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Go Back   FZ1OA Message Board > FZ1 & Fazer Owners Association > Tires, Brakes, Suspension & Steering > Gen 2 Tires, Brakes, Suspension & Steering

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Old 11-12-2016, 09:28 PM   #1
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No Rebound Damping - Found Problem

If you are curious, here's what the guts of a Gen 2 FZ1 rebound cartridge look like:

How'd I get here?

Some mornings, I need to go around my community's security gate because it doesn't register motorcycles and there are no cars around to open it for me. I ride up a sidewalk break and then drop off the curb after passing the gate. Back in about June it started topping out hard when the front wheel would drop off. As I had changed the fork oil just a few months prior I thought maybe I didn't get the right amount of oil back in and it was sucking air. Soon after I had an engine running problem that made this seem unimportant.

Well, I got the engine running again and today was the day to add fork oil. I got the leg off and once I got it open I found there was plenty of oil. Next, I pulled the spring out so I could manipulate the damping rod. What I noticed was that there was no rebound damping at all and the adjuster made no change from full hard to full soft. At that point I knew I had to finally figure out how the cartridge came apart. It turned out to be easy but I figured there was a serious problem when loose parts fell out. These turned out to be he upper bypass system that opens during compression events. Ultimately, I was able to get the piston stack out and I learned that some threads at the very bottom of the damper rod shaft had broken. There is a nut that holds the valve on but there are now no threads to mate with the nut.

So, coupla questions:

1. How does this happen? The top out spring keeps the top-out loads from reaching the valve. Note that I did go for Duken's 5/10 comp/reb oil mod when I changed the oil. I haven't heard of any problems from this, though. Seems like it's gotta be a decent amount of load to break off the threads. Maybe just fatigue? No, it's not from excessive wheelies.

2. I am seeing some references to Race Tech Gold Rebound Valve for Gen 2 FZ1. Is that accurate? I would think we'd hear more people installing them if it were true. If that is, indeed, a Gen 2 fitment, does it replace the nut part that is just below the top-out spring?

3. Does anyone know the order that the upper and lower shim stacks go together? On the top, I think it is valve body-shim-spring-plate. There is a short spacer that I believe goes between the top out assembly and the upper plate. It, for sure, goes above the valve body. Does it maybe go inside the spring? Also, for the bottom stack, I was able to keep the shim stack together so I know the right order and which side is up. But, there are 2 small washers that I presume go between the bottom plate and the nut that holds the whole shebang together. Is that where they go?

Now, off to find some fork internals.

Thanks for any assistance,
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Old 11-13-2016, 04:01 PM   #2
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Damping, glorious damping. I was able to fix it without replacing parts. Explanation and more pics to follow.

Editted to add:

So, this morning I was thinking that, if the part whose threads got broken was easy to make, maybe I could make a replacement part rather than wait to get ahold of a used cartridge. I was able to get the damper rod out of the part and this is what was revealed:

The sharp part sticking out of the damper rod is the needle that is responsible for changing the damping when the adjuster is turned. The inside of the valve is way too complicated to make reverse engineering and manufacturing a new one worthwhile.

Now, yesterday when I saw the threaded end clearly had broken threads and 2 tiny chunks of steel came out with the guts, I stacked the valve parts on the end of the shaft only to be left with zero threads for the nut to grab onto. Well, today I looked a little closer at the parts and where the burnishing/wear marks existed and I determined that I was stacking the parts on in the wrong order.

I had them stacked onto the shaft from left to right. The 2 things I noted today that I missed yesterday is that 1.) the axial length of burnishing marks on the shaft where the spacer appeared to sit didn't match up well enough with the actual length of the spacer and 2.) the shim was a really sloppy fit to the shaft but was a nice fit with the spacer. You can see this in the first pic of the first post above where the spacer is still on the sahft. That's wrong.

The right way is the umbrella plate (my terminology) with the 4 holes goes on first, then the small cylindrical spacer, then the spring, and finally the upper shim. Once I rearranged the order of the upper parts it looked like this:

Then, I had a closer look at the valve body and figured out that I was trying to assemble it backwards. One side looks like this:

and the other looks like this:

I must have been a little careless yesterday because I thought I kept the valve body in the same orientation (top vs. bottom) as I pulled it out. But, when stacking it up today, I noticed that the spacer fits in the recess shown in the second pic really nicely and that the first shim on each side had different outside diameters in addition to different inside diameter. Once I got the valve body and lower shim stack on in the right order, viola, there was just enough to get the nut on and tightened down:

In this pic, the difference in shim diameters is more noticeable than when they were laid out on the table.

Although a thread or thread-and-half had broken off the end, there were enough left to take the tightening torque (which I had to guess on...tight but not gonzo tight) and I used red Loctite for insurance. Once I got the cartridge back in the fork and poured some oil in, I could tell right away that I had it together correctly. I got only a little resistance in compression with lots of resistance in extension. I temporarily put the top cap on and when it's on full hard it is quite difficult to pull out but the same low effort to compress...just like it should be. Got it all put back together, raised the forks in the trees (something I had been wanting to do), and took it for a ride. As you might imagine, it feels a lot better mid corner now that it isn't pogo-sticking back at me.

I think that the nut loosened from vibration and broken the last thread or so when that was all that it was hanging on by. I have had a lot of problems with the ignition on this bike and when it is not running fully on all 4 cylinders it is not real smooth.

So, there you have it, a Gen2 FZ! rebound cartridge autopsy and revival. If you've read this far, even if you never have occasion to need this information, I hope you've found it interesting.


Last edited by XJtoFZ; 11-13-2016 at 05:19 PM. Reason: Explanation and more pics
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Old 11-13-2016, 04:51 PM   #3
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Originally Posted by XJtoFZ View Post
Damping, glorious damping. I was able to fix it without replacing parts. Explanation and more pics to follow.
do tell
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Old 11-13-2016, 05:20 PM   #4
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Refresh the thread.
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Old 11-13-2016, 07:12 PM   #5
Picture added for humor only
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I have found it interesting. Glad you were able to figure it out and affect a fix. Good job!
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Old 03-24-2020, 12:14 PM   #6
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How does one get the damper apart in the first place? are the two parts threaded and screwed together? Is loctite used?
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Old 03-24-2020, 03:07 PM   #7
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Originally Posted by Thatdude View Post
How does one get the damper apart in the first place? are the two parts threaded and screwed together? Is loctite used?
I hope you get a response. This thread is 3 1/2 years old.
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Old 03-24-2020, 04:56 PM   #8
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That is odd, as the factory install has the threaded end of the cartridge rod peened over the nut and likely loctited.

I did Stoltec valves on my Super T and now that I am familiar with this stuff, toying with contacting Traxxion for their kit to install a proper compression side cartridge in place of the stock needle/orfice setup on the FZ1. I had to grind off the peened bit on my Super T's innards to get the stock pistons and shims off so I could replace them with the blingy anodized Penske pistons.

The one thing with the Super T that I imagine is typical is the threads on both ends of the catridge tube have nuclear powered yellow guerrilla snot loctite on them. The only way to undo it is to torch it until it smokes. Would never have done that if not inspired by a YouTube video on this. Once suitably hot, it softened up and unscrewed no problem.

Attached are some photos from my Super T job. The first shows the stock base valve, which screws in at the base of the fork with it's bolt facing the axle. The threaded part screws into the cartridge tube via the aforementioned yellow locking snot. Note the peened threads above the nut I was referring to.

The 2nd pic shows the fancy blue cartridges on the base valves with their ground off threads and loctited nuts. The stock rebound valve still on the end of the damping rods is in the middle of the pic.

The last pic shows the stock disassembled rebound valve in relation to how it came off the rod to the right. There is the cap and spring on the rod still, the thin check valve washer which allows flow through the ports it covers on compression, blocking them off on rebound, piston, rebound shim stack, base washer and nut. Note the different heights of the ports on the piston itself in the last photo, the smaller higher ones blow off on compression via the thin check valve, the bigger ones feed the rebound valving on extension.

Note the small hole on the damping rod - that is the low speed rebound, the aluminum rod that fits inside the damping rod that is adjusted by the clicker blocks off varying amounts of this hole to adjust the low speed rebound. The high speed rebound is handled the shim stack/valving.

Basic forks really like ours are not that complicated. The Super T rides much better on proper fork springs and the Penske/Stoltec valving
Attached Images
File Type: jpg base valve.jpg (39.9 KB, 44 views)
File Type: jpg cartridge.jpg (56.3 KB, 43 views)
File Type: jpg rebound.jpg (39.8 KB, 43 views)
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Old 03-24-2020, 07:24 PM   #9
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I still get emails from this forum and am happy to help.

Matt, if you PM me an email address I'll send original pics with explanation. Everything screws together. I don't recall any Loctite on disassembly and only used it on the nut when I re-assembled it. You will need a tool to keep the cartridge from spinning when you're trying to loosen or tighten the foot bolt.

I cannot agree with you more, was a strange failure. If the factory peened it, the peen marks would have been on the broken chunks I removed. I didn't peen anything because there wasn't any male shank protruding past the nut. Getting close to 3.5 years and 20k miles without issue. YMMV.

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Old 03-25-2020, 12:26 AM   #10
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Duken4evr - thankyou very much for that further information. XJtoFZ, Thanks for getting back to me.

What a helpful forum, thanks chaps
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