5th gen fork conversion.

http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

FYI

 

Whew, now there's a read that's very informative.

 

So this brings up a crazy WTH question in what was Honda thinking not putting a drain plug in the fork lowers on VFRs, Sheesh!!

 

That brand comparison chart that you found Norcalboy, is the one I used to decide on which oil to use.
I settled on Maxima Racing fork oil 125/150 7wt. I like the action of my forks with it.
You can see that PJ1 fork tuner 2.5wt is nearly the same viscosity.
I don't get the stupidity of different manufacturers plucking numbers from thin air when there is a standard.
I don't think a drain plug would make much difference, to do it properly you need to dismantle the forks anyway.
If you're going to the trouble of doing something, do it properly my old boss used to say accompanied with a kick up the arse.
It is amazing how much crap builds up in the forks after a short time. Cleanliness is paramount when doing forks.
Fork oil rarely gets above 55*C, rear shock oil however rarely gets below 70*C, and can easily climb above 100*C. That's why they use a vacuum pump to remove air and moisture of rear shocks before they charge them.

 

That's because you're trying to find forks that fit the VFR as is.
Friends I know with Ohlins UDForks use CBR or R1 forks with custom triples.

 

My fork legs have drain plugs, the manufacturers doing away with drain plugs has to do with charging you more and giving you less. Side bar; you really need to remove the fork leg from the bike to do a proper oil change anyway, so a drain plug on the bottom of the stanchion is a moote point imho Cheers happy/safe motoring

 

I know , I was kinda referring to the dirt bike days where it was no big deal, pop out a screw take the cap off wa-la, give it a couple pumps and 90% of it is out. Now on these VFRs unless I'm going about it all wrong, I pull the whole fork leg out, then install it in a well padded clamp/vise at a 45 degree angle, then take out said lower cartridge bolt with an air impact to get it lose, if I use a ratchet drive 90% of the time it just spins, never really getting a good bite so it can thread out on its own. Then I take the cap off, leaving the spring in helps hold the cartridge in place enough to get the bolt out. Well that's the idea anyway, some times it works, some times it doesn't, Yes , don't use loctite when reassembling. But it's during that process oil gets all over the place, just be nice if 90% was all ready out IMO.

 

I leave the cap on, and turn them upside down and use a fast impact gun.
I also make sure the bolt and threaded hole in the compression valves are very clean before I install.
First time I did it, I followed the manual and used locktite.
I remember thinking 60 seconds after I put them in, "That seems like a stupid thing to do".
It was, I even had to invent new swear words to deal with it the next time, the english language just didn't have enough options.

 

Sounds like you uttered "Garage Words", Oz. We've all been there.

I do use a trace of Loctite blue (add a drop, lightly wipe threads to take off excess) and like you, I have disassembled/re-shimmed/reassembled my forks numerous times. I also made sure the threads were very clean using a tap and die before assembly. I've never had a problem pulling the forks apart since (just with a hand operated hex key driver, no rattle gun). I loosen the hex bolt before I pull the fork cap off (I loosen the fork cap while the forks are installed in the triples).

I was using the C32 stack with the standard HMAS rebound valve (with DMr shims) but since I put the Gold Valve on the rebound side, I have gone to C33. AFAIK the small HMAS ports in the rebound valve cause some additional high speed compression damping, which the GV should not really suffer from. C32 felt too soft with the GV in rebound. I have tried many shimming variations on compression and 2-3 0.15 x 17mm shims seems to be the sweet spot for road use. I'd next like to experiment with varying the bypass port size on the comp valve but it's not reversible if I go too far.

Makes you wonder how hard it would be to modify some SH lowers to add an external compression adjuster? I have also heard of tuners drilling a bypass directly through the cartridge wall (presumably below the maximum travel of the rebound piston and above the compression valve) and leaving the stock HMAS valve in place.

 

I spent a few minutes thinking about your statement, and I think youre right Cadbury.
The rebound valve has 2 sets of ports, 1 lot operates when the forks are in compression and the check valve is fully open.
The next lot only work when the forks are rebounding and the check valve is fully closed.
Either way oil has to go through one of the rebound ports.
The standard pistons are very rtestrictive, so even in compression you still have oil travelling through the rebound ports.
Great Scott, you might be on to something.
Unless I'm missing something, it makes sense.

As far as the shim stack goes, don't forget I'm using slightly heavier oil then you, and my oil height is 110mm.
So it gives me slightly faster high speed compression, untill the air gap comes into play, then it acts like a secondary spring on the last bit of fork travel.
Think of it as an extra high speed stack that only works on the last 20mm or so.

Isn't this great, brain food.
You are never too old to learn something new.

 

informative for sure, good thing is once the front ends are set on most bikes, its set-it and forget it. I always use an impact on the bottom allen bolts before I remove the fork legs from the tripple tree. Just use a hammer on the end of the socket before you go to town with the impact gun, I have stripped these out in the past and its not a fun experience, but not the worst either :frusty: Peace

 

So all that read makes me ask, with fork oil, what brand, weight, and how much? that's if it isn't a trade secret Oz, Cadbury

 

What brand: Picked by the viscosity and not the weight, changes in viscosity changes the actual damping, both directions.
Oil height: Changing the height changes the compression ratio...which subsequently changes the spring rate...i,e, the progessivenss of the springs. It also effects the bottoming characteristics.
Springs: 98% of the time people pick too light of a spring and then spend too much time messing with damping and oil adjustments.
Preload: My experience has settled on running as little spring preload as possible
Geometry: Very important to extract the correct "feeling" from suspension that a rider believes requires additional adjustments.

I weigh 82 Kilos without gear, 81.8 to be exact, and I have always run 1.0 KG springs. My personal feeling is that any aggressive rider would benefit from 1.0 KG springs, not varying stock oil heights by much, and running zero preload. Never use anything but straight rate springs and get your pistons and stacks correct for your style. The major (i.e. reputable) manufacturers and suspension folks have thousands of entries into their respective databases and can usually get things very close....as long as you tell them the truth as to what your true capabilities are, how you actually ride, and are not afraid to give your weight in an honest number.

Standard issue 6g forks can be made very good with little effort. Springs, pistons and stacks with quality oil. There is also no better money spent than getting your chassis measured by a chassis measurement company like GMD Computrack, or RaceTech. This measurement will save you a ton of time and money by getting the geometry in the correct place before you start screwing around with major changes.

 

Well I tend to use Motul 5W because that is what my local shop stocks, but Oz is absolutely correct, the W viscosity rating seems to have little correlation with measured viscosity, so the Peter Verdone page listed above is a good resource.

The 5th gen and VTR need less than 500mL per leg so a one litre bottle is all you need. I don't measure the volume going in, I measure the air gap above the oil to the top of the fork tube, springs out, fully compressed, cartridge fully primed. Under suspension travel the air get compressed as the fork compresses which increases the air pressure and adds an air-spring effect. The smaller the air gap, the bigger the rise in pressure and spring effect, giving more resistance to bottoming. The shop manual calls for 130mm, I use 120mm and I note Oz uses 110mm.

To get the correct oil height I use a 20mL syringe with a piece of air-line tube attached passing through an old stove knob held in place with cable ties on the tube. I set the distance from the end of the tube to the underside of the knob to my required oil height, fill slightly above what I want, then put the knob on top of the fork tube and suck out any excess oil. You can do the same with a tape measure and tipping excess oil back out of the fork.

You can feel when the cartridge is properly bled of air. When you start it is full of air, as you pump the cartridge through its stroke you can feel the damping resistance change. When you have fluid resistance through the whole stroke, you are done.

When you compress the forks fully, you will strike extra resistance in the last 10mm or so of travel, which is when the oil-lock piece thar lives at the bottom of the leg comes into play and creates extra damping to stop hard bottoming in use.

 

I agree about the recommended settings from folk like Race Tech and Daugherty being close to spot-on. I've tried compression and rebound damping stacks either side of the recommended RT stack, and they generally are more of a compromise than the recommended one.

 

I have spent too much time thinking about the way the cartridge works. Whoever devised these did a great job as in principle the rebound and compression effects should be completely separate.

During compression, the rebound piston should play little part in creating damping force, because the check valve should be wide open. The small ports in the HMAS piston mean that some force will be created, with the much bigger Gold Valve ports, the effect should be less. So the volume of oil displaced by the rebound piston should just pass easily from the underside of the piston to the top. However as the shaft enters the cartridge, oil must be displaced out, and this has to exit the cartridge through the compression valve and the shim stack bypass port.

On rebound, the check valve in the compression stack should be fully open to let oil back into the cartridge, so the compression valve should now play no part in rebound damping. The check valve in the rebound piston is now closed so oil trapped between the rising piston and the top of the cartridge has to pass through the rebound shims and the shim stack bypass port.

Because of the dimensions of the cartridge (10mm od shaft, 20mm id tube) the oil volume displaced by the shaft is only 1/3 of the volume displaced by the rebound piston (according to my maths, anyway).

Many, many cartridges use these exact same dimensions and so the same basic parts/shim stacks can be used across a wide range of bikes and forks.

 

I have done "it" by measuring the amount of respective oil and pouring it into said fork leg. The proper way is to fully compress the fork leg without the spring and measure it from the top of the leg to the oil. They have tools (read: low tech) to do this with a rod that goes into the fork leg and something to rest it on top of fork leg. Its good to have a good flash light handy and some decent magnifier glasses. You can use ATF too if its not your bike :loco: Peace

 

Here's a little video clip I made this morning, showing my forks hard at work!

[video=youtube;63DMixgS_SQ]https://www.youtube.com/watch?v=63DMixgS_SQ&feature=youtu.be[/video]

 

I also use a syringe with a long hard tube marked at 100/110/120/130, works a treat.
I've tried a few different oils, but I've stuck with Maxima Racing Fork Oil 125/150, it has a viscosity of 26@40*c.
I like the action of my forks with this oil and current set up.
A bit stiff, but has great control and feed back.
I have to add for anyone reading this, that suspension set up is very personal. There is no right or wrong, well there is if its too far from ideal, but what might suit me might not suit anyone else.
There is not just difference on people, but difference on tyre/weight/riding style/personal preference.
As well as tolerances and wear on the same type of forks.
However, 2 years ago I had no idea how damping tubes worked, and it looks like many suspension tuners don't have a clue either (not the ones I found anyway).
So I took matters into my own hands, learned along the way and now regret I didn't do it 20 years ago.

People that still have the standard suspension on their bikes have no idea how much better the VFR will handle.

 

Too true.