Triple Tree Binding

[billpedalino]

Hi All,

After so many years of installing front forks I've come across a new problem that I haven't quite figured out yet. I have a 1979 frame and am installing the upper and lower fork trees. The lower tree (with new bearings and races) installs correctly using either the old style fork stem nut 48330-48A and separate upper dust shield, or the newer style combined stem nut/dust shied 48330-48B. When I tighten the lower stem nut I'm able to properly pre-load the neck bearings and the lower tree turns smoothly.

However, when I place the crown plate (top tree) and start to tighten it's top nut, the entire assembly starts to bind in the bearings. The fork legs aren't installed yet, thereby isolating the problem to the tree assembly. I'm using the flat upper nut (45718-60) and its lock-plate (45717-63).

This doesn't make sense, as once the lower nut is set, tightening the the top tree nut should only force the top tree down against the lower nut and should have no impact upon the bearing compression, as this is controlled by the lower nut only.

Stated another way; tightening the upper tree (top) nut should only tighten the upper tree against the lower fork stem nut and hold the lower nut in place at its pre-load setting and not increase the load on the neck bearings. The tension applied by tightening the top nut should be resisted ENTIRELY by the lower stem nut and not transferred to the bearings.

Am I incorrect? Has anyone experienced a similar problem? .

Thanks,
Bill Pedalino

[Rubone]

Fairly common Bill. It has to do with the threads and amount of clearance they have. The top nut can force the lower to a tighter fit . Usually leaving the lower nut slightly looser allows the thread play to get the tension where you want it. It can be a bit of a PITA to get right. It is all about the tolerances in the machining of the components.

[billpedalino]

You're exactly correct. The trees and hardware that I'm working with are all aftermarket (this is a period-modified machine, at best), so the actual Pacific-Rim thread class that I'm working with is obviously inferior to OEM.

I usually install the top tree and then have to slightly 'adjust' the lower nut by taping it loser or tighter using a small screw driver and light hammer and then re-snugging the top nut - most often in several cycles until the adjusted pre-load feels right. I always assumed it has to take up any play in the lower nut-to-stem nut tolerance as you've confirmed . However, this case is a lot worse so I've questioned it here.

In my opinion, the EL/FL Springer and early Sportster neck setups are-better designed for achieving a more positive feel during the bearing loading process. However, the Timken bearing setup certainly is far superior to the earlier assemblies as it eliminates the the point loads generated by ball bearings.

Thank you so much for confirming my position!