Tuning AC RD350 front suspension

[oxford]

It's been a while since I have messed with emulators.  If you don't want to mess with splitting the pin, you should be able to tap threads into the the outer piece and then use a dog point setscrew.  The points go into the hole in the rod when the pin went.

Use oil resistant blue Loctite on the setscrews (243?? I think it is).

[teazer]

when you get it its obvious what you need to do. looking at the rod from the top, the roll pin is pressed all the way across the opening. take the middle section out, to clear the bottom of the bolt/nut that protrudes into the rod. a dremel with a carbide bit to cut it i think is what i used.

as a side note, i did add preload adjusters from economy on my bikes since the original post. mine is on the lightweight rd, its about 115? lbs lighter than a stock bike, so i had to tune mine lighter, i used 5wt fork oil and actually reduced the preload a hair.  however, i've done this the other way as well. I know, for a fact, these make a huge difference (the emulators) when set up right.  heres the instructions for the XS forks, which the top is different than the earlier 34mm forks.

https://www.2strokeworld.net/wp-content/uploads/lightweight-rd/forks/fork-valve-emulators-1.pdf

That damper rod in the instructions is the same as late model RD250 or 400.  but on a 350 they really need a racetech adapter with piston ring IMHO.

[m in sc]

they dont. i'm running a set. have been for years, no issues.     could you fit rd400 or uk 250 dampers? sure. but not necessary at all.

[IR8D8R]

That plastic piston ring on the adapter makes it a real b*tch to get it in the fork tube. I had to make a little cone ring compressor out of aluminum sheet to get it to go in without applying force that made me uncomfortable.

IR8D8R

[m in sc]

heres the thing. the ring is supposed to basically stop the leakage past the rod, which i get. but that leakage is a constant, albeit tiny, amount that can be compensated for by adjusting the valve. erego, the ring isn't needed. ;)  .02


actually, thinking about it, you could lathe up a spacer with grooves around it , would basically do the same thing as the ring.

[JBeasty]

So let me see if I've got this right. Here is my 77 RD damper rod (at least I think it's the original). I cut and drill where I have it marked in red. Then with the end cut off I can get to the roll pin and Dremel it out of the passageway. Correct?

[teazer]

heres the thing. the ring is supposed to basically stop the leakage past the rod, which i get. but that leakage is a constant, albeit tiny, amount that can be compensated for by adjusting the valve. ergo, the ring isn't needed. ;)  .02

actually, thinking about it, you could lathe up a spacer with grooves around it , would basically do the same thing as the ring.

You may be right, but most later damper rod forks use a diagonally split phenolic resin piston ring to reduce that leakage an an aluminum spacer that restricts leakage would probably add too much stiction. Measure the ID of those fork legs and if it's around 28mm, I think that a spacer with a GL1000 or GT750 piston ring would work fine with less friction than racetech plastic rings.  In forks that already have a piston ring, the spaces is just a straight aluminum tube.  They don't need both seals/rings.

[m in sc]

but we're talking about early fork internals, and they work just fine with no ring, or valve. the valve is smaller than the top of the rod so i dont see it as being an issue. 

[1976RD400C]

Here's a video how they work. This is how I understand how they are fitted to a 400. You have to make sure the emulator is sitting on the top of the damper rod and the two surfaces seal. The 400 needs a spacer because it is impossible for it sit flush after you cut the top off, like you marked in red. I think the diameter of the shoulder of the emulator is too big to fit down in the cut off damper rod to seal it. Once you make a spacer to adapt the two there is no need to seal the outside of the spacer to the inner diameter of the fork tube. The piston ring on the rod is doing that. You could put a o-ring seal between the flush surfaces of the spacer and the emulator, but if it is a nice fit, I don't see a need. On a 350, like the one in the vise pic, it fits nice, without any adaptor, other than the roll pin needs to be cut out of the way. 
https://www.youtube.com/watch?v=j3QYZEQoN_M

[oxford]

FWIW, there is a ton of info (at least there used to be) on Racetech's site about emulators, all of it wasn't easy to find but it was there.

IIRC regarding "adapters" and cutting the tops off there was a specified "distance" they called out.  I can't remember what it was or from where.

A while ago, I put emulators in a set of Kawi triple forks.  Instead of modifying the top of the rod and using an adapter I machined a new top piece.  Overall length of that was based off of that info on the RT site.  How critical it is, I'm not sure.  Here are some pics of the modified rods I did for the Kawi forks.  I did quite a few of these for board members at the time.

[oxford]

Also IIRC, actual RaceTech emulators came with a lighter preload spring for the top of the emulator to use with the RD.  Clones from Mikes XS didn't have the lighter spring.

Hopefully someone on here can chime in about actual use on this.

[JBeasty]

So I guess if I order them (the Mikes XS emulators), I'll see better what you're all talking about. I've read through this thread (a couple times), read the instructions, and watched the video. My shriveled up retired brain is just barely grasping all of this...

[m in sc]

Also IIRC, actual RaceTech emulators came with a lighter preload spring for the top of the emulator to use with the RD.  Clones from Mikes XS didn't have the lighter spring.

Hopefully someone on here can chime in about actual use on this.

i can absolutely guarantee i have the lightest rd anyone has used the mikes xs emulators on, on rd350 shafts, which made tunign it way harder than you might expect. As said, they work fine, with the springs in them that came with them. also stock rd springs, which i felt was good for this application.. but probably not most.
In the pic up top, I turned them in about 1 full revolution after this was tested from the pic.  keep in mind, fork oil weight absolutely plays a role here as well , which i mentioned on page 1. It took a  few days to get it sorted correctly, few adjustments on the spring, and 3 different fork oil weights...but i got it.

tuned in this order:

adjuster at lightest setting, 20 wt oil. too stiff to react.

10 wt oil, way better but still a bit skow to react over 'washboarding' road on rebound.

5 wt, a bit too soft on compression but liveable.

adjust valve spring. +1/2 turn, +1/2 turn, +1/2 turn, back off 1/2 turn.

in regards to the preload adjusters, which i bought later, after having the valves in for a few years,  (remember, the valves add preload if you don't that height out of the spring spacers) so, i already had the preload already up by that amount. I actually measured the total travel of the adjusters, and cut 1/2 of that value off the spacers so that i could legitimately add or subtract where i had started from. wasnt a huge difference but it def was better.  ( i actually took some preload out to get better static sag)

loaded sag is now at about 1/4 total travel and handles bumps nicely with no undulation. 5.5 oz per leg fluid.  200 lb rider, 241 lb bike.

[oxford]

Good to know about the emulator springs.  Did you play with the slow speed bleed holes any? 

[RDFL]

So I guess if I order them (the Mikes XS emulators), I'll see better what you're all talking about. I've read through this thread (a couple times), read the instructions, and watched the video. My shriveled up retired brain is just barely grasping all of this...

It's always easier to do something than imagine or explain it.