Bicycle Mechanics - Crown Race just slightly too small to fit fork....facing? or?

hi!
sorry in advance if this is covered elsewhere...

so i have a 1inch threaded fork, and 1inch threaded headset. Crown Race, even with a crown race tool (well, a pipe and thick washers) i cant hammer the crown race down.

basically the crown race slides down the steerer tube fine, but the last 1inch or less of "seat" (or whatever thats called) prevents the crown race from going down to the very bottom.

I have read about "facing" or machining this area of the fork to take off a touch of material, but cursory google searching shows such tool is crazy expensive....and i have had a falling out with my LBS for numerous reasons so i would really like to NOT go there for help....

anywho is there some magical trick to getting it on? perhaps freezing and heating? (i remember a little from physics class lol)....is it bad idea to try to file it down myself? (sounds super time consuming)...

also, while ive noticed other crown races are split, this one is not. im assuming being split would probably help in this situation....oh well.


anyway thanks in advance for any advice!

You could try heating the crown race to enlarge it. Not hot enough to lose the temper, just a couple hundred degrees.

how big is the fork crown race seat? have you measured it?

seek out a larger crown race? If it's a sealed cartridge bearing headsdet
a split crown would be OK as the cartridge bearing is still a complete circular ring.

loose ball headset , .. ? what headset did you buy, what is the ID of the crown race?

although i do have some coming the mail, as of now i do not have calipers to measure with.

yes, the headset is sealed cartridge.


so is it OK to use a crown race that did not come with the particular headset? i had just assumed no since ive come across a few crown races that seemed slightly different...

Try using the mallet to tap it down. Worked for me when I reused the old crown race for the replacement rigid fork.

You could try heating the crown race to enlarge it. Not hot enough to lose the temper, just a couple hundred degrees.

Bad advice while it might work, crown races are through hardened and not able to tolerate much distortion. The amount of allowable expansion is engineered into the level of interference. If expanded with heat it'll be over stressed as it cools and contracts and may crack.

Assuming your fork had a crown race before, and the new one doesn't fit, it's likely that the crown is JIS (27.0mm) vs the more common 26.4mm. JIS is japan industrial standard and is ised on forks intended for the Japanese home market but often show up in the US. they were common on Specialized bikes for a number of years, but were also used on many other brands.

Before forcing and maybe cracking your race measure the crown seat. It should be no bigger than 26.45mm (0.05mm interference) or 27.05mm for JIS. and make sure the crown race matches.

If you don't have a caliper, but have the original crown race compare the two by hanging them over the 1" section of the fork and using an improvised feeler gauge, to see if they're the same.

If it turns out your fork is milled JIS you can purchase the right headset or just the crown race, or bring the fork to a decent mechanic who can Hollow-mill it down for a 26.4 crown.

If it's a new fork, that never had a crown race fitted, it needs to be checked and maybe milled to spec.

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

differences: ISO, JIS
crown race: 26.4, 27.0mm
frame cup: 30.0, 30.2mm

DO NOT TRY TO FORCE IT.
When I built up my Colnago the Chris King lower race would not quite fit over the Colnago fork crown lug. My LBS had to borrow the correct facing tool from a friend to dress off the fork lug.
Do it right, forks are not cheap.

You can just use a file and file it down to fit. It doesn't take much to do .

a loose ball headset is different from one made to go with a sealed bearing headset.
and so are the crown races.

Wait till you have that caliper in hand to know what you have
and how far out you are ..
may be better to get a second crownrace , of appropriate diameter,
if available, for the brand and model of headset you bought.


perhaps you should take bike and headset down to LBS and have them install it.
crown race cutter in the bike shop's tool box is a better way to go.
perhaps head tube needs to be faced too...

You can just use a file and file it down to fit. It doesn't take much to do .
Just make sure you file it concentric with the steer tube axis or you may find it difficult to adjust without binding and/or wobble.

Bad advice while it might work, crown races are through hardened and not able to tolerate much distortion. The amount of allowable expansion is engineered into the level of interference. If expanded with heat it'll be over stressed as it cools and contracts and may crack.

Ah, an unfounded internet conclusion ;). FWIW, Slightly heating parts is a common method for installing races and bearing sets in industrial machinery.

Ah, an unfounded internet conclusion ;). FWIW, Slightly heating parts is a common method for installing races and bearing sets in industrial machinery.

Absolutely, if they're dimensionally correct for the job. The fact that the crown race can't be pressed on with a slide hammer indicates that the crown is larger than the 26.45 (.05 oversize) for the race and ignoring that is a good way to crack the crown whether it's by excessive pressing force or by thermal expansion. As far as I'm concerned the OP or anyone else is welcome to force the race on, after all it's their race, but they should be aware if the likelihood of fracturing it.

This whole discussion would be much more useful if the OP would tell us:

Brand, model, and size of headset

Brand, model, and size of fork

1" threaded is not specific enough to answer the question...

This whole discussion would be much more useful if the OP would tell us:

Brand, model, and size of headset

Brand, model, and size of fork

1" threaded is not specific enough to answer the question...

More info would help, but brand and model don't really help. The issue is whether the fork and crown race are ISO, or JIS (hopefully both the same) and whether the fork was ever prepped -- Forks where the crown race seat are part of the crown may need to be prepped, those where the crown seat is formed by bulging the steerer don't.

If the OP has access to a caliper actual dimensions would help, but by this time the OP has enough info that once he measures things he won't need us anymore.

AEO did give sheldon's relevant data
differences: ISO,.. JIS
crown race: 26.4, .. 27.0mm
frame cup: 30.0, .. 30.2mm

pick up a 27.0 *version of the crown race, and mill the fork if it doesn't fit.

*It's the larger ID, perhaps it will drop on,

pick up a 27.0 version of the crown race, and mill the fork if it doesn't fit.

Why spend dough on a crown race he may not need? This thread is rapidly proving my signature line that one measurement is worth 1,000 opinions. We haven't reached 1,000 yet, but we easily could without solving the OP's problem.

The OP needs to measure both the fork crown and the race. That and the info provided here already will tell him all that he needs to know, and without actual measurements no opinion can do any good.

BTW- though the nominal size of a JIS crown is 26.4 the crown seat on the fork should be 26.45 to provide for the correct interference fit. Likewise for JIS, 27.0 nominal, 27.05 actual.

If you just need to get a little material off the fork crown. rather than file the fork crown, you could try sandpaper. Get good cloth backed paper (not too coarse), cut a strip about 1/2 wide & 10+ inches long, secure the fork, take one end in each hand. Run back & forth over the crown. You can count the # of strokes, rotate the fork, repeat, and it should come out pretty even.

thanks all for the sound advice....much which admittedly i have not taken lol....sorry but this might irke quite a few of you....but....

lets just say i dont know the make of the fork. it was NOS off ebay for around 30 bucks. chrome, lugged, threaded. thats all i know. considering this is for a beater singlespeed coaster brake bike built around an old Phillips 3 speed frame from the 60s i bought for 10 dollars, the lazy/impatient side of me got the best of my meticulous side.

i surely would have waited for the calipers i have coming in the mail, measured the fork crown seat and the crown race and then had it machined professionally by the LBS (although admittedly i am trying to boycott them for various reasons, hence trying to do as much home mechanic work as possible without them) if it was for a nicer build...

HOWEVER i just went the brute force route and took a file to the fork last night. i think i did a pretty good job filing evenly around, by counting to 10 strokes from 12 oclock to 1 to 2 to 3 oclock, etc.....

and it worked! didn't need much filing at all. about a TV show's worth. even put the fork in the freezer while i did it, then put the crown race under very hot water. not sure if it helped or not, but all in all the crown race is finally on and im happy.

NOW, was this the right way to go about it? probably not. will going about it this way result in catastrophic failure? im thinking no. but ill definitely report back if still alive when it does :)

thanks everyone.