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Tuning AC RD350 front suspension

Started by 2t Fan, October 02, 2021, 04:12:41 AM

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m in sc

Quote from: oxford on January 31, 2023, 06:44:28 AM
Good to know about the emulator springs.  Did you play with the slow speed bleed holes any?
i was prepared to if i needed to but nope, didnt feel it needed anything aside from opening up the larger ones in the bottom.

JBeasty

Quote from: oxford on January 30, 2023, 08:54:31 PM
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.



















I think I'm gonna drill my holes like you did, 4 of them staggered, and leave the 4 that encircle the rod in a straight line alone. I'm afraid if I tried to enlarge them it may weaken the rod.
One a side note - I just joined my local "Makerspace." They a have huge old Southbend lathe, and a Bridgeport mill. Plus MIG & TIG welders, and any other metal working tool you can think of. Plus lots of other stuff I'm afraid of...    AND, they have people who will help you learn how to use it all! $50 a month. 2 miles from my house. Watch out!!
1977 RD400

sav0r

The rods are in compression. Even with some holes they are capable of holding relatively massive loads compared to what a motorcycle will exert while operating.
www.chrislivengood.net - for my projects and musings.

Striker1423

So, what does this actually do to improve things?

JBeasty

Quote from: Striker1423 on February 08, 2023, 08:36:17 AM
So, what does this actually do to improve things?

If you mean adding emulators, it apparently enables you to adjust compression damping (with the little spring tension), and rebound damping (with oil weight) individually. I say 'apparently' because I don't have any experience with them. But if Mark says they work, I'm all in  :haw:
1977 RD400

m in sc

I'm by no means the expert, but they worked for me for sure. it controls the flow of the fork oil better than just the drilled holes.

Dvsrd

Quote from: JBeasty on February 08, 2023, 12:49:47 PM
Quote from: Striker1423 on February 08, 2023, 08:36:17 AM
So, what does this actually do to improve things?

If you mean adding emulators, it apparently enables you to adjust compression damping (with the little spring tension), and rebound damping (with oil weight) individually. I say 'apparently' because I don't have any experience with them. But if Mark says they work, I'm all in  :haw:
It's more to it than that. The compression damping curve is improved, i.e higher low speed damping forces, and lower high speed damping forces. This cannot be achieved with the stock (or even modified) fixed orifices

m in sc

^ with the valve in the flow path, it will somewhat proportionately react to the speed of the movement as well. this can be dialed on my tightening or loosening the spring.

I don't have a great explanation, but that's about all i have. 

JBeasty

I read through this a couple times, pretty much explains everything they claim to do.

https://racetech.com/page/title/Emulators-How%20They%20Work
1977 RD400

oxford

Quote from: JBeasty on February 08, 2023, 12:49:47 PM
and rebound damping (with oil weight) individually.

If you look at the pictures I posted earlier you will see a weld spot on the rod and another pic with a small hole drilled.  This was done to "adjust" (change) rebound, the original hole was welded shut and a new smaller hole drilled.

I did the hole size based on recommendations off one of the triple boards.

m in sc

so, I actually rode mine in to work today, its been a few mos.  My commute, in sections, has washboarded roads, some big truck tire indentations and I cross 2 sets or failroad tracks, one at about 30 degrees at the top of a hill, so not ideal in some spots. trying to be objective riding it.. its not cushy, but is def responsive wot feel stable and safe. one section of flat road i did take it up to about 90 mph and felt really good. I'll be honest, would it be better if it was a -hair- softer, probably, but not really super necessary. I have a big fzr1000 rotor and a blue dot caliper, and hitting the brakes hard compresses the forks at speed about 2.5-3"


sav0r

DSVR described a "digressive" damping curve. It's basically what all good dampers do. You want "platform", basically chassis support in low velocity movements. However, on a big hit you want it to deflect. That's a pretty simplified explanation, but it works.

Rebound is easy, it's based almost strictly on spring rate as it is more or less a known quantity, as a result it's not that sensitive.
www.chrislivengood.net - for my projects and musings.

m in sc

rebound is also controlled by fluid flow, and can be manipulated with a 2 step valve on these forks but thats way overkill in this application. the return holes in the legs will control this though.
some modern sport bikes will have rebound adj on one fork, and dampening adj on the other as weird as that sounds. its important as it will keep the front end planted better as well.

sav0r

Rebound is an amazing tuning tool, probably the most valuable of them as far as dampers are concerned (lots of nuance to be explored in this realm). However, these ancient forks suck so bad that we need emulators and we aren't even worried about rebound. Even a lot of very high level dampers still use orifice style flow adjustment (looking at you, Ohlins) and it is just wrong. They do all sorts of weird stuff. That's partly why emulators work so well.
www.chrislivengood.net - for my projects and musings.

Vintagetz

#44
I use racetech valves in my race forks and they gave me a huge improvement. 

The pictures above are perfect to show the modifications and the adapter.

This has been covered in various answers, I will try and share my experience with installing and tuning emulators..

Fork Springs are a VERY IMPORTANT part of getting the front end right.

the stock damper rod uses fixed-diameter orifices, which means they are not speed-sensitive.

First, understand standing what each component does.

The spring holds the front end of the bike up  (I use straight-wound springs)  the more the bike and rider weigh the stronger the spring you need.

Compression damping absorbs the energy of a bump and also controls the rate of spring compression during braking and at times both.

Rebound controls the release of energy stored in the compressed spring as the front end rebounds from a bump or braking or a combination of both.

The gold valves provide speed-sensitive compression damping through a combination of a washer stack and an adjustable spring with rebound damping being controlled by the weight of the oil.  the more you tighten the spring the more it restricts the flow of oil during fork compression.  Too much compression damping will lead to post-bump chatter,  this can be while straight up and down under braking or leaned over in a corner (VERY SCARY).  Not enough can lead to over-compression (front-end dive) under braking.

The reason the damper rods have to be drilled out is that the existing compression damping system must be eliminated, it uses the smaller diameter holes to restrict oil flow BUT it provides very little in the way of speed-sensitive damping, speed meaning the rate of available flow to adjust for the speed at which the forks are compressing.

You can see the small diameter bleed holes at the base of the damper rod, these get drilled out to 5/16"/8mm.   My forks use Daytona damper rods which do not have the flow restrictor on the top of the rod, they are the same as the RZ350 with an open top and RZ350 emulators drop right in.

There need to be 3 sets of larger drilled holes through the damper rod.  On most forks, there are two smaller sets at the bottom about 10mm apart and at 90 degrees to each other.  a 3rd set is drilled the same distance above at 90 degrees to the top set (use a pilot drill to add the 3rd set or you will have an issue drilling them straight.  They don't have to be perfectly aligned, they are there to pass as much volume of oil as possible up to the gold valve.

NOTE THE HOLES NEED TO BE WELL DEBURRED, drilling through the tubing will leave some nasty burs that can fall off later (I use a dremel with a small ball end burr)

For the early damper rods and 400 damper rods an adapter that seats on top of the rod and provides a nice flat surface for the emulator to sit on is all that is needed.  the spring seats on top of the emulator holding it in place. 

As was previously stated if the top of the damper rod is open and the same ID as the steel rod this is all you need together with the adapter.  400 Damper rods other than Daytona) need to have the top cut off.  While doing it on a lathe makes for a nice even cut it is not absolutely necessary as the emulator sits on top of the adapter - spacer. it needs to be cut off far enough down so the emulator fully seats and fits flat on the adapter spacer. I think a nice even cut with a hack saw that is fully deburred will work fine.

Adjusting compression is a matter of adjusting the tension on the spring.  I run mine at 3.5 - 4 turns down.  you back the center screw out until the spring is loose, then wind it back until the spring is in contact with the emulator and the top washer under the head of the allen, then count the turns down. The fewer turns from contact the lighter the compression damping.  Too much compression damping with cause the front to chatter as - after you hit a bump.

Rebound damping is controlled by bleed back holes in the damper. Rebound is adjusted but changing the weight of the fork oil, I use 15wt.

Once you have modified the damper rod it is only a matter of assembling the new setup.

SPRINGS:

This is an important part of the upgrade.  I run between an 8.5KG and 9KG straight wound spring,  I can't really tell much of a difference.

As far as setting pre-load, sag is an important indicator that you have the preload correct,  Max at Traxxion dynamics gave me a rule that I have always followed for pre-load, a spring should never be compressed more than 20mm-3/4", if you need to compress it more than that you need to go to a stiffer spring.  I run a 10mm spacer. PVC makes a fine spacer

I can understand that for street use a progressive spring will yield a more compliant ride at lower speeds, I'm not worried about that on the track as even the out-lap is at a good pace.

I have not modified any  76-78 400 forks, all of my stuff has been Daytona, RZ, FZ/FZR and R6.  I will try and film doing a set, honestly, it can be done with a standard drill, a center punch, a couple of drill bits, and a saw if you are careful and pay attention to detail.