Threadless stem on threaded 1 1/8 fork.
 

I know this is generally discouraged due to potential stress risers from clamping on the threads. If I used JB Weld to fill the gaps and then sanded/ filed smooth and or used copper shim stock would this be sufficient to make this a workable go around? This is a quality steel fork so initial strength should not be a limiting factor.

Fail, get a threadless fork, or real good health insurance

That is not the issue. This is a steel Vintage MTB frame and finding a NOS 740 gram DB quality fork with the CORRECT rake, A-C length and steer length is not such a easy endeavor. I can have the existing fork threads extended and steer tube cut but finding a local shop with the correct tool and a mechanic with such skills may be a worse risk than my suggested workaround. I have done a bunch of searching and have yet to find a report of a actual failure from clamping a steel fork in this manner and none who have been prepped as I am suggesting. . Perhaps melting brass might be a better alternative if I cant find a local mechanic with a die. You could very well be right and I will weigh your opinion. Thank you

Filling the thread will protect the stem, but does nothing to restore the strength of the thread. Threaded forks work with quill stems as long as the stem extends well below the last thread, thereby buttressing the threaded area.

Since a threadless system depends 100% on the integrity of the fork's steering column, and has no internal buttress coming from the stem the risk of failure at a thread is very high.

That said, if your fork is long enough that the stem overlaps the non-threaded area by 1" or more, than what you propose would work. You don't need to bother with JB weld, any body filler will work. Note that the 1" overlap is a minimum, and I'm talking about the stem itself, not any spacers. You're skating on thin ice, so don't push it any farther than that.

BTW- just curious here, why are you asking? The original threaded fork wouldn't be long enough for a threadless conversion, so is this a fork you're taking from a taller frame? If it isn't already a fork you already own, my advice would be pass on it and buy a threadless fork, or one tall enough that you'll be cutting off the threaded section entirely.

You are correct, the fork is from a larger frame. My frame (95 Prestige Stumpjumper) has a 95 mm head tube and the fork has 150mm of steer tube with 30 mm of threads. I do not believe that I could get 1" of unthreaded tube one the space of a headset is added in. I guess my only solution is getting the threads extended and cutting some length off. BTW I appreciate the information you often bring to this forum!

I understand. You're in that narrow window, too long for threaded, too short for threadless. Feel free to PM me if no one will give you a decent quote for extending the threads.

Barracuda bikes had a few model years (~1994, 95, 96 or so) where they supplied bikes with threaded steerers and threadless stems and headsets. It was a stupid idea, but I don't know if they ever experieiced a failure, either. Likely they did have a couple failures. Barracuda is no longer around and maybe that was part of it.

If I were you, I would go for the longer fork/thread extension/cut/quill stem option. It isn't that crazy an operation - I have done it multiple times.

Would help in knowing what you are doing, vintage MTB, do you mean a Klunker from the 70's or one from the 90's, if from the 90's, just stick any current rigid fork on, even suspension corrected won't affect handling too much, and maybe inprove it. Getting a fork like a Kona K2 or Ricthey Prestige shouldn't be too hard, or even a carbon one.

Any machine shops local to you? They might be able to machine the threads further down the tube. That way you wouldn't have to worry about having to find a bike shop with the correct die. It doesn't hurt to ask, but it may cost more to do it this way, it would be one off custom work.
Good Luck

there are quill to threadless conversion plugs, to grip a threadless stem around,
and still use the threaded headset around the fork.

and a tube type stem raiser, with a quill at the bottom, reduced section.
tube is formed so as to have the OD at the bottom, and the ID at the top, the same.

and the OD at the top the same as the fork OD at the bottom.

If you wanted to use a threadless headset, a compression plug at the top,
would come out to get to the quill bolt, and operate as the removable substitute for a star nut.

BBB has a most clever combination for their stem raiser. long quill of aluminum,
a bolt to pull the wedge tight that is made to be internally threaded at the top,
a bolt threads into it to, for the top cap for adjusting threadless headsets,
and a stack od spacers with a key tab, that engage a keyway extruded in the stem quill.

I got one of those [BHP-21] to bring the height up, on my Trekking bike,
enabling a second stem to be fitted, beneath its Trekking handlebars,
for my handlebar bag's KF QR Mount.

I found a local shop who will cut 1" of thread for $ 20.00 which should give me all I need. Thanks for your help!

Hi all,
I had the same idea as Fred Smedley (yes, J-B Weld and all). So I figured "Well, somebody needs to try it...." . I would certainly not try this with the intention of downhill or single track, but for a touring bike, I'll give it a go.

I've got 5/8" with no threads, 7/8" threads with J-B Weld applied and sanded down. Sure, I would rather have 1" without threads, but I don't. Check the pics. I think it does add a bit of strength (maybe I'm wrong). Also, the threads won't leave grooves in my stem.
http://bikeforums.net/attachment.php...hmentid=211019http://bikeforums.net/attachment.php...hmentid=211020

it is possible to mix and match,, threadless headset, + a 'locking spacer',
in the unthreaded portion.
Then a quill stem raiser, BBB BHP#21 is the best in this application.
As it shifts the adjustment
to the top of a custom manufactured internally threaded bolt .
or, you can use the locknut on the threaded bit,
and do the headset pre load there ..
the quill stem raiser reinforces the threaded portion well ..

a steel tube type stem raiser for 9/8" forks is made also,
quill is in a 1" reduced diameter portion of a steel tube.

then the locking spacer and threaded nut will do the adjustment,
OD at the top is like the OD of the fork steerer... 9/8"

top of the tube.. just put a cork in it.