Have I just trashed my steerer tube?

[Bodhbh]

Hrmm, the problem with doing bike mechanics on a nice sunny day with a few beers in hand is the enthusiasm sometimes gets the better of you...

The steering was either loose or sticking on my Roadrat with no happy medium. After fiddling around a bit, I noticed a horizontal gouge in the aluminium sleeve just above the crown race where metal had been rubbing against metal. So, I figure if I gouged out some more with the back of a file, there'd be no metal left to rub anymore and problem solved. See picture..

It did solve it. However it didn't occur to me at the time, maybe it would effect the structural integrity of the thing, or that I should maybe have diagnosed why the metal was rubbing in the first place.

So have I just gone and borked my forks? Or doesn't it really matter as long as I don't file down into the underlying steel (I assume it's under there?) For what it's worth, they're Kinesis DC19s.

 

[GrasB]

What you now nee to work out is how far down the main steerer tube actually goes. Most of the time the tube goes all the way to the base of the crown. This means you're okay. However some forks have the steer tube end quite high up & in that case you may have compromised the forks.

PS. the forks must be HUGE considering you propped them up on a house

 

[accountantpete]

Yes - unfortunately you have trashed your forks.

Manufacturers do build in a wide margin of safety but when the forks are compromised as much as that you would be insane to let your safety depend on it.

 

[Bodhbh]

What you now nee to work out is how far down the main steerer tube actually goes. Most of the time the tube goes all the way to the base of the crown. This means you're okay. However some forks have the steer tube end quite high up & in that case you may have compromised the forks.

PS. the forks must be HUGE considering you propped them up on a house

Ha - there wasn't the space to crop it out!

I had a look down the tube, it all seems one piece with the crown.

The contact the steerer was making was with the inside of the bottom headset cup. The steerer tube is straight, so not sure why it would do that. I put in a different set of sorks with the same crown race in the frame and they had no problem - just the DC19s that seemed to be doing it. Hence my 'brainwave' they were too wide and needed 'trimming'.

Yes - unfortunately you have trashed your forks.

Manufacturers do build in a wide margin of safety but when the forks are compromised as much as that you would be insane to let your safety depend on it.

I am in agreement really.

 

[GrasB]

Okay I've just cut through the crown of my wrecked DC19 forks. At that point you 8mm of metal in the tube wall. Basically the steerer tube at that point steps in & sits on top & inside the crown. The crown has apron 4mm of wall depth & the steerer tube the same. There is only a small amount of resin near the top of the joint, this seems to be more to fill in the space between the crown & the steerer where they don't quite meet at the top. The main joint is actually down in the crown of the forks. I've managed to bend the steerer tube trying to pull it away from the crown.

 

[Bodhbh]

Okay I've just cut through the crown of my wrecked DC19 forks. At that point you 8mm of metal.

Cheers for that. I've just been inspecting the inside of the steerer tube again. The inside diameter of the steerer from the bottom to about about an inch above the crown race is more or less a cm (which agrees with your wall 8mm thickness). So there's plenty of metal there. Hrmm.

 

[GrasB]

I cut away the mangled part & cleaned the cuts up a bit with a grinder. It's cooled down enough to touch & we have photos (let me know if they need more work to see details):

 

[Bodhbh]

GrasB, that's perfect - thanks for that ! I'm inclined to think they'll be okay. I couldn't have used them without filling that metal away - and I did do it iteratively - it took a several passes before enough metal was removed that it didn't make contact. The photo also looks worst then they are 'in person'.

 

[accountantpete]

GrasB, that's perfect - thanks for that ! I'm inclined to think they'll be okay. I couldn't have used them without filling that metal away - and I did do it iteratively - it took a several passes before enough metal was removed that it didn't make contact. The photo also looks worst then they are 'in person'.

If you have the same design fork then there's plenty of metal left to play with so you should be ok - phew!.

What had worn the sleeve part down anyway?

 

[GrasB]

If you have the same design fork then there's plenty of metal left to play with so you should be ok - phew!.

What had worn the sleeve part down anyway?

They're both DC19 forks so I'd expect them to be the same. From experience aluminium crown forks & steerer come in 2 varies - heavy & ludicrously over engineered (as per DC19) or light & susceptible to damage. The lighter ones are basically thin walled tubes using some kind of resin similar to epoxy, heaver ones are interference fit with some kind of resin which doesn't seem to have much bonding strength. It wouldn't surprise me if the DC19 steerer tube is spin welded onto the crown, there's a square key at the bottom of the crown which would be perfect for spinning the crown onto the steerer tube.

 

[Bodhbh]

If you have the same design fork then there's plenty of metal left to play with so you should be ok - phew!.

What had worn the sleeve part down anyway?

It was making contact with the inside of the bottom headtube race, where it fits in the headtube. I had a feel up there and found where it was roughed up and making contact. I wonder whether when facing the forks that sleeve part gets removed anyhow, as my other forks don't have it

tbh it was a bit of a deathtrap, loose one minute and siezing up the next. Thanks again for taking the trouble to hack up those forks Grasb, you helped towards saving me a few bob!

It's not quite finished but might post some photos of the build tomorrow.

 

[02GF74]

I am puzzled by this - wouldn't the solution be to fit headset that will not interfere with the forks? ... and I am not following on what is going on with the fork - is there some sleeve fitted to the bottom of the fork?

Anyways, looking at the thickness, it looks like the "modification" would not have affected the integrity of the fork.

 

[Bodhbh]

I am puzzled by this - wouldn't the solution be to fit headset that will not interfere with the forks? ... and I am not following on what is going on with the fork - is there some sleeve fitted to the bottom of the fork?

Anyways, looking at the thickness, it looks like the "modification" would not have affected the integrity of the fork.

If I knew what headset gets on with the DC19s I'd have bought it, but as far as I knew it was a regular pair of 1 1/8 inch threadless forks and I faced the crown and stuck on the race and was ready to go. There is no seperate sleeve as such, just the word that best describes the marginally wider section above the race (the bare aluminium bit in the photo that I've hacked into).

Like I say, I am guessing there's some facing tool maybe to trim off all that excess metal, but I really don't know. The headset is a Cane Creeek S3 from memory and should be fine with any 1 1/18 threadless forks.