As many of you know, there are two types of turbos on the 617 engine. The KKK turbo has an externally adjustable wastegate and the Garret/Air-Research turbos have an adjustment that is concealed under the cover.

Since the KKK turbo is easy to adjust, this post will detail the correct adjustment of the Garret/Air Research style wastegates.

Prior to this modification, you need to check your boost pressure in accordance with Mercedes-Benz service recommendations. You should also ensure your engine is mechanically sound and the turbocharger is free of any defects.

Keep in mind that you should never exceed the boost pressure specification for your particular engine.

Record the amount of boost pressure and compare it to the manufacturers specification. The difference is the amount of boost pressure you will need to dial in.

Now, on to the removal of the diaphragm cover and subsequent adjustment.

The cover is retained by a flat, circular snap ring that is easily removed with a pocket screwdriver. The ends of the ring have a small cutout that can be easily pulled outward with the screwdriver. Once the end is removed, simply rotate the ring out of the groove in a circular motion.

You may find the cover is partially filled with engine oil. Don't be alarmed as this is normal on higher mileage engines. Clean the area with Brake Cleaner and blow dry with compressed air.

On top of the rubber diaphragm, you will see a threaded stem and a 8mm x 1.0 lock nut with a 13mm hex. This is where you will make your boost adjustment.

The threaded stem is actually the wastegate valve stem. If you look closely, the stem is hollow. This serves as a pressure bleed and prevents 100% of the boost pressure from acting on the diaprhragm. Shoot a little spray cleaner into this opening. If it is clear, the fluid should run out the rectangular opening in the side of the diaphragm housing.

You will need a very thin 14mm end wrench to grip the flat areas on the metal portion of the diaphragm piston. You can purchase a special wrench from Snap-On, or grind one down to meet the needs of this service procedure.


Once you have gripped the diaphragm piston, loosen the 13mm lock nut and remove it from the wastegate valve stem.

Now, you will need a machinist's ruler to measure the amount of threads above the diaphragm piston. These are the little steel rulers, approximately 6" in length, available from all tool suppliers and many auto parts stores.

The stock setting for the wastegate will be approximately 7mm (.275") of exposed threads above the top of the diaphragm piston.

The threaded stem of the wastegate valve is 8mm x 1.00 pitch. This means each full turn of the diaphragm piston will expose another 1mm of threads.

With a popsicle stick (or suitable non-metal tool) gently pry the rubber diaphragm away from the housing in a circular motion.

Now, with the thin 14mm wrench, turn the piston clockwise (CW) the approximate number of turns required to reach the desired boost pressure.

Each full turn of the piston will result in 1.0mm of travel and an increase in boost pressure of about 1.0 psi.

Each 3.0mm of piston rotation (CW) will yield approximately 0.15 to 0.20 BAR of boost pressure or roughly 2.25 to 2.94 psi.

If you have the turbo apart and would like to test wastegate function on the bench, you may elect to use the following procedure.

You will need to remove the 4-bolt cover over the back of the wastegate valve and have the 8mm x 1.00 lock nut removed from the valve stem. The cover will need to be replaced so you can use shop air pressure on the diaphragm to simulate boost pressure.

The steel shim gasket is available from most turbo repair shops, such as Turbo City in Orange, California. However, it can be reused if it is not broken.

Take the Acetylene Gauge (0 to 30 psi) from a common set of welding regulators and attach it to a paint gun air pressure regulator with a common 1/8" Male Pipe to 1/4" Female Pipe Reducer Bushing.

Now, apply regulated air pressure to the (assembled) diaphragm housing and record the pressure reading when the wastegate valve begins to move off of its seat.

Correct adjustment (stock setting) will be acheived when the valve is fully closed at .69 BAR (10 psi) yet begins to open at around .70 to .78 BAR or roughly 10.3 to 11.2 psi.

The valve should be approximately 13.0 to 14.0mm (.500" to .550") off its seat at 1.0 BAR (14.7 psi) of boost pressure.

Keep in mind, this will approxiamte the factory setting and I recommend you always measure boost pressure and threads above the diaphragm piston before making any modifications.

Due to the different skill levels of the automotive hobbyist, I can assume no liability for damage and/or injury for misuse/misinterpretation of this service data.

I hope this information is helpful. Best of luck on your projects...Bert