engine block bolt hole behind water pump

[Jacks1965230sl]

Hello, I took out my water pump on my 1965 230sl last week as I needed to replace the thermostat housing.  While putting the long style water pump back, I noticed a bolt hole insert located on the engine block behind the water pump housing which I have no idea if it needed a bolt installed.  I don't recall taking a bolt out of it, so am confused as to it's purpose.  Any ideas?

[Jacks1965230sl]

Photo added of the hole.  What is this for?  Does it need to be plugged with a bolt?

[clunker]

Which of the bolts A-D behind the water pump are you referring to? (see attached image I got off the forum some years back.)

I recall a similar mystery empty bolt hole on my M130 at hole D when I took out the elephantine AC bracket a while back. The AC bracket (M-B installed at delivery) used hole B (among others) that may have needed a bolt to seal it when removed. Hole D was unused (I believe) and may not have needed sealing. I did put in short blank M10 bolts to seal them, just to be sure.

**Note that hole D is close to the sweep of the crank balancer so the smaller the bolt head size you use the better - check for interference.

[Jacks1965230sl]

The silver hole above “C” is my question.  Does anything attach to it or does it take a bolt to plug it?   Thx

[clunker]

Ah, sorry our posts crossed - not sure about that hole, but since it behind the water pump mount one might assume it would not accept a bolt (as not a bolt through the pump mount) and left as is. But others here will be much more familiar.

[dirkbalter]

The silver hole above “C” is my question.  Does anything attach to it or does it take a bolt to plug it?   Thx

I had the same question when re-assembling the auxiliary parts on my engine. Metric told me that these are timing chain rail pins and that I don't have to be concerned with them. They are only threaded for the purpose of removal and installation of them.

[Jacks1965230sl]

All you guys are very knowledgeable, super helpful, and just awesome!  Thank you all who responded for bringing peace to my mind.