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Discussion Starter · #1 ·
I just took a look at the top portion of the Tiumph pre-unit single down tube frame loop I have in order to tap in the tappered roller bearing conversion cups. The bottom of the neck has a recess that alows the cup to be tapped into while the top of the neck doesn't.

It looks like only the stock smaller bearing will fit in it. Is there a solution for this? I am using Ceriani trees (thus larger diameter stem) so maybe this is part of the issue? Do I machine and weld on a recess to the frame that will accept the roller bearing conversion cup then just like the bottom of the stock neck has? Any help is appreciated. Thank you
 

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I'm sure some one here will chime in with more detail, but there is a range of years of preunit that have the small upper bearing and the roller conversion won't work.

I have the roller bottom bearing and stock loose balls in the top of my 54.
 

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If it is a pre-1956 frame, then the bearing conversion kit will not work. I have seen a few kits that were made to work on the early frames, but not in a long time. If you have an early frame, you can always modify the headstock, or machine a custom top race to take the roller. I have seen both done well.

-Shaggy
 

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Discussion Starter · #5 ·
Thanks for the replies - I will have to look at teh loose ball setup - I dont have the stock pre-unit stem but I think the ceriani stem has a larger outer diameter than the tirumoph one. In addition, I dont know the original pre-unit top tree or bearing setup even looks. I dont think the two peices are simialr enough to where i can just use the original loose ball setup.
 
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