Problems with threaded, knurled headset

Hi all - I have a threaded headset with a knurled top race and then two locknuts above it. There's a keyed canti hanger between the locknuts. When I grab the front brake and rock the bike forwards and back, I can feel the fork shifting slightly in the headset.

If I loosen the locknuts and tighten the top race by hand, the fork no longer rocks back and forth. If I then snug the bottom locknut up to the race and tighten the top locknut onto it, using a pair of c-wrenches, the play seems to creep back into the system. It's as if by tightening the locknuts the top race is being moved out of alignment or is otherwise deforming itself.

Has anyone else had this problem? Am I doing something wrong, or is the headset just not working properly? Thanks in advance!

1 Attachment

Turn the wheel and rock the bike again, is the play still there? If it's not, the issue isn't with the headset

Thanks for the tip. The play is still there if I turn the bars through 90 degrees and do the same test, which I think rules out any play in the brake. The wheel bearings also seem to be solid. Is there anything else it could be other than the headset?

I’ve had something similar on a bike and it was the threads in the nut being worn. I think it was cross threaded at some stage and threads got chewed up and therefore left little thread behind for there to be any grip. It’s like it would jump out of the threads. Fixed with a known good lock nut.

Ah, that's interesting. The canti hanger is taller than the washer that was originally on there, and maybe that means the top nut has fewer threads to grab onto. I'll try swapping it out for a thinner steel hanger.

Thanks!

Don't think you need both of those locknuts? Maybe add a spacer and just use the one above the hanger. I also find you need to "over tighten" the headset slightly before you nip up the locknut to get the preload just right.

Huh! That's another interesting idea. The locknuts do both look like they belong with the headset, but it may be that someone before me has frankesteined it together.

I'll try overtightening the top race before tightening up the locknuts to see if that works (although it's hard to get it really tight enough without being able to use a spanner). If not, I'll try dropping a locknut. Thanks!

This seems to have done the trick. I've tightened the top race a bit more than usual, and it seems to be working, even with both locknuts still in place. Fingers crossed it doesn't just loosen itself again!

One of the cups isn't loose in the frame is it? Or wrong standard as there are a few different 1" standards.

It doesn't seem to be. Or at least, overtightening the headset slightly seems to have fixed the problem, so if one of the cups is loose then I'm not seeing it. But thanks for the pointer!

From bikes that were put together from random bit, does the bottom cup in the frame fit with no play? Then the bearings (in a holder) fit the cups in the frame. Or if they are loose ball bearings that isn't the issue. Then the Crown race on the fork. Is there just one bearing surface. Trying to work out the that the bottom race is the right one. Have had issues with french frames and forks mixed with Raleigh proprietary stuff.

Also over greasing means needs a little adjustment later. Worn threads could be an issue so maybe a light thread locker would help keep things in place

Thanks for the tips. Making sure everything is nice and tight (but not, I hope, too tight) seems to have solved the problem.