To face a headtube means to smooth away metal from the edges of the headtube. To ream a hole, means to make larger the diameter of the headtube hole through which fork's steerer tube passes through. The key here is to know what was your size headtube bore hole you had before you brought it in to the LBS.
- 1" Standard - also called ISO. 30.2mm cups
- 1" JIS - 30.0mm cups.
As you can see, the 1" JIS headset fits into headtube that is reamed with a 0.2mm smaller bore than the 1" standard headset. Stated another way, the head tube bore hole for a 1" Standard headset is 0.2mm greater than the head tube bore hole for a 1" JIS headset. Stated another way, on the headtube the JIS bore hole is a tiny bit (0.2mm) smaller than the standard bore hole.
If you know what bore hole your old mtb was reamed at before you brought it to the LBS, then you will know what the hell the bike shop did to change that bore hole.
What was the brand of the original headset you had in that old mtb? If the old headset was a 1" standard, then you know the bore hole was reamed for a 1" standard headset. It is highly likely that your old mtb
was originally reamed for a 1" standard headset, because 1" JIS headsets are not very common at all, except on some very old Japanese road bikes.
I wonder if it is possible that the bike shop mechanic could accidentally ream out your old mtb with a 1 1/8" reamer, instead of a 1" reamer? To me, this sounds like what might have occured. The difference in millimeters between a 1" reamed hole and a 1 1/8" reamed hole is 1/8" (3.175mm). You need to find some way to accurately measure the diameter of the reamed out hole in your headtube. Get to Home Depot and buy some digital calipers. It's Memorial Day today and they have some on sale. like this one.
PS- the top pic is a 1" JIS bore hole. the bottom pic is the 1" standard headset cup. See how the 1" JIS is designed to fit a 30.0mm headset, while the more common 1" standard headset is designed to fit a 30.2mm hole?