USD Forks

Stereordinary wrote:

I was thinking the same thing. It certainly wouldn’t be hard to design it as a hex, so I might as well. Still, there wouldn’t be a problem with using a little thread locker as long as I apply it carefully, and give it time to set up before adding fork oil, right? 

Indeed

Stereordinary wrote:

 I’m wondering if it would be a good idea to use a thread locker on the male part of the extension as it threads into the cartridge. Thoughts? 

Yes! Use thread lock on the male thread into the damper rod.

For more ground clearance get a KTM 640 Duke or LC4  WP USD front fork!
It´s full adjustable, get it for 130 € as a used part.
Did a conversion for a good buddy on his FXDWG HD with WILBERS shocks on rear, WP USD front with 6 piston brake caliper.
Best driving and braking performance HD never ever think about to developed like that.
This winter he get a 18" big spoke rear instead the 17" wheel to matching the 23" front wheel optic...

 
 
 

Here's an updated screenshot of the extension with a 20mm hex outside profile. Unless anyone can see any reason why this wouldn't work, I think it makes sense. And hex bar stock in this size is easy enough to come by:  www.mcmaster.com/6607K6/



Currently I have it designed for only 20mm of extension. However I've been doing the math and it looks like I might need to go up to 27mm. As Zed has pointed out, it's possible to get as much as 32mm, so I know I'm safe within that limit. However one acquaintance of mine has said that "as you lengthen the distance of the damping rod you increase the pressure placed on the rear contact points and 'oblong' the lower." Does anyone know anything about this? I have been trying to find a source to back up that comment, but I can't. I've also found a place that sells an extension kit for Harleys that is a full 3" (76.2mm) of extension, which if this comment about "oblonging" the lowers is true seems dangerous. 

Aaaaaannnnnnnddddddd, here we go. Updated to be 27mm length, and with a 21mm hex. Turns out I don't own a 20mm socket, so I went up instead of down in size. I did a "dry" test fit in the fork lower and it seems like everything fits fine. Again, unless anyone can see any reason these won't work I'll go ahead and get them off to the machinist. Anyone need a pair while I'm ordering?

Stereordinary wrote:

However one acquaintance of mine has said that "as you lengthen the distance of the damping rod you increase the pressure placed on the rear contact points and 'oblong' the lower." Does anyone know anything about this? I have been trying to find a source to back up that comment, but I can't.  

That's because it's cobblers.
For such a short increase in length it's won't oblong anything..

As for the hex bar for the extension. No problem with that.
I only did the round bar with a couple of flats milled on because i used whatever i had to hand .
If i had some hex or some fatter bar to mill a hex on at the time i would have used that.
 

Stereordinary wrote:

 However one acquaintance of mine has said that "as you lengthen the distance of the damping rod you increase the pressure placed on the rear contact points and 'oblong' the lower." Does anyone know anything about this? I have been trying to find a source to back up that comment, but I can't. I've also found a place that sells an extension kit for Harleys that is a full 3" (76.2mm) of extension, which if this comment about "oblonging" the lowers is true seems dangerous. 

I am with "Zed" on this one, what are the "credentials" of your acquaintance ?
I accept that extending will increase leverage on the bushings (approx $20) however IMHO that will be almost insignificant. Given that unless you are circumnavigating the globe these bushes seem to last "in excess" of 20 years, a lifespan reduction of "a few percent" is insignificant. That being the case there is no chance of "sudden failure" so not a safety issue at all.
You are obviously a "deep thinker" so people like this will get in your head if you let them

Something to consider - metric hex bar stock is hard to come by in the US. Likely this design will result in two operations - one lathe setup and one mill setup. Also more material removal which is more machine time. Potentially if your machinist is high tech and has a lathe with live tooling it could be done in one setup but that is usually reserved for mass production. If you select a nominal fractional hex size like 3/4" or 7/8" it can reduce it to just a lathe op and a much cheaper part.