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FCP Euro Service Kits

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Mercedes 450SL Valve Adjustment


Have an hour to spare this weekend? Then check your valve clearances. Yes, it seems ever so complicated and something that can only be done by a highly skilled professional, but that is just not the case.

As it pertains to many classic diesel or gasoline Mercedes-Benz, the job is very straight forward. From what I understand the last year the 450SL needed feeler gauge type adjustment was 1975 as the 1976 received hydraulic lifters. Regardless, if you are working with a pre-hydraulic lifter Mercedes, it’s time to check out your clearances.

Before we launch into this topic, I have been quite amazed on the many and various opinions on how this job is to be done. As I have mentioned in previous articles, there is no secret to working on cars, the answers are all in the manufactures shop manual, leaving no guess work.

While I will agree photos and real-life demos are very helpful, all specs must follow factory directions.

It is important to begin by cautioning that in this particular case and contrary to opinion, you MUST have the proper Mercedes valve adjusting tool to do this job properly.

I have heard and read quite a few who suggest using a 17mm crowfoot with extension will do the job just fine, but that is just not a wise move. When it appears the Mercedes, or Hazet tool is labeled “17mm” it is not. When putting a high quality micrometer to a high quality 17mm crowfoot and the valve adjusting tool, you will note the following significant difference. The Hazet valve adjustment tool measures 16.71mm, while a standard 17mm crowfoot measures 17.11mm leaving a difference of .40mm difference. The Hazet tool is also designed with a lip to keep the wrench properly seated while turning—a big help.

We are also faced with another dilemma. By using the wrong tool with a loose tolerance of 40mm, you will more than likely slip off and successfully round out at least two corners of your adjusting nut. Why? The valve adjuster ball stud is quite difficult to turn, which is the final reason to have the proper tool. If indeed these studs were easy to turn, the proper tool would more than likely not be necessary. Notice the driver size, 1/2 in. and just the right size for an 18in. breaker bar. Yes, that is correct, you will more than likely need a breaker bar to adjust these valve adjusting studs. However, should the studs move easily, you will need to change out the appropriate shims (I will not be covering this process). If you do settle for a loose stud, it will not hold to the setting for long, allowing the valve to either tighten or loosen.

At this point we have truly gotten the most difficult part of the process behind us, well, perhaps other than locating the specified valve adjustment tool. Unfortunately, these tools are no longer manufactured and are now only available through a really good friend or on Ebay. You should be able to find a used one for about $100, but don’t choke on that, because it will run you hundreds more to have someone do the job for you. It is also worth having the tool if you plan on keeping your ’72-’75 350-450SL. Mercedes recommends doing a valve check and adjustment every 10,000-12,000 miles.

Now the truly easy part, prepping for the adjustment. You will need to remove the fan, shroud, and upper radiator hose. NOTE: Be sure to replace any lost coolant when reassembling the system. The air cleaner and valve covers will also need to be removed. This is also a good time to see if you need to replace your air filter, valve cover gaskets or the leaky oil filler cap gasket while you are at it.

Next, prepare to turn the engine clockwise (only) by way of the crankshaft hex nut. An 18 in. breaker bar, 6 in. extension and socket will be needed to do this.

With that in place, turn engine so that one of the 16 cam lobes is pointing vertically as shown in the image from Mercedes below.

The following image from Mercedes shows the valve order for exhaust and intake

Now that the first lobe is in position, a feeler gauge will be used to measure the distance between the lobe and the rocker arm as shown. It is important to note that the valves are to be checked with a cold engine and must measure at: 0.08mm for intake and 0.20mm for exhaust. The feeler gauge should have a slight drag when passed back and forth. If the gauge is free of resistance, the stud is to be tightened and vice versa if it is difficult or impossible to pass the gauge between the lobe and the rocker. To loosen rotate nut to the right and to tighten to the left. Be sure to mark each valve that you have checked and/or set.

The following two images below show the valve adjusting tool seated on the adjusting nut.

The following image shows the Hazet tool with an extension and breaker bar. The extension is not necessary, but it does make it easier to maneuver. NOTE: It is not possible to use an extension when working on the valves for cylinder No. 8.

Continue to turn the engine clockwise until you have carefully checked each valve for proper clearance. Remember to pass the gauge through several times to be certain you have the correct reading. This process is well worth the time as you will be rewarded with a better performing engine when done precisely.

When you have checked your last valve, be sure to remove any markers and return the valve covers. Be sure not to over tighten the valve cover bolts. Mercedes specifies 26 inch lbs. of torque for both valve covers.

When all is back in place start the car and take a good listen as the car warms up, making sure there are no unusual sounds from the valve train. If all checks out, you are good to go for another 10,000 miles.

 

Possible Parts Needed

  • Valve Adjusting Shims
  • Valve Adjusting Ball Stud
  • 2 Valve Cover Gaskets

 

Shop Mercedes Benz Parts Online Catalog Lifetime Warranty

 


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Written by :
Alex Fiehl


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