Threaded headset keeps loosening

[nikki]

I have a one of these on the adventure commuter:
https://www.sjscycles.co.uk/headsets/mpart-elite-1-inch-threaded-headset-black/

It keeps working loose though. 
(At the top race and locknut.)

I've not really done threaded headsets before - is this A Thing?
Am I really not putting enough force into tightening the locknut?

Expanding collar design means once you tighten the headset, it stays tightened

Is this a lie?
Is something else going on?

Halp!

I'm riding a lot of bridleway kind of stuff that can get a bit chonky, so it's not exactly getting an easy ride ...but also I'd really like for it to not come undone!

[Gattopardo]

Stupid question are you tightening the top nut with a spanner holding the next nut down?

[LittleWheelsandBig]

Headset spanners are 250-300mm long and the locknut and adjusting nut need to be tightened against each other quite hard. Are you doing that? ‘A loose-fitting tool can round out an aluminium locknut’ is how hard I tighten them against each other. That headset has very short spanner flats, which limits how much you can lean on the spanners.

There are a few gotchas that can result in a loosening headset e.g. locknut bottoming against the top of the fork rather than tightening against the adjusting nut, though that particular situation is unlikely with a rubber seal on the locknut. If the head tube is not faced parallel and the cups aren’t aligned, it might be impossible to stop the headset loosening.

[nikki]

Thanks.

I'm using the relevant Park Tool job and a 10" spanner.

I've had a quick look and haven't spotted anything untoward with the seating of the cups. I've also tightened it again, giving it max power.

If that doesn't hold I suppose strip it down to inspect the threads and try to see if the locknut is bottoming out.

[nobby]

FSA used to do it a top nut that had two 3mm Allen screws through the sides so that it could not loosen. It was called the Sure Lock Top Nut. There is one on eBay at the moment.

[rogerzilla]

This is generally because the head tube and crown race seat need facing.  This means removing the headset and using specialised cutting tools on the frame and fork to ensure the mating surfaces are parallel.  Any half decent bike shop can do it.  I also have the tools (I have a lot of 1" bikes) but you're nowhere near me.

[nuttycyclist]

I had this issue on a new bike some decades ago.  I'd bought it at a new bike shop near me, which didn't last long.  Can't remember why I didn't go to the decent bike shop a small distance away.

I took the bike to the decent bike shop, who were also a main dealer for the brand of bike I had.  Fault was that the shop who sold me the bike had overtightened the headset and stripped the threads on the fork.  I have a recollection that they managed to get the forks replaced under manufacturer warranty somehow.

[nikki]

FSA used to do it a top nut that had two 3mm Allen screws through the sides so that it could not loosen. It was called the Sure Lock Top Nut. There is one on eBay at the moment.

Interesting. This bike has a 1" steerer, but I'll file that away as something that might come in useful one day.

This is generally because the head tube and crown race seat need facing.  This means removing the headset and using specialised cutting tools on the frame and fork to ensure the mating surfaces are parallel.  Any half decent bike shop can do it.  I also have the tools (I have a lot of 1" bikes) but you're nowhere near me.

I've got a head tube facer if it comes to that. Things are holding up okay after today's bridleways and towpath, so hopefully not needed, but it's not a crisis if it is.

Fault was that the shop who sold me the bike had overtightened the headset and stripped the threads on the fork.

Yeah, I'm not yet ruling out me having undertightened the headset and knackered the threads. That'd be annoying!

[fruitcake]

Great that you've sorted it. I'm sure you know this already, but cleaning then greasing the threads can make it possible to get the nut a few degrees tighter, which can be just enough to make it stay tight.