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Fork Steerer Alignment. Is there a simple test?

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Fork Steerer Alignment. Is there a simple test?

Old 11-19-12, 09:26 AM
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rootboy 
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Fork Steerer Alignment. Is there a simple test?

Hope someone can help me here. I just replaced the head set on a bike I acquired. Head set was and is Campagnolo Nuovo record. I made tools to press in the new cups. Went very well. However, when I installed the new crown race I notice it didn't seat all the way. There is a very small gap, maybe 1/2 mm, on one side between the crown race and fork crown. The rest of the race, about 340 degrees worth, seems to be seated tight. I'm wondering if I could have somehow, inadvertently, tweaked the steerer tube ever so slightly.

I've been looking at fork alignment jigs on Google but would hate to have to go to that extent just to check one fork. Is there a "simple" way to check that the steerer tube is properly aligned with the fork blades? Thanks.
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Old 11-19-12, 09:32 AM
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There are "facing" tools that can cut the crown race seat to assure it's square with the steerer tube and most good bike shops should have one. However, I'd assemble the complete headset and fork first and see if it rotates smoothly when properly adjusted. If it rotates with no binding or rough spots, I think i'd just ignore that tiny gap.
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Old 11-19-12, 09:51 AM
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Thanks HillRider. You know, I didn't inspect the crown race shoulder all that closely. Just cleaned it well and installed the new race. Old one set on there perfectly as I remember. I did install the fork, with caged bearing, dry, and it rotated just fine and I could see no obvious visual misalignment, but it's tough to see such things by eye. I am going to remove the crown race and try to re-seat it after turning it 90 degrees, but have to wait until a proper crown race remover arrives, which I've ordered. Thanks.
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Old 11-19-12, 11:31 AM
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Originally Posted by rootboy View Post
Old one set on there perfectly as I remember.
Did you examine it carefully before you removed the old one? It may be that it had that gap as well. The race could actually be seated very well but just looks like it is misaligned. I doubt that you could have damaged the steerer tube during removal but if you wailed on the race with a punch, who knows? Good idea to remove and inspect.
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Old 11-19-12, 12:56 PM
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Well, as far as I remember the old one was set down on there all the way around. But I could be wrong because I didn't inspect it all that carefully before I removed the old one. I didn't wail on it. I used this tool I made and pressed it down on there with my hydraulic press.

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Old 11-19-12, 01:02 PM
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Did you support the fork by its dropouts when pressing on the new crown race? In any case when you remove the crown race - and you should if you care enough to post this on the internet - take careful measurements of the internal diameter of both crown races and the diameter of the crown race seat.

Last edited by ryker; 11-19-12 at 01:05 PM. Reason: reflect post in the meantime
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Old 11-19-12, 01:23 PM
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rootboy- There is a very simple way to check fork alignment without expensive tooling. First is the need to understand the axises of alignment. Drop outs need to be the proper width apart, centered on the axis of the steerer. Drop outs (blades included) need to be of equal length from the steerer/crown. Ideally (but not actually needed) the front axle should be parallel to the fork crown. Lastly the drop out faces need to be parallel to each other.

Drop out width is pretty straight forward, being the same as the front axle OLD. Easy to gauge with a wheel or measure with a ruler.

Face parallelness can be checked with an axle bolted into one drop out and extending just to the other drop out's inner face. How the axle's free end lines up with the second drop out shows how parallel it is. Repeate for other side.

Axle/crown parallelness can be compared with an axle in the drop outs and a straight edge placed across the top most part of the blades. Sighting the two straight edges (axle is one edge) shows this comparison.

Blade/drop out lengths can be checked with a centered (dished) wheel placed in the drop outs and looking at how centered the rims is between the blades upper portion.

The last two alignment aspects is a little bit trickier and requires a home made tool. If you placed the same wheel in the drops and were able to sight through the steerer and the rim's valve hole to the wheel's other side (about where it would touch the ground in use) you effectively have a straight "edge" close to 3' long. The tool that lets you sight down the very center of the steerer is a piece of small diameter tubing (maybe 1/4" ID) with masking tape wound around it in two places along the tube's length. the tape is wrapped around the tube just enough to become a centering shim and slide into the steerer. So you end up with a sighting scope of sorts running down the center of the steerer. Rotate the wheel so you can see through the valve hole. From the top of the steerer's sight tube look through it, the valve hole and you'll see the rim on the oother side. How centered is the rim in the field of view shows if the wheel is not in line with the steerer. If the rim is centered between the blades by the crown and the viewed rim if off center the blades are not centered WRT the steerer. If the viewed rim is centered and you then loosen the axle nuts (or QR) and let the rim settle into the drop outs fully and the rim is off center between the blades then one blade is longer then the other (or one drop out slot is not deep enough).

I usually do the steerer/drop out centering first (ans set the width at the same time), then the axle/crown parallelness next, drop out face parallelness next and blade length last. i'll go round this process a couple or three times to make sure one adjustment hasn't affected another.

I came up with this system a long time ago and have aligned a lot of forks over the years, in the shops i've owned or worked in and in my own building. Included is a photo of the sighting tube resting ontop of a steerer with a wheel in place. The sight tube would be slid into the steerer during actual alignment checking.

I now have a precision fork clamp mounted on my flat surface (and then can use height gauges and machanist's squares) and have checked out how this compares to the my steerer sight tube method. They tend to agree with each other to a high degree. Andy.
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Old 11-19-12, 05:55 PM
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Originally Posted by ryker View Post
Did you support the fork by its dropouts when pressing on the new crown race? In any case when you remove the crown race - and you should if you care enough to post this on the internet - take careful measurements of the internal diameter of both crown races and the diameter of the crown race seat.
No, I supported the fork by placing the bottom of the fork crown on a block of hardwood in my hydraulic press, then placed the above tool on the crown race and pressed it on. Both crown races measured exactly the same before I put the new one on.
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Old 11-19-12, 06:03 PM
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Thanks Andy,

That's all good input, thanks. I especially like the sight tube idea. Very novel. And that may be the most useful in this instance as I was suspecting that the alignment between the fork crown/ fork blades ....and the steerer tube...may be the culprit. In other words, I think everything from the crown to the dropouts is OK but suspect the steerer is a bit tweaked in relation to the fork crown. But, I'll run these test to see how well everything lines up. Thanks much.
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