scale

i have acquired a really nice frameset only to find that it appears someone tried to file down the the fork crown to 26.4 from 27.0 by hand using a dremel. There are small nicks on the fork tube that i can see so i imagine that is what happened. THen i imagine that person just gave up and sold off the frameset. Its a 1 inch threaded steel fork to be clear.

If i measure around the crown race seat it is 27mm in spots and slightly smaller.......26.5 etc in others so it isnt 100% round anymore. I know the tool for facing is a cutting tool that fits the fork tube nice and snug so having a shop grind it out to 26.4 is probably the way to go?

I have to imagine a shop that has the tool could do this job properly and take the whole thing down to 26.4 in about 5 minutes and do it properly vs me continuing to finish whatever the previous person started here.?

CliffordK

You might start by simply seeing how securely a 27 crown race will fit on it.

I haven't used it, but your idea of simply milling to 26.4 sounds reasonable.

scale

yeah...i could try that. The race area has some spots that read 27mm....so that just might be good enough.

I know i have had lesser quality bikes in the past where the crown race just sat there......but not tightly. It wasnt press fit and the crown race could even be spun on the fork crown. It didnt seem to cause a problem and seemed to work fine.

Dan Burkhart 

If your local shop has a crown race milling tool, it can quite easily be milled down to 26.4. If they also have a knurling tool, once it has been made round, it can be knurled and re milled to 27mm. I have the tools to do this, and it works.

scale

Interesting. Ill have to look up that knurling process.

If i look close at this crown face it isnt entirely flat. I suspect the best thing to do here is to grind it out to 26.4 and face it flat.

SurferRosa

Unless I had a headset ready to go with a 27mm ID crown race, I would have my LBS mill it to 26.4 ... and press the new race in the same visit in case a bit of the crown needed to be knurled afterwards.

But I trust my LBS. I wouldn't take it to just any place.

If, after milling, the race fit worries you, I've heard you can use Loctite 660 (quick metal) to seal it in place.

CliffordK

I woudn't go with a loose fit, but if it is snug, you may be just fine.

Perhaps the Knurling could be done before simply machining it to 27.

Hoopdriver

A lot of shops don't want to invest in the proper cutting tool (and the expense of replacing cutters) so they opt for the hand file method. Just not enough demand to justify the expense. It can work fine if they take care.

If you can find a shop with the milling tool and the know-how, go for it. If not, I'd be tempted to clean things up with a file yourself.

fleslider 

I did this to my Peugeot Team Festina so i had a better choices of Headsets. park's tool Crown Race cutting tool (CRC-1) worked like a charm. we have one at our CO-OP . (park website)

I went from a JIS 27mm to a ISO 26.4 size


Before


During


After

Old Yeller

3alarmer 

...the last one I had to do was the result of an unfortunate overspray incident on a powdercoating gone awry. I am lucky to have a custom frame builder not too far away, and I think he charged me 15 bucks to do the job with the proper tool.....which is what I would recommend at this point. there's little chance you are gonna freehand that thing back to the proper diameter of 26.4 and still have it centered, and I suspect 27 mm is just a memory now.

The tool to do it is just expensive enough that I did not buy one, because this is not something I will do again in the foreseeable future. But it is easily applied, and works well when used correctly. Centering on the steering axis is sort of important for a crown race.

dddd

"...Centering on the steering axis is sort of important for a crown race."

Especially with any fork that can't later be cold-set into alignment.

I had an Epic fork that had been hand-cut, the press fit was too tight anyway, so in back of an old shop in L.A. mounted in in a lathe, found center just above the seating area and cut it to a very round 26.4mm.
Don't spin it too fast though, the fork tip offset might pull the crown race off center during the cutting operation.

I also recall that the Campy cutter wouldn't fit over the bonded crown race area of the Epic fork, why it had been hand-cut in the first place.

busdriver1959

dddd

What about the centering of the cut with respect to the steering axis and dropouts?

If the fork was aligned in it's original state, and then material was removed in a way that didn't preserve concentricity with the original seat, won't the Campy cutter follow the rough positioning of the distorted seat?

It's a difficult call here, I might prefer to first build up the bike and 27.0mm headset to verify self-centering steering before cutting further following the existing "mangled(?)" seat. If it rides fine then likely the Campy cutter won't put the new 26.4mm seat off it's proper center.

markwesti

Nice work ! @fleslider