If I were going to put a rolled pin in I would drill it all the way thru, that way you get twice the strength and then some.
If its only pinned on one side as the two surfaces try to slide against each other there is nothing holding the pin straight and it will twist and work itself loose easier. When its pinned all the way thru, the pin is held straight and will have less give if the bars are twisted hard. Its a matter of leverage being applied over about 1/8" between the two surfaces, or more than an inch, if its all the way thru and held from both sides.
Personally I would be inclined to take a step back and try to figure out why the bars wont lock down from being properly torqued on the hex bolts. If the handle bars are slightly too small in diameter and the gap on the mount is closing all the way, you cant squeeze it any tighter.
Use to run into this a lot with Stingray (hi rise) handle bars on bicycles when i was a teenager. Sometimes you had to put a shim around the handlebar to open the gap on the stem a bit more. A very thin shim, like aluminum foil, could be enough to open up the gap enough to get enough squeeze on it (at least on a bicycle).
If it was a dirt bike or an ATV, and the stem and handlebars were clean steel (not chromed)... I might be temped to braze it in place If I was having a problem with it coming loose.
The comment was really more to point out that once you pin it in place, its there forever (no way to adjust it again), so its permanent as if it were welded in one position.
EDIT: one more thing: If you are going to drill the mount and handlebars to put a pin in, you need to take them off the bike and secure them in a vise in a quality drill press or mill. If you do it with a hand drill, and drill it all the way thru, the top hole will be washed out and sloppy, and the rolled pin will never seat in tight and snug.
Last edited by KCW; 11-30-2018 at 10:21 AM.