650B Forks - What's going on here?

[Richy]

My 75 XS650B needed new 34mm fork stanchions, ( lots cheaper than re-chroming) The first photo shows my old fork tube and the new one just received.
After pulling the internal valving from the new tube there are clearly some differences, whilst the new one shows all the parts as per every diagram I have seen but the old one has items I have not seen in any diagrams.
Both 34mm but the new one has a smaller ID, the damping rod does all fit right but the tapered spacer that sits at the base of the lower fork leg with the bolt through it sits in the bush when fully compressed is 20mm ID, the old bush is 18mm ID so is a snug fit and the new one loose.
I hope I have explained this coherently !
Anyone come across these fork internals?

 

[DogBunny]

No, I have not come across those internals.
If I understand correctly, you need a tapered spindle with about a 2mm larger OD (and same ID). Digging through my parts I have one. But only one, and I don't know what it came off of.

It appears the new 34mm stanchion has a larger ID, not smaller as you wrote? Isn't the other end of the damper rod also going to be too small of an OD, just as the tapered spindle is?

It would be nice to know where you got your stanchions, and what they claim the year and model compatibility is.

 

[gggGary]

you might find an answer here?
https://www.xs650.com/threads/emulator-knock-off.67609/

 

[GLJ]

To me the old stuff look like 72-73 parts.
New stuff may be for a 75, not sure though.

 

[DogBunny]

The new stuff is nothing I have ever seen before. Because of the larger IDs of the new stuff, they look like they are intended to be used with the damper rod and tapered spindle that comes with 35mm stanchions (77 and later). Maybe that's what you need:
https://www.ebay.com/itm/177537096177
or:
https://www.ebay.com/itm/185000070255

 

[GLJ]

I know this damper rod is from a XS2. It sure looks like the one marked old in the pic.

 

[DogBunny]

GLJ, yes, you are right, and I was wrong. I deleted my misleading info from my previous post.

In any case, I strongly believe your stanchions are meant to be used with 77 and later damper rod assemblies. 1972-1976 damper rods all have the same diameter, and all use the same tapered spindle. Here's what 74-76 damper rods look like:


So, replacing your 72 internals with 75 internals won't help anything.
I suspect that whoever sold your stanchions first started making 35mm XS650 stanchions. Then, they said, "Hey, if we just reduce the OD and get the length correct, we can also sell them as 34mm XS650 stanchions," without ever bothering to study the internal differences.

 

[GLJ]

So, replacing your 72 internals with 75 internals won't help anything.

It might solve his problem. I put 75 internals in my original XS2. I had to change all the parts in my pic above. I did it to see if the forks would work better.

77 and newer internal parts will not fit in 72-76 tubes. Size of all the parts are different, length of damper is way to long, Last winter I bought a set of forks for a XS2 I'm building. What I got was not 72-73 tubes. I think they may be for a 75 but I'm not sure. What I ended up doing was making a set of dampers. Since I had to make a set I made them so I could use emulators on them. I put the new tubes and dampers I made on my resto-mod. Them used the tubes and dampers from the resto-mod on the XS2 that is under construction.

 

[gggGary]

WOW, what great info!

hmm 34mm stanchions that take 35mm internals I can see some good things about that.............

 

[DogBunny]

77 and newer internal parts will not fit in 72-76 tubes.

Correct. But 77 and newer internal parts might fit into his aftermarket 75 tubes, which is what he bought.
Could be an illusion of perspective, but in his first pic, the new aftermarket internals look to be sized for a 77 and later rod. And in his second pic, the sloppy fit of his original tapered spindle in to his new aftermarket piston looks like it would be corrected by using a 77 and later spindle, which has a larger OD.

 

[gggGary]

Correct. But 77 and newer internal parts might fit into his aftermarket 75 tubes, which is what he bought.
Could be an illusion of perspective, but in his first pic, the new aftermarket internals look to be sized for a 77 and later rod. And in his second pic, the sloppy fit of his original tapered spindle in to his new aftermarket piston looks like it would be corrected by using a 77 and later spindle, which has a larger OD.

The downside would if they made that all work by reducing the wall thickness....

 

[DogBunny]

WOW, what great info!

hmm 34mm stanchions that take 35mm internals I can see some good things about that.............

The problem I see, if my speculation holds true, is that in order for the aftermarket 34mm stanchions to accept 35mm internals, the tube wall thickness has to be less, and thus the stanchion is less strong.
Admittedly, lots and LOTS of speculation on my part going on here.

 

[DogBunny]

The downside would if they made that all work by reducing the wall thickness....

You beat me to it by a minute...

 

[GLJ]

WOW, what great info!

hmm 34mm stanchions that take 35mm internals I can see some good things about that.............

But 77 and newer internal parts might fit into his aftermarket 75 tubes,

No 34mm tubes will not work with 35mm internals. I just made the 34mm damper I made work with the 35mm emulator.

 

[Richy]

No, I have not come across those internals.
If I understand correctly, you need a tapered spindle with about a 2mm larger OD (and same ID). Digging through my parts I have one. But only one, and I don't know what it came off of.

It appears the new 34mm stanchion has a larger ID, not smaller as you wrote? Isn't the other end of the damper rod also going to be too small of an OD, just as the tapered spindle is?

It would be nice to know where you got your stanchions, and what they claim the year and model compatibility is.

The stanchions came from Yambits in the UK appear to be well finished.
The lower end on the new stanchions do have a smaller ID to the old ( 26mm to 28mm) but the bush (photo) that is fixed by circlip into the lower end of the stanchion does not have the same ID, this has a 20mm bore where the old bush has an 18mm bore courtesy of an internal shoulder.
I think I will machine down the OD of the old bush to 26 mm and all will assemble and work correctly.

 

[Richy]

I know this damper rod is from a XS2. It sure looks like the one marked old in the pic.
View attachment 365634

This is the same damper rod in mine.... 75

 

[DogBunny]

Good solution. I regret not believing you when you said the new stanchion had a smaller ID, but that otherwise everything worked except the bush, and instead hallucinating about what the new stanchion was and speculating as to why.