Front fork adjustment

Ok so final word?
ATF ok?
motor oil froths to much.
20w fork oil is good but $$.
..and just for shizzles what is the procedure again?
to change/refill oil?
 
I assume it is a feel thing. The bubbles dont allow proper dampening?
I havnt tried anything yet as my forks are still with original oil. I am going with fork oil though.
 
yep, its called cavitating. the fork will go real soft after a little ride and bounces everywhere.

buy the proper stuff it will be in there for years!
 
..and just for shizzles what is the procedure again? to change/refill oil?
The shizzlic way: Drain the forks, siphon all the gas, hang the bike upside down and inject the right amount of fork oil into the drain holes with a free oral syringe from a drugstore. :wink2:
Caution: don't just reverse the process without first installing the fork drain screws, or you'll be :cussing:
 
I'm 5'8", 150lbs and put 10 weight in mine, which is pretty nice. Get yourself a liquid measure if you don't already have one. Be precise. Consider my height/weight against your own and then decide on 15 vs. 20 weight oil.

Then, mind what Drewpy is saying. Look where the oil ends up when you follow the manual. That will make things easier the next time you do it.

Am I right, Drewpy?
 
Wait... hang the bike upside down? From what?
"High from the highest tree"? :shrug:
Actually, when I did it that way on my 250, I simply laid it down twice (once on each side) on a couple of old car tires which were placed on the side of a small hill - just steep enough to get the drain holes above the rest of the forks.
 
I followed the service manual procedure and had the Mrs. help with the little locking ring at the top of fork spring caps. Pretty easy.
Went with 20w 'maxima' HD fork oil ( came in a 16oz container for $6.50) eezy peezy. Much better!
 
I followed the service manual procedure and had the Mrs. help with the little locking ring at the top of fork spring caps. Pretty easy. Went with 20w 'maxima' HD fork oil ( came in a 16oz container for $6.50) eezy peezy. Much better!
I'm sure the proper way of doing things is nearly always the best, and I am certainly hoping that all the bits in the top of the xs400 forks will be there and working properly when I have to change that oil.
The spring caps on the 250 wouldn't compress, the retaining rings were either missing or seized - and I had drained ALL of what little black ooze had been in there.
I had to think, "what would the Lone Ranger do?". Especially if he had no Mrs. (or Tonto) to help with the locking ring. He would lasso a big horizontal branch, attach it to the front wheel and lift those drain holes above the rest of the tubes.
In my case - no lasso, so I used the side slope and the tires. Getting oil in the forks was worth it though. It improved the handling quite a bit.
 
haha...No Mrs. ...no Tonto? Truly the "Lone(Lou) Ranger"! Hehehe
Hey if it works...:shrug: shucks, lets go with that! Been there done that! :eek:
No Tonto, but I do have a lovely wife, a wonderful wife - almost as terrific as B-W's (if we are to believe he doesn't wear rose-coloured glasses). :pimp:
She (mine not B-W's) loves that I have and enjoy my xs400 - but she really isn't into being responsible for losing a spring.
B-W's would probably be happy for me too if she had to think about it..... :umm:
 
So I gotta reopen this thread - if anyone sees this and could comment on how wise or foolish this sounds, it would be much appreciated. My '78 XS400 forks were butter soft and since lowering them a couple inches with my clip-on handlebars mounted above the upper triple tree, I was bottoming out the forks a LOT!!!, I smashed the business outta my front fender and had to remove it and introduce it to my Peter Wright Anvil and a hammer.

My first instinct was to rebuild the forks, (they weren't leaking by the way) - I just figured that stripping them entirely apart, cleaning them to perfection, inspecting the bushings and dumping heavier oil in would do the trick. So I did all this and unsurprisingly, the bushings looked just fine (only about 20,500mi on the bike) and I knew the seals were fine too so I simply cleaned them up, reassembled and dumped in what I figured would be stouter oil than the black mud I dumped out, I don't know the specs on it but I used Harley Davidson Heavy Fork Oil (used this when I rebuilt my 2001 HD Fat Boy forks in May 2015). I figured if this oil is heavy enough for a 750 pound Harley, it should definitely stiffen up the front end on my wee lil' XS400. Based on what I read on a Harley forum, this fork oil is either 10W or 15W - not much consistency there. Regardless of what weight that oil actually is, I perceived absolutely no difference and once again clobbered the fender when I bottomed out on one of these horrendous Chicagoland roads.

So my next attempt at this flaccid fork fix was to cut two equal lengths of PVC pipe and stuff them under the main springs thereby pre-loading the springs markedly. I settled on 2 inches as the length, cut the pipe, had to turn it on my lathe in order for it to fit down the tubes. It was a righteous and noble feat to compress the springs with the plugs using an Irwin wood working clamp but I got it, installed the clips, and now I have a proper stiff front end, no more bottoming out (and I tested it WELL), handling is terrific too! The only questionable bit was that the rebound experience when hitting potholes involved a good knock with the increased spring pressure. I know the damping piston has a rebound spring to absorb impact but...since I've not found evidence of anyone doing this on this forum, I'm curious as to whether or not I should worry about my damping rod cracking, or the additional 2" of pre-load causing the top spring clips to fail and a pair of plugs and springs flying at my beautiful face as I cruise down yonder road. Frankly, I much prefer the design of my Harley as the spring plugs are threaded thus I have no concern of failure. Thanks to anyone who offers feedback or advice.
 

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I'll give this a go, but you will probably regret thanking in advance.

Threaded top caps are more prone to failure. Threads are easy to cross thread or strip or loosen. That little spring steel wire retaining clip on your XS's top caps would have to be sheared to let the caps free. As long as it is not rusted to nothing, you should be more concerned with how low your forks are when riding crap roads. Seriously, put your fashion sense on the back burner for a minute and think about all the negatives of what you've done and how any one of them could lead to a bad ending. Only trailered bikes should be that low. Smashed your fender twice and still haven't learned? The first time was your wake up call from reality...

Anyway, onto your spring preload. I'm going to bet that since you didn't bother measuring the forks for travel before lowering them too far, that you also didn't measure for spring coil bind when you made your preload spacers. Yeah, I know it involves grade school math and all, but it really does matter. But more importantly, adding excessive preload to weak springs doesn't make the springs stronger (which is what you need), it just raises the ride height (what you apparently don't want). Cutting coils off the springs will slightly increase their rate, but I'd guess not enough for your needs. Replacing the springs is the only proper solution to your dilemma. You need shorter and stiffer springs. Probably have to get them custom made.

Damper rod forks suck (yes, on your Harley as well as XS). They can't be adjusted or tuned much, and they perform poorly under all conditions. Under damped on small hits, over damped on large hits. They are cheap, that is the reality of them. After the springs, oil viscosity and volume can be changed, and that is about it. In your case, I'd suggest adding a few ml / oz more oil to the forks. This will reduce the air volume in the forks and help prevent bottoming by building more air pressure in the fork when it is compressed. You will know when you have too much oil in the fork as it will feel like it is always bottoming out, even though it isn't. That is bad and may blow out the fork seals if left that way. The volume does not have to be the same in both forks, if you have a sturdy brace between them. Once you have the volume of oil determined, you can change viscosity to fine tune the feel. Under damped, use thicker oil. Too harsh, use thinner oil. Then you go back to oil volume and repeat until you've had enough and settle for what you've got. You really should take good notes and measure well. This is complicated stuff.

I know that was harsh. But hopefully not nearly as harsh as getting bucked off your bike when you hit a pothole and the forks bottom, then a texting soccer mom runs you over with her SUV...
 
Thanks for your feedback - I do know what spring bind is and I can confidently say the springs have sufficient travel to accept 2" pre load without binding. I also know how much of a mess a blown seal would make so I chose to experiment first with PVC. As far as lowering my bike and how horrible of an idea you seem to feel it is, that's your opinion and you're most certainly entitled to it but take a closer look at the beautiful build on the front page of this website - not intending to throw anyone under any bus but I replicated his work ergo, I'm not venturing into foreign territory here. The gentleman who built that machine said he "stretched" his springs 2"...Don't know how one stretches so stout a spring without heating, stretching, and re-tempering it so I simply opted for preloading. Of course you'll also note that that particular build doesn't have a front fender so he's got another 1" at least of travel than I have...I get caught in rain from time to time so I plan on keeping my fender.

Like I said from my 25mi test ride, it handled bumps (ugly ones too) beautifully with a nice response rate, at no point was I remotely close to getting bucked off the bike - springs ain't that strong. I've rebuilt thread capped Harley forks more than once and had no issue with stripping or cross-threading them and having done so, I'm well aware of the fact you pointed out that my harley forks are the same as my xs400 - same maker too I'd wager, Showa has that market cornered.

I don't intend to keep the bike this way, my game plan is to cut the PVC down to 1", drain the oil, refill with 20W (since there's poor consensus on the actual weight of that Harley oil I used), and see how that goes. Having 2" preload is just too much of a bear to deal with if I want to open them up and add more oil. It was a proof of concept experiment which cost only a couple bucks in PVC but effectively answered the question I had - can I stiffen up the front end sufficiently to allow good handling and not hit the fender - yes.

At the end of the day, in my defense, I had to do something with these forks. Even before I lowered them they were so soft they never rebounded all the way back up when you pushed it down (without even sitting on it). My Harley and Honda both rebound all the way without issue. Yamaha should've thrown stiffer springs in from the start...but if the shorter PVC and oil addition doesn't help, then I'll invest in XS650 springs.

Cheers!
 
The featured bike certainly looks nice, and I have no doubt that a ridiculous number of hours have been invested into getting it to look that good. But, just like it takes many hours to make me look presentable, that has no bearing on function. I'd also point out that the stock front fender is also a fork brace, running without it makes the forks sloppy and the steering vague.

I ride my bike, and you also ride yours. Our roads and weather are similar. There are practical considerations that out weigh fashion. You wouldn't wear nice leather dress shoes out in a snow storm to shovel the drive would you? I'd wear insulated boots. Not fashionable, but certainly practical. That is my mindset and where I'm coming from.

Here are some terms I've learned over the past years when researching suspension setup:
Static sag - how far the bike settles the suspension without the rider.
Dynamic sag - how far the bike settles the suspension with the rider onboard.
Suspension travel - the distance the suspension moves from fully extended to fully compressed.

Properly setup suspensions have some static sag otherwise they "top out" harshly when the suspension is unloaded. This not only unsettles the bike when riding, but can damage fork or shock internals. By your description, your Harley and Honda have too little static sag, possibly from too much preload? After a bunch of measuring, including mocking up the stock springs on threaded rod to test for coil bind, I've put 25mm / 1" preload spacers in my forks. That is about right for my setup and leaves me just clear of coil bind at full compression. With a 23L / 6 US gal / 5 real gal. tank and a sometimes heavy tank bag, it is difficult to be just right, but that is my reality. Obviously, dynamic sag is greater than static sag, and I've read that dynamic sag should be somewhere between 1/3 to 1/2 total suspension travel. I'm closer to 1/2, but without investing in new, higher rate springs such is life. General consensus is that progressive rate springs are to be avoided as they result in an unpredictable, impossible to tune suspension. Yet most springs commonly available are progressive rate. Fancy words sell parts better than science.

You stated earlier that your fender was smashing into the lower clamps. This then shows that the forks were set too high in the clamps for their travel. It is possible to make spacers that internally limit the fork extension or compression. But that is beyond my knowledge. I can tell you that 20 wt fork oil was very stiff in my forks, and not in a good way. Every little road imperfection was transmitted to the bike. Some people (most magazine writers!) think this is good. I'd argue that if you are going to pay the weight penalty for a suspension, it should be working for you not against you! Hard hits were drastic impacts with 20 wt, they unsettled the bike. In cold temps this gets even worse, unless synthetic fork oil is used. After a short time I switched to 10 wt synthetic fork oil and put slightly more oil in the forks than called for. This resulted in a smoother, more compliant suspension that stiffens on compression. The only time my forks bottom out is when I'm riding too hard off road. Bottomed it twice and boy is that a hard hit! I've decided it is easier to slow down than try to keep up with the enduro boys with their long travel suspensions. I've read that it is possible to adjust the size of the holes in the damper rods to change the damping rate. Larger holes for less damping, smaller for more. But again, that is beyond my knowledge. I will suggest being careful to not make the holes so large as to weaken the damper rod.

So, there you have my brain dump on suspension. I hope some of it is useful.
 
I don't believe I explained my Harley and Honda effectively. When I stand off of the bike and just push down on the handlebars to compress the forks, they rebound all the way to where they sit normally (static sag if you will). I was incorrect to say they top out - they're not far from top out but certainly not there. The Yamaha however does not rebound to the static sag position when I push the forks down...until now. As far as your arguments for practicality, well...in my XS, I'm not concerned with practicality, it's a very very fun little bike to cruise around town on, I've learned a lot from tinkering with it ...but I'm not planning on road tripping with it - that's what my HD Fat Boy is for - I've taken that machine through almost 40 states but I don't think my gluteus maximus is max enough for more than a few hundred miles on the Yam. Thanks again for sharing your knowledge on suspension!
 
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