Fork work question - paging Scott F - others
Posted March 12, 2001 - 06:03 PM
Looks like I need to get the teflon re-done on the compression rods. I was thinking C-Cycle. Anyone else? Would a regular coating shop be able to do this? May need some new seal head bushings as well.
Posted March 12, 2001 - 08:48 PM
C-Cycle or WB should be able to sell you some new seal head bushings.
Posted March 13, 2001 - 12:03 AM
Well it's a sad story, but I must come clean.
I ruined my...ummm...first set of rods when I polished off the Teflon following some poorly thought out instructions that were part of a valving (piston) kit. No names mentioned.
Turns out there's a lot of Teflon on those things. Shortly after reassembly, I lost compression. Excessive oil was flowing past the seal heads so I assumed it was due to what I had either done to the rods or something else. In either case, it seemed obvious at the time that I needed to replace them.
So off to the dealer with a small loan for some new cartridge assemblies. Put those in, and after about 20 hours of riding I lost compression again. Sure enough it was the result of too much oil flowing past the seal heads. I have yet to figure out why. A suspension guy at Scott's told me that the shims in the factory seal heads can wear which allow too much oil to flow past. It was the only explanation I had, so it was obvious that I needed to replace them. But why just me?
That's when I installed the C-Cycle bottoming cones. I punched out and in the factory bushings, however, I nicked one of the rods during the work so I had to smooth the area out.
The bike handled fantastically for about 20 hours of riding.
Then during my last ride, I lost compression again. So tonight I pulled the forks apart and found that the oil is flowing past the seal heads again.
In addition to this, the oil was filled with small particles of very fine aluminum flakes and each rod had a section where the Teflon has rubbed off and the metal has begun to wear. Not a dig-in wear, just a smooth long polish. The one rod that I re-worked had significantly more damage to it than the other.
It's as if the slightest inconsistency in the Teflon coating wreaks havoc on the proper operation between rod and bushing.
However, the bushings still have good Teflon coverage and I didn't feel any burs or such on them. And no bare spots.
The tolerance between seal head bushing and rod seems to be very critical for proper fork operation.
So without really knowing what has caused this, I was just going to start re-working everything involved. In this case, the rods and bushings. I'm figuring if they are returned to perfect condition that this will not happen again.
Other than that, I'm trying to think if there is something else that I am doing, say during assembly, that is causing the rod to flex and/or bind with the seal head, causing the Teflon or something to get over worked.
Any thoughts on this would be greatly appreciated.
Posted March 13, 2001 - 10:51 PM
I took a closer look at the bushings this morning and it looks like I put just enough of an edge on them to cause this problem.
I'm not sure what is on the rod from the factory, but I know that just polishing the rod won't fix it.
Perhaps a standard anodizing will do.
Posted March 13, 2001 - 08:41 PM
As for your suspecting oil bypass or leakage, I do know of one other possible cause. When you drill out the cartridge dimples, you have to keep the hole size close to 1/8". If you drill too large, oil will bypass the threads.
How did you determine that "the oil is flowing past the seal heads"?
How much did the cartridge assemblies cost? Did they come complete? I'm thinking maybe you sacked out your midvalve each time, and you are mistaking it for oil bypass. I kinda think that a little leakage between the rod and bushing would not be that critical. The stock seal heads have seals, and the C-Cycle heads do not, right? Also, the stock seal head has shims inside of it, but the C-Cycle head does not. You could tear an old one apart to check it out. I believe these can get sacked, but the midvalve is a more likely culprit.
The rods are anodized, and probably teflon coated. You could have it redone, but I don't know if it is cost effective.
You could order '98 cartridges with the steel damper rod, or I might sell mine to you.
Posted March 14, 2001 - 12:11 PM
The factory seal heads have a valve, a shim stack, and the same bushing that is pressed into the C-Cycle cones. The oil flows around the valve with resistance via the stack. There’s a rubber area that’s part of the valve, but does not work as a traditional seal would.
The new cartridges were about $240 each. The re-work on the rods is $110 for the pair. The rods from the factory have a Type III anodizing, (not Teflon or Nickel Acetate). The factory thickness appears to be .002 to .003, and the worst loss I have, on one small area of the two rods, is .004. Hence the fine metal particles in the oil. The other areas that appear wore down were too minor to get a measurement on.
The plating shop is concerned about loss due to stripping, therefore maintaining a finishing job to par with the factory spec, as well as being able to evenly apply over a small round surface. So it’s a risk. I’ll find out on Friday.
As in the past, I’m able to watch the oil flow past this area while working the rod in a tank of oil or when it’s in the fork. However, oil should flow past so it’s very difficult to determine how much is too much.
So yes, I’m becoming very suspicious that it may have something to do with the mid-valve. Perhaps it’s allowing too much oil to pass, which is therefore allowing too much pressure against the seal head.
I’m also beginning to think that even though I screwed up the bushings during removal and install, that the only result of this was a loss to the rod coating, and not the cause to the excessive oil flow.
But am I the only person on the 400/426 to have three mid-valve failures? There’s got to be another reason for this. Could it be oil compatibility? Doubt it. But then what else? Unless others are having mid-valve failures but are not sensitive enough to their suspensions to know the difference. Doubt that too because of how poorly the bike handles when this occurs.
I’m going to take a very close look at the mid valves and tubes tonight and see what I can find. If you can think of anything else let me know and I’ll look for that as well.
Posted March 14, 2001 - 06:25 PM
Can I remove the cartridge by using an impact wrench on the base valve or must I have a damper rod holder?
What should I look for?
Where is the mid-valve and how do you tell if it is bad?
I cannot afford to have a shop do this so please help with any info and experience you all may have.
Thanks for this and many other things I have learned on this board!
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Posted March 14, 2001 - 11:03 PM
Break loose the top cap on the forks, about a quarter turn, before you remove the forks from the bike. 19mm wrench.
Now with the forks off, you can either go in from the top or the bottom. My advice is to turn them up side down and use a very good 14mm allen socket with impact gun to spin out the compression valve assembly.
Then rotate the fork over into a tall catch container. Then fully loosen the top cap of the fork. Then pull down the spring from the top cap, and slip in a 17mm wrench on the long aluminum nut that locks up against the cap. This is a tight fit so you may need a spanner or modified 17mm wrench. I use a 17mm Craftsman, but I really need to force it in. You'll work this against the 19mm wrench on the cap. Keep the 17mm tool in place until the second break - which happens after the nut locks down on the rod.
Then the cap will come off, allowing you to remove the spring. No tension.
Then lift the compression tube out of the fork keeping it over the catch container. Then move the compression rod up and down to pump the oil out of the compression tube. Go slow.
Then extend the fork tube all the way up to release the oil between the two tubes (it's not much). And that's about it for getting the oil out. Then it's time for wipe down.
If you want, you can remove the dust seal, then the large c-clip, then slide hammer the two tubes apart. This will pull out the bushing from the upper tube. If you do this, it's best to have a bushing driver to properly get the two back together, (Motion Pro has ‘em). If this is just an oil change, and you don't have a lot of debris in the oil, AND you don’t want to inspect the bushings, I would keep the tubes together.
Be very careful about using solvent since it can get trapped in many areas that you may not be able to get to. And some solvents leave a film. AND...some solvents attract moisture when shot from a can (since it cools on contact). You may just want to use clean lint free rags.
As for all the other stuff, it's hidden inside the compression tube and you have to drill out the four machine punches that hold the seal head in to get to them. Don't do this unless you're making mods which I don't recommend unless you have a purpose for doing so.
As for re-assembly, the proper way is to have a cartridge tool so that you can torque the valve assembly to spec. I set my gun on a lower impact setting and spin it back in. Simple as that. Put a little lube on the o-ring before doing so.
After the spring is back in, the cap will need to make contact with the top of the rod, so make sure the long aluminum nut is turned fully down the rod before spinning the cap on. You may also want to back out the rebound screw all the way before doing so.
If by chance you ever want to hold the rod, say to remove the nut or for any other purpose, only do so by two jam nuts on the threaded portion of the rod (you can get them at a hardware store that sells metric nuts). Don't ever EVER clamp anything down on the rod.
You can also pull the long aluminum dowl (spl?) in the center of the rod out without any harm. There is a little spring at the end, but I don't think I have ever seen it slip out in that direction.
And of course, make sure to fully work the compression tube and rod while adding the oil to make sure it's fully filled. And run the outer fork tube all the way up then down before setting fork oil level.
Let me know if you have any questions or if you’re nervous about it, I'll give ya my phone number and you can call me if you get stuck along the way.
Posted March 15, 2001 - 09:43 AM
Type III anodizing is a hard coat, right? I'd be concerned about maintaining a rod thickness as close to original as possible. Too tight or too loose would not be good, but I would prefer smaller than larger for sure.
I checked for oil leakage when I had the cartridge in a bucket of oil, pumped the rod, and could see where it leaked out. The mid valve wouldn't affect leakage, just performance. Those shims can easily be damaged during normal use. I've had some mangled ones in my forks. You could order new ones, especially the big ones, and put them in there once or twice a year. The magazines have been crying about this for years. The real problem is that it is so difficult to replace those shims.
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