Now then,

As the title says realy; stem cap bolt has become seized in the SFN. Consequently the SFN and cap bolt just spins round in the steerer tube when you try and undo it.

At the moment i'm not sure whether its best to drill the top cap bolt out or turn the bike upside down and attempt to knock the SFN flangey bits in with a long thin metal rod.

Anyone else had this problem?

Thanks in advance

Trying to knock the SFN the wrong way can damage the steerer. I'd just take a cold chisel to the top cap and smash it.

I'm not sure if i have the skill to whack it with a chisel. It may result in me taking my fingers off.

I'd go with drilling the head off the bolt then knock it through the right way, unless you can use a screwdriver or something to wedge the threaded part of the sfn and stop it turning.

Chisel on top cap – TWWWWWAAAAAAATTTTTT
then hammer the bolt and sfn down the steerer

new one in – done

Consequently the SFN and cap bolt just spins round in the steerer tube when you try and undo it.

that sounds unlikely to me, and I suspect that the threaded part is no longer clinched to the spines of the SFN – otherwise the whole lot would just pull out if it were no longer gripping the inside of the steerer.

Chisel on top cap – TWWWWWAAAAAAATTTTTT

eeek! I'd be far more inclined to drill out the bolt!

Totally agree with RR.

Hitting the top cap with a chisel will result in it splitting with little effort. They're just thin alloy after all. It's a 5-second job. You're more likely to make a mess with a drill.

My top cap is plastic!

Surely drilling the bolt wouldn't achieve anything and the bolt would just spin in the hole? Unless you used a big drill bit to takeout the middle of the top cap too?

If you drill the bolt you'll be able to remove the top cap and then knock the SFN out.

Adam – Drill the head off the bolt then the top cap will lift off.

my top cap isn't thin alloy, and is also quite bling so I'd rather not trash it, and drilling the bolt seems to me the least destructive approach. Once the head of the bolt is off you can remove cap, stem and forks from the bike and put the fork in a vice for hammering 🙂

Surely the bolt will just spin when the drill is, err, drilling?

Something else you could try would be to loosen the stem bolts, pull down on the forks, up on the stem and try undoing the bolt at the same time.

"Surely the bolt will just spin when the drill is, err, drilling?"

The bolt spins round but its not loose enough for it to spin that freely, if ya see what i mean.

Soak with plus gas and wind the f@*ker out.