OM606 Engine Block Guide – NA vs Turbo Blocks, Oil Squirters and Main Girdles

OM606 engine block construction is better than its reputation suggests and today we cover exactly what separates NA blocks from turbo blocks, oil squirter differences and how to correctly install a main girdle.

These Engines Are Not Weak

A common claim online is that the OM606 block is too weak for serious power due to petrol-sized bearings and inadequate construction. This is wrong. CDI cranks fit the OM604 and OM605 sharing the same bearing sizes. The turbo block of the OM605 and OM606 is not weak – it is simply a smaller displacement engine than American V8 counterparts.

The OM606 is 76 centimetres long and displaces three litres. Compare that to American engines at 5.9 or 6.7 litres and yes it is a smaller engine. But smaller does not mean weaker in construction. The BMW M57 is also a three litre six cylinder and nobody calls that weak.

These are European engines built for all-motor diesel performance. Boost plus diesel fuel equals power. No nitrous, no water methanol injection, no additives. Every time you press the throttle the car goes forward. That is the design philosophy and within it these blocks are extremely strong.

NA Block vs Turbo Block – OM605 and OM606

The OM605 and OM606 turbo versions use a different block than their naturally aspirated counterparts. The turbo block has slightly stronger construction and different oil squirter specification.

The OM604 is only available as a naturally aspirated engine so it always has the NA block specification.

For the OM601, OM602 and OM603 – the older engines – NA versions do not have oil squirters. This is a significant limitation when boosting these engines. For moderate power levels of 200-250 horsepower the lack of oil squirters is manageable. For serious power builds oil squirters are an important feature to have.

If you are building a boosted OM601, OM602 or OM603 start with a turbo block from the beginning. For OM604, OM605 and OM606 you can take an NA block, source turbo specification pistons and rods from scrap engines, fit the correct turbo oil squirters and build a very capable turbo engine.

Oil Squirter Differences

OM604, OM605 and OM606 engines all have oil squirters fitted regardless of NA or turbo specification. However the squirter nozzle design differs between NA and turbo versions.

Turbo pistons have an internal cavity underneath the crown. The turbo oil squirter nozzle enters this cavity and sprays oil directly inside the piston for cooling. NA pistons do not have this cavity so the NA squirter nozzle design is different.

If building a turbo engine using an NA block order the correct turbo specification oil squirters from Mercedes. This gives your NA block turbo oil squirter capability and makes it functionally equivalent to a turbo block in this respect. The block structure itself remains slightly weaker than a turbo block but at 400 horsepower you will never notice the difference.

The 290 TDT Direct Injection Block

The 2.9 litre V-pump E-class direct injection engine has a different block construction. It can be used in stroker builds – we have used it in a 2.9 litre OM605 build – but it requires machining because the block differs in several areas from standard OM605 specification. Not impossible but not straightforward.

Main Girdles – Plate vs Billet Cap Girdle

There are two types of main girdles available for OM606 engine block reinforcement.

Sump plate girdle – a steel plate that bolts underneath the main caps providing lateral support. When installed correctly and properly torqued as a single unified assembly this does its job effectively.

Billet main cap girdle – a machined billet piece that replaces the individual main caps entirely with an integrated one-piece component. Stronger, stiffer, more precise. Also significantly more expensive.

The plate girdle works well when installed with precision. The critical factor is that all spacers between the main caps and the girdle plate must be machined to identical height. Any variation causes the girdle to apply uneven load across the main caps which distorts the block.

The correct installation process: machine all spacers simultaneously on a magnetic table to ensure they are within hundredths of a millimetre of each other. Use long studs through the main caps so the stud extends beyond the cap. Torque the main caps first, fit the spacers, fit the girdle plate and torque to the girdle specification. Everything becomes one integrated unit.

Installed incorrectly a girdle creates more problems than it solves. A 10-15mm steel plate torqued with 20 bolts that are slightly misaligned will twist the entire block. The same distortion happens when over-torquing head bolts without a stress plate during boring – torque distorts components and must be accounted for.

If your budget allows the billet main cap girdle is the superior solution. If installing a plate girdle do it with the precision it requires.

Summary

• OM606 engine block construction is not weak – these are strong European diesel engines designed for all-motor boosted performance
• OM605 and OM606 turbo blocks differ from NA blocks in construction and oil squirter specification
• OM601 OM602 OM603 NA blocks lack oil squirters – start with turbo blocks for serious boosted builds
• Oil squirters differ between NA and turbo specification – always fit turbo squirters when using turbo pistons
• Plate girdles work correctly when installed with precise spacer machining as a unified assembly
• Billet main cap girdles are superior but significantly more expensive
• Incorrect girdle installation distorts the block – precision is everything

See you in three days. Bye bye!