Mercedes OM606 Rebuild, common faults & everything you need to know
A complete guide to Mercedes' legendary inline-six diesel - a timing-chain DOHC with prechambers. From a frozen crankcase breather to 400-horsepower turbo builds, with factory-verified torque specs and workshop prices.
We have built and reconditioned Mercedes inline-sixes for decades. The OM606 is one of the most durable diesel engines Mercedes ever built - a timing-chain DOHC six with a cast iron block, aluminium cylinder head and prechambers (indirect injection). The bottom end with seven main bearings is extremely robust, and these engines often run well past 500,000 km. What needs attention sits in the ancillary systems: the timing chain and its plastic rails age, the crankcase breather can freeze in cold climates, and the mechanical or electronic injection pumps and injectors wear over time. The OM606 is also an interference engine, so a timing chain failure can bend valves. We handle everything from cylinder head reconditioning to complete engine reconditioning with our own machine shop and a 12-month warranty.
The OM606 at a glance
Data for the OM606 series. Torque specs read from the Mercedes factory manual (Mercedes WIS, for the OM604/605/606 family) and cross-verified.
| Variant | Displacement | Power | Torque | Compression |
|---|---|---|---|---|
| OM606.910 (NA) | 2 996 cc | 136 hk | 210 Nm | 25:1 |
| OM606.912 (NA) | 2 996 cc | 136 hk | 210 Nm | 25:1 |
| OM606.962 Turbo | 2 996 cc | 177 hk | 330 Nm | 22:1 |
| OM606.961 Turbo | 2 996 cc | 177 hk | 330 Nm | 22:1 |
| OM606.964 Turbo | 2 996 cc | 177 hk | 330 Nm | 22:1 |
Torque specs
Read from the Mercedes factory manual (Mercedes WIS, AR-numbered worksheets for the OM604/605/606 family) and cross-verified across several independent readings. Stretch bolts (cylinder head, mains, connecting rod, flywheel) are angle-tightened - always fit new ones. The OM606 is a diesel: there are no spark plugs, only glow plugs, and the cylinder head is tightened by the angle method with a rest period.
Cylinder head & valvetrain
Engine block & bottom end
Flywheel (by bolt type / gearbox)
Intake & exhaust
Note - Stretch bolts: cylinder head, main bearing, connecting rod and flywheel bolts are angle-tightened stretch bolts (TTY). Mercedes specifies new bolts, and Meksta always fits new bolts on disassembly. The reason: stress accumulation is invisible, and the cost of new bolts is negligible against the risk of failure. The cylinder head bolts are M10 and are tightened in sequence by the factory angle method with a specified rest period of 10 minutes between the steps.
NOTE - Diesel, not petrol: The OM606 has no spark plugs, only glow plugs for preheating, and indirect injection via prechambers. Always use the diesel values - never mix them up with a petrol engine. The factory connecting rod bolts are 40 Nm + 90° on the diesel; the same factory table shows 45 Nm + 90° for a related petrol engine (M111), which must not be used here.
NOTE - Flywheel/flexplate: the torque differs by gearbox and bolt type. Manual (TMF) is 40 Nm + 90°, automatic 35 Nm + 90°, and the alternative straight stretch bolt (found on dual-mass flywheels among others) 45 Nm + 90°. Use the torque that applies to the bolt type actually fitted.
NOTE - Harmonic damper: the centre bolt is tightened to a high torque followed by an angle and requires a holding tool. The hub is a press fit on the crankshaft nose.
Some torque values (cam sprocket, cam bearing caps, injector holders, oil drain plug and turbo mounting) were not confirmed in the factory source read within the time frame and are therefore not listed here - we never borrow a value from another engine. Factory tolerances (bearing clearance, deck height, piston clearance) for the OM606 are documented separately and published once cross-verified. All measurements are checked against factory tolerances with our own machine shop.
Common faults on the OM606
This is what we see most often when an OM606 comes in. Symptoms, causes and how we fix it.
Timing chain & guide rails wear
High mileage • High- Symptoms
- Rattling noise from the front of the engine, especially on cold start. A stretched chain gives retarded injection timing. In the worst case the chain jumps, bending valves.
- Cause
- The double-row timing chain and its plastic slide rails stretch and become brittle after high mileage. The OM606 is an interference engine, so a broken rail or tensioner can let the chain jump and the valves hit the pistons.
Injectors & prechambers wear
High mileage • High- Symptoms
- Hard starting in the cold, white or blue smoke, knocking diesel running, reduced power and higher consumption. Weeping injector bores (black soot deposits around the injector).
- Cause
- The injector nozzles wear and lose their spray pattern, and the prechambers (the combustion chambers in the cylinder head) develop cracks or burn damage over time. Neglected service and poor fuel quality speed up the wear.
Crankcase breather freezes (cold climate)
Cold winter climate • High- Symptoms
- High oil consumption, rough idle, oil mist in the intake, and in the worst case oil seals pushed out by pressure build-up in the crankcase.
- Cause
- The oil separator and crankcase breather can freeze up in a cold climate, building pressure in the crankcase. Very relevant in cold-climate markets. We clean and replace breather parts and check the hose routing.
Oil leaks (valve cover & oil filter housing)
Common • Medium- Symptoms
- Oil on the manifold side, oil smell, drips under the engine. Oil around the oil filter housing and the rear crankshaft seal.
- Cause
- Aged gaskets in the valve cover and oil filter housing. Common and not serious in itself, but oil on hot exhaust parts is a fire risk and should be addressed.
Turbo wear (turbo variants)
Turbo models • Medium- Symptoms
- Blue smoke, whistling, oil leaks in the charge air system, reduced boost and power loss. Axial play in the turbine shaft.
- Cause
- The turbocharger (on 606.961/.962/.964) wears in its bearings and shaft seals after high mileage, often accelerated by neglected oil changes or shutting the engine down hot. Reconditioned or replaced.
Big-end and main bearing wear
High mileage • Critical- Symptoms
- A knocking noise from the lower engine under load, low oil pressure, metal shavings at oil changes.
- Cause
- Worn bearing shells after very high mileage, oil starvation or neglected oil maintenance. Requires crankshaft grinding and new bearings. The bottom end is robust but not indestructible.
OM606 rebuild prices
Prices based on OM606 specifications: 6-cylinder inline diesel, 87 mm bore, 24 valves, 7 main bearings + 6 big-end bearings. We do cylinder boring, crankshaft grinding and cylinder head resurfacing with our own machine shop. All prices exclude VAT and parts.
Cylinder head reconditioning
Bottom end
Full rebuild
Performance
Cylinder machining (6 cyl, 87 mm bore)
| Service | Price |
|---|---|
| Cylinder boring 6 cyl inline block (87 mm) | 4 977 kr |
| Plateau honing 6 cyl | 1 450 kr |
| Stress boring 6 cyl | 5 980 kr |
| O-ringing block 6 cyl (high-boost) | 3 600 kr |
| Deck resurfacing block 6 cyl | 2 700 kr |
Crankshaft work (7 mains + 6 big-ends, 12 counterweights)
| Service | Price |
|---|---|
| Crankshaft grinding (7 mains + 6 rods) | 5 000 kr |
| Polishing standard | 1 022 kr |
| Cleaning 6-cyl crankshaft | 920 kr |
| Straightening (large) | 1 400 kr |
| Camshaft journal grinding 14 (DOHC) | 4 312 kr |
| Remove/refit counterweights 12 | 3 066 kr |
Valve reconditioning (24 valves)
| Service | Price |
|---|---|
| Cutting 24 valve seats (standard) | 2 730 kr |
| Cutting 24 valve seats (large) | 4 158 kr |
| Valve guide replacement 24 (light alloy) | 3 822 kr |
| Manufacturing valve seat rings 24 | 4 620 kr |
| Bronze sleeves fitting 24 | 3 402 kr |
Resurfacing diesel (I6, large cylinder head size)
| Service | Price |
|---|---|
| Cylinder head resurfacing 6 cyl (standard) | 1 800 kr |
| Cylinder head resurfacing 6 cyl (large) | 2 100 kr |
| Block resurfacing 6 cyl (standard) | 2 400 kr |
| Block resurfacing 6 cyl (large) | 2 700 kr |
| Resurfacing manifold 6 cyl | 3 800 kr |
Connecting rod work (6)
| Service | Price |
|---|---|
| Small-end bushing replacement 6 (Ø22 mm piston pin) | 3 360 kr |
| Manufacturing small-end bushings 6 | 4 347 kr |
| Length adjustment connecting rod 6 | 4 347 kr |
| Press-fit piston replacement 6 | 2 373 kr |
| Piston ring replacement 6 | 1 659 kr |
| Big-end resizing 6 | 3 528 kr |
| Inspection/straightening connecting rod 6 | 2 121 kr |
| Full reconditioning connecting rod 6 | 4 746 kr |
| Shot peening connecting rods 6 | 3 402 kr |
Pressure testing & balancing
| Service | Price |
|---|---|
| Cylinder head pressure testing 6 cyl (small) | 2 814 kr |
| Cylinder head pressure testing 6 cyl (large) | 4 200 kr |
| Pressure testing cylinder block | 1 400 kr /h |
| Rotating assembly balancing inline 6 cyl | 5 100 kr |
| Weight matching connecting rods 6 | 1 974 kr |
| Weight matching pistons 6 | 1 638 kr |
| Flywheel balancing | 2 100 kr |
| Balancing flywheel + clutch | 2 842 kr |
Indicative prices for the OM606 configuration (6-cylinder inline diesel, 87 mm bore, 24 valves, alloy cylinder head with prechambers, cast iron block). Diesels normally need the cylinder head resurfaced during a rebuild. Labour prices exclude VAT and parts (piston rings, bearings, gaskets, stretch bolts, injectors). Request a quote for an exact price after inspection.
Tuning the OM606
The OM606 is one of the most popular diesel engines to build on. The heavy cast iron block and the robust crankshaft take a lot of boost - the big power comes through a larger turbo, intercooler and tuned injection on the turbo version.
- 1
Pump tuning, boost & flow
Adjusted injection quantity, raised boost and freer intake and exhaust give a noticeable gain on the turbo version while keeping reliability.
200-220 hk - 2
Larger turbo & intercooler
A larger turbo, a bigger intercooler, upgraded injectors and thoroughly worked injection. The stock bearings handle more boost well with the right margins and turbo work.
260-300 hk - 3
Forged internals + large turbo
Forged pistons and con-rods, ARP bolts, balancing and a larger turbo. This opens up the power window considerably for a diesel.
320-400 hk - 4
Full build
A complete bottom end, ported cylinder head, large injectors and a big turbo for track and drag. We build the whole chain in-house with performance engine building.
400+ hk
Questions & answers about the OM606
The questions we hear most often from OM606 owners.
What does it cost to rebuild a Mercedes OM606?
A cylinder head reconditioning costs about 7,500 - 10,500 SEK (labour), a complete engine reconditioning about 28,500 - 43,500 SEK. On top of that come parts (gasket, bearings, piston rings, stretch bolts, often injectors), typically 8,000 - 20,000 SEK depending on condition and variant. On a diesel the cylinder head resurfacing is normally included. We give a firm quote after inspection.
Is the Mercedes OM606 an interference engine?
Yes. The OM606 is a DOHC diesel where the piston and valve can meet. If the timing chain jumps or snaps, the valves hit the pistons, causing bent valves and often further damage. That is why the timing chain guide rails and tensioner are critical - we check and replace them during a rebuild.
What is the difference between the NA OM606 and the turbo OM606?
The naturally aspirated engine (606.910/.912, 136 hp, 210 Nm) is fitted to the W124 and W210 E300 Diesel, runs 25:1 compression and a mechanical or electronic inline injection pump. The turbo version (606.961/.962/.964, 177 hp, 330 Nm) is fitted to the W210 E300 Turbodiesel, W140 S300 TD and W463 G300 TD, runs lower compression (22:1), oil-cooled pistons and an electronic pump (EDC). The bottom end is essentially the same.
How long does a rebuilt OM606 last?
With a proper rebuild and regular maintenance: a very long time, often 500,000 km or more. The bottom end is hard-wearing. Keep an eye on the timing chain, crankcase breather and injection (injectors, pump), and the OM606 is one of the most durable diesels Mercedes ever built.
Can you tune an OM606?
Yes. The turbo version responds very well to pump tuning, raised boost and a larger turbo. On stock bearings 260-300 hp builds are common, and with forged internals 320-400 hp or more. Many use the OM606 as a base for swap and tuning builds thanks to its robust bottom end.
Why is the OM606 hard to start in the cold?
A prechamber diesel relies on preheating. Hard starting in the cold is usually down to worn glow plugs, tired injectors or worn compression. We check the glow plug system, measure the compression and test the injector spray pattern to find the cause.
Should you rebuild or replace the engine?
For the OM606: usually rebuild. A used engine has an unknown history and the same wear points (timing chain, injection, crankcase breather). A rebuilt engine has known tolerances, new wear parts and a 12-month warranty. We ship worldwide.
See also: The OM606 belongs to the Mercedes OM604/605/606 family of inline diesel fours, fives and sixes. We service Mercedes diesel engines from the classic prechamber engines to modern common rail diesels and carry out engine reconditioning on all of them.
Have an OM606 that needs looking at?
Call us directly or send in a quote request. We reply within 24 hours.