I got my 9 year old son an older Intense JR for his Bday We finally got out to ride it today and no matter how tight I got the head set and stem the bars would still move on the stem.
I took it apart and the headset seems too big for the stem of the forks. As in the pinch bolts will never be able to tighten enough. Is it possible that the fork stem is too small for the headset or is it one size fits all and I'm just missing something? I have attached a pic for reference. Any help is appreciated.

In which order are you tightening the bolts? Always loosen/open the pinch bolts on the side first so the handle bars can turn without the wheel moving, tighten the top bolt down so theres no play, then tighten the pinch bolts.

measure the steerer tube, please... is it 1 1/8", or 1"?

both sizes are available in an unthreaded style.... looks like either the tube is 1" diameter, or the clamp is 1 1/4" I.D.

is the fork firmly seated at the top bearing?

whatever the case, over-tightening the clamp screws will only possibly damage the stem.... which would be dangerous, eh?

I'm guessing a shim was used that is no longer there. Either pirated for another bike or lost and prior owner just tried to cinch it down. I've never used a shim, but a lot of people have no problem with them.

John

Steer tube is 1" and the clamp measures about 1 1/8 with the bolts tight. So it looks like they are not matched correctly. Short term I'll try a homemade shim unless there is another short term option?

Ive tried both ways.

Yep, 1" steerer with 1 1/8" stem. You just need something 1/16" thick to fashion a shim. Copper, brass, even styrene or ABS would work, just not last as long.

For a stem to steering tube, I'd either buy a 1" stem or if you want, a specific steering tube shim for it from a bike shop. Even though a lot of people have no issues, I've never been a fan of erector set fixes, especially a home made one for a 9 year old son where failure impacts being able to steer or stop (not stem related). Two pretty important areas for me.

John

get the correct shim, or a correct stem...