I had a crash on a bike. My frame suffered a small buckle in the top tube, a reputable frame builder said replacing the fork would be fine. The only problem is the fork I have was a custom made 1 off for a 69CM monster bike...

There are several inches of thread on the steertube. Can I effectively have a huge stack of spacers provided there is enough thread on the steertube? this is a vintage threaded fork and not a threadless.

Is there enough thread to allow the top cup to snug up to the bearings? How many inches of thread are you talking about?

If you have enough thread to be able to tighten the headset, the only "problem" that I see is that you want to make sure that the stem goes far enough into the steerer tube that the wedge is below the threaded portion.

All threaded forks are fitted to the length of the headtube, one off or not. I would think that that many spacers could lead to a bent steerer and/or ovalized headtube. I remember hearing the rule of thumb is 1 1/5 times the steerer diameter, but that might be a bit conservative. Most bike shops can cut the threads on your steerer down to to a level so it can be cut to fit your bike.

You need enough thread for the upper headset cup to thread tight before running out of thread. Then you can add spacers to the top nut.

However that's only half the story. The stem must be inserted deep enough that the bottom is about 1" or so below the upper HS bearing. (and beyond the last thread) Otherwise there's too much cantilever stress and you risk the the steerer snapping at the headset.

You might be better off finding a proper length fork, or threading and cutting this down to work correctly, or possibly going threadless, depending on the fork length.

BTW- if you have a slight buckle in the top tube, odds are there's a more serious buckle in the downtube. Make sure to check that. If ti's a steel frame, it'll probably be OK to ride (leaving that judgement to the builder who saw it), but be sure to check both top and down tubes for signs of crack propagation at the sides of the buckle. The first sign will probably be some visible cracks in the paint.

Also note that small cracks in the paint at buckles are often points of entry for water, and the tube will form hairline rust patterns, accelerating the demise of the tube. Keep this in mind if this is an all weather bike.

thats not good at all.. is this being repaired.. ? they will crack there with more flexing at that bulge..

Quote:

a reputable frame builder said replacing the fork would be fine.
The only problem is the fork I have was a custom made 1 off for a 69CM monster bike...

sounds like its suitable to convert to a threadless headset and stem and cut the fork down after the ideal height is determined.