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Discussion Starter · #1 ·
A forum newb here, an old school 350 boy. I'm finishing up a restored K1 SL and doing road ready dial in. Testing 1-2-3.

I won't be doing any motocross or canyon jumps with this bike,but mostly 40mph back roads and two tracks, occasional pavement @ 55. So said...

The front forks on his bike are far too stiff for comfort. I read (Honda shop manual) that trans fluid is recommended and studying up, that dampening can be better controlled by using fork oil of appropriate viscosity, which makes perfect sense to me. I'm hardly about to replace the forks or mess with the internal springs.

Lets just say it rides like a cement truck-stock and there must be a sweet spot between front tire pressure and/or dampening. Way stiffer than my CL ever was and too stiff for on-road comfort. Overkill beat-me-up stiff. Nor do I have any clue what sort of fluid or oil is currently there.

I am fishing for some wisdom snippets here; Ideas and Insights. Approach this with some clue of what I'm into.

This is a '71 SL designed for off road with stiff suspension, which I am wanting to soften up a tad. Rear, too, when I get that far.
 

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You could start by getting the front end lifted off the ground and then remove the fork top nuts and see how much preload you have in the springs;preload is usually the way people make the forks stiffer and amounts to spacers place on top of the original(or possibly aftermarket)fork springs.The previous owner may have installed preload spacers.

Welcome to the forum ;)
 

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The SL forks were very undersprung and squishy stock. if yours are stiff they've either been modified or something is wrong with them.

start with a full disassembly, cleaning and inspection. transmission fluid is for transmissions...fork oil is for forks...ATF is approximately 10W fork oil.
clean em and reassemble them with new seals and 10 weight fork oil then report back
 
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Discussion Starter · #4 ·
I have zero history on this bike as far as previous owner(s) prior to the guy I bought it from and what he had done. So basically I assume nothing and am going through the bike inch by inch. It hadn't been ridden hard enough to really debug it.

This "fork issue" began with a "tromping" of the tire which I found mis mounted and the wheel 1/4" R-L unbalanced... which I corrected by tweaking the spokes. Much improved, but still there at 55mph. So now I am starting to look at the forks. No clue what sort of oil (if any) is in them or if the amounts are equal. Taking your suggestions to check for preload spacers and replace whatever oil is in the forks with recommended and equal amounts of #10 fork oil. See how that goes. Seems logical that a cross over fork brace might help, too. Keep the forks more synchronized. All I know right now is that something isn't right and the forks seem overly stiff for general purpose back road riding. A little softer would be more comfortable. My guess is the fork oil has never been checked since 1971???
 

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The forks are probably filled with sludge from oil and water over the years. Follow Outobies advice (Can't go wrong there)and remove, disassemble and clean...I differ from Outobie on the fork oil slightly, I think ATF is OK. It is hydraul9ic fluid with anti-rust and anti foam and is what Honda called for. I do agree that Fork oil is a better choice, though, but ATF would still work acceptably. However, since ATF is 10 weight, you have no choice is you want thicker or thinner oil....
 

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Discussion Starter · #6 ·
Since posting last time, I drained both forks and found this purple/brown antique sludge, I assume '70s vintage trans fluid. Roughly 6 oz in one side that came squirting out... 3 oz on the other side that dribbled out. I worked the forks "dry". I then replaced the sludge with non detergent #10 sewing machine oil (I had on hand) which I'll replace this week with either #5 or #10 fork oil. There are no preload spacers above the springs.

So tested it yesterday, 40 miles on both dirt and paved roads, Substantial improvement! I'm still getting some wheel tromp at 50mph plus which is either a balance or cheap Korean knobby tire issue (or both). I can live with that since I won't be doing a lot of highway riding. I think I have become fixated on tuning the front end to what I used to... being much larger-heavier road bikes. I've not been on a smaller dirt bike in 40 years and it takes some adjustment.
 
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