Fork Rebuilding Questions

Hello everyone, Im rebuilding the forks on my 82 Seca 750 and I have a few questions.

First off, can I hone the lower fork tube out? I bought new bushings from XJ4EVER and I want to make sure they last as long as possible.

If I should in fact hone the lower does that mean I can hone the inside of the inner too? I think the damper rod rides in here.

Are there any rebuild parts available for the anit-dive units that mate to the bottom of the forks? Mine were seized so I disassembled them but one of them is missing the nylon washer inside.

Can I sand the inner stanchion with 1500-2500 grit sandpaper to remove any ridges on it that might damage the new lower bushing?

I'm sure I'll have other questions before its over but this should get me started reassembling. Thanks in advance!

 

How will you know if the bushes are damaged when in use? A knocking or grinding noise? So you'll replace them will you? I don't think so.
The first thing you will notice that will need replacing are the seals and when you replace them it is common practice to replace the bushes at the same time. If any of the other fork components are past it you'd replace them too.
By all means try and make the bushes last a bit longer, i think you'll be wasting your time.

 

IMHO. they are 30 years old, and forks are a pain in the ass.... id just do it all.

 

Don't hone anything in the forks. Very poor idea.

Worn or broken parts should be replaced. Not familiar with your anti-dive so not sure what's broken there.

 

I already bought $400 worth of new orings, seals, bushings, gaskets, circlips and snaprings so yes I am replacing everything inside my forks. My forks are already fully disassembled.

I'm worried that if I don't hone/sand the upper and lower they will wear the seals and bushings out quickly. But I'm not sure a hone will leave a clean enough surface.

Yeah and these darn forks have the antidive and the air assist. The antidive is impossible to find literature on, or replacement parts.

 

Solid advice. Don't.

 

The uppers are chrome plated. If they have minor scratching you might polish them. If they chrome is pitted anywhere the seals run on them there is no way to prevent them ruining your new seals - order replacements from Chacal.

 

Thanks for the replys guy, glad I didnt start honeing it out without asking. Instead I stuck a shotgun bore cleaner into my Dewalt drill chuck. I polished the inside of the outers and the inside of the inners. One leg is fully reassembled, now I have to clean and reassemble the other leg.


My only major hurdle now is how to repair the antidive units. Once I rebuild them I can reattach the units and fill/air the forks. Does anybody know where to get the parts for the antidive?

 

Pm Chacal here on the board. He has all that type of stuff. Just search him when you go to make a Private message. He is our supporting vender. Has sourced every part my Maxim X has had rebuilt on it to date including: Ss brake lines, caliper rebuilds, fork rebuilds, master cylinder rebuild, and all the hard to find gaskets and advice I could ask for. He'll probably have what you are looking for as well as some "tips and tricks".

 

Minor chips and scores to chrome uppers can be filled with arraldite (2 part metal glue) and sanded back smooth (2000 grade) with light oil as lubricant.

best as a winter project, plenty of time for glue to cure. I have had some success with this in the past.

 

I'm sure y'all are used to hearing the same dumb questions over and over again.

My chrome inners are straight and don't have any rust or blemishes on them, but the bushings I got from chacal set me back $150 so I wanted to be sure to do everything in my power to ensure they last a long time. You don't want the teflon coating on the new bushings to wear off.

I've emailed chacal already about the anti-dives so we'll see what he says but he didn't have any antidive parts listed on his catalog when I ordered the fork rebuild parts. I guess I was hoping to find anyone who tinkered on or repaired some antidives before

 

I'm reluctant to share this but it's been awhile since anybody stirred up an ants nest.....

I'm pretty well convinced that anti-dives don't do much. There is a pretty sharp guy on the VentureRider forum that has actually cut up a set of Venture forks. His conclusion was that the anti-dives only come into play in the last 2" or so of travel.

The consensus there is that progressive springs with disabled anti-dive units is a better answer than stock. There is some debate about whether they should be disabled blocked or open. Most just block them with no apparent ill effect. This is the second reason I don't think they really do much.

Finally, as far as I know no manufacturer is currently using them. Another reason I think they don't do much.

The big question is how to disable them on the 750 Max. I have no idea.

 

Not sure on the blocking thing, maybe they really don't do much but I doubt it as Yamaha wouldn't have spent the extra money on componentry & machining etc for nothing/not much... I know that on certain other antidive systems like Kawasaki's if it's blocked off the forks go rock hard & blow seals left right and centre.

Wonder if it's possible that Yamaha's system is less "anti-dive" than it is "anti-bottoming" hence the reason it only works in the last bit of travel? If that's the case then the people with it blanked off wouldn't really notice much difference until they get to that part of the travel.

That said, I guess if that IS the case there won't be a great deal of harm in having them blanked since it would also stop bottoming out situations when not on the brakes (possibly at the expense of the fork seals eventually)

Just a theory, don't nobody bite my head off for it!

 

I need to get a usb cord so I can upload pics but this is what I gather from disassembling/reassembling the SECA 750 forks.
The rebound is restricted more than the compression because there is a sort of one way valve on the damper tube(the tapered spindle).
The antidive is blocked by the upper bushing when the fork is fully compressed. The bottom inch of fork travel will render the antidive useless because the bushing blocking the top hole of the antidive will essentially make the fork act as if the antidive is fully engaged(regardless of whether it is.

 

All I know about the anti-dive is after "rebuilding" mine (cleaned, installed new o-rings and freed up the pistons on the brake side of the unit) the forks don't compress nearly as far when the front brakes are applied as they do without. I've only been able to bounce the front in the garage so far; I'll let y'all know what happens once I take the bike out for a ride sometime next week.

 

It seems to me that it's reasonable to presume the anti-dives are needed more extended than almost bottomed out. I suspect the analysis I referred to isn't correct.

I do know that people are replacing the anti-dive valve on Ventures with a blank plate and don't seem to notice any problems.

The impression I have is that the anti-dive valve shuttles oil around the oil lock below the damping rod when the brakes aren't applied. When the brakes are applied oil cannot bypass the oil lock. I assume the wavy springs above the oil lock allow it to travel to relieve some pressure.

It seems to me that if the valve were replaced with a blank the oil lock and springs should be removed. Problem is on motorcycles without anti-dives there is another piece that replaces the oil lock. That part might be important to the functioning of the damping rod. Or, it may simply locate it so you have a chance of finding it with the bolt. :?

You are correct Special_edy that there is more damping on rebound (at least in a non-braking situation). The idea is to transfer the energy of the bump into the spring and then release it gradually. If there weren't damping the forks would be pogo sticks.

 

Hey I just remembered, my bike's basically a 750 engine'd 900 rolling chassis, guess I can check what difference if any the anti dive makes when I replace my brake lines. I'll try with it disconnected first & after making sure it's functional, with it connected and maybe with it blanked too. Be a while before that happens though potentially.

 

The info I could find out on the anti-dive system comes from the 1983 issue of Cycle World which reviewed the 83 Seca 750:

The anti-dive front suspension is linked to the brakes; it uses brake fluid pressure to restrict oil flow through the fork damping holes, and has a blow-off valve to permit suspension movement if you hit a hard bump while braking. The set-up also helps keep the bike flat and stable during hard braking. The forks still dip a little, but the movement is smoother, less abrupt, and less exaggerated than the reaction exhibited by other bikes under similar circumstances.

The front suspension is adjustable in two ways. The damping of the anti-dive system can be changed by turning a screw beneath the anti-dive fitting in each fork, an adjustment that changes the amount of oil restriction as the forks compress.

Hope that helps. I'll scan the article and get it into my dropbox before long.