CBR600F3 Fork Cartridge Install: Taking the Plunge!

[tgold]

A little back story: I decided to put an SV650 fork on my project bike which is basically an XR650R engine in an FZR400 frame and pretty much custom everything else on the bike. A common low-cost suspension modification for the SV is to take the fork tubes and cartridges from a CBR600F3 and bolt them into the SV650 sliders. The only modification that needs to be done is to drill out the bottom bolt hole in the slider from 8mm to 10mm. This gives you adjustable rebound damping with compression damping being adjusted through changing oil viscosity.
So I bought a set of CBR600F3 forks off ebay and when I got them I found that the upper tubes were slightly bent. That meant that I could use the cartridges but I still needed straight tubes. I've been searching for a good deal on some straight tubes for about two months and coming up short when my new 250 Ninja racebike came into the picture. I decided that the little ninja would get the priority for race prep for next year and was debating whether to go with gold valves and springs for the front or just buy something like the Andreani or Bitubo cartridges. I had decided to go the emulator/springs route when I finally found a decent set of straight CBR F3 forks on ebay. So I got an idea: Buying another set of complete CBR forks would also leave me with a spare set of CBR cartridges. Why not put 'em in the Ninja? Then I would have two very similar setups on both my racebikes. I'm not aware of any other 250 Ninjas that have been done like this, so I think that I may be breaking some new ground. If it works out, I think that this may be a fairly cheap mod (around $200.00 all-in with new springs and oil).

Stay tuned!

[csmith12]

[sharky nrk]

Are the stock F3 carts rebound adjustable only?

[tgold]

Originally Posted by sharky nrk

Are the stock F3 carts rebound adjustable only?

Yes.

I don't know if it's feasible to go the one rebound leg and one compression leg route, but I'll keep it simple at first and have adj rebound in both and adjust compression damping by viscosity if necessary. I'll start with Redline Medium viscosity oil which is considered a 10wt oil. It also has a very high vicosity index which means that the viscosity changes less as it's temperature increases. That in turn means more consistent damping as the oil temperature changes.

[sharky nrk]

Originally Posted by tgold

Yes.

I don't know if it's feasible to go the one rebound leg and one compression leg route, but I'll keep it simple at first and have adj rebound in both and adjust compression damping by viscosity if necessary. I'll start with Redline Medium viscosity oil which is considered a 10wt oil. It also has a very high vicosity index which means that the viscosity changes less as it's temperature increases. That in turn means more consistent damping as the oil temperature changes.

hmm, learn something every day

I thought they were comp/rebound adjustable but never really looked into it, and thinking about it, it makes sense as there is only one location for a clicker. I too like the Redline suspension fluids - its good stuff and I have started using it in place of the Motul Factory Line options.

[TnNinjaGirl]

Well that's a cool idea. Sub'd for updates

[tgold]

Short answer: You can install the CBR600F3 cartridges in the Ninjette forks, but that doesn't mean that you should. There are a few things that make it a challenge to install with probably the CBR cartridge has an external top out spring. It looks like it is possible to remove the external top out spring from the cartridge and install a new internal spring. It was supposed to be simple.
I though of taking pics to explain it, but I just think that there are easier routes to take.

Since I already irreversibly modified one of my Ninja fork tubes, I was thinking about just buying a replacement tube and going the cartridge emulator route. But I've been learning so much about front suspensions and cartridges that I don't want to abandon the idea of doing an inexpensive cartridge install that really works for the little Ninjas.

Soooo, in my researching of what to do to solve the problem, I came across some info on installing GSXR cartridges in SV650 forks. The main difference being that the Ninjette fork is smaller in diameter and that can make things more difficult when trying to get the proper clearances so that the suspension functions properly. There are enough similarities between the SV and 250 Ninja forks that I think that it's worth a try to do a similar GSXR cartridge install for my 250.

The cartridges from the USD type GSXR forks have an internal top out spring and that makes things much easier. PLUS!: You can do an extra very simple modification to allow external adjustment for rebound and compression damping.

So I bought some slightly bent 2004 GSXR600 forks off ebay for $78.00 and I'll have them in about a week.

To be continued.......

[InvisiBill]

Intiminators drop in like Emulators, and give you shim-based compression damping as found in cartridge forks. Rebound is still handled by the stock fixed-orifice circuit.

[tgold]

Originally Posted by InvisiBill

Intiminators drop in like Emulators, and give you shim-based compression damping as found in cartridge forks. Rebound is still handled by the stock fixed-orifice circuit.

Thanks InvisiBill,
I've looked at the Intiminators and I know that they are supposed to be more sophisticated than the Racetech emulators, but in the end they are still pretty much emulators. My goal here is to do a better modification for the same money or less. Beside that, if I were to go the Intiminator or the race Tech route I would have to buy a new fork tube because I've already started modifying one and I can't go back with it.

[bruce71198]

Have you given any consideration to cartridges offered by Andriani, for under $500 or Bitubo's gas charged for under $400? Also Zoran @ TWF racing modifies the stock fork with a cartridge, which one I don't know.

[sharky nrk]

Well, interesting about the CBR forks. Are the CBR units still intact? I have some CBR F2 spare forks that those could drop into.

[Yamahawk]

I found a nice bent set of 06 GSXR600 USD forks dirt cheap, and was wondering if the cartridges in them would be able to be used for this, Timm? They have a lower rebound damping adjustment, as well as the high/low speed compression adjustment up top... What do you think about something from these forks? @tgold I think you are on to a good thing here, brother!

Charlie

[tgold]

Originally Posted by Yamahawk

I found a nice bent set of 06 GSXR600 USD forks dirt cheap, and was wondering if the cartridges in them would be able to be used for this, Timm? They have a lower rebound damping adjustment, as well as the high/low speed compression adjustment up top... What do you think about something from these forks? @tgold I think you are on to a good thing here, brother!

Charlie

Hey Charlie, a couple of things to consider: The forks can be bent, but not too bent. There is room for the parts inside to stay relatively straight even if the outer tubes are bent. The hollow tie rod that holds the adjuster rod and keeps the fork together might be able to be straightened if they are slightly bent, but I would avoid trying to straighten the tube that the valves are contained in. Any out-of-roundness there and you would have a nightmare of inconsistent damping.

As for the 06 forks, probably the most important thing is the outer diameter of the cartridge. If it's too big there won't be enough room between the cartridge tube and the inner wall of the fork tube, so that would make it act as a part of the overall damping instead of totally depending on the valves inside the cartridge. I'm pretty sure that the 04 cartridges that I'm getting will work, but I know that the 06 cartridges are different. Whether the OD of the cartridges is different I do not know and I'll let you know the diameter of the 04 GSXR cartridges when I get them and we can compare them to the 06 carts to see if they are both usable.

One more thing: the top adjustment on the fork is the rebound adjustment. That's good because pretty much everything I have read says that rebound is (relatively) more important than compression as far as adjustments go.

With the fork mod that we are talking about that leaves us the choice of putting a compression adjuster that is accessible from the very bottom of the fork, or leaving the compression adjustment as a fixed orifice which you then control by changing oil viscosity.

I'm working on a source for the special bolt that allows compression adjustment from the bottom of the fork. I'll post when I can confirm that it is still available.

[tgold]

Originally Posted by bruce71198

Have you given any consideration to cartridges offered by Andriani, for under $500 or Bitubo's gas charged for under $400? Also Zoran @ TWF racing modifies the stock fork with a cartridge, which one I don't know.

Bruce,

Thanks for the info. I have seen both on ebay and I think that's not too bad of a deal, but I'm working on the GSXR cartridge mod for a couple of reasons. If I get it right, this mod will be easily under $200.00 including springs and oil, and I can apply this to my other racebike.
Second is that I've decided personally that I want to become proficient at tuning my suspension because I'm convinced that suspension by far the most effective mod for going fast and the confidence that good suspension imparts just makes things more fun on the track.

Right now I'm learning a ton about how suspension works and I want to be able to share intelligently about what I've learned too.

[tgold]

Originally Posted by sharky nrk

Well, interesting about the CBR forks. Are the CBR units still intact? I have some CBR F2 spare forks that those could drop into.

I have done a couple of minor mods to one cartridge, but I think that they might still be usable. PM me if you'e interested and we can talk about it.

[Yamahawk]

Timm said, "As for the 06 forks, probably the most important thing is the outer diameter of the cartridge. If it's too big there won't be enough room between the cartridge tube and the inner wall of the fork tube, so that would make it act as a part of the overall damping instead of totally depending on the valves inside the cartridge. I'm pretty sure that the 04 cartridges that I'm getting will work, but I know that the 06 cartridges are different. Whether the OD of the cartridges is different I do not know and I'll let you know the diameter of the 04 GSXR cartridges when I get them and we can compare them to the 06 carts to see if they are both usable."

Timm, I have looked at pictures of both internal cartridges on eBay, and they look about identical. I found a set of 06 forks that are straight, but were burnt, I may buy them just because they are really cheap, $35 shipped, and that I could afford to risk. I believe the internals are the same according to the pictures, and the fork orientation. We can compare dimensions when I get them. What do you think?

[tgold]

Originally Posted by Yamahawk

Timm said, "As for the 06 forks, probably the most important thing is the outer diameter of the cartridge. If it's too big there won't be enough room between the cartridge tube and the inner wall of the fork tube, so that would make it act as a part of the overall damping instead of totally depending on the valves inside the cartridge. I'm pretty sure that the 04 cartridges that I'm getting will work, but I know that the 06 cartridges are different. Whether the OD of the cartridges is different I do not know and I'll let you know the diameter of the 04 GSXR cartridges when I get them and we can compare them to the 06 carts to see if they are both usable."

Timm, I have looked at pictures of both internal cartridges on eBay, and they look about identical. I found a set of 06 forks that are straight, but were burnt, I may buy them just because they are really cheap, $35 shipped, and that I could afford to risk. I believe the internals are the same according to the pictures, and the fork orientation. We can compare dimensions when I get them. What do you think?

Charlie,
I saw those same forks. My slight concern was that the heat affected the valve bodies. They are plastic. IMO still not too bad of a gamble.
Let me know if/when you get them and we will compare notes.

I have some plans as to which oil to use on these as well. I'll share that stuff in the thread later.

We are in somewhat uncharted territory. Saturday practice of the first round next season will be important to dial these in.

[Yamahawk]

Hey Timm, here is an eBay link from the fellow Matthew Patton that sells/makes the cartridge conversions for different bikes. Read through the ad and there is a lot of good info in it, and perhaps an idea or two could be gleaned also. @tgold

http://www.ebay.com/itm/Full-adjust-...tUoRNZ&vxp=mtr

[Yamahawk]

I just bought a right fork from a 96 ex250 to use as a donor fork to try the fitment out of the GSXR cartridge. I am looking at a cartridge from a 04 GSXR that should work for fitment also. Once I get them both, I will see the logistics better.
I decided to get those burnt ones instead lol, be useful for fitment!!

[tgold]

Originally Posted by Yamahawk

Hey Timm, here is an eBay link from the fellow Matthew Patton that sells/makes the cartridge conversions for different bikes. Read through the ad and there is a lot of good info in it, and perhaps an idea or two could be gleaned also. @tgold

http://www.ebay.com/itm/Full-adjust-...tUoRNZ&vxp=mtr

I'm familiar with his work from SV rider. It looks like he does a nice job, but the key would be if you could get the price where you're not in the territory of the Andreani or Bitubo cartridges.

[Yamahawk]

Originally Posted by tgold

I'm familiar with his work from SV rider. It looks like he does a nice job, but the key would be if you could get the price where you're not in the territory of the Andreani or Bitubo cartridges.

....and hence, why we strive to break new ground! I thought you may have been familiar with his work, I am just reading up on all this so I might be of some small help to you, and perhaps reap the benefits for us and others to get a do it yourself type of mod for these little ninja's! I'm thinking, if the cartridges fit into our 36 and 37mm forks, that it will work with minor valving, and spring rate mods. I am excited!! Thanks, brother!

[tgold]

Got the GSXR forks this morning and pulled the cartridges at lunch to see what we're up against. The initial look confirms there three challenges to overcome when installing cartridges in 250 Ninja forks:

Challenge #1. Ninja fork inside diameter.
Challenge #2. Ninja fork inside diameter.
Challenge #3. Ninja fork inside diameter.

We're basically trying to stuff 10lb of.... ummm.... sugar in a 5lb bag.

Then there's two other challenges to overcome after installation:

Tuning:
1. Will it be in the ballpark?
2. Can I do more than just get it in the ballpark?

So I find myself at a crossroads. Do I continue down this road with the possible future benefit to all ninjettekind? Or do I abandon the idea and go a well-trodden/proven path of cartridge emulators?

I'll have to study things a little more and consult with Yamahawk too before I make a decision.

[Yamahawk]

Originally Posted by tgold

Got the GSXR forks this morning and pulled the cartridges at lunch to see what we're up against. The initial look confirms there three challenges to overcome when installing cartridges in 250 Ninja forks:

Challenge #1. Ninja fork inside diameter.
Challenge #2. Ninja fork inside diameter.
Challenge #3. Ninja fork inside diameter.

We're basically trying to stuff 10lb of.... ummm.... sugar in a 5lb bag.

Then there's two other challenges to overcome after installation:

Tuning:
1. Will it be in the ballpark?
2. Can I do more than just get it in the ballpark?

So I find myself at a crossroads. Do I continue down this road with the possible future benefit to all ninjettekind? Or do I abandon the idea and go a well-trodden/proven path of cartridge emulators?

I'll have to study things a little more and consult with Yamahawk too before I make a decision.

I know what you are saying, brother! 4-5mm id difference is a lot to deal with, but hey that's where we can get creative also! Sent you a PM on this as a reply!
I received the donor fork today, and should receive the GSXR600 forks by monday at the latest. If the ID is too much, perhaps there are other cartridges that will work better, or maybe we can adapt springs that will work better.

[tgold]

The reality is that I wouldn't be testing the cartridge forks until the first race weekend of next season and if the cartridges aren't in the ballpark right away, that would be a major problem. There's enough to do with getting back in the saddle after a long winter and adding the stress of emergency suspension work to the mix isn't my brand of fun.

So, I've decided to pursue a parallel development path and go the emulator route for now and purchase a second set of forks for cartridge development purposes. The emulator forks will have the added benefit of providing a benchmark for evaluating the performance of the cartridge forks.

My learning style is a very visual hands-on sort of thing, so I'm thinking of taking a couple of fork legs (both cartridge and damper rod style forks) and making some cutaway models for us to educate ourselves on how our suspension actually works.

[Somchai]

@tgold - Timm when you want to do the best for your forks I would like to recommend this to you http://www.ebay.de/itm/Czech-HKS-GGV...trsG7aXKhn-7Vw

For translation please read my post here https://www.ninjette.org/forums/showthread.php?t=212845
And please don't read it as fork oil what I falsely wrote, it is an addition only.

I'm looking forward to your setup with the emulators, good luck

[Yamahawk]

Originally Posted by Somchai

@tgold - Timm when you want to do the best for your forks I would like to recommend this to you http://www.ebay.de/itm/Czech-HKS-GGV...trsG7aXKhn-7Vw

For translation please read my post here https://www.ninjette.org/forums/showthread.php?t=212845
And please don't read it as fork oil what I falsely wrote, it is an addition only.

I'm looking forward to your setup with the emulators, good luck

Looks like a good anti-friction additive! It looks like it would be something to try, for sure! I wonder if it is silicon-based? My dad had a small bottle of pure silicon lubricant he got when he worked at Boeng in Seattle in the early 60's, and a couple drops on a rag would do a whole shotgun barrel/ action, and it would protect and lubricate the metal. Good stuff!

[Somchai]

Originally Posted by Yamahawk

Looks like a good anti-friction additive! It looks like it would be something to try, for sure! I wonder if it is silicon-based? My dad had a small bottle of pure silicon lubricant he got when he worked at Boeng in Seattle in the early 60's, and a couple drops on a rag would do a whole shotgun barrel/ action, and it would protect and lubricate the metal. Good stuff!

For better understanding let me say that the translation for GGV is 'Fork-Slide-Improver'.
I don't think its silicon-based, this would be too easy to copy I guess and the company (a small one) doesn't talk about their secrets.
Some guys from the many in Germany who use this, say that Caramba 70, WD40 or Ballistol (cleaner for weapon) give the same result.
But everyone is enthusiastic after they'd try it for the first time, with only the Triumph riders say that at the usd's from the Triumph the result is not as good as with others, even when the fork after applying it feels better than before.
But with another product of that company everyone is enthusiastic in the highest level, that's the lubrication for the chain what I didn't test until now but will order and use with the new chain.
They say it makes the ride very smooth and this last for 2500 km (1,500 miles) even with riding in the rain and there also should be no more noise coming from the chain.

[Yamahawk]

Timm,
I took apart the 06 GSXR600 forks today, and it looks like the valving is totally destroyed from the heat. Which, I think will not matter as they springs and valving would have to be swapped for smaller diameter springs and valving anyway, to fit the cartridge into the 36-37mm fork tubes of our Ninja's. The OD of the springs was 36.6mm or so, and that would not fit in either set of Ninja 250 forks. So, Thinking outside the box, the stock springs may be able to be cut down to fit onto the cartridge internals,or some other spring fitted, and then some different valving made to fit. Never say never, what do you say Timm?

[HoneyBadgerRy]

@Somchai your Unregistered command got me there for a second... Now If I could get the command to work for my signature.

[tgold]

Originally Posted by Yamahawk

Timm,
I took apart the 06 GSXR600 forks today, and it looks like the valving is totally destroyed from the heat. Which, I think will not matter as they springs and valving would have to be swapped for smaller diameter springs and valving anyway, to fit the cartridge into the 36-37mm fork tubes of our Ninja's. The OD of the springs was 36.6mm or so, and that would not fit in either set of Ninja 250 forks. So, Thinking outside the box, the stock springs may be able to be cut down to fit onto the cartridge internals,or some other spring fitted, and then some different valving made to fit. Never say never, what do you say Timm?

Charlie,
Cutting down the springs will actually increase the spring rate, so you would be putting an unknown into the mix there. There are a few ways that I'm thinking of modifying the cartridges which may allow us to use the stock diameter springs.

Another problem is that the GSXR preload adjuster has a really big diameter and I'm not sure that there would be enough meat left between it and the fork cap once it is turned down enough to fit in the ninja tube.

I think that we could still use the GSXR cartridges (at least ones that aren't melted ). In any case, we aren't going to get what we want without some creative modding.

Makes the F3 cartridges actually look like an easier option!

[Yamahawk]

Yeah, these 06 GSXR600 cartridges are big! The spring is larger OD (36.6mm) than my tubes are, so that is why I am thinking of smaller OD springs. Not sure what the F3 cartridges are OD wise but there is the convention fork GSXR600 cartridges also, from a 01-03 GSXR600 also. I know you have some F3 cartridges, what is the OD of the valving/springs on them?
Also, I was thinking of using the stock fork caps of the EX250, drilled out for the adjusters from the top caps of the cartridges. That would be an alternative to turning down the caps.

[tgold]

Well, it is possible to put the Gsxr cartridges in the 250 fork. Zoran from Twin Works Factory does it for $500.00 if you send him that cartridges and your forks. I have no doubt that his setup would be spot-on from the start as he has an excellent reputation for tuning racebikes.

The challenge will be for us to figure things out without screwing it all up while only spending a couple of Benjamins.

I've already turned down one of the CBR caps and interestingly the GSXR adjuster rod threads right into it. Could be that it'll be a sort of fork mashup that gets us where we want to be.

[Yamahawk]

Originally Posted by tgold

Charlie,
Cutting down the springs will actually increase the spring rate, so you would be putting an unknown into the mix there. There are a few ways that I'm thinking of modifying the cartridges which may allow us to use the stock diameter springs.

Another problem is that the GSXR preload adjuster has a really big diameter and I'm not sure that there would be enough meat left between it and the fork cap once it is turned down enough to fit in the ninja tube.

I think that we could still use the GSXR cartridges (at least ones that aren't melted ). In any case, we aren't going to get what we want without some creative modding.

Makes the F3 cartridges actually look like an easier option!

Precisely! The stock Ninja 250 springs are very light already, and we need like a .75-.8Kg spring for racing. So, I was thinking that the Ninja springs cut to length might not be too much spring rate.
Don't know if Zoran changes the springs for the cartridge install, but have you measured the springs on the GSXR600 cartridges you have, and are they the same diameter as the ones I have? Let me know what diameter the spring and cartridge is on both the GSXR600 and CBR600F3 cartridges that you have. Good to hear that the caps will thread the adjusters from the GSXR600 to the CBR600F3 caps! We always have the option of drilling and threading the EX250 caps, too, with the o-rings already there.
Charlie

[Somchai]

Yami's showing what all is possible if the manufacturer only wants to...
37 mm USD
Swing arm from aluminum
LED's
150 cc for ~ 2,600 USD
http://yamaha-square.com/charoenmoto...9%83%E0%B8%88/
Maybe get this forks and make them competitive...

[Yamahawk]

Nice bike!! I am a Yamaha guy at heart, and they really know how to build a bike with 'Kundho' (spelling may be wrong), the philosophy for their passion in musical instruments, and motorcycles...

[howlinhoss]

Fyi guys I have Matthew Pattons gsxr cartridges in my 300 forks. I was his test dummy since I live near him. I can say that the gsxr fork cartridges retrofit is possible and they work great. In fact I got his gsxr cartridge retrofit done to my fz07 too. He does great work and I would suggest you contact Matt if you have any questions about his install. Here is my build thread if you want to see pictures.

https://www.ninjette.org/forums/showthread.php?t=238885

[Yamahawk]

Hey the forks looked good, I can see that the adjusters mounted inside the tube diameter, it looks like at least 2mm or more of thickness in the cap that the adjusters thread into. That is a positive thing for the 37mm forks in the 2008-2012 EX250 and your EX300. Now, I m wondering if it is possible to fit them into the 36mm EX250 forks from 88-07. That might not be able to get accomplished. I have to get the diameter of the earlier GSXR600 fork cartridges, as the 06 GSXR600 springs are definitely too large in diameter at over 36mm, to fit inside the tubes. I hope Timm has some time soon to measure the cartridges he has and let me know the diameter of the 04 GSXR600's. I believe that Matt Patton uses the 01-03 GSXR600 cartridges, also, correct me if I am wrong, and that they are conventional forks not USD ones like I have. That may be the way they fit, as conventional cartridges will have smaller spring diameters, in theory. It will be interesting to find a way to accomplish this in the older 36mm fork tubes. I have another set, and an extra right fork tube, so I can experiment with whatever I can find. Your bike build looks very cool!! Thanks, @howlinhoss!
Charlie

[pattonme]

@howlinhoss summoned me so here I am (the guy who does cartridge retrofits).

Choose Ricor Intiminators (Spears Racing) over RT's GVE. It's just a better product. But neither can hold a candle to the real deal.

TGold, if I build you a set of cartridge forks they'll be spot on, right out of the gate. Same can be said of Zoran. Stock donor valving (GSXR etc.) not so much. I did a set for an R3 racer never having seen the bike and he's over the moon and railing around Blackhawk Farms.

> while only spending a couple of Benjamins

Yeah, keep on dreaming there, friend.

I'm guessing folks are sourcing the Andreani from Italy (technically illegal for them to sell to USA). I have a close relationship with the USA importer who is also an Ohlins supplier so while I can't advertise below MAP, as part of a package deal or with "installation/rework" I can pass the savings on to you. The Andreani design has several tradeoffs that I can fix for improved performance though if all you ride is smooth race tracks the limitations don't come to the fore as much. Anything bumpy or on the street you'll find their OE limits.

You can get replacement stanchions for a decent price. I haven't picked thru his store to see if he has anything in 37mm but some of the Honda items might be the right size. I deal almost exclusively with 41mm forks so my knowledge of the others is a bit thin.

http://stores.ebay.com/Gingstore?_trksid=p2047675.l2563

Here are some pics of the modified GSXR fork cap.

[pattonme]

Originally Posted by Yamahawk

is possible to fit them into the 36mm EX250 forks from 88-07.

yes. You use EX250/300 springs in EX250/300 forks. The GSXR top-out springs and main springs are trash.

All 20mm cartridges have a tube of either 24mm or 25.4 and either way you have to gut the EX tube of the 'barrel' in the bottom. So all top-out functionality has to be internal to the cartridge. Andreani uses lengths of plastic rod and a fat O-ring, I use proper springs.

Originally Posted by Yamahawk

I believe that Matt Patton uses the 01-03 GSXR600 cartridges, also, correct me if I am wrong, and that they are conventional forks not USD ones like I have.

Correct on both counts. the USD cartridge can be used too. It's just that the 01-03 is easy(er) to get ahold of. Send me your forks and the donor cartridge you have and I do what's necessary.

[Yamahawk]

Originally Posted by pattonme

yes. You use EX250/300 springs in EX250/300 forks. The GSXR top-out springs and main springs are trash.

All 20mm cartridges have a tube of either 24mm or 25.4 and either way you have to gut the EX tube of the 'barrel' in the bottom. So all top-out functionality has to be internal to the cartridge. Andreani uses lengths of plastic rod and a fat O-ring, I use proper springs.



Correct on both counts. the USD cartridge can be used too. It's just that the 01-03 is easy(er) to get ahold of. Send me your forks and the donor cartridge you have and I do what's necessary.

Thanks, Matt! I have confidence that you know what you are talking about. I messaged you on eBay today, and appreciate your quick reply! I have my eye and an offer on a couple of 03 GSXR600 fork tubes, and if/when I get them, I have an extra set of EX250F (1996) low mile forks and they would be the ones to fit the cartridges into. They are 36mm, and I need to keep that size to be 'stock'. My 89 VTR250 Interceptor actually has 37mm CBR600F1 Hurricane forks in VF500 triples, to keep the stock mounting of the fuses and ignition switch. If you didn't notice the dual disks, you would think it was stock. I had Jamie Daugherty set up the forks with springs and his own emulators, and it handles pretty good with the CBR600F3 rear shock that he did for me also.
Now, I am in need of some decent suspension for the 86 EX250E model. I already have grafted on the EX250F forks, and 17" EX500 front and rear wheels, and will be adding an 06 GSXR600 rear shock also. I will email you as per your request, and perhaps we can get this done sometime before spring. I have a set of 06 GSXR600 forks, but the springs are really large diameter, and wouldn't work without the springs swapped for a smaller diameter. The valves were junk, also, as the forks were burnt in a fire. Anyway, nice to see you here!
Charlie