Front fork oil ??

[dgloor]

The front on my bike is really soft. I am assuming it is low on oil. Is there a way to add or check the oil without tearing the forks apart?
From what I have seen it looks like taking them apart requires replacing the seals. Which I don't have and am concerned about getting.
Is this true? Or is there a way to drain and refill?
Oh by the way it is a '74 Suzuki GT550.

[Suzsmokeyallan]

If you are taking the forks apart its best to replace the seals, especially if its been years since they were apart or they have never been apart for years.
You can pull the tubes out without removing the seals in the lower legs and now will be a good time to do the damper rod mod as well.
Use a good quality 20 weight fork oil and stick to the correct levels, the fork seals are still available from Suzuki and reasonably priced as well.

[tz375]

Allan is correct that the seals probably need to be replaced, but you may like to just try fresh oil first and work out if you need different springs as well - so you can do it all at once.

There is really no way to check the standard oil level, so I'd drain the old oil by removing the drain screws on the sliders and then flush the forks out with ATF and drain that.

You could try a 20Wt fork oil with the amount specified in the manual, but do one leg at a time. 20Wt is a little light in these old bikes and sometimes 30Wt is better but start with 20 and work up or down from there.

BTW, slightly more oil than stock = stiffer ride, but not too much more or it will blow the seals.

Springs are typically too soft on these bikes so measure sag and if it's much more than 35mm from fully extended, the springs are probably too soft. You could add a little preload to see if that helps or replace the springs.

[dgloor]

I would like to try to just drain it and refill for now. Maybe when down this winter I will try out the damper mod and check the spring. Right now, if the drain and refill work, I would just like to get it on the road. Again if it's safe!
I can see where to drain it no problem, but where do you put the oil in? Nothing I've seen says anything about it. If you have to pull the seal, I might as well do the whole thing now.
Thanks for your input.

[Suzsmokeyallan]

Now you know whats going to happen, murphys law will step in and after you've drained them and put in new oil, they will start leaking after a few weeks.
The oil goes in from the top of the leg so you have to open it to remove the spring anyways to do a flushing.

[tz375]

Oil goes in through that large top hex nut on each leg. Only do one at a time or else you will have all sorts of trouble as the bike collapses.

We'll keep our fingers crossed with you that the seals will last until winter.

[BRP Tourer]

The procedure I usually use...
Break loose the large hex nuts on the tops of the forks while the bike is sitting stable on the ground, but do not remove them at this time.
Raise the bike on the center stand and use a jack or piece of 2x4 to raise the front wheel off the ground.
Remove the top fork caps and drain screws to drain the old oil.
Remove the fork springs and spacers, if any. Keep track of what order they come out.
When the oil is done draining, lift the front wheel to work the forks up and down to work the old oil out.
Some will add some ATF and repeat the previous step to flush them, as I change my oil yearly I find this step not needed.
Screw the drains back in and add the proper amount of fork oil to each leg. (20 or 30 wt fork oil, or, since I like a rather soft suspension, I use type F ATF, and set my preload higher).
I usually use a small ruler or piece of wire to make sure the oil level is equal in both legs.
Re-install the springs, spacers, and caps.
Lower the bike and final torque the caps.
Take the bike out and ride it like you stole it!
Note: The only way I know of to check the oil level in the forks is to remove the springs and measure the level in the tubes, if you are going through that much trouble you may as well change it. AND in my experience, if the seals are years old, they will probably start leaking with fresh oil, may as well do that at the same time.

[jkevinlilly]

Avoid smelling the drained oil. If it is original, it may be fish oil.

Just think about what 37 year old fish oil may smell like.

Kevin

[Suzsmokeyallan]

If its original oil you don't need to smell it, it will smell up the whole place so you'll have no choice. Do it outside, you will be thankful you did.

[tz375]

Where di the old Fish Oil urban legend come from? I have seen it in a few places, and over the years of stripping old Japanese bikes never came across it. All old oil smells and gearbox oil is among the worst. And it's carcinogenic I hear.

I was rebuilding and restoring CB72s and T500's back in the late sixties and early seventies and never encountered the mythical fish oil.

[Suzsmokeyallan]

I never saw the fish oil either but the fork oil takes first place for pungent smell if it stays in there for years. I've seen it so bad it actually stained the forks aluminum parts a brown colour.
As for smell it, after ten years in a fork it just reeks of its carcinogenic properties, a mixture of steel and aluminum microscopic filings and of course the old oil.