure builds up. Left untreated it can progress into a persistent rattle, rough running and fault codes for camshaft versus crankshaft position (P0016/P0017). Because the OM651 is an interference engine, a chain failure bends the valves.
- Cause
- The timing chain sits at the rear against the gearbox together with the gear drive to the balance shafts, and is driven by a hydraulic tensioner whose internal mechanism can wear or stick. Neglected oil changes and oil sludge make the problem worse. The chain sits at the back, so replacing it requires separating the engine and gearbox - we replace the entire chain kit with rails, tensioner and sprockets in one go.
Injectors - copper washer leak and early piezo injectors
Common • High- Symptoms
- A smell of diesel, hard starting when hot, a rhythmic "chugging" exhaust note at idle and visible soot build-up around the injector seat. On early engines (up to around 2012-2013) the piezo injectors can also cause cold-start problems and diluted engine oil.
- Cause
- The copper washer that seals the injector against the cylinder head ages and leaks combustion gases, which builds up a self-reinforcing layer of soot. Mercedes switched from piezo to solenoid injectors in running production around 2012-2013. Left untreated, the soot can seize the injector in the cylinder head. We test, reseal and replace injectors as needed.
Swirl flaps in the intake
Common • High- Symptoms
- Power loss, limp mode, an intake flap fault code and, in the worst case, a broken flap arm or bushing being drawn into a cylinder.
- Cause
- The intake's swirl flaps and their plastic link arms clog up with oil mist and become brittle from heat cycling, which makes them stick and eventually break off. We replace or blank them off properly and clean the intake.
Clogged EGR valve & intake
Common in city driving • Medium- Symptoms
- Rough idle, power loss and coolant loss with no visible external leak if the EGR cooler is affected.
- Cause
- Soot and oil mist build up deposits in the EGR valve and intake ports, especially on short journeys. The EGR cooler's passages can also crack from thermal cycling and let coolant into the exhaust flow. We clean the intake and EGR in connection with cylinder head work.
Oil leaks - water pump, valve cover, crankshaft seal
High mileage • Medium- Symptoms
- Visible oil or coolant leak, a smell of oil in the engine bay, a falling coolant level.
- Cause
- The electric water pump's plastic housing cracks from heat cycling, and the valve cover gaskets and rear crankshaft seal harden and leak with age. We replace seals and gaskets in connection with larger engine work.
Mercedes OM651 rebuild prices
Pricing based on OM651 specifications: 4-cylinder inline, 83 mm bore, 16 valves, 5 main bearings + 4 rod bearings. We carry out cylinder boring, crankshaft grinding and cylinder head resurfacing with our own machine shop. The timing chain and turbo are handled separately. All prices exclude VAT and parts.
Cylinder head reconditioning
Bottom end
Full rebuild
Performance
The price covers machining work only. Parts and assembly/disassembly labour are charged separately.
Cylinder machining (4-cyl, 83 mm bore)
| Service | Price |
|---|---|
| Cylinder boring 4-cyl inline block (83 mm) | 3 318 kr |
| Plateau honing 4 cyl | 1 050 kr |
| Stress boring 4 cyl | 4 603 kr |
| O-ringing block 4 cyl (high-boost) | 2 800 kr |
| Deck decking block 4 cyl | 1 974 kr |
Crankshaft work (5 main + 4 big-end, 8 counterweights)
| Service | Price |
|---|---|
| Crankshaft grinding (5 main + 4 big-end) | 3 010 kr |
| Polishing standard | 1 022 kr |
| Cleaning 4-cyl crankshaft | 784 kr |
| Straightening (medium) | 1 190 kr |
| Camshaft journal grinding 4 pcs (DOHC) | 1 540 kr |
| Remove/fit counterweights 8 pcs | 2 044 kr |
Valve reconditioning (16 valves)
| Service | Price |
|---|---|
| Cutting 16 valve seats (standard) | 1 820 kr |
| Cutting 16 valve seats (large) | 2 772 kr |
| Valve guide replacement 16 pcs (light alloy) | 2 548 kr |
| Manufacture of valve seat inserts 16 pcs | 3 080 kr |
| Bronze sleeves fitting 16 pcs | 2 268 kr |
Resurfacing (I4, standard cylinder head size)
| Service | Price |
|---|---|
| Resurfacing cylinder head 4 cyl (standard) | 1 330 kr |
| Resurfacing cylinder head 4 cyl (large) | 1 596 kr |
| Resurfacing block 4 cyl (standard) | 1 988 kr |
| Resurfacing block 4 cyl (large) | 2 114 kr |
| Resurfacing manifold 4 cyl | 2 842 kr |
Con-rod work (4 pcs)
| Service | Price |
|---|---|
| Replace con-rod bush 4 pcs | 2 240 kr |
| Manufacture con-rod bush 4 pcs | 2 898 kr |
| Length adjustment con-rod 4 pcs | 2 898 kr |
| Replace press-fit piston 4 pcs | 1 582 kr |
| Replace piston ring 4 pcs | 1 106 kr |
| Resizing big-end housing 4 pcs | 2 352 kr |
| Check/straighten con-rod 4 pcs | 1 414 kr |
| Full reconditioning con-rod 4 pcs | 3 164 kr |
| Steel shot peening con-rods 4 pcs | 2 268 kr |
Pressure testing & balancing
| Service | Price |
|---|---|
| Pressure testing cylinder head 4 cyl (small) | 1 876 kr |
| Pressure testing cylinder head 4 cyl (large) | 2 800 kr |
| Pressure testing cylinder block | 1 400 kr /h |
| Balancing rotating assembly straight 4-cyl | 3 742 kr |
| Weight matching con-rods 4 pcs | 1 316 kr |
| Weight matching pistons 4 pcs | 1 092 kr |
| Flywheel balancing | 2 100 kr |
| Balancing flywheel + clutch | 2 842 kr |
Indicative pricing for the OM651 configuration (4-cyl inline, 83 mm bore, 16 valves, alloy head, cast-iron block). Labour prices exclude VAT and parts (piston rings, bearings, gaskets, stretch bolts, injectors, timing chain kit, turbo). Request a quote for an exact price after inspection.
Tuning the Mercedes OM651
The OM651 responds well to remapping thanks to its turbo capacity, especially on the Biturbo variants. The cast-iron block is robust - but the timing chain, injectors and EGR system must be kept in order before any power increase.
- 1
Remapping & intake/exhaust
A Stage 1 remap and a freer exhaust system give a noticeable gain in torque thanks to the turbo capacity. The bottom end handles this well with a healthy timing chain and a cleaned intake.
220-240 hk - 2
Upgraded injectors & Stage 2
Solenoid injectors in good condition and a Stage 2 remap take more out of the Biturbo system's margin. The stock bearings handle more with the right margins and a healthy turbo.
250-270 hk - 3
Turbo upgrade
A hybrid turbo or an upgraded charge system together with a reinforced fuel system. Read more about turbo upgrades.
270-290 hk - 4
Full build
A balanced bottom end, a ported cylinder head and a large charge system. We build the chain mainly in-house with performance engine building.
290+ hk
Need a whole engine?
Sometimes the damage is too extensive for a rebuild to be worth it, or the car simply needs to be back on the road as fast as possible. That is when a ready-made replacement engine is the right way to go. Our replacement range includes reconditioned Mercedes OM651-engines, quality assured to Meksta's standard and checked at our workshop before delivery, with a 12-month warranty and no mileage limit. Since the same engine code often covers several generations, we always verify against your chassis number before the build is ordered.
Questions & answers about the Mercedes OM651
The questions we hear most often from OM651 owners.
What does it cost to rebuild a Mercedes OM651?
A cylinder head reconditioning costs around 5 000 - 7 000 kr (labour), a complete engine reconditioning around 19 500 - 30 500 kr. On top of that come parts (gasket, bearings, injectors) and possibly a timing chain kit or turbo, depending on condition. We give a fixed quote after inspection.
Why does my OM651 rattle on cold start?
The classic OM651 sign is a short cold-start rattle that goes quiet after a second or a few seconds. It comes from the hydraulic mechanism of the timing chain tensioner, mounted at the rear against the gearbox together with the balance shafts' gear drive. If the rattle is ignored over a long period, the guide rails and tensioner can wear out completely. We recommend always checking the chain system at any sign of noise.
Is the Mercedes OM651 an interference engine?
Yes. If the timing chain jumps or snaps, the valves hit the pistons, causing bent valves and often major engine damage. A cold-start rattle must therefore never be ignored.
Which cars have the Mercedes OM651?
The OM651 is fitted to the C-Class, E-Class, A/B-Class, CLA, GLK/GLC, GLE/ML, S-Class (S 250 CDI) plus the Sprinter and Vito/Viano, at power levels from around 100 kW/136 hp to 150 kW/204 hp.
Can you tune an OM651?
Yes. A Stage 1 remap often gives a noticeable torque increase, especially on the Biturbo variant. With upgraded injectors, Stage 2 and a possible turbo upgrade you build on from there. A healthy timing chain and injectors/EGR in good order are a prerequisite before tuning.
See also: we recondition and build turbo engines and diesels from Mercedes and other manufacturers. Feel free to compare with Mercedes' larger six-cylinder diesel Mercedes OM642 or BMW's equivalent four-cylinder diesel BMW N47. If you only need the turbo sorted, we do that via our turbo reconditioning. See all our engine types. Would you rather have a finished, reconditioned engine straight away? Buy a Mercedes OM651 exchange engine in the shop.
Have an OM651 that needs looking at?
Call us directly or send in a quote request. We reply within 24 hours.
Other engines we recondition
We recondition more engines than we have time to write guides about. Here are more that we see often.