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What Fork Oil Wt With F4i Internals Mod


marid2apterbilt

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I plan to do the F4I Internals Mod on the forks of my VFR and looking for what weight Fork oil to try or to start with. Sugestions Please... sorry if this post seems long but I figure set up and the reason for wanting to do this Mod would help those giving answers/sugestions..

I would really like to hear from those who have done this Mod.. And what Weight fork oil you used. How does it feel, along with what surface types seem to be a issue still..

Reason for change..

When I was at Barber Motorsports a few weeks ago I had a very bad pogo feeling along 1 of the strait aways, Also it got worse as the day went on. Also I get the same pogo feeling on a few short stretches of area roads. Bridge drop offs feel very abrupt also but the comp side feels as if it is soaking it all up very well..

Current Bike setup..

1.0kg sonic springs in OEM forks (All Stock)

18kg rear spring W/ CBR600F4I Rear shock.

Rear shock Lengthened 3/8-+ inches for a total ride height increase of 1.5" (Cant go any higher with OEM parts)

Note the rear feels very compliant on any surface condition I have ever found..

Future Mod..

I plan to use the OEM Comp valve for the vFR with the OEM F4I rebound valve. has any one else done this and what weight oil do you sugest or did you Use..

And for the Suspension Guru's on here what oil Weight would you suggest be used or to start with....

Thanks..

My head feels like a yoyo doing the pogo trying to figure out the best guess for this.. sO thanks for your time and Knowledge..

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I went through all of this when I added stiffer springs, I switched to 5w after installing 1k fork springs myself, it helped with the stiffness of the compression valve, however it gave me a super bouncy rebound. So you have to revalve, less compression and more rebound - stiffer springs need more rebound - changing the shim stacks helps, basically the rebound valve has all the same size shims adding one or two more will help. I cant remember off hand the sizes, but you can remove one from the compression stack and add it to the rebound stack. Or go all out and get it vavled professionally - jamie D had a good offer going for that. I opted for a set of racetech vavles and did it myself. Placed the vavles into an f3 cartridge, and replaced the bushings too, and of course the oil seals.

Changing oil wont help with the basic problem of having not enough rebound compression for the stiffer spring.

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I went through all of this when I added stiffer springs, I switched to 5w after installing 1k fork springs myself, it helped with the stiffness of the compression valve, however it gave me a super bouncy rebound. So you have to revalve, less compression and more rebound - stiffer springs need more rebound - changing the shim stacks helps, basically the rebound valve has all the same size shims adding one or two more will help. I cant remember off hand the sizes, but you can remove one from the compression stack and add it to the rebound stack. Or go all out and get it vavled professionally - jamie D had a good offer going for that. I opted for a set of racetech vavles and did it myself. Placed the vavles into an f3 cartridge, and replaced the bushings too, and of course the oil seals.

Changing oil wont help with the basic problem of having not enough rebound compression for the stiffer spring.

So even with the F3 rebound adjustment there wasn't enough rebound there?

The F4/F4i used even softer springs than the VFR and weighted a lot less, I would think 10w Ohlins oil(Ohlins #5) and add a shim to each stack or at least the rebound. :blush:

Several others have done this mod and it's been too long for me to remember what they did with theirs! :blush:

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So even with the F3 rebound adjustment there wasn't enough rebound there?

The F4/F4i used even softer springs than the VFR and weighted a lot less, I would think 10w Ohlins oil(Ohlins #5) and add a shim to each stack or at least the rebound. :blush:

Several others have done this mod and it's been too long for me to remember what they did with theirs! :blush:

I have been thinking the same Actually But not the part of swapping a shim or 2.. I looked on racetechs site for shim stack #'s but it seems you must have a access code good for 1 time only..

Isnt the stock OEM fork oil in a VFR 10 Wt ?

Another good ? does anyone know the actual flow differences between the f4I and VFR cOmp/Reb valves.. That would really make things easy huh... Or where to find them..

Thanks for the info so far BR and HS....

anyone else got anything to Add ?

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The VFR and F4i (and most other Honda's) all use the same valves for comp & rebound so the shim stack is the only difference! Also since RaceTeck valves are completely different and use HUGE ports on them a reccomended shim stack would be meaningless when using Honda valves so don't waste your time there! :rolleyes:

I had/have the stock shim stack set-up for both somewhare! :biggrin:

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Yes, stock oil is 10W. I am trying 5wt when I get around to doing my RT setup, but you're a bit bigger than me, you could try mixing 5 + 10 to make 7.5W(or just buy 7.5). Whatever yo udo, don't put 5 in one fork and 10 in the other! Seen it done, not pretty!!

I have the compression stack #'s for the Race Tech comp. gold valve, but that won't help much w/ a stock valve. I have a second set of VFR forks that are bent, I've been meaning to pull them apart and see if I can mod the stock valves to resemble the RT parts...

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Almost Halfway thru but I have to run to Lowes and get some PVC to cut new spacers.. The Throttle side is done except for the spacer..

Remove wheel, Inside bottom of fork is this Allen Bolt, Be sure to have a bucket under it.. Mine didnt leak till I loosened the fork Cap..

1000788.jpg

You can then remove the VFR fork cartridge..

1000789t.jpg

Here are all the parts inorder laid out.. You must remove a small C-Clip to get the Comp valves out of the VFR fork.

1000790.jpg

F4I fork cartridge with VFR comp Valves all back together..

1000791zpo.jpg

I started out not removing the forks but ran into a snag. Some washers I was using were just a hare big also there is a Silver end cap for the cartridge that fell donw to the bottom of the fork. They were actually very easy to remove...

The one on the throttle side is almost ready to go back in.. Install is just reverse of removal..

1000793v.jpg

Still not sure what Im gonna do about fork oil.. I have a quart of 5wt and 1 10wt quart. I could reuse the old stuff but I noticed when it was draining it had some water in it (brown/grey milky color) but not much.. Also I dont have a fork oil guage.. This also brings up another question HOW MUCH Fork OIL.. do I use the F4I measurement or the VFR ?

Maybe I can get KWR to make a road trip with his fork oil guage ?

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Welll the forks are all together but I got to thinking today..

I didnt check to see if the VFR or F4 damper tubes were the same length.. As I just put the VFR Damp valves inside the complete F4 cartridge..

Unfortunately im back on the road too and Kevin Kwr8728 is supposed to go measure and add fork oil..

Does anyone know If the cartridge length is the same between the 2.. Im thinking the Vfr cartridge may be longer and I should have only used the Reb valves and dampening rod from the F4 and put them into the VFR cartridges ? ? ? ? ?.

Gonna be 3 weeks before I can check myself.. This iss gonna drive me nuts..

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Sam, there are different lengths, but it doesn't seem to matter! I assumed you do just as you did by using the complete F4i cartrige w/ VFR comp valve. I'm not sure if you can or can't use the longer VFR tube body? I think the F4/F4i tubes have two large port holes in them different than the VFR tubes, I also don't remember if that aluminum spacer is used or not. :cool:

Sorry, been to long since I've read about this swap!

BR

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I replaced the comp. and reb. with racetech on my forks and they seem to work great. Had Race Tech do the work. Wanted to do a F3 transplant on my 5th gen but no time and cheaped out.

My only comment was you seemed to be rushing this swap compared to the proceedures recommended by race tech for doing your own work. Should have taken the forks out initially and flushed them out real good before putting them back together.

My wife is a nurse so we have a lot of these large syringes used for flushing wounds. I added a peice of aquarioum tubing to the end that corresponds to the proper fluid level(from top of fork) and used this to remove excess oil from the tubes.

By the way I did the same kind of rush when I added stiffer springs on my own bike. Ended up having to take them apart again to make sure I tightened the jam nuts on the pre-load adjusters. :cool:

Hopefully the length is a non issue.

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Sam, there are different lengths, but it doesn't seem to matter! I assumed you do just as you did by using the complete F4i cartrige w/ VFR comp valve. I'm not sure if you can or can't use the longer VFR tube body? I think the F4/F4i tubes have two large port holes in them different than the VFR tubes, I also don't remember if that aluminum spacer is used or not. :excl:

Sorry, been to long since I've read about this swap!

BR

Reason Im asking is the F4I cartridge is too short to be able to apply preload.. Adj the preload once they are together just lengthens the fork tubes..

The parts Fiche shows a similar aluminum spacer for the F4 as the one in the bottom of the VFr forks.

Guess I will tear them apart again when I get home and measure the cartridge tubes, If it is the case that the vFR tubes are longer I will use those.. The extra length from the VFR cartridges will help keep the fork length a little closer.. and may be that little extra that is needed..

VFR Capt Bob..

No Im not rushing it. I never get in a hurry, I just had to leave midday to go back on the road.. I knew I didnt have time to finish. Unfortunately Im not home everynite like most people so I cant just walk into the garage and do what ever.. I also knew I didnt have the fork oil or guage.. I will finish it some time when I get baclk again.. Until then I have plenty of time to ponder on the situation or order things I may need for the project..

My problem is the longer I have to think about it the more O.C.D. kicks in. But I have never forgot to tighten a nut or bolt.. I always check 2 or 3 times to make sure all nuts and bolts are in or tight.. real pita when your replacing a engine or rebuilding a tranny.. As for the Race tEch Instructions.. There are no Racetech parts being used..

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Reason Im asking is the F4I cartridge is too short to be able to apply preload.. Adj the preload once they are together just lengthens the fork tubes..

The parts Fiche shows a similar aluminum spacer for the F4 as the one in the bottom of the VFr forks.

Guess I will tear them apart again when I get home and measure the cartridge tubes, If it is the case that the vFR tubes are longer I will use those.. The extra length from the VFR cartridges will help keep the fork length a little closer.. and may be that little extra that is needed..

I know the F4i cartrige is shorter, but also know that this is a common mod done by suspension shops, I just don't know what exact pieces they are using.

We need someone who had had this done and remembers what was used. I don't know if you can just use the the longer cartrige tund or not, top out spring locations are different as well as a few other things.

Let us know what you figure out! :excl:

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In theory and I wish I had this thought before.. Also its gonne be 3 weeks tilll I can comfirm..

I just not OCD with a tape measure, But I will play with the functionality of something till im satisfied its RIGHT..

You should be able to just use the Reb valve and comp Rod in the Vfr cartridge. The Rod/Reb valve is gonna top out regardless I assume. and I may have to build a litle preload into the Spacer length when I put them together for the final time.. I had to buy some more 1" Electricl schd 40 pvc so I have a 10ft piece at the house to play with..

Hopefully someeone who did this mod will eventually stop in n post..

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In theory and I wish I had this thought before.. Also its gonne be 3 weeks tilll I can comfirm..

I just not OCD with a tape measure, But I will play with the functionality of something till im satisfied its RIGHT..

You should be able to just use the Reb valve and comp Rod in the Vfr cartridge. The Rod/Reb valve is gonna top out regardless I assume. and I may have to build a litle preload into the Spacer length when I put them together for the final time.. I had to buy some more 1" Electricl schd 40 pvc so I have a 10ft piece at the house to play with..

Hopefully someeone who did this mod will eventually stop in n post..

You should have about 1" or a bit more of preload spacing from the top of the fork tube to the bottom of the cap before assembly. And never reuse any fluid for anything! Its also the best insurance to have clean new fluid going back in what ever you have taken apart. .02

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In theory and I wish I had this thought before.. Also its gonne be 3 weeks tilll I can comfirm..

I just not OCD with a tape measure, But I will play with the functionality of something till im satisfied its RIGHT..

You should be able to just use the Reb valve and comp Rod in the Vfr cartridge. The Rod/Reb valve is gonna top out regardless I assume. and I may have to build a litle preload into the Spacer length when I put them together for the final time.. I had to buy some more 1" Electricl schd 40 pvc so I have a 10ft piece at the house to play with..

Hopefully someeone who did this mod will eventually stop in n post..

You should have about 1" or a bit more of preload spacing from the top of the fork tube to the bottom of the cap before assembly. And never reuse any fluid for anything! Its also the best insurance to have clean new fluid going back in what ever you have taken apart. .02

Im bbeginning to wonder if anyone has even read this thread..

Yes Im going to use New fluid..

Due to using F4 internals the 1" may not apply.. The F4 forks are shorter than VFR forks and Im mixing the components of both to gain rebound Adjustment in the OEM VFR forks....

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  • 3 weeks later...

Ok I finally got all the parts sorted that I needed and a few mods along the way.. First off the parts you will need from a Honda CBR F4/F4I..

Fork Cap

Rebound valve and adj/connector rod.

Yes that is all you need, you dont need the F4 Catridge tube, Just everything associated with the F4 rebound..

Disassemble the VFR cartridge removing the dampening rod with attached Reb valve, Insert F4 dampening Rod with attached Reb Valve and reassemble.

Important Notes....

I highly reccomend cutting a new spacer for the spring 1/4 to 1/2" longer than you need. When complete you will only have about 1/4 of preload Adjustment Or Less IF YOU DON"T DO THIS..

As one of my earlier worries of the rebound valve topping out, That is a NON- ISSUE..

With 10wt oil and 1.0kg front springs the F4 valve still isnt stiff enough with the adjuster all tthe way in.. I reccomend addding 1-3 shims to the valve if possible.. I plan to research this soon.. Or use 15wt Fork oil.. I think the First would be better. This is also a sugestion from Ken Wheeler, I took the bike to him this morning to get it dialed in. He made a few adjustments to the front and rear and noted that he didnt like the feel from the rear being so high. Alsso If I lower the rear some this will help with my problems with the front.. It rides much smoother now in the rear also since his adjustments.. So I will be tearing it all apart again this winter or early spring..

My overall view of the F4 Rebound fork Mod..

So far it is somewhat of a Improvement as I still have a few issues to address with its function. It feels much better than before at High speeds and soaks up major road hazards very well.. I took it over cracked pavement and couldnt feel a single bump, Even hit a piece of tire at 70mph and barely felt it.. At low speeds its still a bit bouncy/POGOey. So a few minor changes will have to be made as I noted above.

Further refinement shouldnt cost much (Fork Oil) so Im going to guess a total cost of around 225.00 - 250.00 (Price includes New Sonic springs)(assuming you find the F4 parts for around 100.00) for a compliant front end.. Add in a set of RaceTech valves for 400.00 for a total of 625.00 and you will have a very compliant setup with Adjustable Rebound..modify_inline.gif

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FYI - The stock VFR fluid is 5w and you should stick with it.

There really isn't a lot of difference between the F4/i internals and the stock VFR800 parts. The biggest difference is the external rebound adjustments (fork caps). You would have/want to keep the VFR compression assembly as the CBR's is setup for an external compression adjustment which you won't get on the VFR. Because of this, there are some tricks to getting it setup properly.

The swap really consists of changing the damping rods only. You should keep the VFR cartridge tube and compression valve assembly. Replace the VFR damping rods, rebound valves and fork caps with the CBR parts. Be careful to check the spring preload as the spacer length needed is usually different than stock VFR length. If you are bothering to go through this much work, you should also replace the springs with ones matched to your weight also.

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FYI - The stock VFR fluid is 5w and you should stick with it.

There really isn't a lot of difference between the F4/i internals and the stock VFR800 parts. The biggest difference is the external rebound adjustments (fork caps). You would have/want to keep the VFR compression assembly as the CBR's is setup for an external compression adjustment which you won't get on the VFR. Because of this, there are some tricks to getting it setup properly.

The swap really consists of changing the damping rods only. You should keep the VFR cartridge tube and compression valve assembly. Replace the VFR damping rods, rebound valves and fork caps with the CBR parts. Be careful to check the spring preload as the spacer length needed is usually different than stock VFR length. If you are bothering to go through this much work, you should also replace the springs with ones matched to your weight also.

Yeps thats what I said , Did, and posted above aside from the fork oil..

Every thing I have found leads to stock oil being 10wt. Are you sure it is 5wt ? Also several in this thread mentioned that 7 and 5wt oil was to light when they completed this mod.

A very well seasoned Local mechanic sugested I try 15wt after taking a test ride with the current 10wt oil i put in there..

I upgraded the springs last year, Front and rear.. 1.0 fronts and 18kg rear..

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Ok I finally got all the parts sorted that I needed and a few mods along the way..

With 10wt oil and 1.0kg front springs the F4 valve still isnt stiff enough with the adjuster all tthe way in.. I reccomend addding 1-3 shims to the valve if possible..

Hey Sam, glad your making progress and posting your findings as it's been awhile since someone has covered this mod!

When you say "F4 valve still isnt stiff enough with the adjuster all tthe way in.. " I'm assuming your talking about rebound.

Since rebound is your only adjustment I would set the front end up to a good feel on the Comp side based on oil weight, level and shim stack config, then valve the rebound to work best in that set-up. Also I think older Honda forks (Showa?) used large 3-port valves that flowed much more oil than the current 4-port valse found in most current Honda forks. There might still an old exsisting thread covering this difference somewhere?

Thanks and keep up your results!

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FYI - The stock VFR fluid is 5w and you should stick with it.

There really isn't a lot of difference between the F4/i internals and the stock VFR800 parts. The biggest difference is the external rebound adjustments (fork caps). You would have/want to keep the VFR compression assembly as the CBR's is setup for an external compression adjustment which you won't get on the VFR. Because of this, there are some tricks to getting it setup properly.

The swap really consists of changing the damping rods only. You should keep the VFR cartridge tube and compression valve assembly. Replace the VFR damping rods, rebound valves and fork caps with the CBR parts. Be careful to check the spring preload as the spacer length needed is usually different than stock VFR length. If you are bothering to go through this much work, you should also replace the springs with ones matched to your weight also.

Yeps thats what I said , Did, and posted above aside from the fork oil..

Every thing I have found leads to stock oil being 10wt. Are you sure it is 5wt ? Also several in this thread mentioned that 7 and 5wt oil was to light when they completed this mod.

A very well seasoned Local mechanic sugested I try 15wt after taking a test ride with the current 10wt oil i put in there..

I upgraded the springs last year, Front and rear.. 1.0 fronts and 18kg rear..

I've never seen Showa (they make the forks) use anything except 5wt fluid. Every set of forks that I revalve uses 5wt fluid - there is no reason to run anything higher. If the valving isn't correct, a heavier weight fluid will only add harshness and not really fix the problem. Getting the correct valving setup is most important

15wt is WAY too heavy, do not use that.

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After buying an fitting an Elka 2-way shock, I originally fitted 0.95 Sonic springs (because that's what their spring calculator recommended based on my weight (around 190poonds) and riding style (normal street). The forks were VERY bouncy, and I couldn't afford to get them revalved at the time, so I drained the oil and put in some Motorex 15W fluid. It helped somewhat, but was still bouncy, so I sucked some out and added some Motul 20W, and dropped the volume slightly.

Still harsh, so I backed off the preload, which made little difference.

Recently, I sent the forks away to be overhauled: new seals and bushes, Racetech valves, modified shim stack, every lined up, measures, optimised. The local Ohlins guru put some very slippery (and low viscosity) oil in, and told me that there is a huge difference between some of the oils being sold, and that as they don't necessarily follow the official standards, the numbers don't mean much. He also said that the standard VFR damping didn't flow enough oil, so was a bit harsh on compression.

The forks felt MUCH better, and matched the rear end better, so the ride was very controlled. It didn't seem as smooth or compliant as I expected, and when I recently did my first test-ride on our crappy country backroads, although the ride was fine at 100km/h (~60mph), it felt too abrupt in action and was very tiring. When I talked to the Ohlins guy about it, he said he could revalve the forks (free of charge) but that he thoght they were probably oversprung, and as he'd valved them to match the springs, probably overdamped as well. Soooo... they're currently away being resprung and revalved. Again.

Apparently, Ohlins' recommended spring rate for the bike is only 0.85kg/mm, quite a difference from the 0.95 Sonic and Racetech recommended, and closer to the 0.74 standard rate. He said that he felt 0.95 would be fine for typical American roads or for the racetrack, which sounds right, as the suspension felt great at higher speeds or on smoother roads.

So, they should be back in the next couple of days, as he was trying to get them sorted before September 9th, when he's off to visit Ohlins in Sweden for a couple of weeks. I'm kinda anxious to get them back, after nearly a week of driving everywhere. I'm also anxious about getting the Elka dialed in; I've got the preload right, and that's about it. The remote has been relocated from under the seat where it was, to on the left pillion peg bracket, so I can adjust it more readily on the road.

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Thanks BR...

Working on getting it sorted out the last little bit. The Comp side IMHO feels fine as is, It is the little Bumps that the rebound side is having a issue with (sounds like Enzed-Viffer's issue) It is almost like a out of balance tire bouncing. But at lower than Hiway speeds..

No more big shake your head type of bouncing as before but a lot of little bitty bounces.. If that makees any sense..

Gonna take a look at a set of valves in pieces and see and or try 15wt oil first.. I may buck up and get a set of racetech valves but for now I dont have the cash..

Jamie D....

I think the key to your experience in your post is that your revalving the forks (I assume Racetech valves) Which from the many posts I have seen on revalve setups with racetech valves take much lower wt oils by design..

Enzed...

Thanks for the info....

I added the 1.o kg springs some time ago (I weigh 225lbs) It didnt seem tooo bad at this setup with stock oil but on ocassion it would feeel bouncy on some rough roads, Currently it feels better, Not too stiff.. The bouncy feeling Im having now feel like very small rises in pavement but you cant see the changes in the pavement. Best way to describe is a Out of balance tire, But instead of it bouncing at Hiway speeds its usually below 70mph, Actually backwards from a out of balance tire..

Before this rebound adj project I was thinking of using 15 wt oil with the stock Reb/Comp valves and my 1.0 springs.. It almost seems too soft on the valving.. I havve also considered .95 springs but Im gonna play with it a bit before I go that route.. The 1.0kg springs feel really good at my weight, Not too harsh or too soft. Im a good sized person at 225lbs and 6' 4".. Geared up I weigh 238lbs..

Damn I wish I was home most wknds like everyone else, It wouuldnt take me so long to get it all sorted out then sad.gif

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The bouncy feeling Im having now feel like very small rises in pavement but you cant see the changes in the pavement. Best way to describe is a Out of balance tire, But instead of it bouncing at Hiway speeds its usually below 70mph, Actually backwards from a out of balance tire..

That's exactly how mine felt too, before the work on the internals. Over bumps, it wasn't too bad except on bigger bumps, which apparently was the ports in the damper being too small and not flowing oil quickly enough.

After the first lot of work, it felt fine at less than 40mph or above 60, but in between, it was harsh, because the damping was set up perfectly to match the springs, but because the spring rate was too firm for my weight, the springs weren't absorbing smaller bumps enough, and it was damping the suspension movement too much.

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I've never seen Showa (they make the forks) use anything except 5wt fluid. Every set of forks that I revalve uses 5wt fluid - there is no reason to run anything higher. If the valving isn't correct, a heavier weight fluid will only add harshness and not really fix the problem. Getting the correct valving setup is most important

15wt is WAY too heavy, do not use that.

Per the OEM manuals, and the color coming out of the forks I've rebuilt, the stock oil for 5th & 6th gens is Honda SS-8(10w) oil.

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