I’ve had two friends struggle to get their Shoei pinlock anti-fog visors to fit properly. When they don’t fit snugly they can be dangerous as they’ll trap moisture droplets or just condensation between the layers and it’s almost impossible to get it to clear when that happens and you’re on a ride. The following method might provide some helpful insight:
The posts which hold the pinlock in place are an eccentric cam. They have a little arrow marker on them which you’d need glasses or a magnifying glass to see. They also have a hex head on them to allow you to gently turn them as needed.
There’s a trick of flattening out the curve of your visor to fit the pinlock – it’s a really helpful tip – I use that method to ease the fitting of the pinlock; I’ll hook one side onto the cam, and with a tea towel on the kitchen bench, place the visor onto the towel, then use my forearm to hold the side which I’ve already fitted downwards, while using two hands on the other end of the visor to manipulate the other end into the other cam. I push down on the visor with my forearm and with my hand on the other end to open it out. – It’s surprising how open you can make it without threatening the structure of the visor. I’m not suggesting it goes completely flat, but it does open up significantly, which makes getting the pinlock into place initially, much easier.
You’d normally mount the new pinlock with the cams in the most relaxed (non-compressive) orientation. Once fitted, you’d try to evenly rotate the cams, while flattening your visor to remove compressive forces and to allow easier rotation of the cam; then allow your visor to return to its normal bent shape, this then further compresses the pinlock against the inner face of the visor – that’s how you get it to fit snugly.