Forkin' ell

[Bristolbadger]

Morning all. Hoping someone might be able to shed some model specific light on these please. Had to rebuild them again after a leaky left one and ideally need to know how much oil they need from scratch.

It might be a bit to worn inside the case and that's my trouble, not the Pyramid oil seal... will soon see.
585mm stanchions.
Cheers

[Johnwebley]

What bike is it?

The 500 series take 160cc,

ATF fluid in my case

Hope it helps

Sent from my SM-A750FN using Tapatalk

[McCabe-Thiele (Ted)]

FWIW you should find the information in one of the manuals in. Aladdins Cave here.

[K2-K6]

That casting type was on the end of SOHC production (750 F2, CB650 I think) then on following twin cam bikes.

150ml not a bad start point if you can't find information as it's not absolutely critical.

Minimum has to still cover damper valves (with spring volume in the fork cavity ) such that it doesn't go into air and not damp. Maximum is more to do with air gap above the oil and going too high here will give hydraulic lock to prevent fork compression. 

This Maximum is usually considered adjustable in level if you want for example to give more air spring effect at full compression in preventing bottom out under heavy braking. Tweaks of 10ml going upward from 150 ml would be normal to assess.  Or measuring down from top of stanchion with a dipstick to set that way.

The 750 F2 manual states 145~155 cc fill volume.

[davefirestorm]

They look same as my CB650 forks and Mr. Haynes states ATF fluid 170ml Dry and 150ml at oil change😁

[Bristolbadger]

That casting type was on the end of SOHC production (750 F2, CB650 I think) then on following twin cam bikes.

150ml not a bad start point if you can't find information as it's not absolutely critical.

Minimum has to still cover damper valves (with spring volume in the fork cavity ) such that it doesn't go into air and not damp. Maximum is more to do with air gap above the oil and going too high here will give hydraulic lock to prevent fork compression. 

This Maximum is usually considered adjustable in level if you want for example to give more air spring effect at full compression in preventing bottom out under heavy braking. Tweaks of 10ml going upward from 150 ml would be normal to assess.  Or measuring down from top of stanchion with a dipstick to set that way.

The 750 F2 manual states 145~155 cc fill volume.

Great stuff, just the info I was hoping for.
I was thinking F1 but the workshop manual wasn't definitive...
Mucho gratis!

[andy120t]

Same as my CB650 ones too.

[McCabe-Thiele (Ted)]

Ok so use ATF but there are so many types of  Dexron grades upwards to  fully synthetics interesting -  when I put my forks back together I will be faced with so many options.

I'm minded to use what I have in stock Fuchs Titan 4400.

Opie oils is often my provider of choice - https://www.opieoils.co.uk/search.aspx?search=ATF

[K2-K6]

I prefer to use Motul fork oil in any fork built now.

Nothing wrong with ATF but these formulated for forks only hold advantage in how they work and with reduced friction I feel.

ATF has a very tight tolerance and good product reputation for automatic gearboxes, but has to stay confined within very close technical performance for clutches etc, which fork oil doesn't need to comply with.

Principally ATF was used as it has high anti-foaming performance which is of value in preventing aeration when used in dampers. Very high wear resistance (spalling etc ) for gear faces that exists at very high torque loading on the gear sets. Although good it is outperformed in forks regarding stiction by good fork oils, this to help with giving a more silky smooth fork travel.

[McCabe-Thiele (Ted)]

What grade of Motul Fork Oil do you is it there seem to be in quite a bit few grades from 5W to 20W?

[Nurse Julie]

What grade of Motul Ft Ork Oil do you is it there seem to be in quite a bit few grades fr ok m 5W to 20W?

We usually use 10W Ted.

[Laverdaroo]

I've got a set of those in the shed Nick, you should have shown me the slidersI would have twigged then! They're off a twin cam 750 which I bought in 2021 as a box of bits, I've the frame and the forks,motor and a few bits like carbs and the like for it still. Yours if you want them.

[K2-K6]

What grade of Motul Ft Ork Oil do you is it there seem to be in quite a bit few grades fr ok m 5W to 20W?

We usually use 10W Ted.

Same as julie here Ted, unless you've very specific reason to shift for some reason. Very high spring rate would generate need to go upward.

Using their 7.5 viscosity in mountain bike forks as that seems to work well. These are (or the riders specifically ) are very sensitive to any additional and unwanted stiction hence my reference to how well this oil works. They are used in 35~40mm stanchion forks with coated aluminium legs and magnesium alloy lowers with low friction bushes fitted, literally everything to reduce stiction is welcome in their use.

[philward]

I enquired on the forum shortly after the rebuild of my 500k2 about what fork oil to use as I found the bike was picking up all the small undulations in the road. I started off with ATF and following K2-K6's recommendations, worked through Motul 10w,ending up with Motul 2.5 w and that improved it considerably. I don't scrape the pegs but works well for my general riding.