When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Unusual Crown Race Size, Unknown Standard

-

SuperDirtMan

Look Ma, No Hands!
Hey All,

Sorry if this is a basic question, I'm still quite new to old bicycles, but I've been having trouble with this. I have a 1950 Monark (the Swedish Monark, not the American Monark) Aerosteel Bicycle, and am in the process of getting it into better shape. The original crown race had a fairly large divot, enough to resonate through the fork when turning, so I had planned to replace it. However, I haven't been able to find a replacement that fits, the original measuring ~25.7 millimeters on the inside.
I was recommended to try an EC30/25.4 headset, but alas the crown race still sat very loosely on the fork.
Is anyone familiar with this particular headset standard? Is this unique to Swedish bicycles?

Thanks.
 
Welcome to the Cabe, I can't help with your question but I'm sure someone here on the Cabe will chime in with your answer.
 
The steerer tube OD, at the base is ~25.6 mm, slightly thicker than the upper portion, around 25.4-25.4 mm, so fairly typical as it seems. It was seated fairly tight, and I haven't been able to find an ideal replacement.

Shims may be the best option in this case.

IMG_4989.jpg
 
I'm considering just replacing the caged bearing with a sealed bearing, honestly. It might be the simpler option, so I can keep the race without risking the bearing.
 
For a 1” steerer tube, I believe that modern replacements are 26+ mm, (and some may be found at ~27mm).
I have found some older bikes that seem to have more like 1” bottom cones, which I do not know if anyone makes anymore.
The good thing about smaller steerer tubes, is that they can be shimmed up to fit the wider bearing cones.
 
In my experience over time shins haven’t held up. But that all depends on how much you plan on riding. And of course every situation can be vastly different. I’m sure a few dozen times a year would be fine. But heavy use or rough terrain will surly test the durability of a shim.

I vote to knurl it, but then tool cost or finding someone to do that might be an issue.
 
In my experience over time shins haven’t held up. But that all depends on how much you plan on riding. And of course every situation can be vastly different. I’m sure a few dozen times a year would be fine. But heavy use or rough terrain will surly test the durability of a shim.

I vote to knurl it, but then tool cost or finding someone to do that might be an issue.
Agreed that shims would likely be only a temporary fix, they seem to want to move under the pressure of actually using the bike.
Cost should not be too much as it would be a 15 minute job for someone with the right machinery. Finding someone with a knurl that will work on a narrow crown race seat right next to that shoulder could be a problem, as most knurling rollers are supported on both sides and clearance will be an issue.
I have had decent luck with using a center punch and carefully working my way around the race seat while properly supporting the steerer. The addition of some Locktite sleeve/bearing retainer might improve even that method.
I have also built the seat area up by brazing and then turning it down on a lathe. Works perfectly but not likely worth the trouble and cost.
 
Back
Top