Fork Oil Change

Hi All

The forks I have on teh 550 are an unknown quantity to me. They don't appear to be leaking but then again there might not actually be any oil in them ! I plan to take the caps off and drain any that's in there and replace the oil with ATF since I have some. It it worth rinsing out the workings with some diesel perhaps - I hear that it can all get very murky in there? I could I suppose replace teh seals but why if no leaky..

Cheers

J

 

you can still dissemble them and clean them with out replacing the seals.

or just remove the front end from bike per factory service manual clean out the tubes replace oil .

you still have to remove the fork caps and this is best done with the tire off the bike or off the ground
remove the spring and clean the insides out I would use seafoam as it is a very seal friendly chemical
let it drain out

 

Thanks plan is to remove each legand empty into a bucket - we don't get Seafoam here (dratted EUprobably banned it) , Looks like it's mostly kerosene which I think we call Parafin (which is close to diesel) with some lighter more volatile stuff in teh mix too.

Cheers

 

ATF works just fine as fork oil. However, let me caution you- as someone who races Vintage MX and experiments a GREAT deal with fork oil viscosity, ATF is only about a 5w oil. So while it will do what needs to be done, your damping will be pretty light. When I did the forks on my 650, I used a 15w fork oil, and they work OK. I also installed some preload spacers to help with diving under braking, but that's a whole other story. Damping characteristics are what the viscosity affects, and you may find that it is too soft with such light/thin fluid.

On a more modern cartridge fork, lighter oils are king, and many newer machines use 2.5-5w oil. But on older, more simplified damping rod units, you need viscosity. I ran 30w motor oil in some old Yamaha YZ forks to get them to hold up once. Even with 20w, they would dive in turns and bottom on the smallest bump. And while of course you aren't MXing your 550, trust me when I say that when you are surprised by forks that are too soft, it will not be a pleasant experience.

 

^ what he said. Most of us find that 15 weight fork oil is just about right for street use.

 

Ok - I'll save the ATF for my 2-stroke gearbox 15 weight it is..

 

Its fantastic for 2 stroke gearboxes, wet clutches love it!

 

I’m getting ready to change the fork oil on my yx600. It uses 10 weight from the factory just like the XJ’s.

Are most still finding that 15 weight is a better option?

 

I know people love it but in any bike I have tried it the gear change has needed more pressure and been notchy compared to a proper transmission oil

I've used it in forks once and found it too light

 

I put 15W fork oil in my '85 FJ600, along with Suspension Techniques springs and new seals. I was quite happy with the results.

 

Right on!

I’ve heard a lot about how much proper front springs can change a bike. I need to research this more.

 

Indeed, agree with that. But I would also add that I found my forks to be quite “sticky” with light weight synthetic oil, so I drained them and put straight 20 oil in there, much better.

 

Realistically, the damping in old bike forks is rubbish, there is very little in the way of valving, hence why heavier oil is needed. When I stripped my first leg I actually though someone had stolen the bits inside...
I’ve heard that you can buy “emulator cartridges”, which have all the required valves and springs etc in them, they aren’t cheap, and I’ve never tried them, so can’t comment.
I’m just a “take your time and enjoy it” rider anyway...

 

Every time I think about upgrading the internals of these forks I usually circle back either sticking with stock or doing a fork swap.

Along with my two yx600’s I have a non-running Suzuki gs500. I don’t have all the information in front of me, but I believe the triple tree from the gs500 will swap with my yx600 (I could be wrong though). The gs500 front would allow me to run modern tires and has many other upgrade options.

Maybe I’ll restore the mechanicals to OEM specs on one yx600 and upgrade the other with modern suspension.. It’s fun to think about , but who knows

 

They make a massive difference with the correct springs, about $585 USD to have it done here and worth every cent, if you haven't ever ridden with correctly tuned suspension you really have no idea how much difference it can make, heavier oils, progressive springs and preload spacers are just band aid fixes

 

Right on.

Race tech has spring rate calculators. I’m going to check their site out to see what springs are recommended for my weight (194lbs. at this moment).

I guess if they aren’t too expensive I’ll “spring” for them. (Yup! That just happened)

 

The Radian weighs about the same as the XJ550 Maxim, which weighs about the same as the XJ550 Seca. The (I mean THE) resident xj550 expert runs 15wt oil in his forks IIRC. I do miss @bigfitz52 He's a treasure of knowledge.

 

I've been reading a bunch about the emulator valves also and considering them on my current fork rebuild. I was a little surprised doing the same spring calculator on the RaceTech site...it lists the stock spring rate as .46 kg / mm and recommends .80 kg / mm. Stiffer makes sense, but that's almost double! And despite some calculations returning lower spring rates, like if you weigh 150 lbs (nope, not since high school), the .80 kg rate appears to be the lightest spring they offer. This is for an 82 750 Maxim.

 

The front springs are supposedly undersized from the factory on a lot of these bikes.

My YX600 comes with 0.385 kg/mm & 0.575 kg/mm dual rate fork Springs.

I’ve read (but haven’t independently verified) when considering the rake angle and the weight of a yx600: -0.385 kg/mm is appropriate for a 6 lb rider and a
- 0.575 kg/mm rate would be appropriate for a 105 lb rider.

When I type my specifics into racetech (195 lbs. w/o gear, Street riding, intermediate/B class rider):
0.75 kg/mm springs are recommended

If this is actually true, upgrading the front springs would likely make a huge improvement

 

Are the front springs undersized cause they have an air fitting? My air fitting I believe I can max it out at 17psi. I recall someone suggesting replacing the springs and then depleting the air.