15W Fork Oil. Does it make that much difference?

[tommyardin]

I've never had a front end problem that many here have experienced, but I had a leaking fork seal so had to change mine the other week (along with a kebab-supplied R6 shock on the back). The first thing I noticed was that the oil that came out was in excellent condition and very, very thick. Much more so than the 15w I put back in. There is no noticeable difference in the front end since the change and I wondered if for some reason fork oil thickens up as it gets old?? Mine had been in for at least 35k miles.

Hey Wookie, Did the old oil stink when you took it out.
I changed mine when i did some modding to my suspension over winter and it was Minging, smell like rotting fish. and was metallic silver grey in colour. 

[tommyardin]

Darrsi is right when he says about the oil levels being slightly different between the Boxeye and the Foxeye.


The Boxeye has 10 millilitres (10cc) less oil per leg than the Foxeye, the reason for this is that the Foxeye Damper Rods in the base of the fork leg sliders/bottoms are shorter they are 190 mm as apposed to the Boxeyes 210 mm, the slight larger Damper Rods in the Boxeye displaces the oil a little more raising the level in the forks so the Foxeye needs the extra 10 millilitres (10cc) to make up that shortfall. Bearing in mind a house-hold teaspoon is said to hold 5cc so we are talking very little indeed, in fact two teaspoons full per leg.

10 Millilitres = 10 Cubic Centimetres, 10 ml and 10 cc are the same amount.

Again bearing in mind all these parameters are set by Yamaha with the Yamaha spring in place, the Linear Ohlins springs that I fitted was very slightly lighter in gauge so the displacement of that spring was slightly less that the Dual Rate Yamaha spring, plus, I had to take into account the Emulators that I fitted, I opted initially for 465 millilitres in each leg, hoping that the slightly lighter gauge spring would compensate for the oil displaced made by the Emulators, but I upped the oil level back to the recommended Yamaha level by 475 millilitres and found the ride to be better, but still i felt in was topping out a little when under a lot of power accelerating hard out of bends. I removed with a surgical syringe and clear capillary pipe 100 millilitres of the 15 weight oil that I used from each leg and replaced it with 30 weight oil.

I took the bike out for a ride and initially did not notice any difference but after about 30 miles or so the forks stopped topping out, due to the slightly slower damping effect of the slightly heavier oil. it took about 30 miles for the two different weight oils to mix and generally upgrade to a slightly heavier oil.

So the oil in my forks are 475 mls, made up of 375 mls of 15 weight and 100ml of 30 weight, again bearing in mind my forks are no longer Damper Rod forks but Cartridge Emulators, with the emulator set at 3 full turns in from the initial Emulator spring contact.

For me this is perfect, plenty of feel with the road, no harsh crashing out as forks plunge under heavy braking or bumpy surfaces also with the oli combination no feeling of the forks topping under hard accelerating.     

[darrsi]

Darrsi is right when he says about the oil levels being slightly different between the Boxeye and the Foxeye.


The Boxeye has 10 millilitres (10cc) less oil per leg than the Foxeye, the reason for this is that the Foxeye Damper Rods in the base of the fork leg sliders/bottoms are shorter they are 190 mm as apposed to the Boxeyes 210 mm, the slight larger Damper Rods in the Boxeye displaces the oil a little more raising the level in the forks so the Foxeye needs the extra 10 millilitres (10cc) to make up that shortfall. Bearing in mind a house-hold teaspoon is said to hold 5cc so we are talking very little indeed, in fact two teaspoons full per leg.

10 Millilitres = 10 Cubic Centimetres, 10 ml and 10 cc are the same amount.

Again bearing in mind all these parameters are set by Yamaha with the Yamaha spring in place, the Linear Ohlins springs that I fitted was very slightly lighter in gauge so the displacement of that spring was slightly less that the Dual Rate Yamaha spring, plus, I had to take into account the Emulators that I fitted, I opted initially for 465 millilitres in each leg, hoping that the slightly lighter gauge spring would compensate for the oil displaced made by the Emulators, but I upped the oil level back to the recommended Yamaha level by 475 millilitres and found the ride to be better, but still i felt in was topping out a little when under a lot of power accelerating hard out of bends. I removed with a surgical syringe and clear capillary pipe 100 millilitres of the 15 weight oil that I used from each leg and replaced it with 30 weight oil.

I took the bike out for a ride and initially did not notice any difference but after about 30 miles or so the forks stopped topping out, due to the slightly slower damping effect of the slightly heavier oil. it took about 30 miles for the two different weight oils to mix and generally upgrade to a slightly heavier oil.

So the oil in my forks are 475 mls, made up of 375 mls of 15 weight and 100ml of 30 weight, again bearing in mind my forks are no longer Damper Rod forks but Cartridge Emulators, with the emulator set at 3 full turns in from the initial Emulator spring contact.

For me this is perfect, plenty of feel with the road, no harsh crashing out as forks plunge under heavy braking or bumpy surfaces also with the oli combination no feeling of the forks topping under hard accelerating.     

Not exactly what i said Tommy.


98/99 Boxeye is different to 00/01 Boxeye & 02/03 Foxeye

[tommyardin]

The term pedantic comes to mind Darrsi.
If it was exactly what you said Darrsi then there would have been no point in saying it. 

[darrsi]

The term pedantic comes to mind Darrsi.
If it was exactly what you said Darrsi then there would have been no point in saying it. 

Pedantic is good, it's all about being accurate.
For example my bike is a 2000 yet my forks are from a 98/99, which don't have the adjusters.
If i wasn't pedantic i would look up the year of my bike and put the wrong amount of oil in the forks. 

[tommyardin]

Well I would have assumed, in fact I did assume that most of the bikes in here are pretty much standard bikes, not ones that are made up of all sorts of parts from all different years.

Years ago we use to call them old dogs


Pedantic: https://www.vocabulary.com/dictionary/pedantic

Pedantic means "like a pedant," someone who's too concerned with literal accuracy or formality. It's a negative term that implies someone is showing off book learning or trivia, especially in a tiresome way.
‎Personification · ‎Pensive · ‎Petulant · ‎Peculiar

Pedantic = Darrsi

[darrsi]

Well I would have assumed, in fact I did assume that most of the bikes in here are pretty much standard bikes, not ones that are made up of all sorts of parts from all different years.

Years ago we use to call them old dogs


Pedantic: https://www.vocabulary.com/dictionary/pedantic

Pedantic means "like a pedant," someone who's too concerned with literal accuracy or formality. It's a negative term that implies someone is showing off book learning or trivia, especially in a tiresome way.
‎Personification · ‎Pensive · ‎Petulant · ‎Peculiar

Pedantic = Darrsi

"...in a tiresome way..."


Tommy, you just wrote a post above that was like reading War And Peace.........about fork oil.
Try keeping things simple fella.


Pot, kettle and black spring to mind in this instance. 

[JoeyMcEssex]

Just ordered fork seals, dust caps and 15W fork oil. hoping it improves the amount of dive.

Mine is a Boxeye with preload adjuster: has anyone tried the preload adjusters like those on ebay?

Would post a link but cant seem to paste into window!!

[Wookee]

Oil would thin out over time, but don't forget you can buy heavier oil than 15w as well.

I realise this which did make me wonder what was put in there. It was almost as thick as diff oil I changed last year.....which I think was something like 75w

[Wookee]

Hey Wookie, Did the old oil stink when you took it out.
I changed mine when i did some modding to my suspension over winter and it was Minging, smell like rotting fish. and was metallic silver grey in colour.

Nope, it was in excellent condition and it was red.

[darrsi]

Oil would thin out over time, but don't forget you can buy heavier oil than 15w as well.

I realise this which did make me wonder what was put in there. It was almost as thick as diff oil I changed last year.....which I think was something like 75w

Highest weight of fork oil i've seen is 30w, but i doubt very much it was that from your description.

[Gnasher]

Measure the air gap not the oil, the spring must be out and the sanction compressed all the way in.  It's vital to get the model year correct the best weight oil, I found to be is 12w this you have to mix yourself, also fit up rated springs job done