Anyone who knows WHY didi Gaggia do this?

My understanding is that Gaggia have configured the Classic at 12 bar so that it works with pre-ground coffee in the pressurised baskets. When grinding your own coffee from beans then adjusting the OPV to 9 bar may produce better results (particularly when using a naked/bottomless portafilter - less channelling etc.).

There are various posts in the forum about adjusting the OPV, the exact method varies depending on the version of Classic - yours may only require an Allen key, other versions require a different spring. Without a gauge you're just guessing - there's a thread in the forum where you can "borrow" a gauge that you fit to your own portafilter (and then send on to the next person), or buy your own gauge, or buy a gauge and portafilter (about £30).

 

If it of any help, I also have a Romanian manufactured Classic (45/2013). When I tested the pre-set pressure using a gauge attached to a portafilter, it was slightly over 14 bar and I had to adjust the OPV by way of an Allen key approximately one full turn anticlockwise to get to 10 bar static, the 'recommended' setting (started by adjusting a three-quarter turn which gave about 11 bar from memory. This would seem to suggest each quarter turn is approximately a 1 bar change).

 

If you have a vernier gauge undo the top bolt on the OPV using a 17mm socket wrench.

Then measure the gap between the top of the OPV to the top of the hex head adjustment screw.

This needs to be 11.5mm to achieve 10 bar pressure.

You will need to undo (anti clockwise) the adjustment screw using a long arm 5mm hex key wrench until it reads 11.5mm on the vernier's depth gauge.

This will give you a very close pressure to 10 bar but may need another slight adjustment after testing. (You need to replace the top bolt before pressure testing!)

With the pressure at 10 bar using a blind basket, the actual pressure at the portafilter drops to 9.5 bar without the blind basket in place and coffee in the basket.

If you want to set the pressure at 9 bar, you will have to set the pressure to 9.5 bar with the blind basket in position.

If the adjustment screw will not turn, do not round off the hexagon on the adjustment screw, otherwise you are virtually looking at a new replacement OPV.

In the case of the hex head screw will not budge (and before you round the hexagon off!) you would need to completely remove the OPV from the machine, and try various documented methods of unscrewing the 5mm hex head screw on your work bench.

 

Thank you very much, I have bought a gauge which fits my bottomless portafilter and will sort it out within the next week or so. Thanks a lot all !!