Help identifying two items

[mnahon]

I'm in the process of overhauling my cooling system and tracking down a coolant leak. I've got the radiator, fan and water pump out. I'm trying to identify a couple of items.

In the first picture below, taken of the front of the engine (showing the coolant breather tube), what is the threaded hole?

In the second picture, taken of the front right side of the engine, what is the big hex nut just below the thermostat housing?

Thanks for any insight you might have...

[WRe]

Hi,
in the second picture you have the timing chain tensioner housing, see here www.sl113.org/wiki/Engine/TimingChain.
...WRe

[280SE Guy]

The threaded hole on the front of the head is for an air conditioner compressor bracket.

[Dave H]

Air con bracket like this.

[mnahon]

Thanks guys, I really appreciate the information.

Regarding the threaded hole, on a car with no aircon, should the hole be plugged, or it can be left open?

[280SE Guy]

You should be able to leave it as it is as it's a blind threaded hole.

[mnahon]

Great; thanks...