F3 cartridge conversion

[shinyribs]

My aim was to find an affordable set of forks to slot in to our trees in the hopes for a quick, inexpensive fork upgrade that anyone could do with basic tools at home. Well, I think it worked out, but it's not quite as "bolt-on" as I hoped. It's still relatively simple to pull off at home. Here goes...

The forks to use will be Honda 1995-98 Honda CBR600F3 forks. Has to be F3 forks. There were a few F2 forks in '94 that had cartridge internals, but I'm not positive they are the same as these. The internals will give you dual cartridges in each leg ( rebound and compression ), externally adjustable rebound clicker and externally adjustable preload. There is no external adjustment for compression. 

My first goal was to just use the F3 forks in our trees. F3 forks are also 41mm like ours. That would retain all factory geometry while also upgrading to larger, floating rotors. But it didn't work out. Fork spacing of our trees is too close together, so the stock F3 wheel would not fit back between them. The stock F3 wheel uses the same size tire and it's twisted 6 spoke pattern would be very close to a visual match. 

Imgur

---

Post with 0 votes and 5 views.

 

 

Moving on...let's see if we can just use our fork lowers on the F3 tubes and cartridges. The answer is, yes!

Stock internals above, F3 bits below. A few thing to note here. 

1- Springs are the same length(the picture is deceptive). Spacers are different lengths, but that's not important. We'll get back to this later. 

2- F3 springs are progressively wound. 

3- What anchors the forks together uses different size bolts. More on this directly below.

Imgur

---

Post with 0 votes and 0 views.

 

Here is the final fastener that actually holds the forks together. Above is the damper rod from the stock forks, below is the compression cartridge from the F3 forks. The stock bolt is a 10mm , the F3 bolt is 8mm.  If you've ever changed forks seals/bushings...these are those bolts in the bottom of the fork lower that want to fight you.  

Imgur

---

Post with 0 votes and 1 views.

Here's what it takes to do the swap. 

When you first disassemble the F3 forks this is what you will see at the bottom of the cartridge assembly. That threaded hole is where is the forks lower attaches. You need to remove that compression cartridge from the cartridge assembly. 

 

Imgur

---

Post with 0 votes and 0 views.

 

Just with your finger, push the cartridge in to the tube to reveal this circlip. Pop out that circlip.

Imgur

---

Post with 0 votes and 1 views.

 

Thread the bolt back in as a handle and pop it out. Easy peasy.

Imgur

---

Post with 0 votes and 0 views.

This is what needs to  be modified. That aluminum piece is just a seat for the cartridge assembly. It sandwiches between the fork lower and the compression cartridge. Since the F3 bolt was 8mm it also needs to be opened up to accept the 10mm bolt needed for the stock fork lowers. The bottom of the cartridge needs to be drilled and tapped to accept the stock bolt as well. This is the only things that need to be modified. 

Imgur

---

Post with 0 votes and 1 views.

Before you do any work to the compression cartridge you need to fully disassemble it. You can not have ANY tiny amount of grit or debris in these components. We're talking surgical clean here. Try your best to not mar the outside of the valve. Use hardwood, sheets of copper, aluminum soft jaws on your vice....whatever it takes...but please avoid pipe wrenches, vise grips,etc. 

All you need to remove is the socket head ( allen head) screw that holds the valve assembly to the valve body. That bolt is threadlocked in place, so get a good grip on things, but you do not need to use an impact or anything crazy.  Now you can drill & tap without damaging the valve assembly.

Imgur

---

Post with 0 votes and 1 views.

You do NOT need a lathe to do this! I never turned the machine on, I just used the lathe to help me align the parts for tapping. I tapped the valve by hand. But note the slip of copper protecting the valve body from the jaws of the chuck. Something like that is all you need. 

The new thread needs to be tapped to M10-1.0.  10mm diameter with a 1.0 thread pitch. 

Your tap should tell you what size drill bit to use. If not, a 8.5mm drill bit is the industry standard to use for a M10-1.0 hole. 8.5mm lands right between 5/16" and 11/32". I used a sharp 11/32" drill bit with perfect results. 

 

Imgur

---

Post with 0 votes and 1 views.

Important! Do NOT drill all the way through the valve body. Only drill and tap as far as needed. You can see it clearly with all the parts in your hands, but remember that the other side of the valve body uses a smaller fastener to retain the valve assembly.  You can see a small step at the base of the new M10-1.0 thread. That is where the smaller thread begins.

New M10-1.0 thread.

Imgur

---

Post with 0 votes and 1 views.

Smaller thread on other side of the valve. 5mm? 6mm? I can't remember...

Imgur

---

Post with 0 votes and 1 views.

 

At this point, you are done modifying, all that's left to do is reassemble the forks as if they were bone stock F3 forks.  You use the forks tubes, caps, internals and lower bushings from the F3 forks. The ONLY  FZ07 parts you will use is the fork lowers, 10mm retaining bolts and upper fork bushing. 

The lower fork bushings from the F3 forks are interchangeable with your stock bushings, but they are actually properly sized! They are not the "too small" bushings Yamaha gave us. So, reuse the F3 lower bushings unless you already have properly fitting bushings that are in good, or better, shape than what is in your F3 donor forks. 

The upper F3 bushings are larger than our stock bushing, so be sure to reuse the stock upper bushing or you will bind the forks. 

Stock on the left, F3 on the right. 

Imgur

---

Post with 0 votes and 0 views.

 

Finally assembly notes: 

Honda and the internet will gine you lots of differing suggestions on what fork oil  and oil level to use. The thing to remember is that our bikes are a good 40lbs lighter than the F3 donor bike these forks came from.  I originally went with 10w oil at 116mm oil level. It was harsh. I am currently using Maxima 52 oil at 120mm oil level and am happy with how the forks feel.

Also, I am 220lbs in my birthday suit.  I do not know what the stock spring rate is for F3 forks, but they springs work for me. However, remember earlier when I mentioned the springs were the same length? If you are happy with your current spring rates, just reuse your stock springs. The diameters are the same, so you're good to go. 

This post is strictly to show what small modification need to be done to install our stock fork lowers on to F3 fork tubes, and what oil weight and level works good for our bikes.. I am purposefully not going in to detail on how to disassemble and reassemble these two different types of forks. There's tons of info on that already. Just disassemble both, drill/tap the valve body and reassemble. 

Ride impressions:

There is no doubt you are riding on late 90's sport bike fork technology at this point. Low speed compression bumps are a tad harsh. Not bone-jarring, just a tad harsh. But everything else is fantastic. Compression and rebound characteristics are VERY good. My stock forks would often jar me at speed. EG, hitting bridge expansion joints at highway speeds. That no longer happens. If you riding on a rough road at city speed (25-35 mph) the forks will feel a tad harsh....kinda like riding a sport bike! But at speed?....oh, at speed...that harder you push the plusher they feel. Throw the bike back and forth between corners and she's solid. No wallow. No wiggle. Just a nicely dampened front suspension. 

Travel:

If you look up the specs on wheel travel on our bikes VS the F3 forks you will think this will give up fork travel. It won't. Yamaha lied. The ONLY way you can get the full 5.1" inches of travel out of the stock forks is if you completely compress the topout springs. Never gonna happen. Wheel travel is the same.

 

Now...here's the "bad" art of this deal. The fork tubes are 2.25" longer than stock. So, if you just want to do this to your bike and leave everything else stock you will be rocking some extra fork tube above the top yoke. Like me! Yeah, you might look like a total squid noob with a lowered bike at first glance, but who cares. 

However....this also give you some pretty nice options!

Been wanting to raise your bike and inch or so? Gotcha covered.

Want to run legit clipons without some bulky,expensive adapter that bolts to the floppy stock bar mounts? Gotcha covered there, too! A set of 41mm clipons ( very common size) could be slid in to place and made to work oh,so easily. So are the long tubes a blessing or a cosmetic con? depends on what you need out of your bike. 

 

 

And yes, I did check for travel with so much tube exposed. You will not crash the fork lowers in to the bottom yokes. The bottom edge of the blue masking tape represents the forks completely bottomed out. Plenty of clearance. 

Imgur

---

Post with 0 votes and 1 views.

 

So, stock fork lowers in order to retain your original wheel and brakes. But add fully cartridge internal, extra height is wanted and the ability to mount clipons. For 100 bucks. I paid $75 for my forks off Craigslist and wasted some oil figuring out what worked good. 

 

Imgur

---

Post with 0 votes and 2 views.

 

 

[Evill_Ed]

Great job, nice write up too

[shinyribs]

Ended up doing about 600 miles on this bike over the past two days. I'm very happy. 

If you commute in town daily and want ultimate plushness, this is not for you. 

I wouldn't call the ride quality harsh. I think "taut" would be a better description. 

There's a reason Cadillac's don't ride like Corvette's. This is definitely sport bike suspension. 

The bike feels so much more composed now. I may try to dig in to the compression stacks and search for some low speed plushness ( I'm pretty familiar with this generation of Showa cartridges, so I have some ideas and good baselines to work from ), but right now I don't have any complaints. However, I will update the thread if things progress. 

 

[firstyammerha]

lucked out with the FZ slider bushings working with the CBR stanchions didn't we? As I recall from my many wanderings through the Racetech website, there was a Suzuki fork with adjustable damping in both directions. May have been a 43mm stanchion though. Gave that swap a thought a number of times but... 

[twf]

5 hours ago, firstyammerha said:

lucked out with the FZ slider bushings working with the CBR stanchions didn't we? As I recall from my many wanderings through the Racetech website, there was a Suzuki fork with adjustable damping in both directions. May have been a 43mm stanchion though. Gave that swap a thought a number of times but... 

gsxr600 but those are 45mm tubes.

Cartridges can be adapted, so can many others. 

F3 is easiest one because you don't need caps made or modified. They can also do both compression and rebound if set up that way. 

[firstyammerha]

@twf and @shinyribs,I'm going to drag this string out some more by asking if the FZ07 bushing has enough width to allow a 45mm id? Is there a bushing with the 45mm ID and X mm od of the FZ07 bushing available? Break out the catalogs boys! And could the fork clamps be spread enough to allow the 45mm Suzuki stanchion to slip through them? 2mm is all I figure they would have to stretch. Sorry, but this type of post gets my wheels turning.

[twf]

Negative on all. 

[shinyribs]

Yeah, twf is correct. No stretching of yokes allowed. There's only enough flexibility in them to allow for clamping. Any extra movement, opening or closing, and they will snap. 

[LamHa]

You legend. 

[firstyammerha]

Oh well, I had great luck moving 38mm Suzuki RM forks to my 36mm PE clamps way back in the 'day' and thought this may work. Maybe Yamaha aluminum is made to different specs than Suzuki aluminum? It seemed that using the FZ07 slider in a bigger stanchion would ease the swap and be an  even better improvement.