17" Wheel Conversion Woes

[ajacstern]

Also apologies for so many little questions but the wiki lists the 89 forks as receiving 395cc / 169mm from top of oil where as the 87 are supposed to get 424cc / 141mm from the top. I did 125mm from the top fully compressed without the spring in on my 87 forks and liked the damping, can I just do the same or do the 89's actually need a different oil level?

[fj1289]

I'd start with the 125 mm - what you are playing with there is how much air is in the fork that will also compress with fork travel.  If you liked just a little bit before - should be similar.  More air "should" give you a little more bottoming resistance.

[ajacstern]

I have put almost everything back together. I believe I actually did 145mm air gap for the '87 forks or something, the '89s are probably 15-20% stiffer on compression at 130mm but I want to run it and see how it feels, may help eliminate brake dive.

I installed the blue dot Yamaha calipers and bled them, several times. Almost no lever pressure. It does grab the wheel and stop it from moving, but almost no resistance in the lever. I noticed there is a loud almost squeaking noise coming from the left caliper. I can't see any leaking brake fluid (though it is still a bit wet from being bled), but it almost sounds as in if a piston seal is collapsing underpressure. If I hold the lever ~70% of the way in and move just a little bit, a few mm, it will repeatedly make the noise every time I pass a certain lever point. When pressing the pistons back in to fit onto the wheel I heard the noise as well. Is that something that is possible? Wondering if all the fluid pressure is going into deforming a seal and thus no braking pressure.

Thank you.

[Millietant]

Squeaking could also be air bubbles compressing. I had a similar issue when I first installed my blue spots (and also had a similar issue with my clutch at one point).

Getting a small amount of brake pressure with a soft lever definitely sounds like trapped air to me - I now "reverse bleed" all of my hydraulics - the idea is that you push brake fluid in through each caliper bleed nipple (one at a time), using either a big syringe or a small hand pump) and you push fluid into the caliper and back up to the master cylinder. As any air in the system wants to rise, it will pop out of the open top of the master cylinder. Just be careful to push/pump slowly and maybe put a cloth over the top of your open master cylinder, in case any fluid spurts out. Just be sure also to not overflow/overfill your master cylinder. I use a small "Laser" brand mini hand pump, filled with fluid and pump it through the slightly cracked open bleed nipples.

Since using this bleeding method, all of my hydraulic problems have disappeared.

[fj1289]

Another trick to help bleed a "new" system is to slightly loosen the banjo bolt at the master cylinder to bleed the air in the line easier.  Pump up what little pressure you can and hold the lever, wrap a rag several times around the joint, and just loosen the banjo just enough to relive the pressure, snug down the banjo and release the ever. 

Then it will usually bleed much easier no matter what technique you use.   

[ajacstern]

The reverse bleed is my favorite method as well, that hand pump looks like a much better option than the syringe I currently use. I also typically find myself using that master cylinder trick when changing master cylinders. However, the issue turned out to not be with bleeding technique. There was some hairline fracture on the bleed nipple which prevented it from being able to build pressure, and I couldn't tell that they were leaking because they were already a little wet from the bleeder hose. Switched the nipple out and it bled properly the first time. The popping / crinkling sound was from the brake hardware being a bit bent / warped out of shape, it turns out.

Got everything together and went out. Much happier with the damping at 125mm, suspension feels way better than it used to (part of that may be from fresh bushings and such as well). The front wheel feels fine, the low speed handling is fixed surprisingly and the high speed handling is slightly improved but I still think I will raise the forks a little bit. Bike feels very communicative and is still comfortable to ride, definitely like these tires, though I can't comment on the limit of grip on the front yet.

Unfortunately, there is always something, and the reason I can't speak to the limit of grip on the front is due to the front brake rotors being fubar. Massive vibrations at high speed, and at low speed I can feel the brake grab and release with every wheel rotation. Right rotor was 10 thousands of an inch out of spec and the left was 2 thousands of an inch. I tried to correct it with a prybar as the braking surface itself is flat, it is the brake carrier that is bent, but as soon as it got hot it returned to shaking. Guess I need to replace them unfortunately.

Are these https://www.ebay.com/itm/265713520064?fits=Year%3A1989%7CModel%3AFJ1200&hash=item3dddc28dc0:g:PgcAAOSwWWZik5As rotors known to be any good? The only ones I see are these Chinese ones, some Arashi ones, and some very expensive EBC rotors. I like the stock rotor design, not such a fan of the Arashi wave unless there is some advantage to it, but not sure if Chinese brake rotors are acceptably safe.

Thank you!