VINTAGE and EVOLUTION SUSPENSION PRODUCTS
SIMONS FORK PARTS
NEWS FLASH for Owners of Conventional Seal
I am now offering a modification to replace the seals with a Seal Carrier (Patent Pending) that uses the 1/4" Pneumatic Seal/Wiper combination.
This will allow the Forks to be used as originally intended, as Air Forks, without the problem of seal failure due to the pressures needed.
Cost is $200 plus rebuild labor and seal parts.
Simons documents: (Specs
and Tips on Simons)
(Not sure which
way the seal/wiper goes in? Click here for JPG diagram)
Normal setup is 5wt oil at 6" starting at 15 psi.
Fork Leg color: Safety Yellow, I use powder, but Krylon Safety
Yellow in the can is a match. Lemon Yellow is close but appears to
be slightly lighter. Later in production, legs could be ordered to closely match all of the major manufactures brand color.
Tubes and legs are all the same length unless
modified after production,
overall length and travel is adjusted by varying the length of the damper rods.
See the Specs and Tips sheet above for how to determine travel by rod length.
Photo of a leg using pneumatic seal/wiper on left, conventional canned oil seal leg on right.
SIMONS FORK SEAL KIT*- consist of
2 Seals, 2 Wipers, 2 Bottom Cap O-rings, and 2 O-rings for the air caps.
* I don't mind doing exchanges if you order the wrong set, provided they are not damaged. If you have never had your forks apart before, please disassemble one and see what you have and save yourself time and postage. Don't assume.... from the top, the 1/4" and 3/8" appear the same. However, the 50mm conventional canned oil seal is readily viewable from the top and is held in by a circlip. Seal size can usually be determined by the Serial Number, up to 2969 should be 1/4", 2970 and up is 3/8" Caution on early 1/4" numbers, I have seen a few sets that someone had upgraded thru a machine shop, but they are rare.
How long will your seals last?
First, it is normal for hydraulic seal/wipers to leave a trace amount of oil on the fork tubes that you can just barely feel, this indicates there is positive pressure in the forks that helps keep dirt out and protects the tubes from corrosion. When it gets to the point where enough oil collects to start running down the fork leg it is the first stage of a leak and is called weeping, this should be treated as a warning sign to replace as soon as possible, you may or may not get 1 or 2 more rides out of them before they blow and you are sidelined.
Simons recommendation back in the day, was to replace annually, regardless of whether they are leaking or not. The reasoning behind this is so that you do not have a failure while riding or racing. I tried to go into the 2nd season on my Simons in 79 without a rebuild, the seals failed after 2 races.
When the fork legs and tubes are in perfect condition, the seals will start to weep before completely blowing out, this will usually buy time to replace before your next event. Condition of the legs, tubes, and piston rings will effect life expectancy. Worn parts will result in play that will shorten seal life. On my own set a couple years ago, the seal on one fork would only last maybe 3 months. I found extreme wear in the fork leg where the tube dug into the lower part of the leg, replaced the leg, but the seal still failed in 3 months. At this point I suspected the fork tube even thou there was no damage to the chrome. Tooling marks or coil like swirls were just barely visible under some of the chrome which is only about 0.002" thick. Measuring the tube with a micrometer showed 0.001" deviation in the OD of the tube. I then had both fork tubes re-chromed, (hard chroming, not the same as show chrome), and the problem was solved.
The next factor on life is the material itself, the seals and wipers are polyurethane, this material has a shelf life of 5 years, once installed, this is immediately reduced by half, and further reduced by condition of parts as noted above and by riding conditions they are exposed to such as fine gritty sand and extreme mud being the worst. Even in the package, polyurethane parts will naturally deteriorate over time just as you may have noticed when doing a rebuild on a set that has not been touched in years. The parts first start to harden, then become brittle, white seals and wipers will discolor to yellow or brown. Buying original seal kits from back in the day is a waste of money unless it is just for display on the wall.
Even if the forks are never used, the bike is a show or museum piece, the seals will eventually fail. After 2 to 5 years, take the bike off the stand, compress the forks, they will most likely weep or leak.
The rubber coated canned seals used in the 50mm kit in the first production of the Simons has a 15 year shelf life, but there is major flaw in the design, if they last a year, they're doing good. The canned seals are not designed for high pressure applications and thus the reason Simons changed to the hydraulic wiper/seal combination. My recommendation is to convert the forks to a conventional setup like the OEM's, replace the air springs with a standard rate for your weight and riding. Install RaceTech Emulators for damping as this was controlled by the air pressure setting. Use no air or just a few pounds to set sag if needed.
Bottom line, one year is the norm, less then that is an indication of a wear issue that is effecting the seals.
SIMONS UDX-60, majority of the UDX-60's use seals with a 66.5 mm (2.623") or 67mm (2.638") OD, recently a customer reported a set with a 68mm (2.677") OD, whether by design or modified is undetermined at this time. You must measure the seal bore before ordering. Oil type is 2-1/2wt at approximately 750cc. Seals are installed app. 3/8" from top. The reason for the gap is to allow you to use a punch to drive in one side of the seal when replacing, this will cock the seal allowing for easier removal.
Air Valves, Cores, and CapsAir Valves, Original replacement, Nickel-Plated, 200 psi sustained, 300 psi peak, metal cap, always install with a fresh layer of plumbers tape which can be found under Tools, #38-0220, $4.50 each
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