Unusual Crown Race Size, Unknown Standard

[fattyre]

Knurling Tool

Knurling Tool The Stein Knurling Tool is designed to increase the effective diameter of cylindrical surfaces to restore a press fit to bearings, as in the case of fork crown seating areas of forks. It can also be used to increase the grip of seat posts, handlebars (in the stem clamping area) and...

steintool.com

 

[Huguenot]

Bingo. I couldn't remember the maker, thanks for posting. With that tool it becomes a "trade-for-a Sixpack" kind of job and the lathe itself isn't needed.

 

[SuperDirtMan]

If machining is the most accessible option, could I get the wearing surface of the race machined down? The rut doesn't seem to be too deep, although I then have concerns about tolerance between the bottom of the race and the bearing cage (although I suppose I could substitute the caged bearing for free bearings, if it comes to that, or have the base of the race machined down as well). It seems like that may be easier to work with than the fork.
I should have supposed that a 70-year-old bike from Sweden might have some outdated parts, but that's the learning process. I'd like to ask any other Flygstal/M104A owners what they've done in a similar situation.

 

[Huguenot]

If machining is the most accessible option, could I get the wearing surface of the race machined down? The rut doesn't seem to be too deep, although I then have concerns about tolerance between the bottom of the race and the bearing cage (although I suppose I could substitute the caged bearing for free bearings, if it comes to that, or have the base of the race machined down as well). It seems like that may be easier to work with than the fork.
I should have supposed that a 70-year-old bike from Sweden might have some outdated parts, but that's the learning process. I'd like to ask any other Flygstal/M104A owners what they've done in a similar situation.

Those surfaces are usually ground as they are (should be) hardened, at least on the surface. Having that done could be expensive, and depending on how much material needs to be removed, you could lose the hardness altogether and the damage would return in short order.
I would try spinning that race on a lathe or drill press (or even a cordless drill) on some kind of mandrel -could be made of wood even, like a piece of broom handle or?
Use some fine emery cloth and smooth out what you can. You won't get it all but may be pleasantly surprised at the improvement.

 

[SuperDirtMan]

Bingo. I couldn't remember the maker, thanks for posting. With that tool it becomes a "trade-for-a Sixpack" kind of job and the lathe itself isn't needed

I do have concerns on how much an increase in the diameter I could get with knurling; I'd need about a 1-1.5mm increase to make up the difference.

 

[Huguenot]

Unless I misread something, you only need about .013" (13 thousandths) which should be easily attainable by knurling.
1-1.5mm translates to 40-60 thousandths, or approx 1/16", it that is the case brazing would be the only real option.

 

[SuperDirtMan]

Unless I misread something, you only need about .013" (13 thousandths) which should be easily attainable by knurling.
1-1.5mm translates to 40-60 thousandths, or approx 1/16", it that is the case brazing would be the only real option.

Most available headsets, even for 25.4 mm steerer tubes, have crown race with an ID of ~26.4 mm (up to 27 mm), which is true for the replacement I received and others I have on hand. I know someone who works with machining, I can see what they think...

 

[Huguenot]

Most available headsets, even for 25.4 mm steerer tubes, have crown race with an ID of ~26.4 mm (up to 27 mm), which is true for the replacement I received and others I have on hand. I know someone who works with machining, I can see what they think...

Oops, my bad. Looks like I'm the one who misread.
Best of luck with your project.

 

[SuperDirtMan]

Oops, my bad. Looks like I'm the one who misread.
Best of luck with your project.

Ah its alright, thanks for the suggestions! No one said working with old bikes is always easy, but it's still a fun challenge.

 

[SuperDirtMan]

Update: after some trawling though a Swedish cycling forum, I was able to find a brief reference to a similar dilemma to mine; unfortunately without resolution, but at least I'm not crazy.

Quote: "You can do both parts. It's standard, but these stems are getting a little harder to come by, and handlebars that fit the older dimension of ~25.8-26mm are increasingly rare.
Here there is a lot of so-called new old stock to botanize in. 3TTT Quid is available in 100mm. I don't know if it's longer or shorter than the stem you have. There are probably plenty of nice strains on Ebay."

At least I think that's what the user was referring to.