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I was considering changing it anyway as it's the same planet X fork that featured in the news recently, with the poor guy that ended up paralysed when his snapped.
I’d send a pic to PlanetX, for their awareness. One hopes that chap’s incident was a one off, but if there’s indications of a flaw in a batch it’s best to make them aware. IIRC that guy’s bike was new, where yours clearly isn’t, so we can only speculate.
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is there a way to avoid the same thing happening in future?
Not really, that point is subject to fretting as a function of the AHeadset design and #everythingisrubber and 20000km is a pretty good run. Something with a steel steerer and carbon legs wouldn't fail the same way, but would have separated at the junction by now 😬
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It’s trash.
This is very common in even big names brand, when they still use compression ring made out of metal, which mean if the headset isn’t preloaded correctly, it can cause a wear groove.
Only recently manufacturer started to use plastic compression ring but ultimately it’s down to how the bike is set up; if you felt a slight play, don’t wait around, fix it.
Example of a fork we wrote off with confirmation from said manufacturer.
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From what you described is two thing;
Stem bolt not torqued enough causing it to move upward.
Steerer expander move when you tried to preload the headset and torque stem.
Its likely the latter, there may be a play where it feel like the brake pads is moving, turn the wheel 90 degree and rock bike back and forth with brake on while having your hand on the junction between headtube and headset, you either don’t feel any movement, or a tiny bit.
Tiny bit = not preloaded enough.
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It was torqued to 5.5nm using a Park tool. Max on stem in 6nm
They're different things. The compression plug will have is own torque setting, they usually seem to be about 8nm from memory but it's usually on there, the top cap probably has a number but it's best to just tighten it until there's no play, give everything a good push against the front brake and check for play again, tighten as necessary (check you've not run out of steerer or need extra shims somewhere) then tighten your stem bolts to 6nm if that's what they want. Tester then says to whack another little bit on the top cap for lels and it seems like a good idea to me too.
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Then go do a few endos and check for play again and get rid if so, then check the headset for play regularly, although I don't think I've so much as brushed against a bike over the last 10 years without noticing if it has headset play, lots of them do, no idea how people don't notice it when riding and especially using the front brake.
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A BSA frame with external cups comes out to something like 89.5mm total width so if your frame has internal bearings and a total width of 86.5mm, you should be able to use a GXP exogram crank or BB30 version if it has the longer axle (the one with the bearing preload adjuster) if you remove the adjuster completely and replace with one or two thin washers.
I think
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A couple of thoughts.
- We seem to be looking at a lot of low price carbon forks which are more resin than fibre, which may explain the rapid wear.
- While running with the headset preload loose will accelerate the problem, it's not necessary to run with a loose AHeadset to have the compression ring fret the steerer, because #everythingisrubber the steerer flexes under normal riding loads but the head tube flexes less, so the steerer axis local to the bearing is cyclically skewed relative to the bearing.
- I have yet to be convinced that replacing the aluminium compression ring with plastic is actually a solution, we have covered soft bushings wearing through hard shafts before.
- We seem to be looking at a lot of low price carbon forks which are more resin than fibre, which may explain the rapid wear.
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Example of a fork we wrote off with confirmation from said manufacturer.
Did you find any dust around the groove? Because we could be looking at two separate phenomena here - on the one hand there's fretting, where we get abrasion from tiny amounts of relative movement repeated many times, and on the other, there's the fact that carbon/epoxy can get smooshed when it's under constant pressure for a long time. I remember taking some bars from a stem, and it was narrower under the clamp area, with a very noticeable bulge around a mm high or more, where it was against the ~15mm hole in the stem side of the clamp. Even steel can creep like this over time, in applications where there's a great deal more force happening.
Although the bulge was odd... As if the bars were pressurised! Can't quite get my head around that
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Mechanics and Fixing Any Questions Answered
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Sadly its all going the other way at the moment..
Thanks for the advice, is there a way to avoid the same thing happening in future? Maybe I've been a little heavy handed with the headset top bolt in the past which could have contributed.
I was considering changing it anyway as it's the same planet X fork that featured in the news recently, with the poor guy that ended up paralysed when his snapped.