suspension fork upgrade

[moleman]

Has anybody managed to fit a 1 1/8th inch fork into a 1 inch frame?
The fork I bought from EBay was mislabeled and I might be stuck with it.
I know that it is trying to fit a 10 pound turkey in a 5 pound bag, but if I can find the right size bearings it might work.

 

[Wolf]

The clearance between the 1 1/8 steerer and the 1" headtube is too tight to SAFELY convert (the bearing cup walls will be too thin if made for sufficient clearance to avoid binding between the inside of the cup walls and the steerer)! The only sensible/safe route IMO, and one which I have done many times is to manufacturer a new steerer tube. If your new fork has a clamped crown/steerer tube assembly then this is not too dificult, if it has a press/bonded assembly then it is more difficult as it requires precise machining and re pressing/bonding.

If you do have a clamped assembly the simplist safe way is to obtain a 1 inch steerer from either another clamped assembly fork (you can somtines buy these off ebay) or from a frame builders supplier and then make a split sleeve from the bottom of the 1&1/8 steerer tube that fits snuggly around the clamped area of the new 1" steerer.
You could cut the fork legs off a carefully selected rigid 1" fork and then carefully grind/file the steerer to the right size but it is doubtful if you will be able to obtain the minimum accuracy needed to make a safe assembly.

There are other ways if you have access to a good lathe.

 

[Multipass]

The vintage BMX guys have the 1 1/8" forks into 1" frames swap sorted out: http://bmxmuseum.com/forums/viewtopic.php?id=40740

It's important to note that not all 1" headsets are actually the same size. If the frame you're working with has the Schwinn/BMX sized 1" headset, you're in business. The swap won't work with a road bike 1" headset though. As always, Sheldon Brown has the detailed specs: http://www.sheldonbrown.com/cribsheet-headsets.html

Hope this helps

-Mp

 

[Wolf]

Cool! I must look into that, never come across the schwinn/bmx head tube Multipass speaks of! Just measured a couple of old bmx frames and they are exactly the same as road bike/old mtb head tubes- admitedly they are are not any high end brand, just cheap kids bmx bikes. The few newer 'bmx' frames I have seen seem to use 1&1/8 inch size headtubes, but as I am not into bmxing I've never really had much to do with them. Was the larger inch head tube only used on American made bmx bikes? Which Scwinn cruiser frames used this head tube diameter? The real problem will be finding a crown race that has the same bearing race crvature angle as the inch cup, not all heqadsets use the same!

 

[g-ratter]

This is how I did it. I cut a slit down the front of the 1 inch head tube. Then I then cut an 1 1/8" head tube from a donor bike and pounded it into the 1" tube. Because of the cut it was able to expand to allow the 1 1/8" tube to slide in. Then I just welded everything together.

Just found these images. I think they help explain.