headset crown race tolerances?

ritjobbie · Jan 8, 2007

I am buying a new fork.

I just measured the headset race on my current fork to be 26.9mm. Pretty much every fork with a 1" steerer that I have looked at has a 26.4mm crown race. The probability is high that my trusty vernier calipers are a little out of whack. If that's not the case, is this small of a margin going to be a problem for a new fork? Was 26.9mm (or rounded up to 27mm) an older standard for a crown race? The fork that I measured (and am replacing) is a Kona Project 2 from a 1999 Jake the Snake.

Half a mm is pretty darned small...

Oh, and threads with interesting pictures get more hits:

View attachment 75788

~eibbojtir

Henry Chinaski · Jan 8, 2007

http://www.sheldonbrown.com/cribsheet-headsets.html

C-40 · Jan 8, 2007

a problem...

You measured correctly. In terms of press fits, .5mm is HUGE. .1mm (.004 inch) makes for a very tight interference fit. You must have the proper crown race to fit the fork you buy.

curlybike · Jan 8, 2007

C-40 said:
You measured correctly. In terms of press fits, .5mm is HUGE. .1mm (.004 inch) makes for a very tight interference fit. You must have the proper crown race to fit the fork you buy.

Also the other standard is 27.1 MM. Use the same calipers to measure the old crown race or a possible new one. Or take the fork to a decent shop along with the crown race and have them cut the fork, that way the bottom surface will be flat.

hfc · Jan 8, 2007

I have nothing to add

except that I thoroughly enjoyed reading the buffalo theory. It's even better when you do the Cliff Clavin voice in your head. Good luck with the new fork!

bahueh · Jan 8, 2007

do yourself a huge favor..

C-40 said:
You measured correctly. In terms of press fits, .5mm is HUGE. .1mm (.004 inch) makes for a very tight interference fit. You must have the proper crown race to fit the fork you buy.

and make TOTAL sure that your crown race fits the fork you buy.....about a month ago I ended up having to file down a crown race seat on a fork I had powdercoated...it took four hours with a hand file and a LOT of frustration...it was about .3mm off.

ritjobbie · Jan 8, 2007

I'll try a different set of calipers tonight, hopefully. Maybe a new headset is in order.

Thanks for repliez!

ritjobbie · Jan 9, 2007

Different metric calipers: 27mm right on the nose. Sucky.

ritjobbie · Jan 10, 2007

I figure a cheap new headset might be in order to get past the crown race limitation. I popped the cups out tonight. I measured 29.92mm on the ID of the head tube and most 1" headset cups are 30.2mm OD. Man, I never thought that 0.28mm would cause me so much trouble...

In case it comes to it, does bahueh have any filing tips?

I might be able to shave off a tiny bit of the OD of the cups if necessary, eh? I guess if this doesn't work out, I'll have a good excuse to give the misses for another bike. Darn...

bahueh · Jan 10, 2007

you just don't want to go there..

ritjobbie said:
I figure a cheap new headset might be in order to get past the crown race limitation. I popped the cups out tonight. I measured 29.92mm on the ID of the head tube and most 1" headset cups are 30.2mm OD. Man, I never thought that 0.28mm would cause me so much trouble...

In case it comes to it, does bahueh have any filing tips? I might be able to shave off a tiny bit of the OD of the cups if necessary, eh? I guess if this doesn't work out, I'll have a good excuse to give the misses for another bike. Darn...

the filing was a nightmare and a total ******* fix, although my LBS said its typically done with these compatibility issues. just make sure you have a fine grain steel file, grab a beer and plan to be sitting there awhile...I didn't have much of a choice in my situation, I'd already purchased the headset and the LBS didn't have any comparable crown races that fit..
my biggest tip? don't force it on (with setting tool) before its ready...I ended up compressing a lot of the metal around the seat by doing that once...which took more time to file down...

ritjobbie · Jan 11, 2007

Well, I got everything put back together. Crown race fits on the new fork. A new headset fit like a dream. Well, maybe a little tight.. We'll see if the head tube splits apart in 2 years... When that happens, I'll have some awesome homemade headset tools chilling out in my garage.

Thanks!

bahueh · Jan 11, 2007

don't leave us hanging..

ritjobbie said:
Well, I got everything put back together. Crown race fits on the new fork. A new headset fit like a dream. Well, maybe a little tight.. We'll see if the head tube splits apart in 2 years... When that happens, I'll have some awesome homemade headset tools chilling out in my garage.

Thanks!

how did you manage it?

ritjobbie · Jan 11, 2007

I used 1" ID copper pipe to drive in the crown race. Soft enough to not bang up the race, not that it really mattered since the new headset (Cane Creek S2) has cartridge bearings instead of loose balls. I used a 3/4" copper pipe split cut down the middle to mimic a real cup removal tool. I pressed the cups with an 8" long 1/2" bolt with a bunch of fender washers. A fine threaded bolt worked great. Everything seated nice and flush. I have to admit, I used what I thought was a little too much force pressing the headset, but it worked out okay so far.

Cheers!

RocketDog · Jan 11, 2007

bahueh said:
the filing was a nightmare and a total ******* fix, although my LBS said its typically done with these compatibility issues. just make sure you have a fine grain steel file, grab a beer and plan to be sitting there awhile...I didn't have much of a choice in my situation, I'd already purchased the headset and the LBS didn't have any comparable crown races that fit..
my biggest tip? don't force it on (with setting tool) before its ready...I ended up compressing a lot of the metal around the seat by doing that once...which took more time to file down...

I did that once... About 30 seconds to turn it on a lathe. It's all about having the right tools.

headset crown race tolerances?

ritjobbie

Henry Chinaski

C-40

curlybike

hfc

bahueh

ritjobbie

ritjobbie

ritjobbie

bahueh

ritjobbie

bahueh

ritjobbie

RocketDog

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