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Topping off fork oil without rebuilding .... yet.

The Alt

Well-known Member
Joined
Sep 2, 2021
Total Posts
99
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Location
Austin
After riding around some, it's clear I need to rebuild my forks, but before I do this, I'd like to postpone and ride it a bit more.
I have no measurement on how much is leaked out, but would like to know is there a way to just add some oil and get a close measurement without completely dissembling?
Perhaps drain out what's there and add X amount? Or just add X amount.
Just looking for a best guess to have some replaced oil in the strut vs letting it run out.

Hard to believe my Bonanza struts are easier to work on.

Alt
 
I notice you're in Austin and you probably still have a riding season until it starts raining.

If you had a measurement from the top of the fork tube, you could add oil, or ATF then remove it to a preset height with a tool like this:
stockton_fork_oil_level_gauge_750x750.jpg


But without that dimension you're stabbing in the dark. If you read about fork oil level as stated by Racetech.com it is yet another way that you can tune your front suspension. I'd recommend adding 15% more oil to what you've got in there, and adding 1/2"-3/4" more preload spacing. Your fork caps will be a b*tch to get back on and I recommend a helper or two and plenty of bbq & cold beer. (I've got relatives out there) and give it a test ride. No need for special oil, just add $.99/qt ATF until you can tear them down and clean them out right.

If you feel like two-finger breaking would be nice add an 11mm master cylinder while you're at it. (Stock 91-03 CB750 Nighthawk) I'll miss my CM400C'S braking the most!


You might be able to get away with draining and refilling, I remember once draining forks in our July 4th heat, forks had been in the sun all day and when I removed those drain bolts it pissed oil far and fast. Seemed to me that one could refill after a purge like that. Then set fork oil level with the tool shown above.
 
You'll need to support the engine first so the front end doesn't drop. Then remove the fork caps and the drain screws/bolts. Drain the forks, reinstall the drain screws being sure the copper washer is on the screw/bolt. Add 4.9 oz, or 140cc's of 10w fork oil and put the caps back on tight. You're done.
 
You'll need to support the engine first so the front end doesn't drop. Then remove the fork caps and the drain screws/bolts. Drain the forks, reinstall the drain screws being sure the copper washer is on the screw/bolt. Add 4.9 oz, or 140cc's of 10w fork oil and put the caps back on tight. You're done.

Thanks, thought it would be that simple, and thanks for the amount to add.
Alt.
 
I looked it up the quantity in the FSM. You've downloaded that right?

Yup. and I saw that. Just saying thanks for pointing it out.
My original post was along the line of not draining out and replacing the FSM amount, but just taking to the top off and using a dowel or something as a dipstick and filling to so many inches below the top with the forks extended.

Alt
 
It's actually pretty common, or there wouldn't be a tool for it. FSMs will still have wet and dry fill amounts though.
 
Granted fully extended with the spring in place is not the way to do it, if you're filling dry empty forks, or forks that have been drained. In that case you'd leave the springs out, slide the tubes down, slowly fill with the correct amount and pump the fork up & down to get all the air out, then measure your air gap at he top with the fork extended, make sure both measure the same oil height. Altering the air gap is a tuning method used with cartridge emulators.

But if you're just adding a little oil, I'd hold the fork extended and just dip a zip tie or something to measure your oil height with the spring still in, add a little oil and measure new oil height in both forks.

And as AD stated don't overfil or yes you'll hydrolock and you won't have soft forks at that point.
 
I will do the
Put on the center stand
Support the engine to get the forks off the ground
Open the drains.
Open the tops
Drain it out.
Then put in the drains and fill up the 4.6
method as it seems the most simple...... till one starts wrasteling with nuts.

Alt
 
Thanks, thought it would be that simple, and thanks for the amount to add.
Alt.
Well Bothernation..... No fork oil drain plugs on mine... so I will have to remove and dump out the top.
Might as well rebuild them then.

Alt
 
I'll have to remember to look that up or ask directly first next time I think about replying to a question like this.

Good point.
 
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