hey everyone. i've got a bike with regular 1 inch threaded fork, but recently switched to 1-1/8th using a stem adapter. now, being that there's no top cap or star nut, it's just the stem gripping the adapter's neck, it tends to slip fairly easily.

anybody have any solutions for me here?

the only thing i can think of is taking some gritty sandpaper to the adapter and the stem to maybe rough up the surface and offer it some friction but i'd rather not.

Some Ive seen are knurled rather than smooth .. you sure the quill isn't slipping in the fork,
instead of the stem grip around the adapter

There should be some rotational slipping.. keeps from breaking so much
when the bike falls over..

yea it's definitely the stem on the adapter that's slipping.
i'm all for a little give but this thing slides as if it's been greased. like, i'll start pulling to go up a hill and by the time i'm at the top the bars are twisted a few inches to the side.

How about some fiber grip (the stuff used for CF seat posts and stems)? Might give enough grip without any damage.

Loctite .. make a shim , such as cut from a drink can, perhaps?
or how about the old standby duct-tape?

the star nut does not provide any gripping force to the stem...something else is wrong. I tried one of those adapters once, it was a piece of garbage. might not be the same one you have, though. is the wedge aluminum? if so, that might be the problem... you might think it's slipping on the 1 1/8 part, but it's really the quill part that's tuning.

regardless, the star nut won't make a difference.

Star nuts go inside steel threadless forks , to have something for the screw thru the top cap to pull against.

seek out one of these : https://www.bbbparts.com/headparts_bhp20.php

You have to find a shop, with the distributor's account , in the US distributor is Bike Mine.

I got mine from R&E in Seattle

Try a better adapter that absolutely will not slip.

Velo Orange stem adapter - silver https://www.velo-orange.com/vothstad.html
Dimension stem adapter - black https://www.treefortbikes.com/product...22361381___314

Or get a nice Nitto knurled surface one for $60. !!!! Absolutely the best quality. https://www.benscycle.net/index.php?m...43ebfafbbc3e04

Or, get some 1-1/8" shims to put under the stem..... lowest cost solution.

uh, you don't even need a starnut on a threadless headset once everything is tight... it really only helps to keep some pressure on the headset bearings while you tighten everything down. You can take it off after that, and it won't matter but will look like ass.

Only exeption is downhill or trials riders who use a bolt that goes all the way thru to the bottom of the crown.

if you can't get the adapter to work without slipping, then there is something seriously wrong with the adapter or you're doing something seriously wrong.

I have 3 different adaptors, one has a completely smooth aluminum wedge, but that didn't cause my bars to slip at all. there might be too much grease or oil being used on the quill, or you're not tightening it enough.

The starnut on a threadless fork acts as a bearing pre-load adjuster, and it does NOTHING for quill adapters.
the top cap on adapters are really only there so it won't have this big gaping hole at the top of the fork.
Threaded forks rely on the threaded portion to adjust the bearing load.

i know the quill/adapter isn't slipping because it has an inset bolt which pretty much leaves a pool to collect water and seize the bolt, so i glued a george washington dollar over it to keep the water out and his head doesn't spin when the bars do.
i've tightened the stem to neck of the adapter damn near to where i'm stripping the allen heads so i'm sure it's tight. i'm just gonna go with the explanation that it's too slick surface to surface.

i'm pretty sure it's the delta adapter, i got it for $10 when i was in a pinch out of state.

When you tighten the pinch bolts on the stem, do they go so far as to touch together? If so, you're losing clamping force and you'll have to shim it with a thin bit of aluminum from something like a soda can. If the pinch bolts are not touching, then I'd suggest picking up some medium grit sandpaper and going to town on the adapter to give your stem something to bite onto.

it's like this stem, where there's only two bolts.


sandpaper it is.

If the gap between the stem pinch bolts close up before squeezing the stem hard enough you can sand away all you like, and it still won't help. A soda can shim to increase the diameter of the stem will do wonders though.