Frame repair {steering head)

[Jules]

Hi all, I've just (tried) assembling the new steering head bearings on my 1956 A10 S/A after repairing the badly mutilated forks/yokes per my earlier threads, and found that the upper bearing cup doesn't fit squarely into the frame. It seems that the cup holder has been badly hammered at the front so that the new bearing cup just will not sit square.
it will need building up with weld and then machining back to standard (and of course exactly parallel with the lower cup holder).
1. Has anyone had this done in/around Melbourne and/or does anybody know of a m/c shop that can do it?
2. Does anybody have the dimensions/relativity to bottom cup holder?
Please...............   
thanks

[KiwiGF]

Not sure if this will help with your situation but the bottom cup on my headstock was oval and hence the new taper bearing i bought was a loose fit in the cup

 I had two pieces of steel bar machined to up a diameter 002 smaller than the cups, about 40mm long with a 16mm hole drilled through them, a piece of 16mm studding through the holes clamped the 2 pieces of bar in place in the headstock top and bottom.

The bottom piece of bar was to act as a "former" for the bottom cup and was made a bit smaller than the cup to allow the cup to spring back a bit after being heated up. The top piece of bar and studding was just to keep the bottom piece square.


Then I used an oxy acetylene torch to heat a section of the cupholder up to red and tapped it back onto the bar, then went to the next section and so on, when it cooled the headstock was round and the cup a good fit once more.

Maybe this method could adapted to your situation?

[fido]

I don't think you should build up with weld as you could seriously weaken this critical area of the bike. It might be worth taking the frame to a blacksmith and asking him to fix it as you may not have the gear for doing something like KiwiGF describes.

[Fast 58 BSA]

Hi Jules,

Same problem here. Contemplated a number of solutions (see older threads on the topic) and first decided on making a plug, heating the head and banging it with a hammer. Gave acceptable results, as I was going to use liquid metal to set the bearing cup anyway. Well, then I discovered that the steering head looked more like the leaning tower of pisa. Surprised I never noticed this whilst driving it, but the bike went straight. Turns out it is off by 2-3 cm. So my quick fix to the bearing holder won't work as the frame repair shop needs the frame with complete front end mounted. They then apply heat to straighten, and my liquid metal would simply melt....
So, decided to have the bearing holder built up with beads of weld (tig) instead. Proper cool down between cycles should ensure that the piece doesn't suffer from any weakening.  Once welded, the whole frame will go on the milltable. My machinist will use neck ID void as guide inserting a nylon bar and run the centering process off it (or so I have been told...) I get the frame back from welder in a week, then a couple of weeks later I'll get the machining completed. Will post pics and I can give you more details about set up/ dimensions.

[fido]

The welding will weaken the structure as you will have a discontinuous grain flow. What I would do is make a plug that will be a drop in fit in the cherry red headstock and machine a flat on it to go where the damaged area is. I would attach a length of bar across the top of said plug to use as a lever. I would heat the headstock cherry red, drop the plug in with the flat lined up on the damaged area then use the bar to rotate the plug so the flat is away from the damaged area. I would then let it cool down then reheat to remove the plug.

[Jules]

thanks for your thoughts on this guys, must say it makes me very apprehensive! The problem is that once somebody has the frame if they stuff it up, then its all over, no going back. I've been talking to some locals about it and I'm gradually gaining some confidence in approaching somebody. Your thoughts Fast BSA are interesting and along the lines I'm thinking however, just a heads up for you, when I was trying to setup the upper and lower bearings with threaded rod centred on the tube bore flares/radii, the headstock angles were all wrong, I guess if you setup on the bore/length of the tube it should be ok ???? Please let me know how you go with this, thanks....
In the meantime, the best suggestion I have from an experienced shop, is to build up with braze/silver solder a new face (ilo the weld heat), then setup the mill based on the lower bearing cup holder and remachine the upper..........
Any thoughts on this approach anybody?
Also, does anybody have any finished dimensions because I anticipate that the fork covers have limitted capability on length variation between the upper and lower yokes??
cheers