Quick question about fork oil

J

jcornwell101

Registered
When filling the oil level in my fork I made a mistake and kicked the bottle spilling some.
This spill made me alittle short for getting correct oil height in one fork.

So I had to use 1.5-2oz of the oils fork oil to make oil height in one of the forks.
So I mixed 7.5w that came with my spring kit with stock 5w.

Oil height is set to 120mm per what hyperpro wanted.

Do you think it’s such a small amount that I will really notice any difference? Or should I just pick up fork oil on the way home and change it out before I put the bike back together.
 
I picked up 2 liters of moterex syn 7.5w while running medical supplies for work. I plan on finishing the bike in the morning, I had to wait for a spanner wrench to come from amazon for the steering head castle nuts. I decided while I had everything apart to do steering head bearings so I know what I have with a bike that has 16k on it.

So this bike has now new brake pads, clean/adjusted chain, cleaned chain box and clutch pushrod, flushed all fluids, rebuilt forks minus bushings because those had no scratches or light spots, new tapered steering head bearings, new shock, returned to stock height, replaced spark plugs, and air filter.

With setting preload on the tapered bearings on my VFR I tightened them down tight and would back them off until they suspension was very light steering and didn't clunk. With the VFR if you had them too tight your bike would start wondering at speed.

Is this the same with the Hayabusa? From what I read I assume so, I just want someone who has done it to validate that or give me the brain duster.

bike already came with new pilot power 5 tires from the dealer

I usually do all current maintenance on the bikes and cars that I buy. Just kind of anal in that aspect since I work on equipment in the medical field for a living.
 
jcornwell101 said:
I picked up 2 liters of moterex syn 7.5w while running medical supplies for work. I plan on finishing the bike in the morning, I had to wait for a spanner wrench to come from amazon for the steering head castle nuts. I decided while I had everything apart to do steering head bearings so I know what I have with a bike that has 16k on it.

So this bike has now new brake pads, clean/adjusted chain, cleaned chain box and clutch pushrod, flushed all fluids, rebuilt forks minus bushings because those had no scratches or light spots, new tapered steering head bearings, new shock, returned to stock height, replaced spark plugs, and air filter.

With setting preload on the tapered bearings on my VFR I tightened them down tight and would back them off until they suspension was very light steering and didn't clunk. With the VFR if you had them too tight your bike would start wondering at speed.

Is this the same with the Hayabusa? From what I read I assume so, I just want someone who has done it to validate that or give me the brain duster.

bike already came with new pilot power 5 tires from the dealer

I usually do all current maintenance on the bikes and cars that I buy. Just kind of anal in that aspect since I work on equipment in the medical field for a living.
Click to expand...

That all sounds great.
I've done several steering head bearings, and always tapered replacements when available.
I just put them in my '03 Gsxr1k a couple months ago.
Tighten them by feel, ride it, and check them again.
I have yet to run across any steering nut that could take anywhere near the torque spec, as the specs all are huge overkill, and will basically lock the steering because it gets so tight, and that is using a calibrated torque wrench with an oem spec spanner attachment.
After exeperiencing this a few times, much reading, and talking to a few engineers, the best bet IS to use your experience and best judgement, and tighten the bearing nut and locknut by hand...and I belive in torquing all fasteners.
 
One thing to remember about fork oil is it can, and should be used as a tool to set up suspension how you like. Not just Viscosity but volume as well. Normally I would recommend buying the Racetech Suspension Bible for more on this, but Amazon is now up to $22 and change for the Kindle Version, which is BS(!) since I bought it not too long ago for like $5! Regardless of price it is a great resource and cannot recommend it highly enough! They talk a lot about fork oil levels in various sections of the book. For an example - the Gen 1 Factory Hayabusa Service manual calls for 98mm (no Spring in either case), whereas Racetech calls for 110mm (with their Springs!). They talk about the volume of the stock spring vs the volume of the aftermarket spring a bit, as they displace different volumes of oil in the fork and subsequently this can affect damping. The "uncompressible" oil creates a "compressible" air space of a given volume in your fork, by varying that air Space you can change the Damping characteristics of the fork. A lot to go into, but heres a few screen captures to illustrate.
1701539107703.png


1701539245505.png


1701539280712.png
 
The race tech bible has good information I have had a gander at some sections.

I am in the process of installing a hyper pro street box. I have finished the forks that came with 7.5wt oil, recommended oil height, and progressive springs.

I am in the process of installing the rear shock, but I need to finish the steering head bearings.

I have the lower bearing pressed on the stem with dust seal and top race installed. I cracked the lower race so I had to order another all balls kit that’s coming Monday.

There was a lip I had to sand down and smooth out. The one race was very hard to remove from the bottom.

I just need to put together the front end and install the new shock. It had lowering links in the back, but I want to go back to stock.

I am a conservative rider, but the progressive setup works well adjusting to 2 up, loaded down riding, and when I wanna ride hard. I have run it on my vfr since 2010. Great setup for the money.

Just learning the hardway I need a bearing race driver and some proper fork tools. But, I got that all sorted out now and know how to do it for next time. This bike is kind of hard to work on compared to my vfr lol. But that’s 95-2017 big difference in tech lol.
 
jcornwell101 said:
The race tech bible has good information I have had a gander at some sections.

I am in the process of installing a hyper pro street box. I have finished the forks that came with 7.5wt oil, recommended oil height, and progressive springs.

I am in the process of installing the rear shock, but I need to finish the steering head bearings.

I have the lower bearing pressed on the stem with dust seal and top race installed. I cracked the lower race so I had to order another all balls kit that’s coming Monday.

There was a lip I had to sand down and smooth out. The one race was very hard to remove from the bottom.

I just need to put together the front end and install the new shock. It had lowering links in the back, but I want to go back to stock.

I am a conservative rider, but the progressive setup works well adjusting to 2 up, loaded down riding, and when I wanna ride hard. I have run it on my vfr since 2010. Great setup for the money.

Just learning the hardway I need a bearing race driver and some proper fork tools. But, I got that all sorted out now and know how to do it for next time. This bike is kind of hard to work on compared to my vfr lol. But that’s 95-2017 big difference in tech lol.
Click to expand...
I have Progressive springs and Gold Tech valves up front and a Progressive shock out back...I have the suspension dialed in a little on the stiff side as I like the feeling in the corners although it's a bit rough on the roads and I feel all the bumps....it doesn't help that our roads suck around here...
 
Thats crazy

With my vfr I was able to get it dialed in that if I rode 2 up I would do a complete turn up front of preload and 2 clicks on the rear shock of preload. No dive and we were comfortable.

Even when I first came back from Iraq and grew laterally to 255lbs we didn’t have any issues. But that kit for the vfr had 15wt oil it came with.
 
Gen1 and Gen2(unsure about Gen3) come with 5w fork oil.
I'm low/mid 190's in gear, and always felt that Busa forks felt flimsy, even with good sag numbers, they would handle well, but I didn't have confidence in their feel.
I swapped my old Gen2's fork oil for 7w, and immediately it felt as it should have.
Of course you can spend as much as you want modifying suspension, and I don't like to bandaid anything, but the 7w oil performed better for me than the stock 5w, and on stock valving, which is kind of strange, but I assume the heavier oil slowed it enough to firm the feel.
 
generally said :

the forkoil last at max 4.5-5 years - then its damping and greasing ability is OFF - can be seen if it is black like ink and stinks like a sewer.

the busa gen2 is usually delivered with 0W or 2.5W fork oil (see manual what there is written) and is as i suppose calulated for light weight - 150-160 lbs (japanes) riders

but not for us with 190 or more.

so changing to stiffer oil like 5W, 7.5 or 10W is the best, first, way to increase the fork´s way to work.

if you install then even stronger springs like those from Hyperpro, WP or Wilbers,
you should first stick to THEIR information on
the filling quantity or air cushion
and use it to test the driving behavior and only then experiment with the filling quantity or air cushion.

____________________________________________________________

and think always about that
your - so to say - ass or at last your life depends on the chassis (as well as the brakes) .
so any experimentation can lead to catastrophic failures.
what ever your´e going to change,
do it in small steps and test the result(s) after every step careflully.

_____________________________________________________________

and yes u can mix the fork oils to change its stiffness .

but if u do mix only the same manufacturer and type of oil
never mix mineralic with full synth - they don't get along and can therefore make a fork undriveable.

the oils differ in their basic properties from the one manufacturer to an other
such as toughness (centi stokes "cSt" etc.)

and THAT changes quite a lot , which is why the general mixing formula then no longer fits.
 
Last edited:
Berlin Germany said:
generally said :

the forkoil last at max 4.5-5 years - then its damping and greasing ability is OFF - can be seen if it is black like ink and stinks like a sewer.

the busa gen2 is usually delivered with 0W or 2.5W fork oil (see manual what there is written) and is as i suppose calulated for light weight - 150-160 lbs (japanes) riders

but not for us with 190 or more.

so changing to stiffer oil like 5W, 7.5 or 10W is the best, first, way to increase the fork´s way to work.

if you install then even stronger springs like those from Hyperpro, WP or Wilbers,
you should first stick to THEIR information on
the filling quantity or air cushion
and use it to test the driving behavior and only then experiment with the filling quantity or air cushion.

____________________________________________________________

and think always about that
your - so to say - ass or at last your life depends on the chassis (as well as the brakes) .
so any experimentation can lead to catastrophic failures.
what ever your´e going to change,
do it in small steps and test the result(s) after every step careflully.

_____________________________________________________________

and yes u can mix the fork oils to change its stiffness .

but if u do mix only the same manufacturer and type of oil
never mix mineralic with full synth - they don't get along and can therefore make a fork undriveable.

the oils differ in their basic properties from the one manufacturer to an other
such as toughness (centi stokes "cSt" etc.)

and THAT changes quite a lot , which is why the general mixing formula then no longer fits.
Click to expand...

Gen1 and Gen2 have 5w fork oil from the factory
 
Over the weekend I drained both forks and put in the motorex 7.5w since I cannot buy the hyperpro one locally.
I have a combikit installed on my VFR750 with front springs/15wt with stock valving. I also have a modified CBR 929 rear shock with progressive spring in the back. I have run this setup since 2010 and it has been great in all riding. Maybe heavier fork oil and messing with the bag would have been enough. But, I just enjoyed the confidence this kit gave me on the VFR.

I also am going back to stock height in the rear with the PSR links that were installed in the second hole which lowered the rear 2".
 
Berlin Germany said:
generally said :

the forkoil last at max 4.5-5 years - then its damping and greasing ability is OFF - can be seen if it is black like ink and stinks like a sewer.

the busa gen2 is usually delivered with 0W or 2.5W fork oil (see manual what there is written) and is as i suppose calulated for light weight - 150-160 lbs (japanes) riders

but not for us with 190 or more.

so changing to stiffer oil like 5W, 7.5 or 10W is the best, first, way to increase the fork´s way to work.

if you install then even stronger springs like those from Hyperpro, WP or Wilbers,
you should first stick to THEIR information on
the filling quantity or air cushion
and use it to test the driving behavior and only then experiment with the filling quantity or air cushion.

____________________________________________________________

and think always about that
your - so to say - ass or at last your life depends on the chassis (as well as the brakes) .
so any experimentation can lead to catastrophic failures.
what ever your´e going to change,
do it in small steps and test the result(s) after every step careflully.

_____________________________________________________________

and yes u can mix the fork oils to change its stiffness .

but if u do mix only the same manufacturer and type of oil
never mix mineralic with full synth - they don't get along and can therefore make a fork undriveable.

the oils differ in their basic properties from the one manufacturer to an other
such as toughness (centi stokes "cSt" etc.)

and THAT changes quite a lot , which is why the general mixing formula then no longer fits.
Click to expand...
As usual, great advice from the old ‘master of Busa engineering’
I always enjoy reading your posts Frank, it always gives me a new perspective on technical data and also of course your years of experience working on Hayabusas and modifying them experimenting on various aspects is invaluable!
I’m about to disassemble my Busa forks today, I’ve had them on the bike for 5 years and have never changed oil, they’ve never leaked or given poor performance so I’ve been lazy and not kept up with the oil maintenance.
I purchased the forks used, 2004 model forks and was told they have Racetech modified cartridge valving and ohlins springs… we shall see about that lol.
I’ll post up some pics later, will be interesting.
 
Kiwi Rider said:
As usual, great advice from the old ‘master of Busa engineering’
I always enjoy reading your posts Frank, it always gives me a new perspective on technical data and also of course your years of experience working on Hayabusas and modifying them experimenting on various aspects is invaluable!
I’m about to disassemble my Busa forks today, I’ve had them on the bike for 5 years and have never changed oil, they’ve never leaked or given poor performance so I’ve been lazy and not kept up with the oil maintenance.
I purchased the forks used, 2004 model forks and was told they have Racetech modified cartridge valving and ohlins springs… we shall see about that lol.
I’ll post up some pics later, will be interesting.
Click to expand...
hi gregg

thank you for the big bunch of praise,

but I'm just presenting my experiences from over 40 maintenance and repairs. (here and at my homepage)

so you will definitely take my following advices seriously.

1. don't smell/sniff the fork too hard when the stopper is out of the top,
or you will need the 10 liter puke bucket.
believe me - a toilet drain / pipe / dirt water sewer hardly smells any worse.

2. when the fork has bled out after about 5 minutes, check the collecting container (i use the 1 kilogramm ice cream box) for the amount of possible sludge that you can sometimes find at the bottom of the container.

personally, I've already found 1-2 large tablespoons of sludge - sometimes it's a real horror what awaits you.

to the question how long the oil inside the fork last - hmmmmmmmmmmm - i would say not more than 3 years.
because
ca. 2 years ago i bled a gen1 fork where the fork oil was 3.5 years old (provable - i made the former oil change myself and noted that job in my excel-maintenance sheet for this bike) with around 10000 km more on the counter .

and what shall i tell?

the fork oil smelled as worse as usual / stronger than a sewer
and
was as black as writing ink
and
again black sludge - not that much like 3.5 years ago ,
but still half a tablespoonful again .

and! - no clue where that sludge comes / came from but it was there - seriously !
 
edit:

guys believe me

it's like drinking too much beer
when at some point the saying comes:
Hiccup said the beer,
here I am again
and I'm even bringing some more food with me.

u all may laugh but that feeling of a starting stomach salto is damn bad !

MY stomach started to do a backwards somersault a few times - but luckily I always was just able to prevent it.

since the 1st time, I've only been fanning the air from my fork lightly with my hand to my nose - it's enough to make me grimace.
 
Kiwi Rider said:
I’m about to disassemble my Busa forks today, I’ve had them on the bike for 5 years and have never changed oil, they’ve never leaked or given poor performance so I’ve been lazy and not kept up with the oil maintenance.
I purchased the forks used, 2004 model forks and was told they have Racetech modified cartridge valving and ohlins springs… we shall see about that lol.
I’ll post up some pics later, will be interesting.
Click to expand...
Here’s what the fork oil looked like after 50,000 kms… not as bad as I thought it might be, and the springs and cartridge are all stock standard by the looks… guy I bought them from told me racetech modded cartridges and ohlins springs, he lied.

96A23F43-425E-4206-8404-FD3AEF252D30.jpeg


F5CCA92A-A179-4FC7-B953-48ADCB70D9A4.jpeg


4D91256C-29B8-43D1-A425-2F5639477DF7.jpeg
 
Kiwi Rider said:
Here’s what the fork oil looked like after 50,000 kms… not as bad as I thought it might be, and the springs and cartridge are all stock standard by the looks… guy I bought them from told me racetech modded cartridges and ohlins springs, he lied.

View attachment 1673901
Click to expand...

hi gregg

50 000 km or better said after 5 years in use ?
i suppose it is more a question of the time in use and less of the mileage.

what did the old oil smell like?

i'm guessing it smelled bad.

new oil, on the other hand, usually smells wonderful - at least that's what I can clearly tell every time I compare the smells.

and one more thing - let the drained, old fork oil sit like that for a day or two and give the sludge time to settle/sink.

the result should be at least “irritating”.

another question about the springs.

are they highly polished, as Wilbers has been offering for a small additional price for a few years now?
(I can't see it exactly in the photo.)

according to Wilbers, polishing is intended to reduce contamination of the oil.
 
Berlin Germany said:
hi gregg 50 000 km or better said after 5 years in use ? i suppose it is more a question of the time in use and less of the mileage. what did the old oil smell like? i'm guessing it smelled bad. new oil, on the other hand, usually smells wonderful - at least that's what I can clearly tell every time I compare the smells. and one more thing - let the drained, old fork oil sit like that for a day or two and give the sludge time to settle/sink. the result should be at least “irritating”. another question about the springs. are they highly polished, as Wilbers has been offering for a small additional price for a few years now? (I can't see it exactly in the photo.) according to Wilbers, polishing is intended to reduce contamination of the oil.
Click to expand...
At 50,000 km I’m calculating about 500 hours in use (100kms a hour approximately)
The oil wasn’t very smelly all, considering the age of it.
The springs are stock Suzuki springs, not polished.
 
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