Identifying forks, gsx750 or gs550?

[fededevi]

So I'm trying to find out what the forks on my gsx750E comes from, mainly to find how much oil to put in them.
The closest thing I found to the suspension I have is those mounted on a gs550m katana:



Double spring, 2 position spring preload cap, 4 bolts anti-dive, 'ambient pressure'.
Is it possible that someone mounted those on a 750, are all those forks interchangeable?
I can't seem to find any reference of those forks used on a classic gsx750e.
And finally does anyone know the oil level/oil amount to put in them?

Ty,
Federico.

 

[hampshirehog]

What year 750 have you got?

 

[fededevi]

Should be a 82', 16 valves, round front lamp, European market.
I don't think the forks are original.

 

[hampshirehog]

Like this one?

https://www.motorcyclespecs.co.za/model/suzu/suzuki_gs750ez 82.htm

They had those type of forks. Good luck with trying to find out the fork oil capacity. I couldn't find it for my 1982 550ez and just plumped for the standard 140 mm level, forks fully compressed with no springs and that worked fine

 

[fededevi]

Yes! that's the one. Thankyou, I've never been able to find the service manual for this version.
I also seen many pictures of this bike (with the round lamp) but with forks without anti-dive, different markets?
I'll do as you did and go for 140mm level, is that somewhat of a standard value?

 

[hampshirehog]

140mm is kind of a rule of thumb value that I've used for years and I've seen others tote it around. I can't remember who told me but it seems to work.

 

[GregT]

From John Robinson's book "Service and setup data" Capacities/cc

SAE 10/30 and ATF Pre 81 327, 81 210, 81 L 241 82 SAE15, 225 (cast wheels) 202 (spoked) 82 S 227 , 82 T 191 , 83 S 227 , 83 E, ES, SAE10 293

I'd doubt the 10/30 and ATF spec is relevant now, probably SAE15 would work. Quite a variation between years and models.
Robbo was good at sourcing thsi stuff.

 

[Gorminrider]

mmm. Maybe Sae 10 is closer to the Multigrade+ATF mix? atf comes in at about 5-7w I think and the 10w30 would neet to get pretty hot to thicken...Funnily enough, Suzuki will call for the "mix" in some bikes while calling for "fork oil" in similar bikes of the same year.

Yes, I often see 6" + for fork oil levels ...140mm (5.5") seems low but IS called for on some bikes.More oil shrinks the "compressible air space" but of course the volume of the actual leg is where the comparison might be made to find a general "airspace-compression" comparison...

 

[Grimly]

I've always taken ATF to be around SAE 10. Seems to work out, anyway.
In the XJ, I just used a synthetic 5w40 and it works ok, too.
I've got loads of that particular 5w40 as it's not a long-lived oil for the engine, so a shelf full of it will keep my forks happy for years.

 

[Steve]

I don't know if the viscosity numbers are different for engine oil and fork oil, but I usually go with 10w fork oil.

The recomended level is usually in the 140-150 mm range.

.

 

[fededevi]

Thanks everyone,
for reference I ended up putting about 225-235cc with a level of 150mm.
Half a liter of oil is enough to fill both forks.