Glad to see there are still a few gentleman around this thread. Decided to mull over and design a very simple test for that contensious first bearing issue today. It had to be simple so it will get done at some point by someone.

I have struggled with the ideal of the number one rod bearing being at the end of the oiling line. At the time decided mercedes would not leave an oiling issue problem alone for a long time usually. At that time I thought the company from the engineering standpoint at least was still well run. They wanted their engines to stand up to wide open running and designed an abnormally effective oiling system to enable this.

Yet from introduction to end of production I think there where no changes implemented for this bearing feed. In Europe these engines may have been pushed substantially harder than over here. So it should have been even a worse issue over there.

I will not go into the merits or lack of them regarding applications etc. of the milli volt test. Although it should be quite adaquate for our purposes as a general indicator easily enough to utilise in this situation in my opinion.

Now anyone with a pressure gauge installed. If they temporarily install a valve anywhere between the lift pump and the injection pump. Let the car run until warmed up.

Then read the mill volts present on the first cylinders glow plug. Next read the milli volts present on the fourth fifth or six cylinders glow plug. Start closing the valve next watching the pressure drop away to say three pounds.

Read the same glow plugs milli volts again. Now if an increasing spread in milli volts has occured and by mathamatics the first cylinders actual miili volts are higher by ratio. To me it might indicate The number ones cylinder temperature has increased somewhat in relationship to the other cylinder.

Idealy the number one glow plug would be producing a higher voltage and your refference cylinder a lower or perhaps simular to the initial reading if the idle speed has crept up a little. This should only occur if the idle has not changed much between the two senarios.

This is very indicative more loading has been shifted to the number one cylinder under low base pump pressure. In my opinion if any positive indicators arise from this test I think the effort can be made to refine the proccedure further.

Even an increase of .2 milli volts or a little more in the spread is a signifigant number in my opinion. Especially if the idle has remained fairly constant between measuring attempts.

For the testers amusement you can decrease the pressure a little further I fully expect the idle quality not idle speed at idle to deteriorate from past observations. Reading the milli volts at that point as well might also reveal something.

Actually since I am a slow thinker it just occured to me that the posting gentleman with the valve on the return line is already fully equiped to preform this test. Thats if he has a digital voltmeter.Or perhaps a friend with one.

With his presently installed valve he can modify the idle pressure enough I believe to see if there is a signifigant voltage change between the number one plug and another refference plug. Although the reference plug should be further away than cylinders number 2&3.
the reasons for this I will leave alone till later. We hopefully will be able to decode his information easily enough if posted.

For his information if he is not aware of the milli volt test. With engine warmed up you set a digital volmeter to the 200 milli volt range. The vast majority of all digital meters have either a 200 or 300 milli volt range.either range is usable . Ground the negative or black probe to the cylinder head or other part of the engine. Only use some point on the engine never the negaive terminal of the battery or body for ground.

Then take the positive lead and touch a glow plug terminal. I have to hope your car has plugs that do not have squiggly wires between the glow plugs. If so the test is not practical. If the engine does not have the series plugs. Used before 1980 I believe. We are good.

On the glow plug relay is a removable harness plug. You can very easily read the voltages on that plug when you unplug it.

Let us know if you are interested in attempting this. It will start to put some things to rest I believe. As well as opening up this thread somewhat to more opinion and speculation.

You probably aleady knew all this but just in case and to perhaps save you time figuring out how to milli volt test the glow plugs.

Do I have to additionaly qualify this by stating we have never met before or corresponded to my knowledge. Certain posted results just might start people wondering.