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RhodeMoto

3rd gen fork setup

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Greetings - New to VFR and forum. I recently acquired a 1991 VFR. One owner, but came via another party so do not have direct access to past history. Bike is not quite as nice as Treestylist,... 70K+ miles. Did come with extra set of wheels and front float rotors (from 4th gen?), as well as a box of misc. air filters, oil filters, manuals gave some hope it was owned by responsible person. Also has a FOX rear shock, so thinking owner did have right idea in mind. Was a great deal, but had to buy - no ride. Had anticipated a complete go through. Had not anticipated bent fork tubes.

I have now read through many past forums on suspension and looking for sage advise. 

I have new tubes on order with Frank's - 

Have all new bushing, seals, head bearings.

Made a stem nut adjust tool so if anyone local needs to borrow can do.

Have head reassembled but trying to find an ounce spring scale to adjust to the Honda spec of 1-1.5kg pull at leg.

In tear down have discovered that this has RaceTech 1kg/mm springs with a preload made from a thin wall electrical conduit,...not to thrilled with that part.

These may be on the stiff side as rider weigh in at 165, no luggage?

It has RT compression gold valve with a set up for their "C33" stack - NO bleed hole?

Not clear if the rebound piston is stock or RT? It has 10 17mm dia. x .01 mm shim stack. - NO bleed hole.

Can someone explain what the bleed hole does as it seems to me that the top of rebound piston has a (by-pass) valve that would allow oil to be forced to the top side that can not go though the compression stack and therefore "Bleed"oil to the top side?? What would have been the result of this being used without the bleed holes? IT must have worked to some degree? I only rode it for a very short distance when loose head bearing (result of whatever happened to forks?) came to light. I did notice it seemed to dive badly on braking.

 

Have called RT to see if they could provide original info from owners name,..They have name in record but no spec's. They are nice but answers are cryptic at best. They suggest that I order a complete new shim set at $60+ and with that get a new "code" to get set up for me. Not unreasonable but think that this set up could be close to correct. I just want to verify the rebound stack - my understanding is that if the rebound is still stock then may not be adequate for the stronger springs and be overpowered on rebound.  What the logic is of the bleed holes and should I add these to both compression and rebound?

 

How is it that no one seems to have put together a spreadsheet of RT data so we can do our own calculations? Would love to hear from 3rd gen owner who have RT set up and any clues  of what works and what does not.

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Wow ! Long post with a lot of questions. 

 

5 hours ago, RhodeMoto said:

They suggest that I order a complete new shim set at $60+ and with that get a new "code" to get set up for me.

 

No need. Just go to the VFRD download section and find the instructions for the Gold Valves. Rebound and compression sheets are available. 

 

E.g. "Racetech Gold Valve Rebound instructions FRGV S02"

 

The only thing your $60 will buy you is RT's pick among their standard recipes (and a few extra shims which you probably won't need). 

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6 hours ago, RhodeMoto said:

Not clear if the rebound piston is stock or RT?

 

If it's gold coloured, it's a Gold Valve. 

 

NB: RT used to recommend keeping the stock rebound pistons on the 3G VFR and simply modifying the shim stack.

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6 hours ago, RhodeMoto said:

t has 10 17mm dia. x .01 mm shim stack.

 

Are you positive they are .10 mm?

 

If so, that's wrong. They should be .15 mm and that's a massive difference as the thicker shims are 3.4 times stiffer !

 

If they are in fact .15, that's very stiff already. See the RT instructions sheet. 

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8 hours ago, RhodeMoto said:

In tear down have discovered that this has RaceTech 1kg/mm springs with a preload made from a thin wall electrical conduit,...not to thrilled with that part.

These may be on the stiff side as rider weigh in at 165, no luggage?

 

1 kg/mm springs seem about right for a stock 3rd gen with a rider your weight, that's the spring rate I use in my 4th gen and I'm the same weight as you. The thin walled tube is likely the stuff RT supply with their springs, don't worry it's 6061 T6 al. and totally up to the task.

 

Quote

Can someone explain what the bleed hole does as it seems to me that the top of rebound piston has a (by-pass) valve that would allow oil to be forced to the top side that can not go though the compression stack and therefore "Bleed"oil to the top side?? What would have been the result of this being used without the bleed holes? IT must have worked to some degree? I only rode it for a very short distance when loose head bearing (result of whatever happened to forks?) came to light. I did notice it seemed to dive badly on braking.

 

Some forks use a tapered needle which screws in and out of an orifice to adjust low-speed damping by metering (bleeding) oil flow past the shim stack. Sometimes this is for rebound only, more modern cartridge forks have separate adjusters for both low speed compression and rebound damping. When installing RT (or Ohlins FPK etc) pistons in cartridges without a low speed adjuster it is necessary to drill a bleed hole to emulate the effect of a partially open adjuster needle, the size of the bleed hole directly effecting the rate of flow. I believe the gen 3 forks are adjustable for preload only, if replacing the stock pistons with RT units I would expect both the compression and rebound pistons would require bleed holes to be drilled BUT consult RT or a suspension shop in your area - I have not opened a pair of 3rd gen forks myself. 

 

I suspect the bypass you noted on the rebound piston is the check plate which opens on the compression stroke to allow oil past the rebound piston and closes on the rebound stroke to force oil thru it. 

 

Quote

Would love to hear from 3rd gen owner who have RT set up and any clues  of what works and what does not.

 

I think having a thread that served as a suspension data base would be a great idea. 

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You can check the spring rate RT recommend on their website. No need for a valving code. 

 

I had a look out of curiosity and 1.0 kg/mm is spot on for a street rider on a 90-91. 92-93 require 0.9. Not sure why. Lighter bike apparently. 

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Do verify the weight that RT has in its system for your bike. what they show for the VF500F is way off.

I also phoned them and asked what the mean by "semi-wet"....  they could not tell me....

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12 hours ago, RhodeMoto said:

NO bleed hole?

 

That's nigh impossible. :huh:

 

If the pistons were not drillled there must be a bleed somewhere else otherwise your forks should be incredibly stiff, especially on the brakes.

 

RT's instructions / kits are pretty generic and won't tell you exactly what to do for your specific model. Your kit fits pretty much all Showa forks with a 20 mm cartridge (Ducati, Aprilia..) 

 

For example, my 6G uses the same kit and has no bleed holes through the comp pistons because there is already a bleed elsewhere. 

 

Look really closely before drilling !

 

It's just weird that you experience a lot of brake dive since the spring rate is correct. :blink:

 

The only explanations I can think of are:

 

1. There is a bleed elsewhere and it is much too large. 

 

2. Your fork oil is abnormally light

 

3. Your fork oil is all but gone and the cartridge is pumping air.

 

Or any combination of the above. 

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I agree with the points that RC36 is making. Compression bleeds (and RT would recommend something like 1.3mm diameter) will be either through the wall of the compression valve to bypass the shim stack, through the centre of the bolt that holds the assembly together (and that is most likely what the rebound valve will have, and what the 6th gen compression valve has) or if someone has been fiddling, I have also heard of a bleed being drilled through the wall of the cartridge tube, usually down low just above where the compression valve sits. The stock set-up for the 5th gen uses a smaller diameter thin washer below the main shim stack that keeps those shims just clear of the sealing face of the valve body, and yet another set-up (in my ST1100 for example) has the bleeds as small machined-out channels in the sealing face of the valve. 

 

If there is excessive dive then you may have an over-sized bleed somewhere as above, not enough oil, or maybe the o-ring that seals the compression valve to the cartridge tube is leaking.

 

I would not worry about the use of PVC tube as a spring spacer; that will work fine.

 

As baseline settings for shim stacks, the C33 (has 3 x 0.15mm x 17mm main shims) is a good standard set-up, and on the rebound side you'd be wanting something like 6 x 0.15mm x 17mm shims; as RC says a 0.15mm shim is 3.4 times stiffer than a 0.1mm, so having 10 x 0.1mm shims sounds a bit light to me, especially with the 1.0kg/mm springs.

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31 minutes ago, Terry said:

maybe the o-ring that seals the compression valve to the cartridge tube is leaking.

 

Good point. :idea3:

 

Could be that the lack of bleed hole was deliberate as a way to counter seepage past the seals. If so, this needs fixing. 

 

Great overview of the different ways the low speed circuit can be implemented as well. :fing02:

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The compression pressure is generated mainly by the entry of the damper shaft into the cartridge, which forces incompressible fluid to leave the cartridge, ideally through the bleed and compression shims. In reality, there will also be a little leakage back up the damper shaft seal at the top of the cartridge as well. The rebound valve also plays some part in compression damping as there is three times as much fluid passing through it, and any change in restriction (e.g. changing an adjustable rebound bleed) has a notable effect on compression as well.

 

I've just fitted CBR600F4 forks with adjustable compression bleeds (fluid passes through a hollow bolt, exits under the valve body and passes though an adjustable needle valve back to the outside of the cartridge) and playing with this is changing my understanding of the ride effect of the compression bleed. 

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5 hours ago, Dutchy said:

Do verify the weight that RT has in its system for your bike. what they show for the VF500F is way off.

 

Why, oh why don't you listen to me Dutchy ? :goofy:

 

I think RT use the sprung weight which is a bit confusing as it doesn't match the overall bike weight but it is the correct weight to use. 

 

Having said that, I obviously cannot vouch for the accuracy of any of RT's figures. 

 

I can OTH categorically say that the stock fork spring rate they quote for the 6G is wrong since I rated them myself and there is no way they are .85 kg/mm. At best, it could be an average rate over the whole stroke. 

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Whew - Great input.

  • NB: RT used to recommend keeping the stock rebound pistons on the 3G VFR and simply modifying the shim stack.
    • This seems it may be the case here, and the first time I have heard reference to this. I was thinking the rebound and compression would have been a set from RT.
    • This is the rebound set up. The shims are 0.1mm x 17mm dia. - 10 
    • The piston looks like what I have seen in photos of SHOWA. NO bleed hole. There are very small notches in every lip as if to allow minimal passage? Next photo
    • Anyone have record of what stock shim valves were and is this greater? It does seem that this should be increased at least 25% (over stock) to match the spring rate,and that just to match original rebound rate.
    • To Terry's point  - This may be too light and may be straight stock - Odd that someone would go to all the trouble of doing this and not get it right. NO bleed holes, not changing the rebound,...
    • While on the rebound piston topic,... If the check valve can open on the compression stroke, is that not acting as just as a bleed hole to meter oil at low velocity? Why do you need additional hole?
    • Displaying 20161101_180956.jpg

 

                     rebound piston.jpg

 

  • This is the compression setup as removed.
  • compression stack.jpg
    • This seems to match the RT - C33 stack.
    • The valve is GOLD and appears to be RT.
    • NO bleed hole - there is no other path to pass the shim stack,..
    • O-ring seals are good but will replace for good measure.
  • To Terry's points
    • I measured oil and was close to spec, no idea on weight but seems thin but I am used to running old school stuff with 15wt.
    • That pre-load spacer just bothers me to have so thin a wall - PVC seems a better choice. I have been toying with the idea of running a short lighter weigh spring as a two stage so small road bumps are absorbed but will bind out quickly so not affect dive?? Would have to turn a stub spring connector and then re-calculate the pre-load,... (OK leave that out -have enough to worry about)
    • So - still wondering about the dive factor and cause? Is it possible that the top side of rebound piston - check valve is allowing too much flow?
  • The cartridge is drilled only below the compression o-ring so no additional bleed through that tube.
  • I like the idea of spacing the compression stack from the face as then bleed can be adjusted.

So in conclusion  - Wish I had junked this front end and swapped for a fully adjustable fork setup,.....

NO - I am determined to get this sorted.

Assuming:

- The spring is right

- The compression stack is right

- The rebound stack flex should be increased.

- Both compression and rebound should most likely be drilled.

 

Thanks for all the input.

 

 

 

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Firstly you have a standard looking rebound valve; I doubt very much that the shim stack is standard, they normally would only have 3 17mm shims, not 10. 10 x 0.1 mm shims is IMO a bit light, but not stupidly so. The notches in the shim sealing face are the rebound bleeds. Don't add any more bleeds to the rebound. The notches allow fluid to pass through the check valve ports when the check valve is closed (rebounding); so some fluid will pass through the bleeds until the flow gets high, then the shim stack comes into play.

 

I agree that the compression valve is a Gold Valve with C33 stack. Very odd that there is no bleed drilled in the valve body then; someone didn't read the instructions methinks. Do double check for the presence of a 1.3mm hole in the gold valve casting. In the absence of either drilled bleeds or a bypass notch, my 5th gen had a 12mm x 0.1mm shim between the OEM valve body and the shim stack.

 

 

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7 hours ago, Terry said:

agree that the compression valve is a Gold Valve with C33 stack.

 

Not quite C33 as there is a .19 shim in there. Measurement error ?

 

The third shim also looks a bit suspect to me. Looks like it is not quite flat judging from the reflection of the light. 

 

I just cannot believe that you have no low speed bleed, no seepage, 1.0 springs, normal oil height AND still experience excessive brake dive. :wacko:

 

Edit: Or maybe I just misread the .19. :ohmy: :blush: :laugh:

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7 hours ago, RhodeMoto said:

There are very small notches in every lip as if to allow minimal passage?

 

These notches are your low speed bleed. Remember, it only takes a single 1 to 1.3 mm round hole so the required passage is indeed minimal. 

 

As Terry explained, the volume of oil that needs to go through the compression valve corresponds to the volume of the damping rod entering the cartridge minus a bit of seepage (as little as possible but surely never zero). 

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8 hours ago, RhodeMoto said:

While on the rebound piston topic,... If the check valve can open on the compression stroke, is that not acting as just as a bleed hole to meter oil at low velocity?

 

Oil needs to pass through the rebound valve as it dives into the cartridge but the volume of the chamber above the valve is reduced by the volume of the damping rod entering so an equal volume of oil needs to exit the cartridge in order for the forks to compress at all. 

 

BTW, if you look closely, you can see that the check valve plate is designed to just lift off (not bend) the piston face under the slightest pressure and that the ports it obstructs are about as large as they can be. 

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On 02/11/2016 at 3:38 AM, RhodeMoto said:

I measured oil and was close to spec, no idea on weight but seems thin but I am used to running old school stuff with 15wt.

 

RT's standard is very much on the light side of 5W so that seems normal. 

sketch-1479221907681.png

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8 hours ago, RhodeMoto said:

Is it possible that the top side of rebound piston - check valve is allowing too much flow?

 

Nope ! (err... I think :unsure:

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Firstly you have a standard looking rebound valve; I doubt very much that the shim stack is standard, they normally would only have 3 17mm shims, not 10. 10 x 0.1 mm shims is IMO a bit light, but not stupidly so. The notches in the shim sealing face are the rebound bleeds. Don't add any more bleeds to the rebound. 

Those are 10 shims at 17mm dia. and all 0.1 thick. If 3 are stock then this should be quite a bit stronger rebound,... Would a tapered stack respond better as this is going to be be full on at rebound. A tapered stack would open early with softer rebound and increase with velocity? Yes?

 

Not quite C33 as there is a .19 shim in there. Measurement error ?

That may be my writing on the check valve measure at 0.4mm -on the rebound. The compression is 3 @ 17mm x  0.15 (second from left is scribbled over). Will have to check caliper as the others I had at 0.11 and most likely 0.10.

 

Has anyone checked out this software? Looks like it could be a great tool, and not much more than RT wants for a shim stack,...

www.shimrestackor.com  

 

Where can you get shims other than RT?

 

 

 

 

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1 hour ago, RhodeMoto said:

 

Has anyone checked out this software? Looks like it could be a great tool, and not much more than RT wants for a shim stack,...

www.shimrestackor.com  

 

I haven't bought the software but I've read all their free material. 

 

I'd buy it in a heartbeat if I was a competitive MX rider but for a road bike it seems overkill. 

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So - if 21 members want to send me $4 I will get this and run their specifications,......

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8 hours ago, RhodeMoto said:

Will have to check caliper as the others I had at 0.11 and most likely 0.10.

 

I wouldn't sweat it. Shims are available in 0.05 mm increments AFAIK so they are likely indeed 0.10. Calipers are not precise enough for accurately measuring to 0.01 mm but plenty good enough for 0.05.

 

Incidentally that makes my remark about the 0.19 shim a bit silly. :laugh:

 

Could be a 0.20 though but RT's kit does not contain any. Only 10's and 15's.

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The OEM stack (for my 5th gen) included 8 x 0.2mm clamping shims on both rebound and compression, just under the 11.4 x 0.4mm spacer.

 

Tapered stacks seem to be recommended by the aftermarket on the compression stack, but the rebound stacks that I've seen do not use the same set-up, just a small diameter (9mm) clamping shim and the 17mm main shims.

 

AFAIK, the compression stack has to deal with a wide variety of speeds and forces, whereas the rebound stack is just dealing with the same spring rebound force each time. 

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I am getting a better understanding of all this,... thanks again for input.

The logic of terry's explanation on rebound shims makes total sense. 

No reason to have tapered stack if we agree that rebound is a fixed rate and not dealing with variable rates of input as compression.

However RT does list their rH stacks as tapered sets?

 

Forks by Frank have been shipped - due in Nov 8. Have heard mixed feedback on these, but decided to give them a try. 

Want to finalize all this valving so I can be onto assembly as soon as they arrive.

 

Called RT again today - Each time I get a few more crumbs,...

Early versions only had the compression valve. The rebound was not offered.

They have NO record of early instructions and can not verify or suggest a rebound stack.

But assume that there was some re-set additional shims.

I can buy a pair of rebound valves at $169 complete with extra shims, free locktite, and a secret code!

Sort of confirmed that the 1kg spring & C33 compression would be appropriate.

The bleed hole must be drilled (compression)- puzzling that this would have been ignored.

Confirmed 5wt oil, at 120mm air gap

 

OK - If the original rebound shims were 3 @ 0.15 - and they are 3.4 times stiffer than 0.10 shims, then that would equal 10.2 shims @ 0.10.

This change would be pointless as I am now (10@ 0.10) equal to stock,....IF the spring is now 25-30% stiffer - then the rebound valving (assuming stock rebound was spot on) should be same increase. Suggestion (Terry) above is 6 @ 0.15 as base, that is 2X stock? Maybe too strong /slow rebound? RT is even greater if you use the 4th setup (relative to the c33 settings?). They use 6 @ 0.15 + 3 more @ 0.10.

My gut feeling is that I would prefer to be on fairly stiff springs with a quick/stiff compression, and have the rebound act relatively fast. 

I do not have any shims on hand so unless anyone feels strongly that this rebound is way too soft I am going to;

Drill the compression bleed hole

Cut some new pre-load spacers.

Use the shim stacks just the way they are

Re-assemble the whole mess - all new bushings and seals

Ride this thing and see what I have.

 

 

 

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