• Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

    When he passed, I worked with his kids to gather the necessary credentials to keep this site running. Since then (and for however long they worked with Coffee), Woodschick and Dirtdame have been maintaining the site and covering the costs. Without their hard work and financial support, CafeHusky would have been lost.

    Over the past couple of weeks, I’ve been working to migrate the site to a free cloud compute instance so that Woodschick and Dirtdame no longer have to fund it. At the same time, I’ve updated the site to a current version of XenForo (the discussion software it runs on). The previous version was outdated and no longer supported.

    Unfortunately, the new software version doesn’t support importing the old site’s styles, so for now, you’ll see the XenForo default style. This may change over time.

    Coffee didn’t document the work he did on the site, so I’ve been digging through the old setup to understand how everything was running. There may still be things I’ve missed. One known issue is that email functionality is not yet working on the new site, but I hope to resolve this over time.

    Thanks for your patience and support!

DIY tuning the Sachs shock

Sparked said:
Hijacking my own thread, now it's about the KYB forks instead of the shock

So I dug into the front rebound today. Getting them apart was a pain in the butt. Strictly speaking, it was making the tool to get them apart that was hard. The actual disassembly is pretty easy once you have the right tool. I measured some things, did a bunch of spreadsheet calcs, re-built the stacks, and put them back together. I had no oil, so I can't test them yet, but I'm pretty hopeful. I basically took the rebound damping curve of the shock that I liked, and scaled it for the forks. I already had some spare shims that fit, and they were necessary.

The stock fork rebound stack: (6mm id)
23 .12 x7
14 .1
22 .12
20 .12
18 .12
16 .12
14 .12
12 .12
9 .2 x2
16 clamp

My first try:
18 .1
23 .12 x3
14 .1
23 .12 x2
22 .12
22 .1
18 .12
16 clamp

The 18 face shim has me a little nervous. I don't think the restackor program is calculating it properly, so I fudged it. The point of the shim is to give a little free bleed without drilling holes in the piston. The shock already had a bleed hole, and from what I could see, the forks didn't have one but need it.

Here's the graph. Stock on the left (yuck), modified on the right (fingers crossed).
huskyreboundstacks2.png
Click to expand...

So, how did this work out?
 
MOTORHEAD said:
So, how did this work out?
Click to expand...

It worked out quite well. I rode the Desert 100 in Washington the other weekend, which is mostly rocks and whoops. It handled the rocks really well- the front was much more planted than before. I've got some more changes planned to help with the whoops. I'll go a little stiffer in the rear rebound damping, and completely re-do the front compression damping. I know what I want in terms of the current valving and clicker settings, so hopefully the software will steer me right again for the stacks.

I have some shims on order, so will see what I can do when they get in.
 
Good deal. Hey, thanks for turning me on to the program. I've spent some time going bacl over some of the stuff I've done in the past using the program and notes I have, so I can get a better idea of what it's telling me. Should be a big time saver, once I invest the time to understand it.
 
Been following your thread, but only now watched the video... now that is some cool stuff!! Was that video before or after the fork revalve? The rear sure looks planted!
 
Yes, reservoir (nitrogen) piston. Motorhead says the spec is in the manual but I sure can't find it!
 
Ok, I made some progress, and then got busy so didn't post any results. I've done basically the same thing to the compression valves (both front and rear) that I did to the rebound valving. And, I increased the rear rebound damping to fix the kicking. It's still not perfect, but it's all been forward progress which makes me really happy.

Starting with the rear rebound. It mostly felt good but kicking more than I liked. I did the spring-mass-damper calculations and my first stack had a damping factor of 0.84. The new stack has a damping factor of 1.02. It works way better. The back tire still sticks, but there's no more kick. For the SMD calculations, I used 6.0 for the spring and 54kg (120#) for the mass. That is my guess for the sprung mass of the back of the bike.

The stack is:
38 0.250
38 0.25
24 0.250
36 0.25
36 0.25
36 0.25
36 0.300
34 0.300
32 0.250
30 0.300
28 0.250
26 0.300
24 4

This is the same as the previous rebound stack with 3 36x.25 shims added to the high speed side. I also switched from 6wt to 5wt oil.

Compression on the rear was just a wild guess, but it seems to have worked out.

Stock:


44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
36 0.20
40 0.20
38 0.25
34 0.25
30 0.25
26 0.25
24 0.25
22 0.30
20 0.30
36 5.00

Modded: The same as everything else- go to a linear damping curve instead of the stock digressive curve.

44 0.20
44 0.20
44 0.20
20 0.30
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
40 0.20
38 0.25
36 0.20
36 0.25
36 0.25
36 0.25
34 0.25
30 0.25
26 0.25
36 5

The new stack has a much smaller crossover to reduce the low speed damping, and then added shims and a much larger pivot to stiffen the high speed.

It feels pretty extreme. Bouncing on the seat it almost feels like the shock is blown, but when riding it feels great.


The forks were giving me trouble at the Desert 100, but I'd had some time to play with the clickers so the software was able to duplicate the clicker changes I figured out. Basically, make the low speed damping like the clicker are open, and the high speed like they're closed.

Modded base valve:
20 0.12
24 0.12
24 0.12
24 0.12
24 0.12
12 0.12
24 0.12
24 0.15
22 0.15
20 0.15
18 0.15
18 0.15
16 0.15
13 0.15
13 0.15

I removed two low speed shims, added a 20mm face shim for some bleed, and stiffened up the high speed rebound stack. Sound familiar?

The new fork valving worked well on rocks, but I think it needs even more stiffening for big bumps and whoops. That'll probably be a mid-valve mod, but will have to wait until I get some actual riding in. All garage and no trail.......
 
Picklito said:
Been following your thread, but only now watched the video... now that is some cool stuff!! Was that video before or after the fork revalve? The rear sure looks planted!
Click to expand...

Thanks!

That was with new springs, the revalved shock, but stock fork valves. Watching it was actually what motivated me to dig into the forks, as the front tire looked to me like it was extending slowly off all the bumps.
 
RE: the reservoir piston.

I'm just forcing it all the way in using air pressure, then releasing the pressure and installing the seal head letting the head's displacement force the piston back from the top of the cylinder. I think I got the idea from someone on this forum.
 
Sparked said:
RE: the reservoir piston.

I'm just forcing it all the way in using air pressure, then releasing the pressure and installing the seal head letting the head's displacement force the piston back from the top of the cylinder. I think I got the idea from someone on this forum.
Click to expand...

Seems interesting.. Let us know how it works!
 
So, more fork nonsense yesterday. I had swapped the fork springs back to stock, based on Vinduro's recommendation in his thread. That was mostly better, but the bike dived into whoops and waterbars even more than before. I tried to fix that with the midvalve. The float is much higher than on other bikes. It was around 0.65mm, though I couldn't measure it very accurately. I added an 8x10x.15 shim to the bottom of the midvalve to get the float down to .5mm. Full fork disassembly just to add a single shim. So it goes.

The new midvalve stack, with the 10x.15 that I added:


24 0.12
24 0.12
24 0.12
22 0.12
20 0.12
18 0.12
16 0.12
14 0.15
12 0.15
10 0.3
10 0.3
10 0.15
22 0.4


With one ride on it, I'd say it's an improvement. If I do anything more to it I'll probably reduce the float a little more to make it stiffer. A couple of points about that. One is that the rebound stack I'm using has a little bleed, which is also acting as bleed for the midvalve. The other is that I'm big and make mistakes. If I were lighter or could be sure that I'd always have my weight way back when hitting big bumps I don't think I'd need as much stiffness in the front end.
 
Are those KYB mid-valve pistons cross-drilled with a bleed hole? I've been working with my Marzocchi 50's to get rid of the dive, and more and more it's looking like the bleed hole in the MV piston is too large. It's certainly larger than I've seen on other forks. I may peen them closed a bit and see how that goes. I have not been in your model of KYB, though. Just thinkin' out loud here...
 
I couldn't see a bleed hole at all. And by the way that the forks reacted when closing the rebound clickers all the way, there isn't one.

What size is the bleed hole in the 'Zokes? I don't know how the flow numbers relate, but if you just calculate the area of the opening, a tiny amount of bleed or float around the shims is the same as a large bleed hole. FrEx, the 18x.1mm bleed shim on my rebound stack creates about the same open area as a 2.25mm hole. So reducing your midvalve float by .1mm would make an even bigger change than completely blocking off a typical bleed hole.
 
Yes, I see. Good point. I do have room to reduce float.

Another "related but different" problem is that bleed is bi-directional. Every time we move the clicker we change bleed on both compression and rebound. Very tricky to get the differential between C and R just right.
 
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