Seeing as there are quite a few On one owners here, are you having any problems with on-one stems coming loose causing the headset to slacken. Are the bolts soft causing stretching? It’s driving me mad stopping every 5 miles or so to tighten up the stem. Any obvious solutions other than throwing in bin and buying an Easton.

throw in bin and buy a thomson. 🙂

do you tighten the bolts alternately a bit at a time increasing the torque in stages?

if not then any dual bolt clamp is going to progressively undo, such as HTII crank bolts.

No, sounds odd. Are you sure there’s not something dodgy with the headset? If the stem is coming loose you will be able to turn the bars while the wheel stays still. I’d avoid riding it until you fix the problem sounds like an accident waiting to happen.

The stem coming loose wouldnt make the headset come loose You could have the stem so loose it spun round on the steerer but your headset would be fine. It could be you Star nut is slipping or your headset is knackered.

The headest would still stay put, unless the stem was loose though

Once the stem is tightned the starnut is surplus to requirements. It is only used for preload. After that its the stems clamping force ont he steerer that maintains headset compression.

Star nut is lightly nipped to apply preload, the stem is tightened and there is no play in headset and everything is fine for a we bit. Then a slight knocking in headset area can be felt. Stem appears tight but there is play in headset. Steering is fine, apart from knocking in headset. It has to be the stem loosing some of its tension allowing play in headset. That is why I think its the bolts. Have stripped everything down, headset appears fine. It looks like a good quality stem, Its light and well finished and was a reasonable price. If it can’t maintain the tension around the steerer then it has design issues and is no good. Stem bolts were tightened gradually etc. Has any body had this problem and diagnosed this fault?

when the headset has become loose can you rotate the stem on the steerer?
Are the stem bolts loose when you go to retighten them?

if not Id be inclined to say there is nothing wrong with the stem or stem bolt forces (yours is the first mention of such a problem) and you arent pre loading the headset correctly?

do you have sufficient clearance between the steerer top and the top cap for the stem cap bolt to do it’s job?

Check the steerer is not pulling up out of the forks. Long shot tho.

Stoner.
Take your top cap bolt out and ride around without it. For say 5 miles. Headset will loosen as steerer creeps. Poss not on niche forks though I guess.

Brant – I have run bikes for months with no top cap. Doesn’t work lose

You can run a top cap bolt backed off from preload tension though cant you?

However, in the name of science I shall do just that Brant 🙂

Really? My experience varies. Perhaps you chaps are more manly and tighten stem bolts up more.

Can’t rotate stem on steerer and the stem bolts are not loose. There is plenty of clearance between the top washer and the top of the steerer. I am tending to think that the stem is creeping up on the steerer causing the headset to slacken. The steerer is alloy not steel. Its a marzocchi mx pro ETA. It has a slightly rough finish like its been sand blasted so there should be plenty of grip for the Stem.

Well you seem to have convinced yourself it’s the stem, so for the pennies involved Id recommend getting a replacement and seeing if the problem persists. It doesnt matter if we convince you that it might not be, you’ll always doubt it 🙂

Brant – motorcycle fork legs and some MTB ones are clamped in the yokes in that manner. If the clamp on the stem is creeping there is something badly wrong.

Buy a new bike 😉

No not at all, I’m open to all suggestions etc, I don’t want to buy another stem if I don’t have to. The stem holds the pre-load on the headset bearing, not the top bolt. The headset is fine for several miles. It cant wear enough to cause play in the bearings that quickly. What I was fishing for is if anybody has had experience of this and any solutions etc. If the bolts are stretching for example I would replace the bolts with some high tensile steel ones. The bolts that are in are stainless ones I think so they are softer, so maybe more prone to stretching.

TJ – my experience is that a stem will creep up without a top cap. I wonder if it’s actually that a stem will creep up when the headset is loose when there’s not a star nut… chattering. Sort of. Will experiment 🙂

I had a set of the first ever RC30 forks (aftermarket). the steerer pulled out 5mm in one ride – exciting 🙂

Is it a 456 stem? Mine wasn’t finished too well on the inside and had a slight ridge internally around the opening. A bit of wet and dry smoothed it flat. It may be worth checking for the same as it could mean it’s not clamping as well as it should.

brant, if a stem ‘creeped’ then how exactly would it stay straight inline with the forks? you cant believe that a stem wouldnt twist if it was slack enough to creep up.

Also, how would headset adjusters that expand between headset and stem work? (as sold by U.S.E amongst others). Not to mention weight-weenies who often remove top-caps/bolts to save weight.

Rich (ridden without headset caps for years)

Sounds like the top cap isnt being tightened. If the stem is not loose then I can’t how it would be that. Have you put another spacer in under or on top of the stem? Then tightening it all up?

Just a thought!

Pics if your stil having a problem!

disregard that last comment just read your last post that theres no top cap!

Top bolt gets a fair nip to set the preload then stem is tightened.
Yes its an On-One Stem. I will take it off and check for burs and see if I can see any distortion probs. Will take some pics. Have built several bikes never had this happen before just nipped up top bolt, tighten stem and away we go.

STATO/others. All I can say is that I’ve had negative experiences of not running top caps.

But I was postulating that perhaps a LOOSE headset when run without a top cap gets looser.

I’m not against admitting I’m wrong. Still don’t know why that stems coming loose though 🙂

I still wonder if the steerer is poulling up out of the fork? Easy enough to check. I know that the marzocchi forks I have are just an interference fit for the steerer into the crown.

I know that the marzocchi forks I have are just an interference fit for the steerer into the crown.

With a big lip on the bottom though!

How long have you had the crown race fitted on the forks? Could be that it’s settling into place. Could also be the cups settling into the headtube, or a cracked headset cup spreading slightly…

I’ve spent ages cursing a slipping starnut/stem only to find that it was the crown race.

Ah – I did wonder about that Brant. Ta

waht paule says is where I was going next, but I was assuming that this has been happening for a long time…?

speculation time:

? maybe you’ve ovalised the head tube (I assume this actually happens – I’m not core enough to have experience) or else fork bushes worn (or headset bearings ???) ?

smart scaredypants – back to the diagnosis!

indeed, is it definitely the headset?
Bushing in the forks?
Centrelock rotor rocking on it’s mounts?
Brake pads slipping everso in the caliper?

do the brake and rock test, but with the wheel truned to 90 degrees. still knocking? if not, then it’s not the headset and ergo it’s not the stem.

I did ovalise a headtube on the tandem – not quite the same symptoms as you would get a knock but no play in the headset – you could tighten the headset until it locked the wheel but it still knocked.

When the rock test is done with front brake you can see the split taper washer moving against the spacer washers above. Will investigate what paule suggests about headset cups splitting. Never thought of that. Oh by the way this fault is new and has just happened, just built the inbred up, it happened first ride. Headset is brand new FSA Pig. The Steerer is fine not pulling up, Having said that it would only take a few thou of movement to make the headset bearings go slack. I don’t think its moving.

bearings in upside down?

TJ – maybe it could act as a sort of cam/lever/thingy & allow a bit of what Brant described up above (stem creep ?)

You’re right though, I forgot to put in the important question – is there REAL slackness in the top cap when you undo the stem ?

hw can you see the split tapered ring?

Its the top edge you can see move maybe half a mm. It gets that slack that quickly especially over rocky tracks.

errr, isnt the tapered washer supposed to be below the cover and so from sight…

have you installed it correctly?

http://www.borislavdopudja.net/img/writings/xtremepro_manual_1.jpg
http://www.borislavdopudja.net/img/writings/xtremepro_manual_2.jpg